Robert Barr writes: But how does one measure bow and twist of an individual
board in a panel?

It is possible to work out the max. bow and twist of an individual circuit
within a panel (as supplied from a vendor) using trigonometry since the bow of
the individual board is a chord on the circumference of the main panel. It's
useful when designing SMT leads to attach at the sides of a board.


Brian Gaynor



But how does one measure bow and twist of an individual board in a panel?
Aren't I really concerned with the bow or twist of the entire panel since
that is what is going through the assembly line?


Bob


Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679
email: [log in to unmask]



Apply the specification to the individual circuit boards.

 Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107





 Guy Ramsey writes: Indeed, .75% may be too much.

My question is "Considering an SMT board in panel format, is the figure of
0.75%
for bow and twist a measure of the  complete multiple up SMT panel or is it
a
measure of the single circuit boad within the panel?

Brian Gaynor







Methods for measuring Bow and Twist are described in IPC-TM-650 2.4.22 and
can be found in the JSTD-001C. You are esentially correct, without going
into details. However, the IPC-A-610C performance requirement states,
"Consider "Form Fit, and Function" and product reliability. The Defect
Condition for all product classes is reached when bow and twist causes
damage during assembly or end use.

Indeed, .75% may be too much.

 Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107


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


What is the meaning .75% of maximum bow and twist allowed for SMT? Is it 7.5
mil per 1"? To me it is too much unless I misunderstood it.

Can someone clarify it?

re,
ken patel

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