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June 1998

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
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Date:
Wed, 10 Jun 1998 11:14:51 +0100
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Cory and Lise,

Following up on my colleagues reply, and to elaborate a little further:

1       Answered by David Greenman.

Note however: A Conformal Coating should be applied to a flat unencumbered
substrate at a cured thickness of 0.003 inch plus/minus 0.002 inch.
However, Acrylics (AR) and Urethanes (UR) may be applied at 0.002
plus/minus 0.001. It is understood that the film thickness around
components will be typically, x 3 or x 4 the flat land thickness.

Obviously, (please note Duane!) to achieve the desired protective effect,
the coating should be UNDER as well as over, the components. The most
efficient and cost effective method of acheiving this, is by dip coating
and you will coat both sides simultaneously.

You can acheive >> 500 assemblies per hour from equipment costing 50% less
than selective systems. The only issue is that of masking. When we have
customers needing to process at this level, then design for manufacture
becomes much more easily acheived. In other words, design the assembly with
all components that should not be coated, on one edge of the assembly, the
dip to that point and no further. Total process cost including capital,
labor and materials will be << $0.05 per assembly. You cannot get these
economics with selective coating systems.

2       Bubbles

As previously given, this will most probably be due to the coating being
applied too thick. This causes solvent entrapment by the surface skinning
over before the solvent has due time to escape. It converts to gas and hey
presto - bubbles.

The bubbles, in this senario, will most probably be around the components
rather than over them.

If they are over them, then your problem may be related to drying too fast.

3       Dipping equipment

We specialise from lab units to +500 bph (boards per hour) systems.

Your request would suggest that you have been trying to dip by hand. So,
for the benefit of those who are interested - wake up at the back! - dip in
at < 12 inches per minute so you don't trap air under the components.

Come out at < 6 inches per minute or slower than the cascade effect of the
material. This permits the surface tension of the material to pull off the
excess. In other words, the faster you withdraw, the greater the film build
the slower out, the thinner the build. By the way, these speeds are almost
impossible to achieve by hand - you really need a machine - and don't use
an electric motor above the tank, the solvents in the coating are generally
highly flammable and we don't want you to fry!

Regards, Graham Naisbitt

[log in to unmask]

----------
From:   Cory and Lise Steeby[SMTP:[log in to unmask]]
Sent:   09 June 1998 11:24
To:     [log in to unmask]
Subject:        [TN] dip conformal coating

We are using a manual DIP conformal coating method with an acrylic coating
and building assemblies to the IPC-610 specification.

1.  Are there other specifications which apply to conformal coating?  610
is brief on the subject.

2.  Our biggest defect is bubbles in the coating.  We are finding that dip
angle, insertion rate and extraction rates all effect the amount of bubbles
on the finished assembly.  Does anyone have similar experience or advice?

3.  Does anyone know of available dipping equipment and / or drying
equipment?  Our goal is to be able to dip 250 assemblies per day (1000
assemblies per day panelized 4 up).

Thank You

Cory Steeby

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