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Date: | Mon, 24 Jul 95 10:03:48 EST |
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To all Curtain Coat Skip Sufferers:
I know of three ways to get around a skip problem, and neither is
without some risk.
1. You can increase your coat weight. Going from 11 g/sqm to
13 g/sqm will get coverage over some skips. There are limits to
what can be attained, and there is the material cost increase.
2. You can reduce your viscosity. Going from 60 seconds to 50
seconds will dramatically increase the fill of small skips. If
you only do that change, you will find the thickness of mask over
conductors and especially the corners of conductors will drop. I
recommend increasing temperature in conjuction with reducing
viscosity. This has the net effect of keeping solids the same
and minimizing the thickness loss over conductors. For example,
increasing the Probimer 52M curtain temperature from 24 C to 27 C
and reducing the viscosity from 60 seconds to 50 seconds results
in no change in solids content (but you will see a different
ratio of coverage on conductor to coverage on laminate).
3. You can increase the temperature of the boards as they are
coated. This has the same effect as raising the temperature and
lowering the viscosity. The downside to this is that you may see
an increase in mottling and runback, with some thinning of mask
over pads.
Any of these conditions will help unless you have channels that
are too narrow. As a rule of thumb, any channel that is not at
least twice as wide as it is deep will get a skip.
Good luck!
Bruce Guttman
HADCO Corporation
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______________________________ Reply Separator _________________________________
Subject: SM SKIP IN CURTAINCOAT PROCESS
Author: JMONAGHAN
Date: 7/24/95 7:31 AM
Hello,
Our company largest DS PCB manufacturer in Malaysia.We are
encountering
the soldermask skip problem.I give below the parameters used.
M/C Burkle Curtain coater
Ink Peters GL2469sm
Viscosity 60to65
Beltspeed 78m/mim
web weight 6.4to 6.8gms/600sqcm
We use pattern plating process and plating thickness 40to 60 microns.
The Sm skip is random and happens near closely spaced tracks(most of
the times).
I Shall be highly grateful if anyone can give info to minimise the
sm skip problem.
Thanks
R.Srinivasan
Likom PCB SDN BHD
Malacca Malaysia
E-mail :[log in to unmask]
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