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October 2003

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Subject:
From:
"Philip M. Yates" <[log in to unmask]>
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Date:
Wed, 22 Oct 2003 10:24:26 -0500
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Mike,

In building the types of high reliability, hostile environment products that
your company appears to produce, validation of the quality of the PWB is
critical.  While working in an EMS environment building these types of
products, my experience has been that the PWB is always the number 1 defect
source.  We would normally perform receiving inspection on PWB's as follows
(typical) to the appropriate IPC specification (and/or customer quality
specifications).

* Visual inspection
* Warpage measurement
* Critical Dimension verification
* Inspection of Cross Sections (we made our own if not provided by the
supplier)
* Ionic contamination testing
* X-Ray fluorescence to validate the composition and thickness of the
surface finish
* Other techniques as necessary (SEM, EDX, etc. to obtain more specifics)

The level of validation was determined on the basis of performance over
time.  Typically, a new PWB supplier, or a new design was inspected at 100%,
then adjusted down as performance warranted.

It might be possible to eliminate inspection completely if a supplier's
performance was exceptional over an extended period of time, but we never
achieved that level.  The cost of building defective product for a critical
performance application is much higher than the cost of not validating the
quality of the incoming material (my experience).

Phil Yates

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Mike Williams
Sent: Wednesday, October 22, 2003 9:00 AM
To: [log in to unmask]
Subject: [TN] Skip Lot inspection


I am looking for some input on skip lot inspection of bare pwb's upon
receipt from the supplier.  We are currently performing our own destructive
analysis to determine acceptability over and above what the supplier
performs.  Any opinions pro and con are welcome.

Mike

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