I've changed the subject since I'm curious what's going on in the world of no-flow underfills these days.  I tested several 7 or 8 years ago and was pleasantly surprised out how robust the assembly process was.  I played with dispense patterns and volumes and it seemed like no matter what I did I still got a good solder joint.One downside is the boards had to be pre-baked to get rid of voids.  This was with SnPb balls and if I had a void spanning the gap between balls I'd get solder extrusion during thermal cycling that could lead to a short.  The other problem is that I'd crack outer layer traces where the underfill fillet met the board.

Have no-flows improved?  Has voiding been reduced to where we don't need to pre-bake the boards?  Do the voids matter with SAC alloys (does SAC extrude like SnPb?).  What about thermal cycle life?

Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana    46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Wednesday, January 19, 2011 10:12 AM
To: [log in to unmask]
Subject: Re: [TN] Handling of PoP on assembly equipment

Mike,

I've liked the no-flow, or flux-underfills in the past.


Steve Creswick
http://www.linkedin.com/in/stevencreswick




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Wednesday, January 19, 2011 10:00 AM
To: [log in to unmask]
Subject: Re: [TN] Handling of PoP on assembly equipment

Certainly there are fluxes suited to transfer printing - it's a known
technique. Another thought:
I confess it's a while since I paid much attention to the insides of a P&P
machine. But if you have glue dispense that might be suitable for flux
dispense


Regards


Mike



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