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April 2009

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Subject:
From:
Tan Geok Ang <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Tan Geok Ang <[log in to unmask]>
Date:
Thu, 30 Apr 2009 09:07:52 +0800
Content-Type:
text/plain
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text/plain (145 lines)
My experience is something what you mentioned ,that is, stencil opening
(solder volume) is the main "issue" which caused the process problem.
With multi-row/column of I/O, the package seems to be similar to LGA BUT
with a much larger heatsink at the center of the package. The I/O will
encounter open issue (related to heatsink pad opening design) or short
issue (related to I/O pads opening design). 
Another way is to "bump" the I/O (not the heatsink), and only open the
stencil at the headsink pad. Apply tacky flux on the I/O pads at PCB
after paste printing process....

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, 30 April 2009 4:12 AM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly

Yes, Steve, I have, outside of GD. It is not fun, very frustrating. The
only tip I can give you is to try using some Kapton tape to experiment
with the aperture openings until you think you have what you need, then
remember to account for the one mil thicker deposit on account of the
tape. Hopefully the next iteration will be the last.
However, I also had so many issues with the exposed copper on the edges
of many of the QFNs and the unevenness and the huge delta CTE issues
that I just decided it was not worth it to screw around with it anymore.


Here at GD we do not use QFN packages, we repackage them. We also work
with the component manufacturer to give us the part in a different
package.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 29, 2009 2:32 PM
To: [log in to unmask]
Subject: Re: [TN] Actel QFN180 Assembly

Hi Jim,

Just having issues trying to find the right balance between the thermal
pad and I/O pad opening dimensions in the stencil. We're about to go on
our third stencil iteration and have a good idea what we're going to do,
but it's frustrating when you follow the design guidelines that the
manufacturer of the device say to do, and they don't work.

But why should I be surprised at that? Sheesh...

Just wondering if others go through this drill too?

Steve 

-----Original Message-----
From: Jim Wolvansky [mailto:[log in to unmask]] 
Sent: Wednesday, April 29, 2009 12:23 PM
To: Steve Gregory
Subject: RE: [TN] Actel QFN180 Assembly

Hello, Steve.

I've got some experience with devices like these, what issues are you
having?

 - Jim

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 29, 2009 9:11 AM
To: [log in to unmask]
Subject: [TN] Actel QFN180 Assembly

Hi All,
 
We just ran a board with an Actel QFN180 device, and followed the
stencil guidelines recommended by Actel in their publication:
 
http://www.actel.com/documents/QFN_AN.pdf
 
but we have had our issues.
 
I was wondering if anyone else has used this component and would be
willing to share their experience with it.
 
We'll figure out things eventually, but I figure it wouldn't hurt to ask
for some advice from this wonderful group.
 
Thanks,
 
Steve

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