IPC Standard 9191 covers this and darn near everything else regarding
defect rates, SPC, and quality control. It is flowed down in J-STD-001. 

-----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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