TECHNET Archives

May 2008

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
Date:
Tue, 6 May 2008 14:00:56 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (70 lines)
When I was working in a FMEA lab I did see the failure mode your fabricator
describes.
Do you need the via on the bottom for test? If not mask the via.  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dharma Kemp-Bresett
Sent: Tuesday, May 06, 2008 1:51 PM
To: [log in to unmask]
Subject: [TN] single sided via tenting and immersion finishes... need both
fab and assy input

Hello everyone,
    I am usually hanging on the outskirts soaking up as much info as
possible from all the knowledgeable individuals on TechNet. It is always
enlightening and quite often amusing so thank you all beforehand for the
wonderfully entertaining education I am receiving. :-)
 
    I am looking for info from both the fabrication and assembly side for
this one as apparently there are varied opinions on the subject. If you can
point me to specific documentation that I can show to my customers that
would be even better! 
 
    A couple of years ago a fabricator/assembler recommended to us that we
should tent vias (component side only) on all dogbones for fine pitch bgas
as there was a chance of shorting to adjacent pads. We incorporated this
into our footprints going forward as standard practice and have had no
problems that I am aware of. However we recently received a suggestion from
one of our fabricators that we should discontinue this practice on immersion
finish boards as over the last year or so it had been observed ( throughout
the industry) that this caused via barrel degradation (due to trapped
solution) that in most cases was not caught till the assembly had been in
the field cycling for a period of time. The recommendation given was to now
encroach rather than tent these fine pitch fanouts. The specific
recommendation given was 2.5-3 mil encroachment on most vias with 2mil
encroachment on 8 mil vias ( the smallest we have used with this particular
customer) with the understanding that the problem gets worse the smaller the
via due to capillary action. The other option was plugging but that could be
cost prohibative so i would like to stay away from that option if at all
possible.
 
What are your opinions on this subject and is there any specific
documentation i can point my customers to that might help us determine the
best course of action?
Thanksin advance,
Dharma
 

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2