The increasing value that consumers place on their electronic devices has heightened awareness of those devices’ reliability. It has also spurred a greater emphasis on, and demand for, protecting these electronics against possible damage from environmental factors.
This demand, in turn, is driving unprecedented growth and breadth in the use of conformal coatings. More types of applications are moving to the use of coatings, and more coatings are being used within a given application segment. For example, more types of smartphones now use coatings.
Conformal coatings are designed to electrically insulate circuit boards, and isolate their components from damage caused by debris and water. The protection they provide helps prevent conductor corrosion, dendritic growth, and electrical crosstalk. Ultimately, that protection can prevent the device failures that may result from such damage.
A silicone conformal coating has been spray-applied to automotive controllers, and fluoresces under UV light to aid visual inspection of the coating's coverage. (Source: Dow Corning)
How much salt water exposure can your electronic devices withstand? Those who recently lived through a hurricane have been finding out the answer to that question. Unprotected copper traces, wires, and components do not get along very well with salt water. Corroded electronics are not especially welcome in a weather emergency, nor in our everyday work and life. Yet, reliability may never be considered strongly enough until it's really needed, or when it's missed.
Although modern electronic devices and components can withstand a lot of abuse, they are not indestructible. Great effort is taken in their design and manufacture to provide suitable durability. However, full testing of durability can typically occur only after a design or build qualification process is already well underway. It's not uncommon that, at the final hour during durability testing, problems may be revealed that require unexpected and unplanned strategies to protect electronics from the environment.
The changes that must then result from these new requirements must be made to work around existing designs and manufacturing processes that are already in place, while also minimizing any cost increases. But they often end up being more expensive, and likely less effective, than if such protection had been factored into the design of a device right from the start.
Environmental protection strategies often involve trade-offs among performance, perceived value, and cost. Added circuitry and component protection can enhance customer satisfaction and the value of a device, but they may not always justify a higher price to the purchaser.
Although many different materials have been used in the past for conformal coatings, three main types dominate for use with electronics. These are acrylics, urethanes, and silicones. Each has its own advantages and limitations.
Acrylics (sometimes abbreviated as “AR”) are often inexpensive and easy to apply. They provide a hard, tough coating that is relatively easy to repair. However, they have a narrow useful temperature range and are typically supplied in the form of solvents. Some of these solvents can pose handling, safety, and environmental challenges. Acrylics generally do not have a cure mechanism; instead, solvent evaporation dries the film.
Removing the coating is not just potentially important in repairs, but it's essential for Design For Disassembly/Design For Recycling practices. Our upcoming May materials feature article addresses some DFD/DFR topics along these lines.
I'm just wondering how important it is to be able to remove the coating, drsmith... We used to have the mindset of repairing a product at board level, then we started board swapping, and now we don't even bother to do that in many cases...our it's broke - throw it away mentality may preclude the need for being able to access the board and if the coating is doing its job - I am thinking that the need for repairs should go down.
You're right about that, of course. Both that I didn't get to take advantage of volume pricing, and the effects of the Walmartization of America. Personally, I don't shop there as my own form of boycotting. The practice of only caring about large numbers especially burns me living in a low-population density area where the whole point is individualized tastes and service--or it should be. Instead, I'm told that YXZ product has disappeared from my local store because volumes aren't high enough. Those practices may work, and make sense, in NYC, but not in a small town of 4000 or 6000 people.
Having run a small business Ann, I am sure you did not get to take advantage of volume pricing like Walmart. That is what is running the Mom and Pop shops out of business and it's a shame - usually the quality is so much better since they take personal pride in their product. What was really frustrating is that we chose the better material, knowing we wouldn't be able to compete but refusing to compromise. Unfortunately initial cost will often call the shots even when it makes sense to do otherwise...and if you don't let it, you'll fail because you can't be profitable.
Nancy, I know what you mean. Seems like that subject--engineers want a better product/component/material, but management/beancounters won't go for the slightly higher cost--comes up a lot in the comment boards. But your point about smaller companies buying smaller quantities is a good one, too. I know that from having run a small business for several years.
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.
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.
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