If your vendor is capable of producing boards with that precision, then for
a small run you should accept nothing less then 100% working boards. If you
accept something like 95%, out of a run of 100 you'll have 5 bad boards.
That is a lot of bad boards for such a short run, IMHO. My experience with
surface mount stuff is that if the vendor isn't setup to work with
fine-pitch parts, no amount of testing will fix the drop-out rate.

Douglas Wood
Software Engineer
dbwood@kc.rr.com

Home of the EPICIS Development System for the PIC and SX
http://epicis.piclist.com

----- Original Message -----
From: "Scott Newell" <newell@CEI.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, May 18, 2001 12:14 AM
Subject: [EE]: Solder bridging on low volume PCBs acceptable?


> What percentage of fine pitch surface mount boards should be expected to
> return from the assembly house with solder bridges?
>
> At my day job, we've taken a couple of new designs into low-volume (100
> boards at a whack) production.  This is the first use of surface mount
> technology at this company.
>
> The current design I'm working on has three fine pitch parts: a TQFP-144,
a
> 48 pin TSOP-II, and a 28 pin SSOP.  Eight of the 100 (supposedly machine
> built) boards arrived today, and four had visible solder bridges, some
> covering more than 2 pins.  All bridges were confirmed to be hard shorts
> with a meter.
>
> Is it considered acceptable industry practice to make the buyer do a
> detailed physical examination?  These designs don't have provision for
> boundary scan or self test, but all I needed was a unaided visual scan and
> a meter to find all the shorts.  I can easily fix the boards with a little
> solder wick, but it seems like I shouldn't have to.  (Considering the time
> constaints and backorder status, we'll probably have to do our own repair
> work in the short term, but I'm getting to where I just want to reject the
> shipments outright.)
>
> Comments?
>
>
> thanks,
> newell
>
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