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]<mailto:[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]<mailto:[log in to unmask]>>
To: [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]<mailto:[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]<mailto:[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]<mailto:[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]<mailto:[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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