Barbara,
Your choice of coating depends on the desired protection level for the
expected environment, and how much your customer is willing to invest. In
the case of paralene / paraxylene (XY), the investment is significant.
XY is one of the coatings flown in space when we need ultimate protection.
Properly coated boards can be immersed in seawater without any problems. XY
is resistant to radiation degradation and atomic oxygen attack, and provides
the ultimate in environmental and foreign-object-debris (FOD) protection.
XY has high material and application costs, with extremely low quantity
production rates. It is extremely difficult to remove, resulting in the
coated assembly being considered non-repairable (it can be done, but it's
painful).
We also fly silicone (SR) and urethane (UR) coatings, which can easily be
applied by spray, brush, or dip process. Both of these coatings are user
friendly, with relatively inexpensive material and application costs,
offering good production rates, environmental, and FOD resistance. Both are
considered removable and repairable.
In a previous life, I worked for a manufacturer that sprayed boards with
clear acrylic (AR) purchased from the local home supply store (brand name
starts with the letter "K"). Worked great, inexpensive, and some of the
environments the finished products were exposed to would be considered worse
than what we see in some of our space applications. AR is fairly easy to
remove and repair, but glass diodes and other sensitive components may need
resilient protection.
You're more than welcome to contact me off-line if you wish.
Regards,
Robert Wm. Cooke
Technical Expert, Special Processes
Advanced Programs and Analysis Division
NASA / Johnson Space Center
2101 Nasa Parkway, M/S NX23/WGI
Houston, TX., USA 77058-3607
Tel.: 281.244.1903
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barbara Burcham
Sent: Monday, May 16, 2005 4:56 PM
To: [log in to unmask]
Subject: [TN] Conformal Coating of Assembled Boards
Well, my company now has an application requiring conformal coating on
some small assembled boards. We need to mask off 3 connectors and coat
everything else.
I have some information on a product called Parylene applied by Parylene
Coating Services, Inc. in Katy, Texas.
We did a small lot with a simple spray-on process, but that is not the
way to do production runs, of course.
What would you recommend?
Thanks,
Barbara
Barbara J. Burcham, C.I.D.
Fairfield Industries, Inc
281-275-7687
[log in to unmask]
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