Nexus has been examining a novel coating technique that may be able to meet all of the environmental demands for circuit board protection and actually be cost-effective.
This process is Molecular Vapour Deposition (MVD) and is brand new to the electronics coating market.
MVD is a hybrid coating technique using ALD (Atomic Layer Deposition) and CVD (Chemical Vapor Deposition) coating processes in combination.
This method uses multiple layers of ultra-thin coatings with differing properties to build a completely protective coating.
The final 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.
Further, the really exciting part about this technology is the cost of processing.
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. Even better, the physical protection is not compromised.
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.
Does MVD sound complex?
Actually, although the technology and chemistry can be a little complex the process itself is fairly simple.
Once the process is set up in the machine the operator just loads, switches the machine on and unloads on completion.
This is a far cry from the sophisticated processes of robotic selective coating or the challenges of Parylene. Further, the process is actually very stable and in reality is tried and test in other industries.
So what does a MVD film look like?
The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material providing the insulating properties and the CVD film provides the barrier protection.
Once the required film thickness is achieved then a final hydrophobic layer is applied that combines with the ALD and CVD layers to provide a highly effective barrier.
Label: The film is built up of alternating layers of ALD and CVD thin coating layers. The ALD is a ceramic-based material and the CVD film is an organic layer.
So how well did the MVD coating perform when protecting circuit boards?
Data was recently presented at Apex in Sand Diego looking at live LED circuits from a customer.
The customer LED product was for outdoor application. For testing, the customer used in-house test methods to prove the technology.
The LED circuit was exposed to customer tests for resistance against salt, moisture and temperature.
The test methods included:
- Initial test submerged in DI water dip for 12 hours
- Second test submerged in 25% concentration saltwater dip for 17 hours
- Third test 2 x 6 hour cycles in water ramped from room temperature to 70°C
After each test the boards were tested for failure or problems.
The LED circuit passed on all tests. All results achieved were completed with no masking of components and zero light loss in LED opacity.
The electrical connections were found to be excellent and the coating did not affect the integrity of the connectors.
So what about the cost of process for MVD?
Since the process is masking and de-masking free then the cost per unit is incredibly low. The performance is also superior to nearly all the traditional methods of coating protection.
Further, the protective properties of the MVD coating in nearly all cases is superior to the conventional methods.
So, you get a lower cost coating with a higher technical performance.
So, just how good is the MVD coating as a protective material for electronics?
Generally, with protective coatings for electronics then Parylene is considered the gold standard in most cases.
So, we compared Parylene with the MVD coating 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 we also identified for the material were some key properties for LEDs.
- The Water Vapor Transmission Rate (WVTR) is superior to Parylene so the coating is far more waterproof for the LEDs
- Coating adhesion is superior as it covalently bonds to the substrate. So, the lifetime of the material will be better on the circuit.
- The hybrid coating is UV stable whereas Parylene in general is not. This is an important criteria for coatings exposed outside on LEDs
- The coating stayed 100% transparent during testing (no loss of lux). That again is important for LEDs.
- 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 the high volume electronics industry is looking for in protecting their circuits.
Need to find out more?
For further information on Molecular Vapour Deposition (MVD) then contact us directly.