If you’re new at or unfamiliar with the soldering process, you might not initially know the purpose of using a soldering mask for your PCB manufacturing, let alone how to choose one that’s right for the types of applications you’re performing. For starters, a solder mask is a permanent, protective layer or coating that is applied to the copper traces and interfaces on PCBs to protect it from oxidizing. The masks are able to withstand the extreme heat that the soldering iron creates, preventing solder bridging and short circuits.
Now that you know the purpose of solder masks, it’s time to choose one that’s right for you! There are different types of PCB solder masks that you can choose from, including epoxy liquid, liquid photoimageable mask and dry film photoimageable mask.
Here is a look into the three types so you can choose which is best for you:
- Epoxy Liquid
If you’re looking for the most affordable type of soldering mask, this is most likely for you. Liquid epoxy is the most basic and commonly used type of mask and is made of a thermal resistant polymer material. The liquid is silkscreened onto the PCB pattern, usually using ink or other synthetic fibers. Once the transfer of the synthetic fibers is completed, thermal curing is performed in the final stage.
2. Liquid Photoimagable
The liquid photoimagable mask is the most commonly used type of mask. They are the most reliable and accurate and make better contact with the board. The liquid can either be sprayed or silkscreened onto your PCB, most often by using the Hot Air Surface Leveling (HASL) method. This operation needs to be performed in a clean environment, free from any contaminants or other particles that could damage the board. Afterwards, the PCB is placed into a UV developer where the film is precisely aligned over the board. The blacked out locations on the PCB will prevent curing in areas where it is unwanted. Afterwards, the uncured areas are washed off.
3. Dry Film Photoimageable
This type of mask is best if your board surface is very flat. The mask must be applied using vacuum lamination to avoid defects and air bubbles, and therefore is not recommended for complex surface features. After applying the dry film, it is exposed and then developed, leaving various openings in the pattern. Copper is then layered onto the board inside the openings using electrochemical processing and followed up with tin to protect the copper from oxidizing. Once this process is done, the film is removed, leaving the copper exposed. The final step is thermal curing.
There are also different colors of solder masks available
that can improve the aesthetics of your PCB. While the most common solder mask
color is green, there are also several other colors that you can use depending
on your design requirements or preferences, including red, blue, black, white,
yellow, orange, purple and clear. Green is most recommended because of its
ability to adhere evenly and its higher resolution. Red typically gives the
best color contrast between a PCB’s components. Blue is more highly coveted
because of its rarity. Black absorbs more heat than other colors.
There’s no definite right or wrong answer for the color and type of soldering mask you should choose for your applications. If you still have any questions about the uses of each type and whether it would be best for you, be sure to give our experts at GoKimco a call by visiting the Contact Us page on our website.