Ed,

I'm interested to see what result you get with wave soldering, but I worry about e-mail access where you are going.

I've had good success with minimizing voids on QFNs by using a window-pane (array of apertures) on the center pad. I aim for 50% coverage of the center pad area. But you have to make sure that your signal pins can accommodate - either the solder paste reduction has to be the same for bottom only terminations, or you need a larger PCB pad (extending out from under the part) for excess solder to flow (so that the center pad solder determines the offset height of the part, not the perimeter solder joints.)

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ed Popeielarski
Sent: Friday, June 29, 2012 12:52 PM
To: [log in to unmask]
Subject: EXTERNAL: [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

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________