Thanks, Jeff. Sorry, I missed you from my list of special thankees, but
your help has been tremendous. I should know today if I have boards that
are flat enough to use.
Cheers
Peter Duncan
Jeff Ferry
<jferry@CIRCUITTE To: [log in to unmask]
CHCTR.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: TechNet Aero/ST Group)
<[log in to unmask]> Subject: Re: [TN] Board Warp
11/20/01 10:54 PM
Please respond to
"TechNet E-Mail
Forum."
Peter,
If the clamping/baking doesn't remove the warp on the first try, you could
give it one more try. What we do in these cases is to slightly bend a pair
of tool steel bars. We then clamp these bars to the warped edge bowing that
edge in the opposite direction. Go through the baking cycle again and cross
your fingers.
Jeff Ferry
CEO
Circuit Technology Center, Inc.
www.circuittechctr.com
[log in to unmask]
978-374-5000
Sign up for our Free E-mail Newsletter at:
www.circuittechctr.com/general/free_email.htm
-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: Sunday, November 18, 2001 9:50 PM
To: [log in to unmask]
Subject: Re: [TN] Board Warp
Dear All,
Thanks a lot for all the info and feedback. It seems to me that things
haven't changed a lot over the years as far as trying to straighten boards
is concerned - it's still a matter of clamping the boards flat, heating
them up and cooling them down again, and hoping you've taken out more bow
and twist than you've added.
Couple of quick supplementary questions: if the clamping, heating and
cooling doesn't quite work first time, will it make any difference to try
the technique again? I wouldn't like to repeat it too often because of all
the effects on stresses, IMC's and so forth that frequent thermal
excursions will promote - is the board straightening method a one-shot try,
or how many times would you risk repeating the technique to try and make
things right?
Many thanks again to all who responded to my distress call.
Peter Duncan
Jeff Ferry
<jferry@CIRCUITTE To: [log in to unmask]
CHCTR.COM> cc: (bcc: DUNCAN
Peter/Asst
Prin Engr/ST
Sent by: TechNet Aero/ST Group)
<[log in to unmask]> Subject: Re: [TN] Board
Warp
11/16/01 09:53 PM
Please respond to
"TechNet E-Mail
Forum."
Peter,
As MoonMan says, this type of problem is preventable by using proper DFM
procedures, but then folks in the repair business like us would have
nothing
to do!
Removing warp is actually rather simple, and is an IPC documented
procedure.
I've attached a link to our online procedure with more details. We find
that
about 80% of the time we can remove warp and bring bare, or assembled,
boards into spec. However, sometimes the inherent stress in the remaining
20% is just too great to overcome.
Bow and Twist Repair Procedure
http://www.circuittechctr.com/guides/3-2.htm
Jeff Ferry
CEO
Circuit Technology Center, Inc.
www.circuittechctr.com
[log in to unmask]
978-374-5000
Sign up for our Free E-mail Newsletter at:
www.circuittechctr.com/general/free_email.htm
-----Original Message-----
From: <Peter George Duncan> [mailto:[log in to unmask]]
Sent: Thursday, November 15, 2001 9:11 PM
To: [log in to unmask]
Subject: [TN] Board Warp
Hi, All,
We have received a number of 12 layer ENIG-finished MLB's with blind via
hole groups, and which are destined to have BGA's (1.27mm pitch) populated
onto them. The boards measure 8.2" x 5.7" and they are warped to the extent
of one corner being raised by between 1.5mm and about 3mm. The axis of the
warp is the long side of a triangle whose other two sides measure about 5.7
x 5.7.
In this age of sensitive boards, does a technology or technique exist for
straightening the boards back into spec - they are class 3 boards - or is
this an area where angels still fear to tread?
The boards are desperately urgent, which is why I'm asking this rather than
simply rejecting them and having them re-made (which takes about a month).
TIA for any help.
Peter Duncan
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