Coating LEDs to protect them from the harsh environments they are placed in is big business.
The volume of manufactured LEDs globally is growing at an exponential rate and there is no end in sight.
However, the challenges to protect the LEDs from long-term failure are not small especially in an outdoor environment.
To combat this problem, coating processes and materials like conformal coatings, Parylene, encapsulates and potting compounds are being used to protect the LEDs in this difficult environment.
The reality of LED lighting demands and the environmental problems faced
LED circuits are being placed more and more in exposed areas and subjected to the full force of the elements. Then the LEDs are expected to survive for long periods of time without failure.
Further, the protection placed on the circuit and the lights must not affect the light output (the lux) of the LED. Nor must the protective coating cause heating problems due to thermal demands.
Finally, due to the general low cost of the LED products in the first place then the protection method proposed has also to be extremely low in price.
This all has to be balanced carefully.
In fact, this final point, the right cost, can be the most challenging. After all protecting the LEDs can be relatively easy with certain coating materials.
However, coating the unit for the right price is the key challenge.
So why is the process of coating LEDs so expensive?
This price challenge is due in most cases to the insulative properties of the majority of traditional protective coatings applied.
Nearly all of the current coating methods require components like connectors not to be coated since the coating ingress into the wrong component would ruin the electronic properties of the circuit board.
This leads either to the requirement of masking components in process or a selective coating processing that leads to increased costs in production.
Further, the demand that the LED light output is not impaired is also a challenging process. Coatings either immediately reduce the light output or can change color with time due to issues such as UV degradation whilst in the field.
Therefore, to provide a high level of protection whilst being low cost is not a trivial task for a coating.
Processes like Parylene, conformal coatings, encapsulates and potting compounds continuously find it difficult to meet all of these criteria and customers are continuously compromised.
So, is there an alternative protective coating for LEDs besides Parylene, conformal coatings and encapsulates?
Nexus, the independent conformal coating center, has examined a new, novel technique that Thin Film Partners is introducing that may be able to meet all of the environmental demands for LEDs and actually be cost-effective.
This process is a hybrid ALD (Atomic Layer Deposition)/CVD (Chemical Vapor Deposition) technique called Molecular Vapor Deposition (MVD).
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.
This means that the cost of process is purely the cost of application of the material and nothing else.
Since the application process is relatively low cost then this does offer a very interesting alternative to the traditional coating materials.
So what does the 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.
The CVD film provides the barrier protection.
These coatings are alternated until the right film thickness is achieved.
At this point a final hydrophobic layer is applied that combines with the ALD and CVD layers to provide a highly effective barrier.
So how well did the MVD coating actually perform in protecting the LEDs?
Nexus worked with live LED circuits from a customer that was for an outdoor application.
For testing, the customers used their own in-house test methods to prove the MVD technology.
The LED circuit to be tested was exposed to the 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 results were extremely interesting.
The LED circuit passed on all tests.
Further, 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 the MVD process?
Since the process is masking and de-masking free then the cost per unit is incredibly low and superior to nearly all the traditional methods of coating protection.
Further, the protective properties of the hybrid coating in nearly all cases is superior to the conventional methods.
So, you get a lower cost coating with a higher technical performance.
How good is the MVD coating as a protective material for electronics compared to other materials?
Generally, with protective coatings for electronics then Parylene is considered the gold standard in most cases.
So, Nexus compared Parylene with the MVD material.
The results are tabulated below.
|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 Nexus 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 hybrid MVD material could just be what the LED industry is looking for in protecting their circuits.
Nexus are now planning to investigate how the MVD material performs on other types of circuits shortly.
Thin Film Partners are also exclusively introducing this coating to the electronics industry and we are expecting good results.
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