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Silver plating over Aluminum 6061

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Hi All

Currently we are working on an RF amplifier which has an aluminum casing and we need to plate the casing by some means to be able to solder components onto the casing. From a local plating shop we plated some sample parts. The samples we plated first copper (Mil-C-14550 [link is to spec at TechStreet] B) and then silver (QQ-S-365 [link is to spec at TechStreet]). But the silver plating peeled off when we removed masking tapes used during paint.

Could anyone suggest us another way of plating or where did we go wrong in our case ?

Thanks

Sertac Gurel
- Ankara, TURKEY

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If the copper peeled off, then the parent metal either was not properly cleaned or properly activated (or both). If the silver peeled off of the copper, then the surface of the copper was the choice above or it was bright copper and had too much brightener.
Talk to your plater, he has a problem.

James Watts
- Navarre, Florida

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If you want any help on this you must give details about the plating process, preplate cycle etc.

Sara Michaeli
chemical process supplier
Israel

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MIL-C-14550 B and QQ-S-365 have adhesion requirements (identical tests) which the plating seems to have failed. But, did you bake the paint at a temperature above 149 C (300 F)? QQ-S-365D, Paragraph 3.3.5 says higher temperatures weaken the adhesion of silver to copper. A barrier layer of nickel is required for long term use at higher temperatures. Do adhesion tests as-plated and after baking (if applicable).

As alternatives, consider matte tin plating or low-phosphorus electroless nickel (EN) plating the aluminum. With tin, if baking the paint, stay below 200 C to avoid melting. With EN, it may be necessary to also silver plate, since baking can oxidize (passivate) the EN surface. But possibly, masking would protect the EN during baking.

Ken Vlach
- Goleta, California

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Thanks for all the comments

The paint was cured around 60 C for one hour. I don't assume this created the problem. However we will also solder components onto this part by using vapor phase process, during which the parts will be exposed to temperatures above 200 C. I think we should use Nickel undercoat.

Sertac Gurel
- Ankara, TURKEY

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I use silver plating all the time for microwave RF housings that need to be solderable... We specify a Sodium Zincate cleaning process followed by a copper underplate and then silver... It's extremely rare (almost never) that we encounter any peeling of the plating... I suspect you are not using a qualified or experienced plating vendor...

Bob Diamond
- Hauppauge, New York

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Hi Again

In our second try, we first plated aluminum case with Nickel and then with Silver. The coating is mechanically fine, also it solders very well. My only concern is about thermal stress. Nickel is a brittle material, could it cause thermal cracking problem after a number of thermal cycles?

Thanks

Sertac Gurel
- Ankara, TURKEY

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Hi there.
I think we must have a answer of your first question to help you. Does the silver peel off from the copper plating and you can use the ground metal or can you use the copper plating?

Nickel can be brittle due to the additives if they are not correct in your solution, but not if by heat treatment because if every thing is correct will the aluminium and the nickel diffuse in a high temeperature about 300 degrees celciuis.

Regards,

Anders Sundman
surface finishing engineer
Sweden

June 25, 2008

We would like know if plating aluminum with silver passivation is better or silver coating with gold flash is better to improve conductivity? which of the two processes are better in terms of durability and cost.

g.r.hathwar
isro - bangalore ,India

July 1, 2008

Hi, G.R.. Silver plating with a gold flash would be a far more reliable and durable contact surface than passivation, but much more expensive.

Regards,

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

February 17, 2009

We have a silver plating shop for silver plating on wrought & cast aluminium. Precleaning & undercoat are the important process to prevent peel off.

HEMANT SHAH
switchgear industry - Vadodara, INDIA

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