[SI-LIST] Re: Manufacturing Issues
- From: Marc Battyani <marc.battyani@xxxxxxxxxxxxxxxxxx>
- To: "Thompson, Gary D (Gary)" <Gary.Thompson@xxxxxxx>
- Date: Wed, 07 Jan 2009 19:36:39 -0500
For very small parts (01005) solder mask seems to be better:
http://www.smtnet.com/library/files/upload/01005Assembly_Process.pdf
BTW has somebody already used some 01005 parts? (just curious)
Marc
Thompson, Gary D (Gary) wrote:
> 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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