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MacuPlex Plating on Plastic Coatings
MacuPlex (Plating On Plastic Coatings)
Technical Package
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Contents Section 1.0 2.0 3.0 3.1 3.2 3.3 3.4 3.5 4.0 4.1 4.2 5.0 5.1 5.2 5.3 5.4 6.0 6.1 6.2 6.3 6.4 6.5 7.0 8.0 9.0 9.1 9.2 9.3 10.0 11.0 12.0 12.1 12.2 12.3 12.4 13.0 13.1 14.0 14.1
Description ABS Plastic Materials Moulding Prior to Plating Moulding Design Criteria Nominal Wall Thickness Ribs Bosses Radius Appearance Design Part Performance Thermal Performance Requirements Electrolytic Distribution Moulding Design Considerations Moulding Considerations Surface Composition Requirements Internal Moulding Conditions Water Cooling Equipment Selection Drying Process Controls Fill Speed/Injection Speed Handling of Moulded Plastic Parts For Plating Checking For Moulded in Stress Moulding For Plating Considerations and Effects Mould Release Agents and Fillers Quality Control of Mouldings Glacial Acetic Acid Test For ABS Red Dye Stress Test For PC/ABS Mouldings Test For Trapped Moisture in ABS Mouldings ABS Plastic Quick Guide Plating Resist Electroplating Rack Design Part Contact Rack Contacts Rack Conditioning Rack Stripping Solutions MacuPlex The Chemistry Pre-Treatment Stages ABS Plating An Introduction
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MacuPlex (Plating On Plastic Coatings)
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Contents Section 15.0 15.1 15.2 15.3 15.4 16.0 17.0 18.0 19.0 19.1 19.2 20.0 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21.0 22.0 23.0 24.0 25.0 25.1 26.0 26.1 26.2 26.3 26.4
Description ABS Pre-Treatment Pre-Etching and Etching Catalysing or Activating Metallising Simple Rules For Plating on Plastic Rinsing Agitation Filtration ABS and ABS/PC Processing ABS/PC Pre-Etch (PC>50%) ABS Pre-Etch Chromic Acid Etch Electrolytic Regeneration of MacuPlex Chrome Etchants Electrolytic Regeneration Process Electrolytic Requirements Equipment Conversion Data Sample Calculation Typical Layout for Single Pot System Typical Layout for Multi Pot System Etch Rate Determination on ABS Materials Neutraliser Pre-Catalyst Conditioners Catalyst Pre-Dip and Catalyst Palladium Catalyst Accelerator Contaminant Limitations Metallisation Ammoniacal EN Technology Non-Ammonia EN Technology Fully Compliant EN Technology Electroless Copper Technology
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MacuPlex (Plating On Plastic Coatings)
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Contents Section 27.0 27.1 27.2 27.3 27.4 27.5 27.6 27.7 28.0 29.0 30.0 31.0 31.1 31.2 31.3 31.4 31.5 31.6 32.0 33.0 34.0 35.0 36.0
Description Troubleshooting Pre-Treatment Systems Chromic Acid Etchant Neutralisers Conditioners Catalysts Accelerators Electroless Nickel Electroless Copper Summary of Problem Areas Locating Roughness on Pre-Treatment System Test For Airborne Chrome MacuPlex Infinity Ionic Activation System Ionic Activation Process Cycle Chromic Acid Etch Palladium Catalyst Reducer Electroless Nickel Rinsing Air Agitation Filtration Ionic Activation Troubleshooting Ionic Reducer Troubleshooting
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1.0 ABS Plastic Materials
Product
Manufacturer
Material
Cycolac 1000 Triax Novodur P2 MC/P3 MC natural Lustran PG Type Ronfalin CP 55 Stapron Stylac Starrex Lucky RP 211 (Coloured) Lucky MP 100 Lustran 1455 MP 211 Sincral M 12 G Terluran (Natural & Coloured) LP 299 Techno A.S. 15 Polylac 727 Martog E.P.C. 350 JSR 21 Cycoloy Bayblend T-45 – 733 Bayblend T-45 – Mn Bayblend KU 235800 Bayblend T-45 natural Faradex Novodur P2 MC – 719 Lustran PG 299
General Electric Plastics Montsanto/Bayer Bayer AG Monsanto DSM (Holland) DSM (Holland) Asahi (Japan) Cheil Ind (Germany) Standard Polymers (USA) Standard Polymers (Korea) Monsanto / Bayer LG Chemicals Eni Chem (Italy) BASF (Germany) Shulman (France) (Australian) Chi Mei Ind (Taiwan) (Australian) (Japan) General Electric Plastics Bayer AG (Germany) Bayer AG (Germany) Bayer AG (Germany) Bayer AG (Germany) DSM (holland) Bayer AG (Germany) Monsanto / Bayer AG
ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS ABS/PC ABS/PC ABS/PC ABS/PC ABS/PC ABS ABS
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2.0 Moulding Prior To Plating The quality of mouldings for plating is one of the most important factors of the process. Poor mouldings give poor results. ABS is a rigid copolymer containing distinct globules of butadiene. In the moulding process it is vital that the butadiene is of the correct size and distribution at the surface of the plastic. This surface should have minimum moulded in stress. In large scale production at least 50% of all problems associated with the plating of ABS can be attributed to either design or operational moulding faults.
3.0 Moulding Design Criteria 3.1 Nominal Wall Thickness The ideal plastic moulding for electroplating would have all cross sectional dimensions that are completely uniform. However these mouldings very rarely exist and the aim of the designer should then be to produce a component with the minimum of variations. It is preferable for the nominal wall thickness to be in the range of, 2.3 – 3.0mm. Because of problems related to uneven cooling in the mould cavity and the tendency of heavier parts to exhibit sink marks, (dips in the surface of the moulded parts) maximum wall thicknesses should not exceed 3.8mm. Large wall thickness changes should be avoided wherever possible, as the uneven cooling during the moulding process will cause shrinkage and warping of the parts. If wall thickness changes are unavoidable then the transition between the two areas should if possible be graduated rather than stepped. As part of the mould design consideration, where there are to be changes in mould wall thickness the part should fill in the moulding cycle from the heavier (thicker) section, to the thinner section. If the mould were to be filled from the thinner section, stresses and material orientation problems would occur. 3.2 Ribs In the creation of plastic mouldings, designers sometimes feel that in order to increase the strength of the component they should increase the whole cross sectional area of the moulding. These large weight to surface area ratios should be avoided as denser parts tend to exhibit problems associated with mould shrinkage leading to thermal cycle failure.
