When producing a PCB we often encounter a green color layer that goes above the copper. This layer is most commonly known as the “Solder mask”. Solder mask has many use cases, often used as a protective finish to cover the PCB from possible defects.
In this article, we will walk over the core principles of the PCB solder mask: how to apply the paste layer during PCB production and what we can do to improve the quality of our PCB board.
We will explain the differences between solder mask and solder paste and the tests that a single PCB must undergo.
If you are reading this article, you probably know that PCB boards are made of copper. But copper is not enough to create a fully working and quality piece of the printed circuit board.
When PCB leaves the production line, the copper traces are exposed, causing the board to be vulnerable to oxidation, corrosion, and other environmental impacts. To protect from those natural causes, a solder paste mask came into existence.
The solder mask is designed to protect the PCB as an additional protection layer. The mask refers to the coating around the PCB, while the paste refers to the patterns applied to the mask. There are different PCB solder masks, but most share the same principles.
When solder paste is pasted over the PCB board, it’s essential to ensure the paste is at the exact amount needed. Not too much and not too less.
This can be done by using proper solder mask expansion. The recommended increase stands for 2-4 mils. This size stands for the distance from the pads and should not extend the abovementioned size.
By ensuring the holes punched in the solder mask are at that size, we can guarantee a perfect amount of PCB solder paste across the manufactured circuit board.
When talking about solder paste layers, we refer to the layers inside the CAD software. Those layers can be exported in a particular format to create a solder paste stencil. The software can generate both the top and bottom layers according to the needs. If the PCB design has only one layer, then the top paste one will be exported by default.
There are different ways to create a PCB solder mask and apply a paste mask. Below we collected the most popular ones that PCB manufacturers use:
There are many benefits of PCB solder masks:
Normally the solder paste mask is applied by default, but the customer can provide the color, thickness, and other configurations according to the project needs.
It’s essential to ensure that the solder mask is pasted evenly. The typical way to do so is called “solder mask clearance.” This technique will check the clearance of the silkscreen and the solder paste, ensuring no exposed copper wires are left vulnerable. This kind of test can be done through most popular CAD software such as Altium designer, Eagle, etc..… The solder mask clearance is an important rule to ensure the quality and consistency of the PCB solder mask production.
During the production process, there are more ways PCB manufacturers could test the PCB solder mask quality:
Every PCB project needs protection for long shelf and project life. PCB solder mask and paste mask were designed for this exact purpose.
We create the solder mask stencils in-house if you wonder where and how such coating can be produced at PCBasic. Unlike many manufacturers that outsource the solder stencil to third parties, PCBasic puts quality first.
By offering a one-stop service and manufacturing the solder mask stencils at our fabrication facility, we control the quality and the speed of the fabrication process.
Whether your PCB is single-sided or double-layered, we can produce stencils and ensure the solder pasting process goes smoothly. In any need, feel free to submit a solder mask stencil quotation request, and our sales team will get back to you in no time.
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