Perhaps we are a little cavalier in our specifications, but we don't specify
a minimum thickness and leave it to the vendor's process. IPC-6012 requires
only that the mask meets the qualification/conformance requirements of
IPC-SM-840, and also gives specific criteria on the coverage, but nothing
specific on thickness. It specifically states thickness measurements are
not required unless required by the documentation. IPC-SM-840 states
thickness shall be sufficient to meet the dielectric strength requirements
of 500VDc per .001 in, and that thicknesses less than .001 in must still
meet the minimum breakdown voltage of 500VDC. We DO specify a maximum
thickness, and that is that the mask must not exceed the height of the SMD
lands (copper foil + finish).
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
-----Original Message-----
From: Phil Nutting [mailto:[log in to unmask]]
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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