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A successful method of gaining strength and rigidity in mouldings without drastically increasing the weight of plastic is to introduce ribs into the mould design. Simple strengthening ribs are generally linear wall projections from adjacent plane surfaces. Interconnecting ribs are also utilised to prevent bowing or warping of large plane surfaces. Ribs are also used extensively in the design of bosses to allow minimum boss wall thickness, without sacrificing strength. 3.3 Bosses Bosses are projections from the part surface, which provide some form of attachment or support for related components. They may be used for screw attachments, inserts or rivet attachments, for locating two mating parts or simply to reinforce a hole. Bosses may be hollow or solid. Sometimes the solid bosses are also referred to as studs. 3.4 Radius The radii at both external and internal plane intersections should be as generous as possible to improve the flow of the moulding material, and to lessen the chance of serious stress concentration when the part is under load. A minimum radius of 1mm external and 0.5mm internal is recommended for all plane intersections. Internal radii are sometimes known as fillets. 3.5 Appearance Design The aesthetic appearance and therefore saleability of the plated plastic part is often one of the most important aspects in the designer’s mind. Bright chromium electroplate tends to highlight surface defects and therefore efforts should be made to design parts which avoid these possibilities. A slight surface crown of 0.010 – 0.015 cm/cm is recommended over broad surface areas to reduce the field of focus and hide surface imperfections that would otherwise be visible. If it is not possible, the designer should consider whether that area of the part could have a textured surface. Without the use of these gently curved, convex surfaces, radiused angles, and a minimum of protuberances, the appearance will suffer. Sharp corners may cause plate build up and burnt deposits on edges and extreme points. Deep recesses will not chrome plate without the use of special anodes.
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Gating (injection points), mould part lines and vents should always be located in non-critical areas so as to avoid visual effects that might detract from the appearance/quality of the part. Possible sink marks should be avoided by using properly calculated ribs and bosses in ratio to the wall thickness.
4.0 Part Performance It should be remembered that during the electroplating process parts designed with sharp edges may build up heavily causing them not to fit or mate properly with other components when assembled. Whenever possible the designer should make recesses in components twice as wide as they are deep. The reason for this is that most components require a minimum thickness of electrodeposit, and in order to achieve that minimum figure in deep recesses prominent surfaces require extremely thick plated deposits. One of the consequences of trying to meet this minimum figure is that heavier deposits tend to be more brittle, which could result in inferior thermal cycle performance. This problem is one of those most often encountered and therefore consideration should always be given to electroplating current densities and resulting plate thicknesses. If the problem cannot be designed out then the minimum thickness in recesses may have to be disregarded and other points used for quality control. The consequence of this action would be that the bottom of the recess would be underplated and subject to premature corrosion failure. It should also be noted that in many cases the recess areas trap moisture and corrosive solutions and therefore provide further potential for corrosion failure. It should always be remembered that corrosion performance in accelerated testing and actual service is a direct function of plate composition and thickness. 4.1 Thermal Performance Requirements It is a pre-requisite of automotive finishing for plating on plastics that components should pass thermo cycling tests. These are typically carried out over three or more complete cycles at temperatures ranging from +80°C through ambient to -40°C. Times, actual temperatures, number of cycles and failure information is normally specific to each of the manufacturers.
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Apart from the area of electroplate distribution there are several other major factors which have an effect on the thermal performance of components. These include part geometry, resin characteristics, moulding techniques, pretreatment processing and electrodeposit composition. The latter of which will also determine how the finished part will respond to severe temperature extremes. Part geometry has a very profound effect on thermal performance. Characteristics that have proven difficult in passing thermal cycle requirements include: Solid plastic, extremely thick cross sections or heavy mass-to-surface area ratios. This is normally overcome by coring out the part and making thinner walls. Closed ring design. This method does not allow the plastic to deflect during thermal expansion. This is more critical on larger parts. The intersection of ribs on the same plane is not recommended. Lowering one rib section by as little as 1.6mm greatly reduces turbulence in moulding, thus reducing stress and improving metal to plastic adhesion. Resin characteristics have a major effect on thermal performance. As a generalisation plastics exhibit a much higher coefficient of thermal expansion than the metals used to plate the plastic. This phenomenon creates very high stresses at the plastic to metal interface during thermal expansion and contraction. The higher the stress the greater the thickness of copper is required to stabilise the expansion/contraction characteristics of the deposit/substrate. Therefore all aspects of the production of the parts including cost, have to be taken into consideration when designing for plating. Moulding techniques affect thermal performance. Gating, runner systems and venting all have to be correctly designed into the part so as to give favourable aesthetic and thermal performance. Just as important are the moulding parameters. The moulding resin must be dry, the melt temperature, pressure and cycle time must all be optimised to enhance the thermal performance of the parts. The use of the correctly controlled pre-treatment system will also have a great effect on the performance of the plated components. Variations in the chemistry or methods of application, all have an effect on the adhesion characteristic of the electrodeposited coating. The composition of the electroplated deposit and the quality of the deposited material will also affect the thermal performance of the part. Plastics, as
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stated earlier have a higher coefficient of expansion than the metal deposits. The most widely used systems today utilise copper, one or more types of nickel and chromium. When all coatings are applied correctly, the bright acid copper provides a very ductile deposit to act as a shock absorber, the semibright nickel (if used) is semi-ductile which acts as a lesser buffer to thermal shock, the bright nickel less ductile than the semi-bright and the chromium deposit is brittle and highly stressed. This system is used because the less ductile nickel and chrome deposits would by themselves perform very poorly in thermal cycle performance. The application of the ductile acid copper deposit provides a more flexible shock absorber during thermal expansion and contraction. This is its main function. 4.2 Electroplate Distribution The main control for electroplate distribution is at the design stage, some of the design criteria, have already been discussed. Selective plating is also another means of controlling electroplate distribution. The simplest method uses the application of an acid resistant paint to areas of the part that do not need an electroplated coating, prior to the electroplating process. The use of a stop-off or resist paint in recessed or low current density areas of a part is another way eliminating the problems of meeting the minimum plate thicknesses in those areas. This method is used extensively in the production of automotive plastic trim. To meet the protection requirements the stop-off is usually given a top coat of paint after the electroplating process. Stop-offs or plating resists are normally applied by conventional spray, dip or brush techniques. Care must be taken at the design stage to ensure that the application of a stop-off is applied in a low current density area at a point where any electroplate build ups will not interfere from the parts assembly or appearance. The use of auxiliary anodes to enhance the thickness of the electrodeposit in recessed areas can also be used. This allows the designer a little more freedom but at the expense of fitting the anodes in production.
