Conformal coatings are very thin layers of material designed to protect the surface of a printed circuit board. These layers are applied to circuit boards or substrates and act as protective coatings from harsh elements. Conformal coatings are used when finished products containing printed circuit boards are exposed to harsh environments. These environments may include heat, chemicals, moisture or anything that could damage the printed circuit or the mechanical structure of the substrate.
The first application is the impregnation process: this can usually be done with automated equipment or with manual application. The PCB is usually suspended by arms and then lowered in a dipping tank containing the coating at a rate determined by the density of the PCB to be dipped. Some advantages of this method are the coating penetration under the components, the coating thickness is guaranteed, the processing time can be fast, and the method has a low-tech process in application. Some disadvantages of dip coating are thin tip coverage, inconsistent coating thickness, and the need for a fairly strong mask.
Spray coatings from aerosol cans or Spray Gun applications are the second most widely used and accepted application of liquid conformal coatings. During the process, the material is diluted and sprayed multiple times, each at a 45-degree angle, to achieve the desired thickness desired. Advantages of spray coating are high volume, which can produce 1000 boards per week, reduced masking compared to dipping methods, better tip and edge coverage, and more uniform thickness. Some disadvantages are that multiple passes are required to achieve the desired thickness, and the coating is less permeable under the part compared to "dipping".
Brush application is typically used for small batches. During this process, it's important to keep the brush full of coats and allow it to flow; don't paint over components. Some of the advantages of this process are that it is extremely low cost and well suited for low volume applications as well as repair and rework of components. The downside is that it can be slow to be labor intensive on large boards, which also makes assembly finished quality questionable.
Selective paint applications are very common in automotive and other high-volume applications where circuit board designs and layouts do not change much over long periods of time. For this application, selective spay creates accurate repeatability by minimizing the amount of masking and providing a highly controlled process to maximize throughput. However, this process has some disadvantages. The board may still require shielding, and it requires a skilled operator to program and operate the machine. In addition to the high cost of the sprayer, programming is also time consuming.
