To further protect and create a strong, long-lasting coat, you can get multiple layers of conformal coating on your products. Specifically with parylene, this coating can insulate against high voltage and contaminants if you should add more layers. Overall, the effectiveness will be determined on how you layer the coating. It is important to be precise and aware of the potential problems that can occur from layering multiple coats.
Here is what you need to know about layering conformal coating.
The Layering Process
The success of the layering process depends on the material, the kind of protection you need, and the type of application, such as dip coating or spray coating. The application method plays a big part in how you can time the layers and bond them correctly. You can use a process called Atomic Layer Deposition (ALD), which is the application of layers using a vacuum chamber.
There are two types of ALD application methods:
- Stationary: You inject one material into the coating chamber, it attaches to the component to be coated, then the remaining residuals are purged from the chamber. After that, the second material is added to the coating chamber so it can form a chemical reaction with the first one. This process repeats until the desired protection is achieved.
- Rotary: This method uses a spinning action to separate the initial formation after the second layer is applied.
Layering Problems and Solutions
It is possible to run into issues when adding multiple layers to your dielectrics. It is not the number of layers that can cause obstacles but how the layers are applied. If the layering is too thick, the coating may crack, and if it is too thin, the coating will have a less effective performance.
Here are some problems that could occur when layering conformal coating as well as their solutions:
Adhesion
Some coatings will have problems sticking to themselves, particularly parylene. When applying multiple layers of this coating, the surface energies may be low, or it may have been exposed to the outside world causing a change in the polarity of the surface.
Solution
The coating interface should be cleaned and applied correctly via the manufacturer’s guidelines.
Curing
Curing is a process in which a chemical reaction occurs, such as polymerization, resulting in a harder or tougher adhesive bond. However, adding a second layer could inhibit the curing process of the first layer.
Solution
Follow the manufacturer's cure schedules to make sure the curing of each layer is achieved before applying another.
Ineffective Keying
On the other hand, some coatings do not require full curing before the second layer is applied. The second layer keys or bonds into the first layer. Solvent-based coating, for example, needs multiple layers to achieve the necessary thickness. However, this can be overlooked.
Solution
For coatings like parylene, make sure the thickness is achieved in one application. This may need to be done through several trials and calculations, but you will want to get it right the first time and with precision.
Lamination
When waiting too much time in between layers for solvent-based coatings, lamination occurs.
Solution
Therefore, make sure to time the layers correctly. This timing could be based on several factors, such as the temperature and humidity in the atmosphere, the extraction rate, the chemical nature, and the solvent flash-off time.
Defects and Excessive Bubbles
When trying to achieve a thicker coat, sometimes excessive solvent can get trapped in the lower layer of the film causing bubbles or blistering.
Solution
Make sure to dry the coating enough to where the second layer bonds to the first layer effectively. You should also clean the surface of the board and remove contamination agents before layering.
When layering your conformal coating, it is important to be aware of the process as well as the issues that may arise. There could be failures due to the incorrect selection of the material, or the surface energies may not match causing incompatibility to bond. At Advanced Coating, we can walk you through the multiple layering process so you can protect your products and have a long-lasting conformal coating.
Want to know more about how Advanced Coating can help with your conformal coating needs? Contact us today.
