Paul, I think what you are looking for here is a calculation of DPMO, or
Defects Per Million Opportunities. These calculations of defect rates are
normalized by the complexity of the board using a calculation for the number
of opportunities per boards, based on the number of components and the
number of pins. You can find information on this in IPC-7912, Calculation
of DPMO and Manufacturing Indices for Printed Board Assemblies. You can
also find some related, but more general information in IPC-9191, General
Guidelines for Implementation of Statistical Process Control (SPC). If you
search the publications list on www.ipc.org, you may find other related
publications on DPMO.
On a related note, we use a software package from Tecnomatix-Unicam that
calculates the DPMO values, overall and for individual defects, based on the
defects that are logged against each board and the opportunity count, which
is calculated from the Unicam job file used to set up each board type. Let
me know if you would like additional information on this.
Dave Roach
Trane GCC
4833 White Bear Parkway
St. Paul, Minnesota 55110
651-407-4294
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Baine
Sent: Friday, August 12, 2005 10:30 AM
To: [log in to unmask]
Subject: [TN] Calculation of solder defect rates
Hello all,
I have not used this forum for a few years so I hope I'm doing this
right.
I have a question re calculation of defect percentages for PCB
Assemblies. The old MIL-STD-2000 standard defined a "defect
rate" as the number of observed defects divided by the "normalizing
number". The standard requires calculation of the following:
(1) an Assembly Defect Rate, which is the assembly defects
divided by the normalizing number, where Normalizing Number is
(total no. of components, component leads, terminals and wires on
the
assembly plus one for the PWB); and
(2) a Solder Defect Rate, which is the solder defects divided by the
normalizing number, where Normalizing Number is (total no. of
terminals plus total no. of solder connections).
I cannot find any guideline in J-STD-001 or IPC-A-610 for
calculating defect rates. I am trying to find some non-time-
consuming method for calculating the Normalizing Numbers. For
example, would the Solder Normalizing Number just be the total
no. of component leads?
I would appreciate some guidance. Thanks in advance.
Paul Baine
Q.A. Manager
C-Tech Ltd.
Cornwall, Ontario, Canada
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