Comparing humidity protection alternatives
In a blog post earlier this week, we discussed moisture barriers and explained how atomic layer deposition can be used to protect electronics from humidity.
When we talk about thin film coatings and moisture protection of electronics, there are of course various technology alternatives to ALD. We believe that ALD offers encapsulation properties that are far superior to the competing technologies, but we understand that it is sometimes difficult to grasp the differences between the alternatives.
If another manufacturer says their coating solution offers high-precision and we say ALD surfaces are extremely thin, what does that mean? Which one is thinner?
If a company claims that their parylene coating for electronics is conformal and we say ALD gives you the ultimate pin-hole free moisture barrier, which one is better?
How to define good humidity protection?
The requirements for sealing vary a lot depending on the application. Food packaging obviously requires much less protection than a circuit board, which in turn can still be ok with humidity levels that will destroy an OLED display.
A common measure for moisture control is water vapor transmission rate (WVTR, sometimes also referred to as MVTR, moisture vapor transmission rate), the unit of which typically is grams per square meter per day (g/m2d). In plain terms, that means that we verify a coating by measuring how much water gets through an area of coating in certain conditions in 24 hours.
Let’s do a quick calculation to compare two moisture barrier alternatives for electronics:
Taking a look at a couple websites promoting parylene moisture barriers, we can say that the best conformal parylene (type C) coatings have a transmission rate of a 0,08 g*mm/m2d, which means that a millimeter thick coating would let 0,08 grams of water pass per a square meter of coating each day (in practice, the coated area is of course much smaller).
Based on the same quick web tour, it seems that a typical parylene coating thickness for circuit boards is 5 to 20 microns. A 20 micrometers thick parylene C coating would therefore have a WVTR value of 4 grams/m2 per day.
Now, looking at ALD encapsulation with Beneq equipment on for example OLED displays, a typical WVTR value of our nCLEAR ALD barrier coatings is 4×10-6 g/m2 per day. That is a million times less moisture through the surface than with the best parylene alternative. Pretty good, right?
What is thin when it comes to moisture barriers?
“Yes, but how thick must the coating be to provide that level of protection?” you may now ask. That is a good question, material savings should be on everybody’s agenda these days.
Parylene coatings are often marketed with comparison tables, where they win easily other options, such as epoxy, polyurethane and silicone. ALD moisture barriers don’t usually appear in the comparison tables, but how would they compare?
As we mentioned, a parylene coating with the above mentioned moisture protection level would need to be 20 microns (2×10-6 meters) thick.
The ALD encapsulation layer we picked as the example (with a million times better insulation capability) is just 20 nanometers. In other words, a thousand times thinner.
Would that make our ALD coating a billion times better a moisture barrier?
That may be marketing talk gone too far. Let’s just say it like this: atomic layer deposition is the best technology we know of for keeping water and humidity out of where they don’t belong.