IPC 600 page 56 section 2.11 on flatness, but your assembly line/ process
really indicates what's acceptable.  Use your least robust machine (the one
that cannot tolerate bow/twist) to determine your REAL requirement.  Each
manufacturer (pick/place) recommends a bow/twist max in mm or in.  It also
depends on PWB thickness - a 0.030" telecon PWB is much more flimsy than a
0.125" high voltage PWB.  In line conveyors hate excessive bow or twist,
especially.

PS. PWBs can be flattened with a soak at warm temps under a weight.

Mike

-----Original Message-----
From: K HERK [mailto:[log in to unmask]]
Sent: Thursday, April 25, 2002 11:11 AM
To: [log in to unmask]
Subject: [TN] BOW/WARP


Is there a chart for PCB bowing ?

I have a typical value of 0.007"/1" bow, but a
customer wants to know the
bow for the specific case of 1.6mm FR-4.  Are there
different "ranges" of
bowing that a PCB is specified at ?

Also, how does temperature affect bowing ?  The
customer says that bowing
occurs during solder reflow where the temperatures are
a few 100 degrees
Celsius.



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