Sorry to bother everyone again. I guess few response
to this topic maybe becasue of Easten Holiday.
Shirley Xiao


Dear All:
  What I have on hand is a old revision of
IPC-6012(1996). section 3.4.4 Bow and twist: "The
printed board shall have a maximum bow and twist of
0.75% for boards that use surface mount components and
1.5% for all other boards. Panels which contain
multiple printed boards which are assembled on the
panel and later separated shall be assessed in panel
form."
  From the PCB user point of view, what is the maximum
bow and twist percentage that the placement machine
can  tolerate?
  While in IPC-4101 section 3.8.4.3 Bow and twist
laminate materials (table 8 bow and twist, mm per 30.5
cm), 3.0 mm per 30.5 cm which is equivalent to 1.0% of
bow and twist (for laminate thickness of 0.79-1.67 mm
double sided with panel size from 200 mm to 300mm).
 My question is the requirement for laminate is even
loose than that of printed circuit board. Is it
reasonable or should we require the laminate vendor to
tighten the bow and twist specification?
  Any comments will be appreciated.

  Shirley Xiao




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