Richard
I would say that is a good technique for measuring the gross warp and twist on the total board, but the local warp and twist could be appreciably larger.
Best regards
Lee
J. L. Parker Ph. D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: Stadem, Richard D.<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Monday, July 13, 2009 3:56 PM
Subject: Re: [TN] Maximum Allowable Bow & Twist for PWB-PCB
That is described in the test method referred to earlier.
The bare PWB is easy, put it on a tool grade flat plate. Push down on
one side at a time and measure the deflection with a dial indicator on
the opposite side.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
Sent: Monday, July 13, 2009 1:37 PM
To: [log in to unmask]<mailto:[log in to unmask]>
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]<mailto:[log in to unmask]>>
To: [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]:[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]<mailto:[log in to unmask]:[log in to unmask]>>>
To: [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]:[log in to unmask]>>
<[log in to unmask]<mailto:[log in to unmask]<mailto:[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]<mailto:[log in to unmask]<mailto:[log in to unmask]:[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]<mailto:[log in to unmask]:[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]<mailto:[log in to unmask]:[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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