Hi Ken,

If the misregistered layer is a signal layer, the connection between the
inner layer trace and the hole wall may be small and prone to heating
depending on the power going through the trace. Hole to uncommon signal
trace distance may also prove to be too small, especially if the layers are
misregistered in different directions. As far as I know, this is a very
common cause for rejects and should be addressed as such. Purchase orders
and designs ALWAYS take precedence over the IPC specs.

If the inner layer you suspect is a power or ground layer and the pads are
wagon-wheeled, then the connection to the layer may be good. However, the
residual dielectric in clearance holes may be insufficient.

By the way a 0.0090" hole with a 0.0200" pad is very tight and leaves a
manufacturer with very little manufacturing tolerances. It may be done, but
the rejection rate may be high.

Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]


-----Original Message-----
From: Ken Patel [mailto:[log in to unmask]]
Sent: October 12, 1999 6:50 PM
To: [log in to unmask]
Subject: [TN] Reliability due to misregistration on inner layer


On one of our product, we have found that one of the inner layer has
misregistration.

Do you see any quality/ long term reliability problem associated with inner
layer misregistration? Our requirement was to have a 1 mil minimum annular
ring on all inner layers. What is the risk cum liability of accepting those
boards knowing that they are misregistered.

Misregistration occurred at 1mm BGA where the finished hole diameter is 9
mil on a 20 mil pads.

re,
ken patel
______________________________________________________
Ken Patel                       Phone:  (408) 490-6804
1708 McCarthy Blvd.             Fax:    (408) 490-6859
Milpitas, CA 95035              Beeper: (888) 769-1808

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