Tin plating over copper blisters at 240 °C

Hi, Aviruth.

 If you or I were asked to "Design a very easy quality control test that will quickly locate all poorly plated parts, regardless of whether the problem be due to poor substrate condition, inadequate cleaning, lack of activation, excessive brightener in the nickel or tin plating tank, overstressed nickel plating, or anything else", the closest we could get to such a quick universal test would probably be to bake the parts to 240 °C and look for blistering :-)

A. So, when you see that the parts are blistering and you'd like to know where the problem lies, you can see that the trouble could be nearly anywhere. Probably the first question should be at what interface is the blistering occurring? Carefully break some blisters and look at the back of the blister and the base underneath the blister.

Does the blister occur between the copper and nickel or between the nickel and tin, or a bit of both? Is there any peculiarity about the location of blisters on the parts? Are they everywhere, or only on flat surfaces or only on edges and corners, or top or bottom surfaces. Unfortunately, while blistering tells you that you have a problem, it doesn't tell you at what step. Good luck and get back to us with more detail.

Regards,

A. I would recommend first confirming that what you are seeing is in fact blisters. As Ted noted, you may see this with high organic matter in the nickel or tin. If there is high organic matter on the surface when the tin reflows, which it will at that temperature, it will cause tin pooling or puddling. This is a blob of tin that accumulates like a water drop on the surface but looks just like a blister. I would use a scalpel to pull back the "blister" and see if it flakes, it not, it is probably more likely the problem that I described.

A. Dear Farisha,

Please investigate further with defected parts.

Possible causes & remedy as below.

1) Poor cleaning - Improve pre treatment
2) Electrical contact disturbance - Check the electrical contacts
3) May raw material composition - rarely improper material composition may cause.

Thanks

A. Hi Andrew. Thanks for the interesting question from which I hope to learn as well. To me, a 'defect' is anything which is not exactly the way it is supposed to be. Any blister or blob is certainly a defect. A 'reject' is something that you have decided is sufficiently defective that you will not ship it (sometimes called an internal reject) or that your customer will not accept (sometimes called an external reject). I think all blistered parts should be internally rejected but would need clarification on 'blobs'.

I googled "reject vs. defect" to check semantic differences, the approaches in other industries, etc., and I didn't immediately see any reason yet to change my mind.

Let me relate an old story to clarify. A bigwig at a power tool company decided that a component of the power tool which was made of diecast aluminum with a deep hollow should be nickel-chrome plated instead of powder coated as an anniversary celebration. The plating shop could not do it with sufficient reliability for a number of reasons like cold shuts in the diecastings, inability to remove all the swarf in the deep recesses, etc. I sat at the conference table -- with the plating shop saying they could not possibly ship these blistered parts, but the tool company project manager insisting they were shippable as long as the blisters were on the "B" surface ... and of course the "A" surface grew ever smaller and the "B" surface ever larger as he resolved to meet the bigwig's orders. This was an example of parts which were very seriously defective, and did not pass the internal reject test, but were shipped anyway because they met the customer's needs. Hopefully it helps clarify what the words mean :-)

Regards,