Those packages you mention are very easy to bridge, unsurprisingly, it comes
from using to much solder (either too big an aperture or to thick a solder
mask)

All of our Surface mount assembly is carried out in house here, and we don't
tolerate solder bridges in manufacture at all, therefore our assembly line
has some very good inspection people, which mean that a surface mount build
fault of any kind is very rare.

So to me, 50%  (or even 4%) of the boards having errors on seems outragous,
but maybe I am used to expecting too much.

Did you (your company) provide the solder mask? If so, this is probably the
cause of the problem, and smaller apertures will lead to improved results -
a couple of thou here and there makes a big difference!!

That said, I would expect any manufacturing facility, in house or external
to take some pride in their work, and a solder bridge between a couple pins
from time to time sometimes slip through the net, but between more than two
pins??????

Regards, Kevin



----- Original Message -----
From: "Scott Newell" <newell@CEI.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, May 18, 2001 6:14 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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