Solder resist blistering is typically caused by insufficient adhesion between the solder mask and the PCB substrate. Common causes include insufficient board surface cleanliness, incomplete curing of the solder mask, PCB moisture absorption, and excessive thermal shock during manufacturing. When oil, oxides, or other contaminants remain on the PCB surface, the solder mask cannot form a good bond with the copper surface, easily leading to blistering and bulging during subsequent soldering or high-temperature environments.
To effectively avoid solder mask blistering, the pre-treatment process during PCB manufacturing should be strictly controlled. Before printing solder mask, the copper surface should undergo thorough grinding, micro-etching, and cleaning to ensure surface cleanliness and roughness meet process requirements, thereby improving solder mask adhesion.
Secondly, the exposure, development, and curing parameters of the solder mask must be strictly controlled. If the curing temperature or time is insufficient, residual solvent may remain in the solder mask, which will expand and form bubbles during subsequent reflow soldering. Therefore, baking and curing should be performed according to the ink supplier's process specifications, and the curing effect should be verified regularly.
Furthermore, the PCB storage environment is also crucial. FR4 material has a certain degree of hygroscopicity; prolonged storage or exposure to high humidity environments will cause it to absorb a significant amount of moisture. When the PCB enters the reflow oven, the internal moisture rapidly vaporizes, potentially leading to solder mask blistering or even board delamination. Therefore, PCBs should be stored using vacuum packaging, moisture-proof bags, and desiccants, with controlled warehouse temperature and humidity. For PCBs stored for extended periods, baking dehumidification before placement is recommended.
During SMT production, reflow temperature profiles should be appropriately set to avoid rapid temperature increases and thermal shock. Simultaneously, selecting reliable PCB material and solder mask suppliers, and establishing a robust incoming material inspection and process control mechanism, can mitigate risks at the source.
In conclusion, solder mask blistering is a quality issue involving multiple aspects, including materials, processes, storage, and production. By strengthening board surface treatment, optimizing solder mask processes, controlling the storage environment, and standardizing soldering procedures, the risk of solder mask blistering can be effectively reduced, improving the reliability and long-term stability of PCBA products.
