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PCB Solder Masks – What are The Different Types Available?

 May 14, 2018

All PCBs used today feature one or more layers of copper, which are laminated between or onto non-conductive substrate. However, it is seen that these copper layers begin to rust or oxidize in the long run. This is where the need for protective coating arises. Solder masks are applied to provide that necessary protective coating. Generally applied on the top of the copper traces, these masks can easily handle extreme heat produced by the soldering iron. There are various types of solder masks used by PCB manufacturers to enhance the performance of their PCBs. What are these types? How do they add value to PCBs? Read this post to find answers to your questions.

Different Types of PCB Solder Masks You Need to Know About

The following are some commonly used solder masks for protecting copper soldering on the PCB substrates:

  • Dry Film Photoimageable: The solder mask of this type is applied using vacuum lamination. After application, the mask is exposed, then developed. After exposing, various openings are produced in the pattern, as well as parts are soldered to copper pads. A copper layer is placed on the trace areas, as well as inside the holes through an electrochemical processing method. Typically, tin is applied on the copper traces to protect them from oxidation. Once the process finishes, the dry film is removed, and the etched copper layer is exposed. In the final stage, the finishing is done through thermal curing.
  • Epoxy Liquid: This is one of the inexpensive and most popular types of solder masks in use today. Epoxy liquid, which is a polymer of thermosetting type, is usually silkscreened on the PCB pattern. Silk screening technique utilizes a woven mesh, which supports ink-blocking patterns or stencils. Ink transfer is done through open areas produced by the mesh. Synthetic fibers and silk are considered for the purpose. However, ink is the common choice, because synthetic fibers are preferred for electronic applications. Thermal curing is performed in the final finishing stage.
  • Liquid Ink Photoimageable: Typically, liquid photoimageable solder mask is applied as an ink formulation. The ink is either sprayed or silkscreened on the PCB. It is then exposed to the pattern. Most times, liquid ink formulations are performed employing Hot Air Surface Leveling (HASL). This technique demands a clean environment, which is free from any type of contaminants, and particles. Next is the UV light exposure stage, which helps dry the film. The mask is then removed using developers, which are basically water sprays directed at high pressure. The final finishing stage involves organic coating, as well as thermal curing.
  • Top and Bottom Side Masks: Soldermask on the top side of the copper layer provides access to the openings present in the green solder mask, which is added to the PCB by ink, film, or epoxy technique. Similarly, the bottom side masks feature openings for the bottom side.

The above mentioned are only a few important types available for consideration. If confused about the right type of soldermask for your application, it is always better to approach an industry expert. Accelerated Assemblies is one of the industry experts with a vast PCB manufacturing experience. The company helps its clients to select from different types of solder masks while meeting their specific PCB requirements.