We Need Leaded BGAs, But They're Only Available Lead-Free

Phil
Welcome to Board Talk. This is Phil Zarrow and Jim Hall of ITM Consulting, in this format known as the Assembly Brothers, Pick and Place. Today's topic of discussion is orientated to you poor, lost souls who are the exemptees for lead-free and have to cope with a lead-free world.

Jim
We've been advising our customers, the exemptees, people out of scope, who have to assemble lead-free products for reliability and other issues. And, of course, one of the hugest issues that comes up is BGAs with lead-free balls on them. Typically SAC 405, 305, or some of the newer ones, 105. How do you deal with the backward compatibility issue?

I'm trying to maintain a tin/lead process, but I have a need for BGA packages for my assembly, and I can only get them with lead-free SAC balls on them. What do I do?

There are many strategies. A lot of people have fooled around, or have tested and validated specific processes for soldering SAC balls with tin/lead paste by changing re-flow profiles and so forth. But, I've always taken a very strong stand that the techniques are very specific to the individual type of component, the environment it's going to see, the size of the pad, the volume of the paste, and so forth.

And so just raising re-flow temperatures... I have never accepted as an across-the-board silver bullet solution. I've always said, for a variety of components, you have to have the reliability. The best thing is to re-ball the BGAs. Take the SAC balls off of them and put tin/lead balls on them, and then solder them as a regular tin/lead process.

I've been saying that, and I feel that the published literature is validating me. If you look at the technical proceedings, SMTAI, and now proposals for APEX and so forth, we're seeing more and more very comprehensive technical evaluations of the reliability of re-balled BGAs, including sheer testing, x-ray inspection for voids, and inner metallic layers. Thermal cycle testing after assembled units after they've been re-balled, drop and sheer testing looking for de-lamination inside the BGA package resulting from the re-balling operation.

The fact that we're seeing these is a strong vindication to me that, yes, re-balling is an important and in some cases I feel the most viable technique for mitigating this backward compatibility issue with lead-free BGAs.

Phil
So, this is Phil Zarrow and Jim Hall, the Assembly Brothers of ITM Consulting bidding you a good day, and whatever you do...

Jim
Don't solder like my brother.

Phil
Don't solder like my brother.