John,
Your assembly house should always give you a straight answer, like a plain and simple NO...
But as a contract assembly house building prototypes, NPI, pre-production and some limited production we are forced to build mixed metallurgy PCAs because our customers either supply the material, dictate what material to be used or the parts are only available in certain metallurgies...
Unfortunately this is the nature of building PCAs in the US because we are no longer the primary supplier of the devices we use in the products we build...
If reliability is the concern verses is it a RoHs PCA, then technically speaking, if the assembler used SnPb paste on a SAC305 ball the concern should be what was resultant joint alloy composition... From that you can determine the effect of the joints on the reliability of the product...
From all the data on all the PCAs I have ever built, in most cases, a completely collapsed reflowed mixed metallurgy joint will survive commercial applications...Normally the failures occur elsewhere and well before the bulk of the mixed metallurgy solder joint fails....
I my humble opinion, because of the differences in the metallurgical and hydrodynamic properties between Pb-bearing and Pb-free solders and fluxes, mixed metal reports built on building and testing PCAs adds additional significant variables to the interaction that are not removable by numerical data analysis techniques... In other words, take the information as a guide not as the facts.... After all there is an IBM report that indicates that Pb-free solder fails faster than Pb-bearing solder in C4 components...
Paul
Paul Edwards
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster
Sent: Tuesday, October 21, 2008 8:21 AM
To: [log in to unmask]
Subject: [TN] Lead Free BGA'S
Our assembly house recently assembled some boards with Lead Free BGA's for us
and when I asked them if they used a lead free process they responded with.
We use leaded solder (Sn63Pb37) with a hybrid oven profile to accommodate the lead-free BGA. I hope this answers your question. Please let me know if you have any more questions."
Is this a common process, is this a reliable process
Any input is appreciated
Thank You
John Foster
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