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Increasing Electronics Reliability With Conformal Coatings

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Nancy Golden
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Very Informative Article - showing SR may be best choice...
Nancy Golden   3/11/2013 11:41:15 AM
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Kent, thanks for the very informative article on a very relevant topic. Initially I was confused by what seemed like conflicting statements:

Regarding Silicones – "However, these superior properties do come at a cost, which is typically a higher price per kilogram."

And "Yet, several factors are influencing engineers to choose silicone conformal coatings over other options to provide greater reliability and durability to electronic devices. These factors are low stress, lower production costs..."

But you did an admirable job explaining why despite the higher cost per kilogram, that silicone may still be the most cost-effective choice, along with its many advantages. It is also a good lesson for those of us who tend to just look at the surface. Initial cost is often the determining factor for a process and Kent's explanation proves that is not always the best case...

My only question is in regards to the final sentence of the summary which states "Studies have shown..." it leaves me wondering which studies are being referred to...is this information internal to Dow Corning specifically or are there some industry studies that have been done by other sources as well that are available?

Ann R. Thryft
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Re: Very Informative Article - showing SR may be best choice...
Ann R. Thryft   3/11/2013 12:20:57 PM
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The discussion of cost reminds me of so many instances I've seen where the initial price/cost of an item itself may be higher than competitive items, but due to various characteristics it costs less to use over time. That appears to be the case here, with a higher initial cost of the material itself vs a lower overall production cost, i.e., cost of using it during production. I think Nancy's right; it's so easy to just look at the material or product cost, not the cost of ownership or cost of use.

Nancy Golden
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Re: Very Informative Article - showing SR may be best choice...
Nancy Golden   3/11/2013 12:37:56 PM
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Unfortunately Ann, on the flip side, sometimes I think the manufacturer is cognizant of the advantages but has to go with the lower cost at start up simply because they can't afford to do otherwise, or if they do go with the higher costing product then they can't market their product at a price to make them profitable...for example we went with the higher cost of furniture grade pvc pipe with our horse trail obstacle business because we knew it was a better and safer product but because we were small fish, we could not afford to buy in volume. This drove our prices higher even with a ridiculously small profit margin and we could not become profitable...

Making good business decisions is a very difficult task especially when you are first starting out and have a very small budget...

tekochip
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Platinum
Wicking and other issues.
tekochip   3/11/2013 12:38:32 PM
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Something not covered in the article is that conformal coatings have a way of creeping into places they don't belong.  Connectors, of course, are the biggest problem.
 
That said, conformal coatings offer so many advantages that I prefer to use them even when not designing outdoor products.  The coatings prevent humidity damage that can be seen even with indoor applications, as well as protection from dust and smoke (some people still do).  Lastly, conformal coatings also provide mechanical support for components preventing damage from vibration.
 
It's a big commitment and increased product cost from many angles, but coatings really do improve a product's reliability.


Ann R. Thryft
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Re: Wicking and other issues.
Ann R. Thryft   3/11/2013 4:46:06 PM
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From tekochip's post, it sounds like this general class of coatings decreases cost of ownership for buyers, at least partly from lengthening product life. I wonder under what circumstances the higher product cost is balanced by lower production costs.

tekochip
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Re: Wicking and other issues.
tekochip   3/12/2013 8:24:48 AM
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For me the applications that use coatings are; agricultural, automotive, washroom appliances, dishwashers and washing machines.


CougFan
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Iron
Re: Wicking and other issues.
CougFan   3/12/2013 12:56:38 PM
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Aerospace applications use coatings for many reasons - one to help mitigate Tin Wiskers.

Ann R. Thryft
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Re: Wicking and other issues.
Ann R. Thryft   3/12/2013 9:55:56 PM
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What I'm wondering isn't so much what apps these coatings are good for, but in what cases the higher purchase cost of the coating gets offset by the lower production costs. Anybody know?

drsmith_m304
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Iron
Silicone Conformal Coatings
drsmith_m304   3/13/2013 11:41:10 AM
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If boards are ever to be repaired, or parts replaced, the coatings have to be removed. With Acrylic or Polyurethanes removal is relatively easy, so the repair is easy. However, silicone coatings are a different story. From the HumiSeal website:

Silicone - This is the most difficult coating to remove and the coating least compatible with all of the other coating types. There are no solvents to remove silicone so it may only be removed by abrasion and this will leave silicone contamination on the board surface. Complete removal is virtually impossible so local repair is generally all that is attempted.

Also, companies that outsource their board manufacturing typically lose their PCBA fabrication kowledge over the years (if they had any to begin with) and are constrained to initially judge coatings based only on their manufacturing costs, which include the material cost and the extra time, equipment and labor to cure the coating. Surprisingly, some of the most popular non-USA Contract Manufactures have little if any experience with coating, coating chemistry or coating processes - so these CM can offer virtually no well considered advice on coatings. Bean counters ask "Which is the cheapest and easiest to apply?" and the answer is usually "Acrylic" due to the similarity with ordinary acrylic spray paints.

Ann R. Thryft
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Blogger
Re: Silicone Conformal Coatings
Ann R. Thryft   3/13/2013 12:53:29 PM
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Thanks for the feedback drsmith. Interesting points about the difficulty of silicone removability, since one of the supposed pluses of silicone coatings is it good adherence to typical board substrate materials. OTOH, Design For Disassembly/Recycling are not yet established best practices everywhere. Stay tuned--our upcoming May materials feature article addresses some DFD/R topics.

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