Mike,
It looks like you have exceeded the plugging criteria on two practical
counts - 1) is that your aspect ratio is too high (6:1 is deemed to be the
limit a hole can be filled to and 2) is that all the fab houses I've talked
with who are experienced with the plugging process baulk at filling holes
smaller than 12 mils and that's with a 4:1 aspect ratio.
I can't say for sure what's happening to your boards, but I would hazzard a
serious guess (given the circumstances) that the VIA plug has been unable
to outgas properly, and since the epoxy has cured, there is nowhere now for
trapped gasses to escape to.
If possible, open out your holes to 15 mils and have a serious word with
your fab house to see if they truly understand the VIA plugging process.
Outgassing the material properly prior to filling, especially for small
diameter/high aspect ratio holes, is of prime importance. I've used this
process on quite a few boards now, and only has two troublesome episodes -
both at start-up with a new fab house, where plating adhesion wasn't as
good as it should have been.
Hope this matches one of your favourite theories.
Peter
Michael.Forrester@
LECROY.COM To: [log in to unmask]
Sent by: TechNet cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
<[log in to unmask]> Aero/ST Group)
Subject: [TN] Dupont CB100 VIA Plug and
Delamination
02/01/02 08:28 AM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to
Michael.Forrester
We have been having a problem with Dupont silver CB100 VIA Plug. The
boards are 12 layer, .062", FR4, Nickel/Gold plated.
We have a BGA pattern with VIA in hole. The VIAs are filled with CB100 VIA
plug and then the board is plated.
The VIAs are .010 causing an aspect ratio of 6.2:1. We are seeing after
solder reflow, inner layer delamination in the area of the
VIA filled BGA patterns. Has anyone seen this before? Does anyone use a
similar construction and had success? There are a few
theories flying around but I wanted to ask the IPC community for any
insight. Thank you in advance.
Best Regards,
Mike Forrester
Sr. Manufacturing Engineer
[log in to unmask]
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