Hi, Ofer,
If the hole aspect ration is not more than 5:1, I would have the via holes
plugged with epoxy and plated over while the PCB is being fabricated
(before final Cu plating and LPI). The epoxy plugs do tend to form small
bumps because of expansion during the hot HASL dip process, but not always.
I have had some impressively flat finishes on HASL coated boards so
plugged. In any event, they wouldn't be enough to interfere with a BGA ball
of 20 or 25 mils diameter and prevent them soldering properly.
I'm slightly curious as to how you can plug from both sides, unless you do
it in a vacuum, without getting air trapped in the middle. I'm trying to
think of an alternative process for you but cannot. Why do you have to plug
all the holes anyway? Gasketing? If it is gasketing, perhaps you can get
away with just tenting over the via holes on one side of the board. I won't
suggest both sides, because I don't like tenting both sides - I get
concerned about the atmosphere left trapped inside the hole.
Peter
Ofer Cohen <[log in to unmask]> 27/05/2003 11:19 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Ofer Cohen
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Plugging under BGAs
Technetters,
Most of our boards carry BGA (pitch => 1 mm). The finish is HASL, which,
from various reasons, can't be changed. The general rule is to plug all the
through-hole vias from the print side, apart of BGA locations, where the
plugging is from the BGA side (mostly components side).
In a new design, there are pairs of identical BGA-packaged components from
both PCB sides, using the same TH vias. I have two options:
1. To select one side to plug (danger of solder balls under the BGA of
the other side), or
2. Plug from both sides (danger of over-stress on the hole plating
during the reflow, because of the air pressure inside the hole.
What is your opinion?
Regards
Ofer Cohen
Quality Assurance Manager
Seabridge Ltd.
---------------------------------------------------
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
-----------------------------------------------------
|