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5.0 Moulding Design Considerations z Integral parts should be used to avoid welded joints z Gates should be put in non-appearance areas and should be 50% larger than for conventional mouldings z Ribs and bosses should be designed to eliminate “sink” marks z Texturing can be used to break up large flat surfaces and hide any defects such as scratches z Draft angles should be at least 1º for easy removal from the mould (preferably 3º) z Parting lines should be put in non-significant areas if possible z “Close tolerant fits” must include the final electroplate thickness requirement in the part design z Wall thickness should be as thick as possible for rigidity and adhesion (minimum 1.5 mm) z Plate uniformity, as a result of high and low current densities must be considered in the initial design z The designer should take into account and be aware of: ⎯ ⎯ ⎯ ⎯
V grooves 90º angles Keep lettering as low profile as possible Make angles as large as practical
z Consideration should also be given to blind recess rack contact areas
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5.1 Moulding Considerations The surface of a moulding, which is to be plated in a decorative finish, i.e. bright chromium must be free of any surface defects. Weld lines, sinks, dull poorly packed areas, flash, gas burns etc. will all show evidence in bright reflective plate. Parts to be plated with satin or Velour’s nickel do not require the same degree of surface finish. 5.2 Surface Composition Requirements In order to obtain the required mechanical bond between the ABS and the electroplated metal, the plastic surface must represent a uniform composition of the two or more components, which are present in a plating grade plastic. With ABS, the acrylonitrile-styrene and butadiene-styrene are uniformly mixed and cross linked in such a way that the surface should always contain a fairly good mix. ABS however also contains varying amounts of pigments, flow agents, anti-oxidents and other ingredients which, when the plastic is subjected to high temperatures and high sheer rates in the moulding operation, may cause a separation of components in such a way that the finished moulded surface is not uniformly constituted. This will often result in hard to etch edges at the last to fill areas of the mould. Correct venting of the mould is extremely important as well as a slow fill speed as these will help to reduce some of the surface variations. ABS is also available in flame retardant grades, and while some are plateable, they always suffer from lower adhesion values than the non-retardant grades. Surface problems also occur in moulding from film build up on the mould faces. 5.3 Internal Moulding Conditions Whilst visually the surface of a moulding is very important, the inside of the component also has to perform. Most plated parts must perform some other function other than being aesthetic. They may have to mate with other parts and therefore will have to be moulded and plated to tolerances. When moulds are constructed they may not meet the dimensional requirements of the component due to shrink rate of the grade of the polymer used. Therefore the moulding parameters are often “adjusted” to control the dimensional variation. This can cause problems when the part is plated. The reason for this is that when it is necessary to increase the size of a moulding i.e. minimise the shrink rate, the part will require over packing. This is often achieved by using a fast fill rate and relatively cool barrel temperatures. This over packing forces stress into the part and two things happen in and after plating.
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First, a cold melt and fast fill speed will create a hard glossy surface which will result in lower plate adhesion, as low as 10% of that achievable with good moulding practice. Second, the moulded in stress will begin to relax when the part is being processed through hot process solutions. This relaxation may cause blisters or loss of adhesion during the plating sequence or in post plating thermal cycling of the part. If parts are moulded to a smaller size (under packed) they may not suffer from moulded in stress, but are likely to suffer from sinks or a non-fill condition. 5.4 Water Cooling Moulds are manufactured with cores for the circulation of water to provide the necessary control of mould temperature. Exact mould temperature control is essential to impart uniform cooling and to minimise stresses within the part. The size and location of the water lines should be carefully considered. Water lines set too close to the surface of the mould can result in hot and cold spots due to the low coefficient of heat transfer. Each of the cores should be spaced equally with separate inlets and outlets for each cavity and core. Zone heating and cooling of large areas, have been successfully used to obtain even flow and reduce moulded in strains. When planning this type of mould the core lines are drilled vertically with no cross sections. The sprue area is normally maintained at a higher temperature than the outside of the part so that the material will remain warm. This will allow the part to be filled with reduced injection pressure. However, cycle times become a consideration if this area is kept too warm. Mould temperature can affect the adhesion on the plated part. Therefore, if adhesion is critical on a given part, the mould temperature should be optimised by trial and error, using experience and adhesion or thermal cycle tests as the test criteria.
6.0 Equipment Selection General purpose ABS resins have been found to be the simplest to mould and plate and are therefore the most common polymer used. The best type of moulding equipment for this polymer is the reciprocating screw machine, which if kept in good repair will achieve mouldings capable of giving about a 60% improvement in the metal to plastic adhesion over that of parts moulded in the alternative ram machine. Of course these figures take into account the process solutions being used at optimum conditions for each type of moulding. It has been noted that the difference in adhesion performance can
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be as great as 170% when screw injection methods are properly developed over those of the ram machine. 6.1 Drying ABS and other polymers are well known for their ability to absorb moisture from the atmosphere. This moisture if not removed before moulding will cause many problems. If not removed the moisture is converted into steam, which is compressed and forced into the part, normally just under the surface of the moulding, forming as bubbles. At the surface of the moulding these bubbles may form blisters or teardrop shaped splay marks. The first indication of these phenomena is usually just after electroplating where heating during processing has expanded the trapped moisture, forcing it in the only possible direction, to the surface of the mould. Moisture held a little further under the skin of the polymer may become evident as blisters during thermal cycle testing. In both cases it is possible to misinterpret the defects as plating blisters. Dehumidifying hopper dryers are recommended where the ABS polymer can be held at 80-85°C, for 2-4 hours before being used. Hopper dryers are available which have sensing devices, which ensure that the hoppers are maintained full, allowing enough time for the polymer to dry out before use. It is also recommended that moisture alarms should be fitted to the hopper dryers. 6.2 Process Controls Consistent repeatable mouldings require control and precision in monitoring and maintaining the temperature of the mould. Therefore properly sized mould heaters and coolers are a prerequisite for quality. When starting to mould a new polymer, it is advisable to follow the recommendations of the supplier with regard to the temperatures, pressure and cycle time, at least as a starting point. All heating zones on the plating machine should be controlled by pyrometers and the indicated temperatures of these recorded at regular intervals. Temperatures should be controlled on both sides of the mould cavity, using temperature control units with indicating pyrometers. The temperature of the plastic melt has a very high influence on the metal to plastic adhesion in the finished plated part. In moulding, the temperature of the melt should be such that the mould will fill easily under slow injection speed conditions, producing a stress free part.
