Evaluating / Qualifying Solder Paste

Hi Rick,

Last year I've test about 15 different solder paste. To procede, I've started with different tests listed in different brochure including IPC. At the biginning, I had 15 different tests to do and at the end ( for the last 7 product ) I've test the following points.

- Always use the same PCB for your test. The most popular product you produce. Use one or two PCB per product. I've start with 5 PCB for each solder paste and it was always the same result. So 1 or two is enough. - VERY VERY IMPORTANT. Be sure your solder paste is perfectly applied ( centered ). If it's not perfectly centered, you will get different result in slump test. - Take a look on every PCB after the printer ( with a magnifier 10X is good ). At this point you will see a difference between each product. Some are perfectly square and other have rounded corners. Take notes after each steps. With experience, only with the print result you can have an idea of the final result. - Place your SMT component and after be sure that all components are perfectly placed. - Finaly pass your PCB in the reflow profil you normaly use. If you need other info for the reflow, do not esitate to ask your questions. - You will see that solder paste can give different results.

That's what I did for production test. I've also did an other interesting test ( slump test ).

With one PCB for each product, print solder paste and go directly in the oven at 150degre for 2 minutes. Be sure that your profil respect these parameters. It simulate the Soak Zone and the two WINNERs for me were perfect in this test. The solder paste square stays perfect ( no slump at all ). For others, solder balls fall beside the pad or slump a little.

I hope this will help you. Frank

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Search the fine SMTnet Archives. For instance: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=11589

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Besides the processing tests (different print speeds, print delay times, etc.) one test we've had to use is humidity exposure. Solderballing due to high outside humidity is a problem in our plant. So we expose paste to 85% humidity for various times to see which one is more likely to solderball.

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