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Date: | Fri, 29 Jun 2012 13:13:50 -0500 |
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Hi folks! We have had the same success as Ben detailed. Our maximum void
requirement is 50% of the pad and by using the window pane approach, we
typically are getting 70%-80% coverage. We have had only two instances
were we needed better coverage due to either a component thermal or a
grounding issue. We still used the window pane approach but had to conduct
a series of DOEs to achieve the required coverage.
And welcome back Ed!
Dave Hillman
Rockwell Collins
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Re: [TN] I'm back and have a question about QFN voids
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
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