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Low melt temperatures demand higher injection moulding pressures together with high fill speeds and should be avoided. The polymer suppliers recommendations for the melt temperature for each grade of material should be consulted before moulding begins. It is normal to use the higher end of the melt temperature range as a starting point, whilst taking care not to degrade or burn the resin. All of the pressure settings, such as clamp, injection, hold and ejection should be controlled. It is important to control the fill time, which is governed by the injection pressure, as this is the most important single constant when moulding for plating. Any variations in the melt temperature or mould temperature will also affect the fill time. (The fill time is the time measured by stopwatch, from when the plunger or screw starts to move forward, until it stops). 6.3 Fill Speed / Injection Speed As stated previously this is the single most important aspect of moulding high quality components for plating. Fast fill rates normally induce high stress levels within the moulded components. These parts when electroplated will not have satisfactory adhesion and so not meet thermal cycle requirements. In order to obtain the highest quality mouldings the fill speed should be as slow as possible in order to produce mouldings with the lowest possible moulded in stress. The optimum fill speed will depend on part size and stock temperature being used. As a general rule, the average fill time required for plating should be twice that for parts of the same size that do not require plating. Any additional time for fill speed would be beneficial in obtaining maximum adhesion from the plated parts. 6.4 Handling of Moulded Plastic Parts For Plating After moulding the components carry a static charge. It is important that they are protected from attracting dust particles. The surface if contaminated may not release these particles even during the pre-treatment process. This in turn may cause a background haze or speckle to be evident after the electroplating process. It is also imperative that the newly moulded components are handled in a clean and careful way, since any less may create surface damage and subsequent reject parts. The slightest blemish on the surface of a moulding is
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very often magnified during the electroplating process and so rejected. It is advisable that operators wear clean cotton gloves whenever handling the polymer mouldings prior to plating. Fingerprints and machine lubricants leave films that may still be visible through the electroplated finish, or worse cause skip plate to occur, especially if there is no pre-cleaning system in the early process stages. It is possible that the components may become contaminated by greases or oils in and around the moulding machines, particularly in moulds that have moving parts. Mould release agents should never be used when moulding parts for plating. The importance of avoiding oils and mould release agents, (especially silicone based sprays) cannot be emphasised too highly when moulding for plating, even to the possibility of airborne contamination from sprays used some distance away from the moulding machine. The degating of parts requires particular attention, especially not to leave surface defects. With some components it is normal to leave the runners intact on the component to provide a means of racking during the electroplating process. The newly moulded components should on extraction from the mould cavity be adequately protected from damage by scuffing or scratching. Tissue paper, cellophane, or polyethylene bags are satisfactory for individual wrapping. Where polyethylene bags are used, the parts should be adequately cooled before packing. Compartmented containers each holding an individual component will ensure safe transportation both to and from the plating shop. 6.5 Checking For Moulded in Stress There are several chemical immersion tests for moulded in stress. There are two simple immersion tests that can be used to give a subjective indication of the degree of moulded in stress. The glacial acetic acid test is a useful method of testing the quality of ABS mouldings for stress and surface uniformity. If after testing the ABS mouldings crack, this is an indication of very high stress levels. Cracking will often converge on gate areas and through other high stress areas such as sharp corners and abrupt changes in mould wall thickness. The severity and location of the cracks can be used by the moulder to improve his manufacturing techniques. The second test involves using a dye containing solvent which is absorbed into the ABS at different rates dependent upon the stress levels at the surface of the moulding. The variations of colour intensity on the surface of the moulding after the test indicate the potential levels of stress.
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Parts with high stress levels are more prone to distort during processing through hot solutions. They are also more likely to fail in thermal cycle testing, because the moulded in stresses will relax, causing a greater movement in the plastic, which in turn puts greater stress on the metal to plastic bond. These tests also give an indication of the distribution of the butadiene over the surface of the component. Uniform whitening or dyeing of the surface of the moulding is an indication of a good moulding. Poor mouldings will have heavy white or dyed areas and dark shiny areas on the same part, these surface variations can lead to both over and under etched areas on the same moulding.
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7.0 Moulding For Plating Considerations and Effects z Use a reciprocating screw moulding machine z Proper Drying of Resin ABS pellet must be pre-dried for 2 - 4 Hrs at 80 - 85ºC immediately before moulding. Moisture in the resin can cause “splay” or delamination on the part that may result in a blister z Proper Fill Speeds Small components up to 90gm Larger components
5 – 7 seconds up to 25 seconds
Too fast a fill speed can over pack a mould thus making it harder to etch which will result in poor adhesion of the electrodeposit. z Proper Melt Temperature 245 - 270ºC Too cold a melt temperature causes internal stress to increase and become incorporated in the part leading to uneven etching of the substrate and thermal cycling test failure. Too hot a melt may cause the plastic material to degrade and thus give poor adhesion z Proper Mould Temperature 65 - 68ºC Too cold a mould temperature will cause the plastic to “skin”, i.e. the first material to hit the mould wall hardens and the hot material under it flows creating a surface skin effect that may cause delamination z Proper Cooling Time Longer cooling times promote the dissipation of internal stresses z Highly Polished Mould Poor mould surfaces can cause defects in the moulded part, such as pits. These show up in the final plate and cause rejects
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8.0 Mould Release Agents and Fillers Silicone type mould release agents should not be used. These compounds are extremely difficult to remove and usually lead to adhesion failures (blisters) or skip plate. Silicones interfere with the function of the etching process. Moulders of plastics for plating do not generally use mould release chemicals, if it is necessary to use a mould release, then a stearate or soap type material should be used sparingly. In some cases, fillers are added to plastics for increasing strength such as glass fibre, fire retardants (antimony trioxide (Sb2O3) or organic phosphate) or to impart colour (carbon black, titanium dioxide, TiO2). These additives may require extra process control in the metallization processes and may result in a poorer grade of surface finish. For example, glass fibres will usually result in a rougher surface to the finished part. Some fire retardants can diffuse to the surface during etching leaving a film that is difficult to wash off and cause adhesion failures. If this non adherent layer can be recognised and removed good adhesion may be obtained. When colorants are etched from the plastic substrate they are normally retained as suspended as particles in the various process solutions. However once a critical concentration has been reached, shelf roughness i.e. star dusting will occur on the processed components. Other fillers such as calcium carbonate (CaCO3) are added for ease of etching of a difficult plastic. These fillers are preferentially etched out of the surface to create the bonding sites required for good adhesion. Large particles or pools of filler can create poor surface appearance. Here the appearance of the final electroplated coating may take on an orange peel effect. It is normal when processing these materials that the customer is willing to accept a slightly lower standard providing the adhesion of the electrodeposit is satisfactory.
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9.0 Quality Control of Mouldings Whilst some defects may be obvious, others are not; moulded in strain, entrapped water and micro-pits are some of the more troublesome, less obvious defects. The following tests may give an indication of faults in mouldings prior to plating z Acetic Acid Test Incorrect moulding practise can cause high internal stress which can seriously affect the moulded component during plating. Glacial acetic acid testing in accordance with ASEP TP-203 will give an indication as to the quality of the ABS moulding. z Red Dye Test for PC/ABS Mouldings This is an alternative test to evaluate the surface of the moulded components. As with the glacial acetic acid test the interpretation of the test results should be taken as an indicator rather than a guarantee that components will not process satisfactorily. z Oven Test Moulded samples may be placed in an oven at a temperature of 90±5°C for up to one hour. Deformation of the part must be related to plated part performance. z Test for Occluded Water Immersion in boiling water for one hour is a useful test for detecting entrapped moisture. However the small blisters raised by this test will never be as severe as water blisters produced during the conditioning and plating process.
