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Lead Free BGA's on non-RoHS Assembly

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#47056

Lead Free BGA's on non-RoHS Assembly | 29 January, 2007

I'm about to begin a job for a customer placing a couple of lead free BGA's/FPGA's on an assembly that doesn't need to be RoHS compatible.

So...my question is...should I process this assembly with lead-free solder paste, to accomodate the lead-free BGA/FPGA process requirements? Will I introduce other potential problems with non-RoHS parts in the design, or should things work out ok for the entire assembly?

The one thing I want to avoid is using lead-free paste for the BGA/FPGA's, and regular eutectic pastes for the rest of the assembly. But I want to ensure the best quality on the entire assembly.

Thanks! ..rob

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#47057

Lead Free BGA's on non-RoHS Assembly | 29 January, 2007

What does your customer want you to do? I would not want a CM soldering one of my boards with leadfree paste if I didn't ask him to. Whatever you do, get approval first. Two things to consider: If the other components are not rated for leadfree temperatures, then using a leadfree paste for the entire assembly could be disastrous to those low temp rated components. However, using a Pb paste with a leadfree BGA means that you may introduce major reliability issues into the BGA solder joints. A BGA uses solder as its pin. If you mix two types of solder with different melting points, there are lots of issues to consider - incomplete mixing of the solders creating intermetallic layering in the ball, reducing longterm reliability. If you do heat the SnPb solder long enough to get good mixing, you may get a lot of increased voiding, with its own reliability issues. Search the archives for more info on soldering BGAs with mixed processes.

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#47059

Lead Free BGA's on non-RoHS Assembly | 29 January, 2007

Many high rel assemblers reball their LF BGA with SnPb balls. In other less demanding environments, SnPb paste with LF BGA produces acceptable reliability.

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aj

#47060

Lead Free BGA's on non-RoHS Assembly | 29 January, 2007

Rob,

We have ran LF BGA's with Lead Paste in the past. We actually got a MicroSection Analysis carried out and a full report which approved the Process.

We had peak Temp around 225oC- 230oC . Its a matter of running the Lead Process at its max and the Leadree at its Min.(ish)...

( wait till you have 2 bgas on board one Lead and the other leadfree - then it gets really interesting...)

Best of luck.

aj...

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#47103

Lead Free BGA's on non-RoHS Assembly | 30 January, 2007

Several paste manufacturers make an interim paste designed for such mixed applications. They work pretty good and give you the strongest joint available.

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CK Flip

#47106

Lead Free BGA's on non-RoHS Assembly | 30 January, 2007

Reflow Oven

PCB Soldering Tools