Solder mask is a thin coating of polymer required to protect the Printed Circuit Board (PCB) from any uncertain short circuits and maintaining the integrity of the copper traces. Resin is by far the most commonly used element in its manufacturing. It is a trade-off between quality and finances. However, it does more good than harm.
Solder masks are available in many different colors including white, black, red and yellow. The most commonly available color is, however green, as most PCBs are compatible with it. Different colors can be chosen based on the customer’s demand e.g. some R&Ds are most likely to opt red PCB solder mask for their PCB prototypes in the stage of NPI so to make them distinct from the stock of other boards. Black solder mask is suitable to encourage compatibility with the color of end product if the boards need to be exposed in the products such as Tesla Coil etc. For instance, the soldering mask of Raspberry pi 3 have been shown below.
Figure 1: Solder Mask of Raspberry pi
Arduino Uno is also available in solder masks of different colors. The accompanied figure clarifies the fact.
Figure 2 : Arduino Uno with different Solder Masks
Use of Solder Mask:
PCB board Solder mask becomes increasingly significant due to the abundant increase in the demand of circuit boards in the concerned market. Technically speaking, solder mask is important due to the following reasons:
1) It prevents tarnish to take place on the covered area.
2) It helps in proper mounting of SMT (Surface Mount Technology) boards through solder paste as it helps in keeping things together.
3) In the absence of solder mask copper will be connected with the solder paste which causes short circuit and the reliability of the PCB is highly compromised.
4) Prevents Copper traces from oxidation and dust particles.
Manufacturing Process:
Solder mask manufacturing involves the cutting-edge technology Solder mask manufacturing is never an easy job. First of all, staunch regulations have to be taken into the account. Secondly, manufacturing process consists of a couple of stages involving high precision and up-to-date equipment. Therefore, it is not possible to manufacture these at home for complicated and large projects. The flow chart below shows the hierarchy of the processes involved.
- Hierarchical Process for Solder Mask Manufacturing:
1. Board Cleaning:
This step aims to clean the board from any sort of possible dust. This is a preliminary process to take a step ahead into literally anything significant.
2. Solder mask ink coating:
Once the cleaning is done the board is then forward for the solder mask coating. The solder coating is made thick considering the need of the project including reliability and sustainability. However, the choice is not that simpler as the board is not smooth all over. Therefore, the thickness differs for different sections of the board. However, standard thickness of 0.8 mils is more than enough for most of the projects.
3. Pre-Hardening:
This steps is conducted to harden the coating and the rest of the pcb substrate left behind is eradicated from the PCB. This helps in quality enhancement of the board.
4. Imaging & Hardening:
In this stage the printed image of the circuit traces are hardened onto the board by means of Ultra Violet (UV) exposure. This stage allows copper to be isolated from the copper traces of the circuit to prevent any short circuits. Correct alignment is to be ensured for proper functioning of the board.
5. Developing:
This stage involves cleaning of the unwanted solder mask so that the designated copper foil can be exposed properly.
6. Final Hardening & Cleaning:
This is the final stage before the assembly and surface finish. This involves complete mounting on mask onto the surface of the Printed Circuit Board.
Precautionary Measures:
Following precautionary measure are taken to protect PCBs from any malfunctioning:
1) No mismatching between copper pads in circuit plane.
2) Careful design file modification.
3) Insufficient solder mask used.
It is highly recommended to contact with RayPCB to be aware of the capability of the solder mask.
Reach RayPCB for suggested solder mask:
RayPCB promises to bring the best for the customers in terms of any sort of solder mask design or color specifications. The design and prototypes shall be eloquently prepared with maximum assurance.