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9.1 Glacial Acetic Acid Test For ABS (ASEP TP-203) Aim This test method is for evaluating raw ABS mouldings for surface stress, rubber dispersion in the surface, and internal stress. This is not a quantitative test and should be used only for identifying and correcting potentially serious stress or rubber distribution problems in raw ABS mouldings. Apparatus A glass or plastic container large enough to completely immerse the part to be tested. A thermometer for checking temperature of the acid. Reagents Anhydrous, reagent grade glacial acetic acid. The acid should be stored in a sealed container to prevent moisture absorption from the air. DO NOT contaminate the acid with water. Do not dip wet parts in the acid. Once the acid is contaminated with water the test will not work.
Procedure 1. Totally immerse the part to be tested in concentrated glacial acetic acid at 24ºC + 3ºC for 30 seconds. 2. Immediately rinse the part in running water to remove the acetic acid, and allow it to dry at room temperature. Do not wipe or hot air dry! 3. Evaluate the part for surface stress and rubber distribution. 4. After making sure that the part is dry, totally immerse the part again in the concentrated glacial acetic acid at 24ºC + 3ºC for 2 minutes. 5. Immediately rinse the part in running water to remove the acetic acid, and allow it to dry at room temperature. Again do not wipe or hot air dry! 6. Evaluate the part for internal stress.
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Interpretation z Surface stress is indicated after the first acid immersion by small dense patterns appearing on the part surface. The more prevalent and dense the pattern, the higher the stress. z Rubber distribution in the surface is indicated by the variation in colour on the surface of the part. Poor mouldings will have heavy, white areas and dark, shiny areas on the same part, indicating non-uniform dispersion of the rubber phase. On an ideal moulding, some surface whitening will occur uniformly over the part. z Cracking entirely through the thickness of the plastic after the second immersion is an indication of very high internal stress in the part. Again, the severity of the cracking indicates the severity of the stress.
Reporting z The report should include the manufacturer of the ABS, the grade, the batch number, and the moulding conditions. z The report should identify the degree of colour variation and cracking and the locations of these areas on the part.
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9.2 Red Dye Stress Test For PC/ABS Mouldings Aim This test method is for evaluating raw ABS mouldings for surface stress, rubber dispersion in the surface, and internal stress. This is not a quantitative test and should be used only for identifying and correcting potentially serious stress or rubber distribution problems in raw ABS mouldings. Equipment ⎯ Nalgene tank or other suitably resistant material ⎯ Safety equipment , glasses/goggles, gloves
Solution Make Up ⎯ Isopropanol ⎯ Acetone ⎯ Ceres Red 3R Dye
750mL/L 250mL/L 0.08g/L
Procedure Immerse part in the red dye solution for the appropriate amount of time, typically between 5 and 10 minutes dependent on material. Immediately rinse part in running water to remove excess dye and blow part dry using cool air. Interpretation Pink or reddish colouration variations are an indication of surface stress. If the colour change is minimal the part may not be etched or the test material may require changing. If the variation in colour change across the surface of the component is extensive the degree of etching may also mirror this change and the subsequent adhesion of the electrodeposit may be compromised due to the variation in stress of the base material and its ability to be evenly etched.
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Reporting The report should include the manufacturer of the ABS, the grade, the batch number, and the moulding conditions. The report should identify the degree, depth and location of colour variation on the components.
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9.3 Test For Trapped Moisture in ABS Mouldings ABS granules should be dried for an absolute minimum of 2 hours at 82 85°C before moulding. Failure to do so will allow moisture to become trapped in the moulded components. If moisture is trapped it will normally lie just beneath the surface of the moulding. The trapped water then erupts as a blister during the plating process.
When blisters are evident on plated components, there are two courses of investigation.
Cut and peel back the blister. Examine the underside of the blister to see where it originates. If at the plastic, check the underside of the coating for delaminated plastic. Check the surface of the plastic for divots, (depressions in the moulded components surface, delamination).
If moisture is suspected, take some fresh mouldings and place in boiling water for one hour. During this time it is normal for most ABS mouldings to deform with the heat from the boiling water. After one hour, remove the mouldings from the water and examine the surface of the components for areas of plastic which have blistered or delaminated from the surface of the components.
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10.0 ABS Plastic Quick Guide 10.1 Resins ABS -
TERPOLYMER A. Acrylonitrile B. Butadiene S. Styrene
EHA -
ABS plus polycarbonate (up to 40%)
BAYBLEND -
ABS plus polycarbonate (45%)
PC/ABS -
Polycarbonate (between 40-80%) remainder ABS
10.2 Defects z
Blisters -
z Adhesion Failure ABS Stress Test -
Moisture or gas entrapment, heat splay, contaminant or contaminated regrind, silicon type mould release. Silicon type mould release, stress. Acetic acid immersion for 1-3 minutes A. Cracking or breaking - highly stressed area B. Exfoliation of plastic - indicated skinning or delamination. C. White discoloration - improper molecular alignment which indicates a stressed area.
z Skip Plate -
Silicon type mould release.
z Pitting -
Surface defect from mould or use of >6% regrind material. Regrind is the use of scrap or previously used ABS material.
z Roughness -
Surface defect from mould, ABS dust, shop dirt or impurities in regrind.
z Burning or Treeing -
Flashing or poor trim on mouldings.
If a defect is present in a moulding, it will be present and magnified after plating.
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11.0 Plating Resist Resist paints are used to mask areas of the moulding which do not require plating. The reasons for this may be economic e.g. large components where the backs of the components are not important. It may be design requirements such as electroplated frames with painted backgrounds. Or it may be a physical requirement where stresses imparted from the electrodeposited coatings could cause warping of the components after processing. The methods by which these resist paints work are twofold. Both methods rely on the resist paint holding enough hexavalent chromium in the coating to be released as a poison during the catalytic/activation process. The first method is where the resist material contains a certain amount of hexavalent chromium which is applied as part of the resist process. The second is where the applied resist material absorbs some of the hexavalent chromium during the etching process. The two types of resist paint used in processing plastic are known as:
Active -
Has chrome mixed with resin.
Passive -
Resin absorbs chrome from etch.
Problems Associated With Both Methods Overplate -
Low paint thickness, neutralised chrome in the resist
Skips or Voids -
Overspray, bleed out, poor quality resist paint with high absorption of chromium.
