PCB Technical - Can the nano coating of PCBA technology be waterproof?

PCB manufacturers here only say that their products can reduce the water ingress rate of the product, and they do not say that this nano-coating can prevent water from reaching the waterproof level, so it should be said that this nano-coating can prevent moisture but cannot prevent water ingress!

In fact, if you have a friend who is driving, you should know that there is a water repellent product, as long as it is sprayed on the front windshield, it can effectively reduce the adhesion of water droplets and the problem of remaining on the windshield. This kind of water repellent It is a kind of nano-coating material.

Many friends may not know that the humid environment is actually very harmful to electronic products. For example, moisture is one of the main killers of CAF (Conductive Anodic Filament) micro-short circuit. If it can effectively increase the moisture resistance of the circuit board, It can reduce the incidence of CAF, or delay the occurrence of CAF.

In addition, many PCB products often cause leakage current or even circuit board corrosion due to the residual flux (Flux) after soldering. They can also achieve a certain product life by isolating moisture. promote.

Another advantage of using this kind of "nano coating" is that when a customer accidentally pours some carbonated beverages or liquids on the product, especially when the serial port is connected, even if the outside of the product has been cleaned afterwards, the liquid It must remain more or less inside the body, and will begin to corrode circuit boards and parts over time.

When considering whether to use Conformal Coating to solve the above product reliability problems, it is actually quite time-consuming and labor-intensive to use Conformal Coating. Paint stains on parts or locations that require contact, such as connectors, causing poor contact after subsequent product assembly. Not only is rework troublesome, some problems are still intermittent, which is really annoying.

And this PCB manufacturer actually claimed that their nano-coating does not require any mask protection for any parts or contact points when spraying, and it can also spray after the whole machine is completed, which means that it can be assembled in the product. After the machine is completed, it will be sent for gluing.

Why does it sound weird? In fact, this manufacturer also recommends spraying on the whole machine rather than spraying on a separate circuit board. The reason is that their nano-coating adopts PECVD (Pulse Enhanced Chemical Vaporized Deposition, plasma assisted chemical vapor deposition) method and cooperates with airtightness. Vacuum equipment, so nano-level coating particles can float along the tiny gaps of the whole product and attach to most corners inside the whole product. Also, because the gap of the coating is smaller than water molecules, it can be lifted. To isolate the influence of moisture on electronic products. In addition, since the thickness of the coating is only about 5-50nm, spring parts (such as connectors) can easily remove these coatings as long as they are rubbed to achieve the purpose of electrical contact, so there is no need for a mask.

The reason why PCB manufacturers say that their products are moisture-proof but not effective against water ingress is because the nano-coating will adhere to any position of the product, and can also close all the small gaps on the product, but for the interface slot, as long as there is The original coating film will be destroyed when the foreign object is inserted and touched, and the function of preventing water ingress will be lost. The coating function can continue to be maintained in other places where there is no foreign object inserted, which has a moisture-proof effect.

Restrictions and possible problems in the use of nano-coating

▪ If you use products that do not require friction, such as silicone zebra stripes, whether they can be sprayed on the circuit board and then assembled, you must do further tests to verify that there is no data from the manufacturer to prove that there is no problem.

▪ Secondly, if this nano-coating is sprayed on the PCBA circuit board in advance, and then assembled into a complete machine, the position of the circuit board must be specially regulated, otherwise there is a chance that the nano-coating will be exposed to the position where the finger is in contact. Grind off.

▪ There is also a vacuum when spraying nano-coating. Some parts may have to be especially careful. For example, products such as electrolytic capacitors and batteries are designed with chemical liquids. When the internal and external pressures of the parts are different, will there be liquid leakage or It is the risk of explosion.

▪ When processing this nano coating, you must use the special spraying equipment provided by the PCB manufacturer. If the quantity is small, the product must be sent to the manufacturer’s factory for processing and then sent back. If the production can be large, you can discuss with the manufacturer about the equipment rental and placement. Own factory, or let the manufacturer join the person with the machine into the field, so that you can avoid the trouble of sending the product to the factory and then returning it.

▪ In actual application, if the product is dropped, the coating on the gap of the product may be broken due to the deformation of the case due to external force.