Hi,

 The only solution I have heard of that makes sense to me is controlling the
amount of solder paste put down (stencil thickness, aperture adjustments)
AND doing something to keep solder from going down holes.

 I recall Indium had some good white papers.

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Friday, June 29, 2012 1:10 PM
To: [log in to unmask]
Subject: Re: [TN] I'm back and have a question about QFN voids

There are lots of articles on voiding (more appropriately avoiding), but you
might look into solder pre-forms first.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popeielarski
Sent: Friday, June 29, 2012 9:52 AM
To: [log in to unmask]
Subject: [TN] I'm back and have a question about QFN voids

Greetings 'netters,

For the past 2 1/2 years I've been lurking because Technet didn't get along
with my employer's email system (specifically during maintenance).

I solved that problem by finding another employer! See how much you guys
mean to me?!

It's good to be "back in the saddle again", so please allow me to begin with
a perplexing question:

I need to solve QFN ground-pad voiding on a 0.038" thick ENIG assembly. The
application is a high power RF amp and voiding as low as 25% causes issues
with reliability.

Many attempts to resolve this with stencil variations, (thickness, star
patterns, etc) and process variables (reflow time/temps) have been
fruitless.

I'm considering re-spinning the board with a via dead center of this 6mm
part, print & reflow only the leads, then wave solder the via (SAC305 with
water soluble flux) in hopes of forcing the volatiles out from the center
due to the wetting forces. Has anyone tried and succeeded with this method
or am I sailing off the edge of the planet?

Thanks for your help in advance.


Ed Popielarski
Engineering Manager

Technical Services, Inc.
970 NE 21st Ct.
Oak Harbor, Wa. 98277

Ph: 360-675-1322
Fx: 206-624-0965
Cl: 949-581-6601

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