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12.0 Electroplating Rack Design 12.1 Part Contact When designing plating racks several things must be taken into consideration. First and most importantly the initial current is only carried through the initial thin surface layer of metal normally using stainless steel rack tips. The tension required to hold the components may result in the plastic being distorted and intricate design may be required and customised racking to obtain the best deposit, hence the number, type and position of rack contacts are very important. In general, 25% more contacts are required for plating ABS than for conventional metal plating. This does not take into account those components that are difficult to secure with evenly spaced contacts. When processing this type of part extra press or point contacts might be used in non-critical areas, thicker electroless metal deposition may be required or the composition of the electroless deposit might have to be modified in order to avoid ‘burn off’.
Sq Decimetres of Component
No. of Contacts Required
0 – 2.32
1
1.55 – 4.65
2
4.65 – 9.29
4
6.97 – 18.28
6
13.94 – 27.87
8
23.23 – 37.16
12
27.87 – 55.74
16
Other general rules for ensuring good contact are as follows: z Contact should be made in medium to low current density areas. z The contacts should be sloped back to the frame to prevent dripping onto parts below. z The contact tip should be made from stainless steel, titanium, or phosphor bronze stainless steel or titanium combination.
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z The contacts should not lose tension after repeated loading. z The contacts should not shade a significant area of the part. z The contacts should not come out of adjustment after repeated loading. z The contacts should be relatively easy for the operator to load. z Use enough contacts to carry the current, even if one is lost as a current source. z Spring contacts should be designed with a sufficient radius on bends to prevent weakening and fracturing of the spring. z Spring contacts should be designed so that the bend closes when flexing and should allow for adjustment of contacts whilst in service. z Orient sharp points and corners of the parts to the centre of the rack. z Areas of the part where contact is made must be properly supported to avoid part distortion. z Avoid placing a contact in a blind hole or deep recess as burn-off or skip plate may occur. z Rounded point contacts should be used where possible instead of flat contacts to avoid skip plating from poor rinsing. z Contacts should not be placed on high quality surfaces due to the possibility of misplating or discolouration in the contact area. z All contacts must be free of plastisol and primer in the area where they will contact the part. If the contact areas are not clean, bipolar skipping or chrome bleed out can occur. After each plating cycle, the build up of electroplated metal on the jig contacts should be removed to avoid nodular build up, and maintain good electrical contact.
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12.2 Rack Coatings The normal rack coating used in the manufacture of plating racks is Plastisol. This material serves four purposes: 1. To protect the rack members from the corrosive plating solutions. 2. To inhibit plating of the rack by the pre-plate system. 3. To eliminate plating of the rack by electroplating solutions. 4. To insulate the contact tips to prevent robbing of current from the part at the point of contact. Improper coating selection will lead to either deterioration of the rack or over plating of the rack coating, usually resulting in the loss of ability to chromium plate parts effectively. Even using Plastisol as a coating, it requires proper application otherwise the effects will be: A too hard coating will become brittle and crack in a short period of time becoming ineffective against cross contamination of process solutions resulting in potential over plate of the rack coating. A too soft coating will become porous and drag solutions from one tank to another. The manner in which the control of rack plating is carried out involves five steps in the preplate system. The best combination of time, temperature and concentration must be determined for each of these steps in order to control rack plating.
1. Retention of chromium in the rack occurs in the etching process, hexavalent chromium poisons the electroless reaction, thus preventing metal deposition. 2. Neutralisation of the excess hexavalent chromium occurs without removal of the chromic acid absorbed in the rack coating. 3. Immersion in the catalyst (activator) solution must be controlled to ensure proper absorption in the plastic, without catalytic absorption in the rack coating.
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4. Immersion in the accelerator must be controlled to remove excess catalytic material from the plastic and to remove any catalytic material from the outer skin of the rack coating. 5. The initiation rate of the electroless bath must be carefully controlled. 12.3 Rack Conditioning If the electroplate rack is to be used in the pre-plate cycle, the rack should be processed through the nitric acid rack stripping process first to remove some of the surface plasticizers. This helps to ensure proper chromium retention in the rack coating for control of rack plating. The same effect can be achieved by soaking new racks in chromic acid etch solution prior to their use in production. Plating racks should be processed through the rack stripping solution after each plating pass. This will ensure that only clean functional contacts will be used. Finally, split or worn jig coatings should be repaired as soon as possible as they can create rejects due to bleed out through solution retention or worse, cross contamination of process solutions, shortening the solution’s effective life. 12.4 Rack Stripping Solutions As already stated it is preferable to strip the plating racks after each pass through the electroplating system. On some plating plants/installations this is not possible either due to age of the process plant, the availability of space or personnel, or production requirements versus the number of plating racks available. The reason that it is advisable to strip the rack tips is that normally the final deposit is chromium. As a deposit chromium is extremely passive and reprocessing chromium plated racks would result in the components failing to electroplate due to misplate whereby the electroless deposit is burnt away from the rack tips thus losing electrolytic contact.
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There are three options for stripping the electroplate build up from plating racks. 1.
After each electroplate pass, either with the rack loaded or unloaded of work the rack can be made anodic in a 100g/l sodium hydroxide solution to remove the chromium. Normally 6v for 5 minutes is enough to remove the chromium deposit. The above does not eliminate the problem as it still leaves the electroplated nickel and copper on the plating racks. These deposits if left unstripped for successive sequences will create misplates by the following means: The deposit thickness will increase until it interferes with the components being processed shielding some of the significant surfaces and not allowing them to electroplate properly. Parts may fall from the process racks during processing as the electroplated rack contacts may not be able to hold the components correctly. Roughness may occur due to metal flakes being lost from the electroplated rack tips as process solutions attack the deposit and subsequent agitation loosens the flakes of metal. This method therefore relies on a proper maintenance regime where the rack contacts are fully stripped after a specific number of passes through the electroplating system.
2.
Chemical Stripping: Nitric acid based rack strippers are available from many sources. MacDermid supply two products. Metex SS2 which is a ready made nitric acid based rack stripper that contains additives that enhance the stripping capability of the acid medium. For those customers who require more control there is an additive for nitric acid called Metex SS2A. This is the additive used in the Metex SS2. The customer has the ability to control both the concentration of the acid and the additive which may enhance the capability of the nitric acid. Both types of solution have a finite life which is dependent upon the concentration of the acid, the operating temperature of the solution and the metal concentration in the strip solution. Processing times vary on the age and temperature of the solution together with the thickness of the electro-deposited metal. The continued use of nitric acid over a period of time will gradually degrade the plastisol coating. However this takes a long time and using this solution will guarantee that any areas of rack plate will be removed. A second stripping solution that can be used is based upon a mixture of dilute sulphuric acid, hydrogen peroxide and MacuPrep G5-S where the MacuPrep material is a stabiliser for the hydrogen peroxide. This stripping solution is normally used when reprocessing ABS components but can be used for plating racks where companies wish to avoid the use of nitric acid.
