Hi Alejandro:
                          IPC-TM-650 Bow and Twist Test Method  Number 2.4.22 in the J-Std-001  is for bare boards. To correct a bow: one way, of many, is to heat up the board to 220 F for an hour, twist back past flat in the opposite direction and bake it for additional two hours. Let it cool off in the oven after the oven is turned off.  To twist it back I have used small blocks/bars of semi soft material and tye wraps. I tried weights and did not have any luck. It turned out to need way too much weight, force that could have been done with material mentioned before. Using the blocks, bars and tye wraps get the board set up and place it in the oven. After an hour, tighten the tye wraps till it bends past flat and place it back in the oven. Good luck.
        Regards,	
        Ramon


TEST METHODS MANUAL 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dominguez Alejandro JuP/TEF8
Sent: Friday, July 07, 2006 1:11 PM
To: [log in to unmask]
Subject: [TN] PCB Warpness

Folks,
I'm looking for information related to PCB warpness on the second pass.  I have heard from PCB manufacturers the so called "memory effect". Apparently when a PCB is being manufactured and the material is not cooled down properly between process, the material gets twisted and the manufacturer places heavy-flat surfaces on top to flatten it and have it to the customers flatness specification. Once the material gets heated again (during the first pass) the material twists again to the manufacturer stage.  
We know that IPC specifies a recommended warpness on raw PCB's but doesn't have any recommendation for material that has been reflowed and that suffers this memory effect.
Does anybody have a standard used with their suppliers for processed material that is being used as a specification for this warpness prior to the processing of this second pass?

> Best regards / Saludos cordiales / Mit freundlichem Grüßen
> 
Alejandro A. Domínguez

> Robert Bosch Corporation
> SMT Process Engineering Manager (JuP/TEF8B) 11970 Pellicano Drive 
> Suite 100 El Paso, TX 79936 - USA www.bosch.us
> 
Tel: 1 (915) 541-8391
Tel: +52 (656) 688-2301 ext 6391  (México)
> mailto:[log in to unmask]
> 
> 

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