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July 2009

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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Mon, 13 Jul 2009 14:53:21 -0400
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Lee,

If you are talking room temperature measurement, then a good, non-contact CMM will do nicely. At elevated temperatures Moire and Digital Image Correlation (DIC) methods can be employed. 

Bev



________________________________



From: Lee parker <[log in to unmask]> 

To: TechNet E-Mail Forum <[log in to unmask]>; Bev Christian 

Sent: Mon Jul 13 14:37:02 2009

Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB 





Bev and Richard

 

How do you suggest we measure to local bow and twist?

 

Best regards

Lee

J. L. Parker Ph. D.

JLP Consultants LLC

804 779 3389



	 

	----- Original Message ----- 

	From: Bev Christian <mailto:[log in to unmask]>  

	To: [log in to unmask] 

	Sent: Monday, July 13, 2009 12:53 PM

	Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB



	Richard,

	Correct as usual, Richard. This was always a big deal at Nortel where completed circuit packs would have to be slotted into card cages. 

	Bev

	On vacation

	

	----- Original Message -----

	From: Stadem, Richard D. <[log in to unmask]>

	To: [log in to unmask] <[log in to unmask]>; Bev Christian

	Sent: Mon Jul 13 11:06:30 2009

	Subject: RE: [TN] Maximum Allowable Bow & Twist for PWB-PCB

	

	Bev, I totally agree with you, but the point they are getting at in IPC

	2221 is that no section of the PWB should have more than .75% per inch

	as a rate of warpage, extending in both the X and Y directions, after

	reflow. This is because if you have more warpage than that you are

	putting a stress on the resultant solder joints that leads to a

	reduction in reliability, especially with a lead-free joint and also

	especially if you need to straighten the CCA when mounting it into a

	chassis or frame.

	I think this specification, like so many others that were based on

	leaded solder, should be revisited for unleaded solders.

	

	-----Original Message-----

	From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian

	Sent: Friday, July 10, 2009 3:24 PM

	To: [log in to unmask]

	Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB

	

	I contend this is old school and if you aren't measuring warpage at

	reflow temperatures how do you know you aren't suffering from head on

	pillow?

	

	I suggest the term head in pillow be dropped because you don't actually

	put your head IN a pillow.

	

	Bev

	RIM

	

	PS Waiting for my Dewism.

	

	-----Original Message-----

	From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard

	Sent: Friday, July 10, 2009 4:20 PM

	To: [log in to unmask]

	Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB

	

	IPC-2221 5.2.4 

	...

	Unless otherwise specified by master drawing, max bow and twist shall be

	0.75% for boards that use surface mount components and 1.5% for all

	other board technologies.

	...

	Values are measured as per IPC-TM-650 Method 2.4.22 

	

	

	Genny Gibbard, P. Eng 

	Manufacturing Engineer, Vecima

	PTS dept. x.4229 

	

	-----Original Message-----

	From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez

	Sent: July 10, 2009 2:15 PM

	To: [log in to unmask]

	Subject: [TN] Maximum Allowable Bow & Twist for PWB-PCB

	

	What is the maximum allowable Bow & Twist value?   Not able to locate in

	IPC-2221, 2222, & 6012A

	

	Victor,

	

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