Scott,
I had similar experiences with 'outgassing' from the PWB, and some solder
masks when at CTS. I did not find it related to the flux underfill - only
degree of PWB prep. I also echo your 'extrusion' observations, but never
had the opportunity to observe trace failures. My laminates were thin,
however, only on the order of 12-18 mils thick, and subsequently diced into
small segments being only about 1/4 x 3/8"
But on LTCC, or glass - Ye haw! Slick!! Even at VERY large die sizes, due
to closer CTE match!
I conceptualize that while the interface between the PWB & first chip may
need to be concerned with PWB 'outgassing', but all subsequent chip to chip
interfaces should be a no brainer. Would think that pre-filling the
interfaces between the chips would make the over-molding process so very
much easier.
I have not heard much lately either. Curious to see if there are many
additional comments.
I'm sure that Mike is being careful not to 'toot his own horn', but Ioan can
check in with him. Maybe he has a few articles/studies which he can share.
Steve Creswick
http://www.linkedin.com/in/stevencreswick
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Post, Scott E
Sent: Wednesday, January 19, 2011 1:03 PM
To: [log in to unmask]
Subject: [TN] No-flow underfills
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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