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Electrolytic Stripping: An electrolytic stripper is available called Metex SS10. It operates at a pH of 6.0-6.5 and at a temperature of 45ºC making it a safer product to use. It strips racks consistently at a given rate, faster than its chemical counterparts. However the customer has to realise that this is a ‘plating solution’ and that without the correct additions of additives it may attack the rack contacts. Properly maintained it is an effective, neutral pH rack stripper. The negative aspect of this process is that where rack plate occurs the electrolytic stripper may not successfully remove it.
Two other points to note are relatively standard when discussing plating racks. The first is to dissuade operators from using pliers to remove rack plate build up. The twisting/shearing action alters the tension and possible orientation of the rack tip. It may also tear the plastisol coating on the springs. This can lead to the racks having a shorter working life as either the spring contact may be lost or chromic acid seepage may cause rejects. The other point is to persuade the operators not to drag the plating racks across the floor as the scuffing action wears through the coating, leading to chromic acid retention in the etch solution that bleeds out during subsequent processing, contaminating other process solutions.
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13.0 MacuPlex The Chemistry Plastic Substrates Suitable for Processing using the MacuPlex ABS System Include: z ABS z Bayblend [A.B.S./Polycarbonate alloy] z Stapron z Noryl z Polypropylene (filled) z Polyamide (Specific Grades) Plastic substrates which are not suitable for processing by the MacuPlex ABS system Include: z Polycarbonate z ULTEM 2310 z Kemetal z Some Polyamides
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13.1 Pre-Treatment Stages z Etching/Surface Conditioning These are surface modifiers that create a structure or topography to promote or enhance adhesion of the metal deposit to the plastic substrate. z Neutralisation This is the removal of harmful process chemistry from the surface of the substrate. It may also create modification of the substrate by further adjusting the surface topography of the plastic and making it more receptive to catalysation. z Catalysation Surface adsorption of a catalysing agent that will enhance and promote electroless deposition. z Acceleration/Reduction This refers to the bringing of the catalyst material to an active state ready for metallization z Metallization Is the initial deposition of a metal by chemical means before subsequent electroplating.
The performance of each stage has a significant effect on the finished product and should be carried out and controlled within strict limits of operation.
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14.0 ABS Plating 14.1 An Introduction The theory of Plating on Plastic substrates is quite simple. A suitable plastic i.e. an ABS terpolymer is chemically treated to roughen the surface of the component. After neutralising the initial chemistry, it is then put into an activator solution, normally containing a palladium tin colloid, which is attracted to the surface of the plastic. The component is then immersed in an accelerator to remove the secondary protective metal film (tin) from the surface of the Palladium. The activated and accelerated component is then immersed in an electroless metal deposition solution, which deposits a thin layer of metal over the whole of the plastic substrate. This metal layer then becomes the conductor for subsequent electroplating. With all of the MacuPlex pre-treatment products their successful operation relies upon the basic laws of chemistry i.e. z Time z Temperature z Concentration By adjusting any combination of 1 to all 3 of these, the characteristics of the various processes will change Time This is relatively difficult to adjust when using some older automatic plating machines. Manual adjustments can be made but these upset production schedules. Modern process machines have the capability for change, however production schedules may still be affected. Temperature Can be altered by adjusting the solution thermostat. Changes are not immediate as time is taken to either warm up or cool the process solution. This can be a time consuming operation when adjusting the temperature of solutions by several degrees centigrade, but it is the easiest parameter to vary up or down.
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Concentration This is the simplest characteristic to increase, as it is a simple chemical variation. To reduce the concentration however may require partial dumping and dilution and this is more difficult to control.
15.0 ABS Pre-Treatment 15.1 Pre-Etching and Etching As ABS is still the most widely processed plastic material, the following section has been written with this in mind. Consideration has been given to those ABS/PC polymers that require some form of pre-etch/surface conditioning treatment. The system discussed is that of a standard colloidal type activation system. Other (ionic) activation systems will be discussed separately. There are other polymers that may use the same method of etching fillers from the surface of the plastic i.e. polypropylene and so the same principles will apply. Lesser more difficult to process plastics may rely on surface conversion chemistry such as a solvent swell; these materials will require processing according to their individual needs. Etching is the action whereby the ABS surface is rendered hydrophilic (water loving) and is chemically roughened to provide a mechanical key for the deposition process. It is advantageous that where possible moulded ABS components should be given a pre-etch treatment. The aim of which is to begin the wetting process of the normally hydrophobic material especially where the components have difficult moulded in knurled or textured surfaces. As the component is immersed in the etch solution the strong oxidising acids dissolve the butadiene particles in the surface of the ABS creating thousands of microscopic holes, thus providing the bonding sites for the metallic layer. This is evident by the degree of matted effect on the surface of an etched and dried plastic substrate, when compared to the gloss surface on a new component. The conditions of etching are very important as the degree of metal to plastic adhesion is wholly dependant on this stage, i.e. if the chemistry is in balance and the temperature is correct then the effect of time would be the controlling factor to achieve the best adhesion. On the next page there are SEM pictures of two different ABS materials, both have been heavily etched to demonstrate the possible variations between different ABS substrates. The honeycomb etched surface can easily be seen on both polymers. Although treated in the same etchant material, at the same time/temp/concentration. the surface topography is quite different. This may be due to the variation in the constituents of the two ABS materials or to variations in the way in which the two components were moulded.
