Nexus, the independent conformal coating knowledge base, has been examining a new, novel technique that may be able to provide superior protection for electronic circuit boards compared to materials like conformal coatings and Parylene but also be highly cost-effective.
This process is called Molecular Vapor Deposition (MVD).
MVD is a hybrid Atomic Layer Deposition (ALD) and Chemical Vapor Deposition (CVD) technique.
It works by applying multiple alternating layers of ALD and MVD ultra-thin coatings, with differing protective properties, to build a completely unique, protective coating on the circuit.
The results so far in both LED and automotive coating have been extremely good.
So, why is MVD so good compared to Parylene and other conformal coatings?
The final MVD coating built up is much thinner than the other traditional coatings including Parylene.
However, its protective performance has been found to be superior to them all in most categories of testing so far.
Key performance indicators like Water Vapor Transmission Rate (WVTR), optical clarity, temperature resistance and hydrophobicity have been found to be much better than all of the other coatings.
Further, the really exciting part about this technology is the cost of processing that is extremely low.
Since the coating is extremely thin then it has been found that no masking is required. This is because when components like connectors are joined together then the ultrathin coating does not prevent electrical connection.
This means that the cost of process is purely the cost of application of the material and nothing else.
Since the process is relatively low cost then this does offer a very interesting alternative to the traditional coating materials.
So how does Molecular Vapor Deposition coating (MVD) actually work?
The actual film is built up of alternating layers of ALD and CVD thin coating layers.
The first coat, the ALD coating, is a ceramic-based material providing the insulating properties.
The second coat, the CVD coating, provides the barrier protection.
First, an ALD layer is applied to the substrate. Then a CVD layer is applied. Then a further ALD layer is applied and so on.
This continues until the correct number of layers is built that has the right protection.
Finally, once the required film thickness is achieved with the alternating layers, then a final hydrophobic thin film layer is applied
This final coating combines with the ALD and CVD layers to provide a highly effective barrier.
So, just how good is the hybrid coating as a protective material for electronic circuit boards?
Generally, with protective coatings for electronics then Parylene is considered the top coating in most cases. However, it’s extremely expensive in most cases to apply.
So Parylene was compared with the MVD material.
|Wear resistance/Handling Ease||Poor||Excellent|
|Water Vapor Transmission Rate||Good||Excellent|
|Temperature Resistance (extended time)||100°C||350°C|
|Adhesion to various materials||Poor||Excellent|
|Scalable to large production||Poor||Excellent|
|Process Time||8 – 12 hrs||8 – 12 hrs|
|Hydrophobicity||Good||Good – Excellent|
|Cost||High||Low – Med|
What was also identified for the MVD material were some key properties.
- The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof.
- Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.
- The temperature range of the material can be up to 350C without any degradation.
- The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed to UV light.
- The MVD coating stayed 100% transparent during testing (no loss of lux).
- The coating thickness of the hybrid material is x10 LESS than the Parylene. This aids light transmission and electric connectivity
So, in reality the MVD material could just be what industries like the automotive and LED sectors are looking for in protecting their circuits where cost and protection abilities are critical.
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