Sometimes I've baked them above Tg with an overcompensation in bow and
twist to yield a flatter assembly after the restraint/weight is removed.
Custom carriers can help, but letting the assembly cool while in the
carrier chews up machine time. If it's a form/fit problem for the next
higher assembly then baking would be done after reflow and or wave.
Edge clamping and board supports in the printer and P&P usually let you
process the board.
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, February 01, 2010 1:50 PM
To: [log in to unmask]
Subject: Re: [TN] IPC-7721 LESSONS LEARNED
Lee,
In my experience of straightening warped/twisted bare board, I've done
it by
putting solder bars on top of the board and then baking them like the
-7721
says, then cooling them with the bars remaining on top.
The board will be flat for printing and pick and place, but it's been my
experience that most of the time the board will re-warp during reflow.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman
Sent: Monday, February 01, 2010 2:20 PM
To: [log in to unmask]
Subject: Re: [TN] IPC-7721 LESSONS LEARNED
No - These are bare unpopulated boards.
Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Monday, February 01, 2010 2:19 PM
To: [log in to unmask]
Subject: Re: [TN] IPC-7721 LESSONS LEARNED
Lee,
Are these populated PCBs?
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman
Sent: Monday, February 01, 2010 7:07 AM
To: [log in to unmask]
Subject: [TN] IPC-7721 LESSONS LEARNED
We got some boards that are warped (bent & twisted that exceeded the
flatness requirements per the J-STD-001). IPC-7721 has a repair
procedure for warped boards. I'm getting a copy of IPC-7721 so I can
familiarize myself with the process. In the meantime, does anyone have
any "lessons learned" from using this procedure?
THANKS.
Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
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