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I have several memory devices that have 2% bismuth in the lead c

Keith Lengling

#32495

I have several memory devices that have 2% bismuth in the lead c | 8 February, 2005

I have several memory devices that have 2% bismuth in the lead coating. Is this enough bismuth to be concerned over the formation of a low temperature SnPbBi alloy? What are the allowable limits for bismuth in an SnPb process for both SMT and through hole parts?

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#32504

I have several memory devices that have 2% bismuth in the lead c | 8 February, 2005

Tough to say. Can you accept the loss of strength of your solder connection if upto 2% of the solder is affected? * Lead and bismuth alloys can form a eutectic composition of Bi52Pb32Sn16 in the grain boundaries. * Melting point of the eutectic alloy is 95*C.

Many times, you have to add: "Overall result is a large decrease in the strength of the joint." But this assumes a large bismuth content. Without doing the calculation, we'd guess that substantially less than 2% of the solder material would be affected.

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