Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

No flow underfills

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No flow underfills | 1 May, 2008

I looked at some no flow underfills about 5 years ago and they weren't quite ready for prime time yet. It's time to give it another look and I'm wondering if anyone is using them in production and how it's working. I'm looking at them for reducing solder joint fatigue in small BGAs (thermal cycling and vibe), not for drop testing.

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No flow underfills | 1 May, 2008

Me too! Last time I evaluated these, voiding was a big problem. I wonder if the technology on these has advanced at all.

Look forward to the forum responses (*rolling my eyes like a sarcastic Rodney Dangerfield*)

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No flow underfills | 1 May, 2008

Voiding was also the issue I had. I could reduce them substantially by pre-baking the boards, but that's obviously not desirable. Hopefully the chemists have come up with a solution.

I extruded some pretty cool looking solder shorts through the voids in thermal cycling. That was with SnPb solder. I'm not sure if Pb free solder would extrude. Some of the materials also cracked outer layer vias right at the edge of the fillets. It took some careful plan view x-sections to find those.

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