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Some considerations based on the SEM pictures are: Constituent ratios of ABS polymers differ and will give variations in the moulding process resulting in different etched surface characteristics. If the ABS materials and moulding parameters are not properly controlled the electroplating process may not be able to overcome the potential problems. If the etching time is too short the cavities will not be etched out completely leading to incomplete coverage and poor adhesion. Conversely, if the etching time is too long the surface layers of the ABS material may be undercut weakening the surface structure of the ABS plastic resulting in poor surface finish and potential poor adhesion of the electrodeposit. The above effects might also be seen by varying either the concentration of the etch chemistry or the temperature of the etch solution. Modern etch solutions are typically based upon a mixture of chromic and sulphuric acids together with a proprietary additive to reduce the surface tension of the process solution. The ratio of the acids is most important as this governs the chemical effectiveness of the etch solution. One of the most common questions asked is “What is the correct ratio/concentration for the make up of these acids?” The answer is that etch solutions will work over a very wide range of concentrations at what is normally referred to as balanced saturation chemistry. What this means is that if either of the two acid materials are added to excess some of the chromic acid will be precipitated, causing blocked agitation coils. Therefore the general rule for the make up of a chromic acid based etch is: As the chromic acid is reduced in concentration, so the sulphuric acid is increased. There are as always some exceptions where customers use a specific mix that is satisfactory for their use, otherwise consider: ⎯ Chromic acid ⎯ Sulphuric acid
300 - 450g/l 320 - 420g/l
e.g. ⎯ Chromic acid ⎯ Sulphuric acid
400g/l 360g/l
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A new etch contains only chromic and sulphuric acids, and is quite aggressive by nature, it is considered by some that the use of a surface tension reducer may not be required at this time. This may be true in some circumstances but for most operations where optimum topography is important additions of a proprietary surface tension reducer such as MacuPlex STR or MacuPlex Floenx NF is recommended. During the etch process some of the hexavalent chromium is reduced to trivalent chromium. This trivalent chromium initially acts as a buffer, softening the aggressive nature of the etching action. However, as the trivalent chromium concentration grows to >20gm/lt, it becomes an etch retardant. The consequences of this are that variations in the consistency of the surface topography are reduced so that areas of greater stress may not be etched sufficiently to guarantee good adhesion of the subsequent electro-deposit. If this variation occurs failures may be evident such as poor adhesion during thermal cycling, blistering of the deposit at or around stressed or gate areas or skip plate, also normally seen around gate areas. For some years the standard remedy or control of trivalent chromium was to either dilute or discard the etch solution. Today electrolytic regeneration of the trivalent chromium back to hexavalent chromium is considered standard practise. The ABS materials processed today may be either classed as a natural terpolymer (pure ABS) or they may contain various additives/colorants that once removed from the surface of the moulding are inert particulate substances which over a certain concentration in the etch solution will begin to cause rejects from a problem known as stardusting. This phenomenon is caused by the settlement on horizontal flat surfaces of the inert particulate matter that is not removed by either rinsing or the subsequent process operations. In order to combat this problem it is advisable to install a filtration system on the etch solution. Due to the solution being extremely corrosive this equipment should be made from a suitably corrosion resistant material such as Kynar (PVDF). Although the filter units are expensive the need for quality of finish versus the costs of frequency of etch replacement make them a cost effective way of maintaining etch quality. Today it is now possible to effectively close loop the chromic/sulphuric acid etch solution. This is achieved by a mixture of etch filtration, regeneration and evaporation. To accomplish this however neither the etch solution or the following cold water rinses should be allowed to be contaminated by anything that cannot be easily removed. A final requirement for this closed loop is periodic high temperature digestion of the etch solution. The reason for this is that as the butadiene is removed during the etching process some of the
MacDermid plc, Palmer Street, Bordesley, Birmingham B9 4EU International Telephone: + 44 (0) 121 606 8100 Fax: + 44 (0) 121 606 8300 Sales Order Fax: + 44 (0) 121 766 6883 www.macdermid.com
MacuPlex (Plating On Plastic Coatings)
Technical Package
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organics from the plastic are dissolved into the etch solution. These contaminants gradually build up increasing the density of the etch solution and affecting its efficiency. The simplest way to remove these organic materials is to break them down using heat and filtration. Once the plastic surface has been etched, the hexavalent chromium that is both on the surface of the ABS and trapped within the etched matrix of material must be effectively neutralised and rinsed away before the activation stage can begin. Neutralisers such as mixtures of MacuPlex 9338 and hydrochloric acid are materials, which at low concentration chemically reduce damaging hexavalent chromium quickly and effectively. Rinsing alone will not be sufficient in removing the hexavalent chromium from blind holes and recesses either in the component or from the plating racks. Failure to remove this chemical may result in skip plate due to ‘bleed out’ where the hexavalent chromium poisons the surface of the plastic. If this type of contamination is allowed to continue it will result in the contamination of the other process solutions rendering them ineffective. There would be no other alternative other than to discard and remake these solutions.
15.2 Catalysing or Activating Standard or classical activators or catalysts are materials, which contain a precious metal i.e. colloidal palladium, together with a protective metal coating (tin) in a stabilising medium which is normally an acid chloride base. Their aim is to allow the colloidal palladium to be adsorbed onto the surface of the ABS plastic, even down into the etched cavities. During processing this may be the first noticeable change in appearance of the component, where it will acquire a light tan to brownish colour, which unless the component is black can easily be seen. Such a visible change in colour is a good indication that the activator is working properly. These palladium/tin catalysts which can be used in an acid or acid/salt (sodium chloride) base are very stable and extremely tolerant to contamination without breaking down. When a colloidal palladium catalyst is installed it is normal to use a pre-catalyst dip of the same chloride base and concentration as that used in the catalyst itself. As most installations use hydrochloric acid as the base for the catalyst solution, it is advised that a 20 25% hydrochloric acid dip is installed directly before the catalyst.
MacDermid plc, Palmer Street, Bordesley, Birmingham B9 4EU International Telephone: + 44 (0) 121 606 8100 Fax: + 44 (0) 121 606 8300 Sales Order Fax: + 44 (0) 121 766 6883 www.macdermid.com
MacuPlex (Plating On Plastic Coatings)
Technical Package
Page 42
The pre dip performs two major functions: It acts as a weak hexavalent chromium neutraliser for any chromic acid, which may have been carried past the neutraliser stage. It coats the surface of the ABS plastic with a solution that is completely stable within the catalyst and will not create any harmful side reactions. It is very important that the concentrations of the hydrochloric acid and tin are maintained in the catalyst, as without them the palladium is no longer stable. The result is that the colloid falls out of solution settling on the bottom of the tank. It is then not possible to rejuvenate this solution only discard it and very expensively make up a new solution. It is inevitable that some contamination of the catalyst process with hexavalent chromium will occur. Providing that this is only in very small amounts the resultant breakdown of the colloid will also be small. This breakdown of the colloid results in a fine particulate or precipitate which requires filtering from the process solution. Failure to do this will result in a build up of the particulates showing as a fine speckle roughness on the surface of the components. When using a filter for the first time some loss of concentration of the bath can be expected, this loss is generally considered to be 50%) Solvent Technology Products:
MacuPlex LE MacuPlex PC/ABS
Function:
To condition the surface of the (>50%) PC/ABS material and render it suitable to achieve a more uniform etch
Concentration:
Refer to individual data sheet
Temperature:
Refer to individual data sheet
Time:
Refer to individual data sheet
19.2 ABS Pre-Etch Standard Technology Products:
MacuPlex STR MacuPlex Floenx NF
Function:
To initiate the wetting out of plastic substrates prior to etching. To initiate absorption of chromic acid into rack coatings to inhibit metallization
Concentration:
Chromic Acid Sulphuric Acid MacuPlex Product
Temperature:
50 - 55ºC
Time:
2’00 – 4’00 minutes
Solution Maintenance:
Analyse and correct once per shift
320 – 400 g/L 0.5 %/vol
