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RoHS Combined with non-RoHS

What happens if RoHS, no Pb processes are mixed with leaded assembly? Some one is telling me this is a real problem where the solder joint can solidif y with different compositions, creating stresses that result in joint failu res.

The context was specifically BGA balls where there would be a significant a mount of solder in the ball combined with a significant amount of solder pa ste on the board. When assembling SM QFP or QFN type packages (and various passives) will this be much of a factor? If the solder paste has Pb and t he pins are tinned only, I can't see it resulting in much of a problem. Bu t then I'm not a metallurgist. Any metallurgists in the group? Anyone wit h experience in this?

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  Rick C. 

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Rickster C
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meone is telling me this is a real problem where the solder joint can solid ify with different compositions, creating stresses that result in joint fai lures.

amount of solder in the ball combined with a significant amount of solder paste on the board. When assembling SM QFP or QFN type packages (and vario us passives) will this be much of a factor? If the solder paste has Pb and the pins are tinned only, I can't see it resulting in much of a problem. But then I'm not a metallurgist. Any metallurgists in the group? Anyone w ith experience in this?

There are companies that specialise in reballing BGA packages with tin/lead solder for military applications, so there probably is a real issue when systems have to work over very wide temperature ranges. For QFP and QFN packages the relative amounts of the two types of solder don't seem to caus e any problems. The issue is likely to be that mixtures of the two are non- eutectic and solidify over a wide temperature range giving low-strength joints.

John

Reply to
jrwalliker

The reason that the liitary insist on lead-bearing solder is tin whiskers, which will short random things out.

It's *very* exciting when a 50-kilowatt 300 Vdc power panel with tin-coated busbars shorts out due to a tin whisker starting an arc between the bars. Nobody was hurt, but the power panel was destroyed. Probably was some collateral damage too.

Joe Gwinn

Reply to
Joe Gwinn

We never mixed lead free/ leaded. For military etc, everything that was only available as Pb free was dipped, cleaned and Pb dipped. BGA reballing was common. Not cheap...

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TTman

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