Hi, Keith,
You're using FR4, which has a high Z-axis CTE. Also your hole aspect ratio
is between 1:5 and 2:17, depending on what you're tolerances are like. I've
assumed that your board thickness & tolerance is 0.093+/-0.008. At 1:5, you
should be OK, especially if you specify a ductility for the copper of
around 20%.
From your pictures, it looks like the crack are occuring at the points
where the barrel plating joins non-functional pads. Normally, I advocate
keeping NF pads, but with high aspect ratio holes on a thick board (and I
still don't know what your copper weights are), it could be that as the
distance delta between the pads increases with expansion, it's pulling the
barrels apart. This would be especially the case if low ductility, thin
copper has been used.
Are your boards for the faulty batches unusually thick? Or are the holes
abnormally small-diameter?
My 2 cents worth for a Monday morning.
Peter
Keith Calhoun <[log in to unmask]> 19/04/2003 11:42 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Keith Calhoun
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] Cracking in vias
These are boards specified to comply with all requirements of IPC-6012A,
class 3, they are .093 thk, fabricated using
IPC-4101/26 material (epoxy glass, Tg 170 deg. C min). The via size is
.015 inch after plating +/- .003 inches
I am still waiting on the microsection report from out vendor to verify
copper thickness, finished hole size, etc.. Many of
the failures have been seen in the vias under a large BGA located near the
center of the board. But we have seen this at
other locations also. So far these failures have only been seen on two
closely spaced date codes, so we are hoping we can
at least contain the problem. Does anyone have any ideas on how we can
save these boards, I have already told my
management that I do not think there are any acceptable repairs for this
type of problem, just wondering if there might be
something out there.
Thanks for the support.
Keith Calhoun
"Mcmaster, Michael" wrote:
Here are the standard questions
What is the copper thickness of the copper in the holes? Hole
diameter? Board thickness? Material (type and Tg)?
Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263
----------
From: Steve Gregory[SMTP:[log in to unmask]]
Reply To: TechNet E-Mail Forum.;[log in to unmask]
Sent: Friday, April 18, 2003 1:30 PM
To: [log in to unmask]
Subject: Re: [TN] Cracking in vias
Hi Keith!
Your pictures are up! Go to: <
http://www.stevezeva.homestead.com> and look at Via X-section
-3.
-Steve Gregory-
We have recently found a problem in several assembled
boards which failed ICT. We found several vias which had
become opens after
assembly. We had the open vias sectioned, I sent Steve
Z. some pictures to post on his site. I would like to
have your opinions on what may
have been the cause for this failure. So far it seems to
have occured only on boards having two date codes from
our board vendor.
Thanks for the support.
Keith Calhoun
-Steve Gregory-
---------------------------------------------------
Technet Mail List provided as a free service by IPC using
LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with
following text in the BODY (NOT the subject field): SIGNOFF
Technet
To temporarily halt or (re-start) delivery of Technet send
e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for
additional information, or contact Keach Sasamori at
[log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV
1.8e
To unsubscribe, send a message to [log in to unmask] with following
text in the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for
additional information, or contact Keach Sasamori at [log in to unmask]
or 847-509-9700 ext.5315
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
-----------------------------------------------------
[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
