[SI-LIST] Re: Manufacturing Issues
- From: Harry Lin <lhdsp5000@xxxxxxxx>
- To: "Thompson, Gary D \(Gary\)" <Gary.Thompson@xxxxxxx>, si-list <si-list@xxxxxxxxxxxxx>
- Date: Wed, 7 Jan 2009 10:20:57 -0800 (PST)
you may get answer for suggestion 1 from this document,
http://www.screamingcircuits.com/Portals/0/documents/Via_In_Pad_Guidelines.pdf
Harry
________________________________
From: "Thompson, Gary D (Gary)" <Gary.Thompson@xxxxxxx>
To: si-list <si-list@xxxxxxxxxxxxx>
Sent: Wednesday, January 7, 2009 12:13:36 PM
Subject: [SI-LIST] Manufacturing Issues
Sorry for the somewhat off-topic nature of these questions. Hopefully someone
here can steer me in the right direction.
I've recently receive a manufacturability review report from a top tier
contract manufacturer, wherein they made some recommendations that I'm not too
comfortable with. Part of me says "they're the experts," and I should accept
their input. The other part wants to sanity check these suggestions just to
make sure I'm not running down a single-source rat hole :^)
Suggestion 1
We're using more and more QFN type packages that have a thermal ground pad in
the middle. Typically, we've just spaced vias in a grid on this pad down to
internal ground layers. The CM says too much solder gets wicked down the vias
leaving the pad too dry. They recommend we 1) move the vias to the outside
edges of the pad and 2) cover them or dam them with soldermask to prevent
solder from flowing that direction. Seems to me most manufacturer-recommended
footprints I've seen do it the way we do, not the way the report recommended.
Suggestion 2
This report claimed soldermask between pads on 0603 and 0402 discretes left a
bump between the pads that promoted tomb-stoning. They recommend removal of
soldermask between these pads. I've never seen this done before, and the CM was
not able to actually quantify the failure rates due to this soldermask. The
last thing we want, though, is a solder bridge under an 0402 part...
Anybody else out there heard of this stuff or have recommendations on a more
fitting place to ask these questions?
Thanks.
==============================================================
Gary Thompson Phone: (512) 821-6521
Systems/Applications Engineering FAX: (512) 821-6810
LSI Corp. Mobile: (512) 751-8115
Network and Storage Products Email: gary.thompson@xxxxxxx
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