This is a request for info. It has been shown that soldering a SAC BGA using SnPb solder results in a connection that does not hold up well to thermal cycling. The cause of the problem has been attributed to non-uniform distribution of Pb in the solder ball after soldering. That nonuniformity is the result of too little time for the Pb to reach equilibrium concentration in the ball before it freezes.

I am pretty sure that I have heard of some contract manufacturers using this process and making it work (i.e., obtaining a uniform Pb distribution) by increasing the reflow solder profile so that the peak temperature is not less than 225°C. This can be done provided that the moisture content of all the plastic-encapsulated microcircuits on the assembly is low enough (so that there is no popcorning). 

Who can comment on this? Is there any publicly available documentation to confirm?

Gordon Davy 

 


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