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Understanding White PCB Solder Mask for LED Lighting Applications

by Harry Kennedy, Field Application Engineer

At NCAB we always say that the PCB is your key component. This is true as new industries are being developed that center around technology.

 

LED lightning with a white solder mask

One example in particular is lighting applications. Found in vehicles, city infrastructure and warehouses, LED lighting is developing into a nuanced application that seeks to bring precise brightness and color for the perfect aesthetic. When it comes to lighting, the PCB can be the difference between a clean white glow in a room, or a dingy yellow tint.

A white solder mask gives a pure white light

The first reason why PCBs are the key component of lighting applications is apparent when determining the reflectivity of the PCB itself. Lightbulbs can be purchased in many different shades, from a warm yellow, to a cool blue. When a pure white is needed, it’s critical to understand how the light can reflect off different surfaces. This includes the PCB itself. The easiest fix to obtain a pure white is to use a white solder mask instead of a green one. This ensures that the white light of the LED bounces off the white of the PCB and gives the end application a desired effect.

The reflectivity isn’t the same for every white solder mask. Make sure you chose a brand that is made for lighting applications. Look for key words like LED Back Panels, LED applications, Bright White, and high reflectance. This will also make sure the solder mask you chose will have other properties that are needed for lighting applications.

Chose a quality PCB solder mask to prevent changes during assembly

The second reason why PCBs are the key component of lighting applications is that the durability of the PCB during assembly can make or break your final light color. Cheap solder mask can change from a bright white to a dingy color during the manufacturing and assembly process. For example, the electrolytic process of applying an ENIG finish has turned some white solder masks pink. This leads to a final light color that is pink as opposed to pure white. Don’t scrap your boards after all the time and money is spent assembling it. Chose a quality PCB solder mask and get it right from the start.

Also understanding how the solder mask will adhere to different metal backed PCBs will help you to achieve the perfect lighting board. When you’re deciding on material, ask about how the adhesion and hardness will be affected by the manufacturing and assembly process. Be aware of the heat resistance of the solder mask such that the board isn’t damaged during the reflowing, or reworking of components.

Based off our expertise in solder mask for lighting applications, NCAB suggest using Taiyo brand materials. The WT series and LEW series are both specifically made for reflectivity in lighting applications.  A few that are popular include:

  • PSR4000-WT02
  • PSR4000-WT03
  • PSR4000-LEW2
  • PSR4000-LEW3

When incorporating this into your engineering process, make sure you understand the supply chain of the material. If a specific material is to be called out, be sure to check that this material is common to many different factories, not just the one that you will be building with. It’s often the case that the material is chosen by a factory becomes the company standard without understanding how easy is it to procure the material.