TECHNET Archives

October 1999

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:
"Michael D. Doty" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 13 Oct 1999 21:07:54 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (98 lines)
     To answer on the bake question yes it can help. I used to bake boards
     prior to reflowing plated tin lead for 4 hours at 275F. The 4 hours
     was to insure that we reached temp for a minimum of 2 hours.This was
     at a large defense plant who shall remain nameless to protect the
     innocent.
     Boards will absorb moisture over time and this is especially true of
     polyimide material.

     Hope this helps.

     Mike Doty
     Hadco TCE


______________________________ Reply Separator _________________________________
Subject: [TN] Board Delamination . . . Boards too old?!
Author:  "Ramsey's" <[log in to unmask]> at smtplink-hadco
Date:    10/13/99 8:48 PM


Should I start out with the excuse? We put in this new ERP system. Y2K
and all. We must have got something wrong, and fell asleep at the wheel.
Any way, we don't make enough boards for a couple of months. Suddenly,
we wake up to real demands (as opposed to ERP demands).

We think (or feel) we need A LOT OF BOARDS FAST.
We ask . . . no DEMAND!  lots of boards on a four week turn to meet our
"new" requirements.  That was February.

In late August, (there is no way we could have stuffed that many boards
in two or three months) we started to see some board delamination, after
ref low usually but sometimes after wave solder.

These are four layer boards with mixed through hole and SMT on both
sides. In our process, they see three temperature excursions, bottom
side reflow, top side reflow and wave solder.
Defect rate is about 1 in 50 boards. Delaminations are between layers
one and two or layers three and four, they range is size from half an
inch to over two inches. Big blisters the kind you can push up and down.

The reflow profiles are a straight ramp at  one to two degrees Celsius
per second to reflow. The conveyor travels at 65 cm per min. Reflow for
35 seconds. The boards see a maximum of 209 degrees Celsius, then cool
at three to four degrees per second.

Our stockroom is air conditioned but has no humidity control, worst case
for a few weeks the boards saw 25 degrees C and 70% humidity. Most times
the stockroom  is 23 degrees and 50%. We are having no solder problems,
we use an RMA paste 89% solder by weight.

Our supplier, who has my sympathies, says that the boards must have
absorbed moisture over the summer, and should be baked prior to use.

These boards, when stuffed, are pretty expensive, containing eight 20
mil pitch DSPs that run at 100 MHz. There is plenty of Flash RAM, PLD
sockets, and glue logic. 96 pin DIN connectors . . .

Will baking the boards prior to using them reduce our fall out? Should
we scrap the boards? We have another 300 bare boards made by the same
supplier only two weeks later (early March) . . .  scrap them too?

If Bake, how long should we bake? At what temperature? Do we need to
ramp to that temperature?
If Scrap, is our supplier in any way responsible for the defects?

Gentlemen. Let's get ready to rumble. Oh, and uh, feel free to edit all
but the relevant stuff out if you choose to quote this message in your
reply.

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text
in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################

ATOM RSS1 RSS2