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February 2010

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Subject:
From:
bob wettermann <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, bob wettermann <[log in to unmask]>
Date:
Mon, 1 Feb 2010 11:57:58 -0800
Content-Type:
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text/plain (177 lines)
Dear Lee:

We are a rework and repair facility/training company.

When we have done repairs of this type for our client per IPC7721 3.2 in the past and we used temperature and pressure (through fixturing) to "repair" these boards to where they can provide the form/fit/function intended for the PCB. In extreme cases you may need to also repair damaged laminate via IPC 7721 3.5.1. 

Regards

Bob Wettermann
BEST Inc



--- On Mon, 2/1/10, Paul Edwards <[log in to unmask]> wrote:

From: Paul Edwards <[log in to unmask]>
Subject: Re: [TN] IPC-7721 LESSONS LEARNED
To: [log in to unmask]
Date: Monday, February 1, 2010, 1:46 PM

Lee,

What we do occasionally is to take the PCBs put them on the belt in a reflow oven and run them to just under reflow temperatures for in an extended profile...
Need to set the oven for a balanced thermal exposure and partial moisture bake-out...Baking the PCBs ahead of time helps a lot...

Pushing the PCB over Tg seem to relieve the stress in the PCB...

DANGER... This may effect the number of thermal cycles you can put on the PCB.  Also depending on the cooling rate and thermal balance you may have additional warping...

I always talk to my customer first then try one PCB...

Paul

Paul Edwards
Surface Art Engineering


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Monday, February 01, 2010 11:20 AM
To: TechNet E-Mail Forum; Paul Edwards
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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