Electrostatic spray solder mask?  Has your customer measured the static
field on the boards prior to spraying?  Has your customer measured the field
after the spraying?  The field must be considered a contaminate unless the
board assemblies will not contain any static sensitive parts and the board
will not be within one foot of any static sensitive part.  Using an
electrostatic spray for any coating on a printed circuit assembly usually
results in a trapped static field under the coating, in the samples I have
been shown.  Each process is different, however, and due to the materials
their may not be a field.  I have even measured a charged field on airless
sprayed conformal coating when applied to printed circuit assemblies.

Al Cash

-----Original Message-----
From: Geoff Layhe [mailto:[log in to unmask]]
Sent: Friday, December 17, 1999 4:10 AM
To: [log in to unmask]
Subject: [TN] Electrostatic Spray Solder Mask


Hi All,

Can anyone help with this problem a PCB fab customer of mine has?
Process - Electrostatic spray solder mask.
Problem - Soldermask missing from areas. This seems to be related to the
base laminate (FR4). When two identical boards on two different batches
of laminate are processed side by side the problem is always on one
batch. What effect could the laminate have?
What other factors could cause the problem?

TIA
Geoff layhe
www.lamar-uk.co.uk

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