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intermetallic question

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intermetallic question | 9 April, 2009


I am in a little problem, theres a problem in one of the components, is a new component that we are working with the leads are tin coated, and after we solder in the reflow oven, with lead solder, we took them to do a some test and on a cross section they find that there was no intermetallic layer, these is coming one out of every ten !, they took a picture in 1000X and you can see a thin layer between the lead of the component and the solder this is in the good ones, on the bad ones you cant see that layer, can someone knows why this happen? and where I can find documentation on the problem?


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intermetallic question | 11 April, 2009

You're correct. You should expect to see an intermetallic layer in a proper solder connection. Try leaving the component at temperature for a longer period.

Growth of intermetallic compounds on Cu surfaces [Klein Wassink]: d = 10^3(exp(-5*10^3/T)t^1/2), where: d = Thickness of IMC in um T = Temperature in K t = time in seconds

For more on growth of intermetallics try: * Metals Handbook Volume 6: Welding, Brazing, and Soldering; EF Nippes, ASM International, 9e, 1983, [0871700123] * Soldering Handbook, PT Vianco, Sandia National Laboratories, American Welding Society, 3e, 1999 [0871716186]

If incresing the time at soldering temperature doesn't help, you could have a component solderability issue.

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Reflow Oven

PDR - SMD / BGA Rework