plating, anodizing, & finishing Q&As since 1989
Masking issue with selective Chrome Plating on a PC/ABS part
Q. Hello Friends,
I am a mechanical design engineer with a double-shot part (30 mm x 30 mm x 30 mm) that needs to be electroplated with 20 micron Copper + 10 micron Nickel + 0.3 micron Chromium (satin finish).
The complication is the double shot part being PC clear (inner shot - not to be plated) and PC/ABS (outer shot - to be plated). We have worked with many platers in Asia Pacific as well as Europe and the main problems are:
1) Unwanted plating on the PC clear. Since the etchant not only dissolves the butadiene but also attacks the PC in both PC and PC/ABS, both PC and PC/ABS become platable. Can we just remove the butadiene if the PC% in the PC/ABS is not high? We do have stringent automotive service requirement for the plating. ABS material for the outer shot is not considered because of a 100 °C/6hrs service requirement.
2) Blistering after -35 °C to 85 °C temperature cycle test at 12 hrs/cycle X 50 cycles.
Any recommended plater?
Mechanical Engineering - Singapore
A. Have you tried stop off paints to protect selected areas?Guillermo Marrufo
Monterrey, NL, Mexico
Q. Thank you Mr Marrufo for your input.
No, we did not consider masking yet due to the extra processes required. We do need the PC inner shot to remain clear ... is there any masking paint and solvent (to remove the paint) that you can recommend?
The fact is that we are able to get good quality parts. However the yield is either low or not consistent.
A. Have you tried to use preplating strips?Lee [last name deleted for privacy by Editor]
- Taipei, Taiwan
Q. Hello Mr Lee!
The main problems we faced are:
1) if the etching is too strong, PC will also be roughened --> becomes slightly plateable --> chrome over-plating
2) if etching is too weak, PC/ABS not fully etched --> skip plating such as pinholes, etc.
Can you tell me more about the function of preplating strips and how they can help?
A. I am having similar problems masking a totally ABS moulding! On the blistering side of things you must ensure that it is a plateable grade of ABS, ensure that there is no pigment, make sure it is not 're-grind' material and also that the surface is not stressed. Try to get more copper on the part as this seems to act as a dampener in thermal expansion. Also ensure that the initial etching material is not at end of life.Chris Love
- United Kingdom
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