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February 2010

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Subject:
From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
Date:
Mon, 1 Feb 2010 15:31:02 -0500
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Agree.  You beat me to make the point.
Or you can check the layout and go beat the layout guy before repair it if the signature on the dwg are clear enough.  Some time, you will find some surprise: the layout was used for different materials.  
--------------------------
Sent using BlackBerry


----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Feb 01 15:03:01 2010
Subject: Re: [TN] IPC-7721 LESSONS LEARNED

Steve,

From an outsiders [microelectronics oriented] point of view it would seem
that the layer to layer copper coverage variance would have the most to do
with warpage.  Like you say, you could force it flat for P&P, but the sucker
is most certain to warp again during reflow.

I bet that is when you beat on the layout guys!

Glad you are feeling a bit better!

Steve C

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, February 01, 2010 2:50 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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