Your supplier should do a double pass of soldermask. It is true that they
can only achieve .001(assuming they are applying LPI mask) and at the knee
of the trace maybe .0005 thick.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Tuesday, September 23, 2008 8:29 AM
To: [log in to unmask]
Subject: [TN] Solder mask thickness

Good afternoon,

OK, here is this afternoon's question.  Solder mask thickness, what is the
"industry standard"?  We currently specify 0.001" thickness and this may be
fine on a large area when tested via IP TM-650, 2.5.6.1.  Now use 2 ounce
copper traces in a normal board configuration.  Our board vendors are
stating that they cannot hold the 0.001" thickness at the edges of the etch,
it is more like 0.0003".  And if we spec 4 ounce or 6 ounce I'm sure it
doesn't get any better.

How are you specifying solder mask thickness on your heavy copper weight
circuit boards?

Do your board vendors use two coats of mask to obtain the thickness needed
to comply?

IPC-SM-840 section 3.4 says it must meet the requirements of section 3.8.1,
thickness of 0.001" at 500 Vdc.

Your guidance is requested.

Thanks,

Phil Nutting

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