Hi Jorge,
It's not as simple as spraying coating on a board and masking components.
I'm not an expert but can share with you some of what I've learned through
our experience here. We are an OEM doing our own assembly and have just
completed our installation of a conformal coating process. One place you
may want to look is the TechNet archives. Just do a search for "conformal
coating" and you will get a bunch of information. Some of it won't apply
to you but you will need to do a lot of research. That's really the best
advise - do a lot of research. It's well worth the time and effort. Using
the wrong coating material or an improper application will cause a lot of
headaches. If you are not familiar with coating materials, you will need
to learn everything you can about them. Get a copy of IPC-HDBK-830
Conformal Coating Handbook. This document is in the proposal stage only
but does contain helpful information. Another helpful document is
IPC-CC-830A (with Amendment 1) Qualification and Performance of Electrical
Insulating Compound for Printed Board Assemblies. There may be other IPC
documents that could benefit you as well. Another source of information is
coating material and coating equipment suppliers. Some of them also have
helpful information on their web sites. Having information will be
invaluable. Some of it will be good, some of it won't. Regarding
application method, if you have other assemblies that could benefit from
conformal coating you might consider selective coating equipment. Using
this equipment on your other boards will help justify the cost. It's
expensive but worth it. If you go this route, buy the best you can afford.
The last thing you need is equipment that doesn't perform well or as
expected. Take some field trips and go look at equipment in operation.
Ask a lot of questions. Another area you may need to look at is your
overall assembly processes. You may need to train your operators in good
assembly practices and change the way you handle components and boards. As
to your specific questions about cleaning, we use no clean here and do not
bake boards so others will need to help you with those issues. However,
component data sheets may give you some of the information you are looking
for. Your question on dryness level is an important issue. Always
remember that when you coat, whatever is on the board and on the components
prior to coating is going to be trapped underneath the coating. That
includes other contaminants as well as moisture. You will need to
determine what you can live with for your applications. As you do more
research, you will also learn that conformal coating will not keep
everything out and give your assemblies immortality. The materials
definitely help prolong life if properly used but they are not totally
impervious to attack by environmental conditions. Once you determine what
materials and equipment you need, you will want to focus your attention on
your processes. This can make or break a successful coating operation.
Obviously, there is a lot more to it than these few points. You need to
consider everything together and realize that what you do in one area will
have affects in other areas. You know - the old cause-and-effect
relationship. So, do research, go see stuff in action, ask a lot of
questions, look at your processes, decide what's best for your application.
Good luck.
---Original Messages---
Date: Tue, 12 Jun 2001 09:01:23 -0500
From: Jorge Santana <[log in to unmask]>
Subject: Conformal coating or not ?
Hi
I am not familiar to conformal coating process and I would like
some advice of using or not conformal coating in this specific
application. The board will located outside and should work
properly for several years, but will be enclosed inside a
WEATHERPROOF and DUST-TIGHT box, this condition is enough for not
use conformal coating ?
Thanks for any advice.
Jorge Santana
Date: Tue, 12 Jun 2001 11:43:23 -0500
From: Jorge Santana <[log in to unmask]>
Subject: Ok conformal coating, but how ?
Gentleman;
This board has some restrictions that I would like to share because
I am not familiar with this process and some advice will be
helpful.
1) Prior conformal coating I need wash the board, but there is 6
SMT photo sensor and more than 20 LED , what cleaning method should
I use in order to not damage or affect performance of this
components ?
2) What level of DRY the board should be before coating, the LED
are heat sensitive and could not be exposed to high temperatures
for baking (more than 125 degree C ), what baking set up should
work ?
3) What kind of conformal coating should I use for spray
application (acrylic, epoxy,silicone or polyurethane), the board
environment will be exposed to 74 degree Celsius in a sunny day (
air temperature inside the box )
4) The photo sensor and LED should not be conformal coated, what
kind of masking should I use, for spray coating.
5) In the back side of the board ( there is no component in this
side ) a heat sink will be attached, and no conformal coating
should be applied since this heat sink will be in contact with a
sheet metal, but the heat sink covers about 30% of area in the
bottom side, It is OK to leave the bottom side without conformal
coating since there is no components at this side, or should I mask
the conformal coating and then attach the heat sink after conformal
coating was applied ?
Thanks for any advice at any question.
Jorge Santana
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