[Not yet Brad... I'm still waiting for it to show up...]
We use a separate .035 in. diameter surface pad (land with no hole) for test
points instead of using vias.
No issues or problems with that method and we avoid the extra cost of the
via-in-pad method. We will save that solution for really unavoidable
footprint issues that must use it.
DFT or 'Design for Test' is one of the subjects being discussed by Gary
Ferrari on Wednesday March 28th at PCB Design WEST in Santa Clara
California... last week of this month.
http://www.pcbwest.com/conf/technical.html
<http://www.pcbwest.com/conf/technical.html> If they want to learn more
about the options and requirements for DFT, I would recommend that they
attend his presentation.
I wish I could go but we have to much do and they can't live without me for
a week... (It's nice to know I'm needed... :-)) Maybe I will get to attend
PCB East this Fall.
You will have to come back to San Diego some time soon and do another great
presentation for our DC members like the one you did at Palomar College in
my classroom on Flex Circuits...
We really enjoyed that one.
All the best,
Bill Brooks
PCB Design Engineer, C.I.D.+
Tel: (760)597-1500 Fax: (760)597-1510
Datron World Communications, Inc.
Vista, California
_____
From: Brad Saunders [mailto:[log in to unmask]]
Sent: Wednesday, March 14, 2007 8:58 AM
To: (Designers Council Forum); Brooks,Bill
Subject: Re: [DC] One sided issue
Bill,
I agree. The volcanic reaction is one form of "popcorning", also I have
seen many cases of solderball spewing from broken LPI at the PTH. I am a
big fan of the plug then LPI method however where folks must use the via for
test (.8 BGA) I love the capped via. That is where only vias are drilled
and plated then filled. PTH for component mounting (ie connector) are then
drilled and plated; this plating covers the existing vias in a copper cap or
also known as Via In Pad: VIP. Thanks for the input, it was a great sanity
check.
[By the way Bill, did you get the copy of that Flex presentation?]
Brad
----- Original Message -----
From: Brooks,Bill <mailto:[log in to unmask]>
To: [log in to unmask] <mailto:[log in to unmask]>
Sent: Wednesday, March 14, 2007 12:55 PM
Subject: Re: [DC] One sided issue
Let me see if I understand the implied issue...
If they are tenting the vias on one side I would suggest recommending
another more reliable option to your customer.
We plug the vias with soldermask here rather than 'tent' them for a couple
of reasons... one, a single sided or broken tent is a moisture or chemical
trap and can compromise or damage the board or assembly during assembly
processing or even in storage.
Two, from my own experience, we had a batch of tented boards make it into
assembly with compromised tents, (ones that did not completely cover the
holes on either side) and when we ran the boards through re-flow soldering
we observed in inspection a large number of the vias expelling solder balls
and contaminants from the holes as the heated gasses and moisture inside
them expanded rapidly... (Kind of like little volcanoes)...
We avoid the single sided tents for that exact reason...
Plugging the holes completely is much more reliable and we have not had any
problems since.
Does that help at all?
Best regards,
Bill Brooks
PCB Design Engineer, C.I.D.+
Tel: (760)597-1500 Fax: (760)597-1510
Datron World Communications, Inc.
Vista, California
-----Original Message-----
From: Brad Saunders [mailto:[log in to unmask]]
Sent: Tuesday, March 13, 2007 2:02 PM
To: [log in to unmask] <mailto:[log in to unmask]>
Subject: [DC] One sided issue
Hello Folks,
What are the reliability thoughts on a PCB configuration as follows: 013 PTH
via ENIG finish (prior to soldermask) with one side without mask and the
other a dryfilm soldermask. The board is approx .080 thick.
Thanks, Brad
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