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PCB soldermask opening refers to the opening in the soldermask layer of the printed circuit board to expose the copper at the soldering location to ensure a smooth soldering process.
Through the reasonable design of windowing, the quality of soldering can be improved to avoid short circuits and damage to the circuit board.
In other words, the soldermask opening refers to the area that is not covered with ink, as long as the part that is not coated with a printed soldermask can be called soldermask opening.
The main function of the soldermask is to prevent oxidation of the metal leads on the circuit board and to avoid accidental short circuits.
The opening operation protects the fine alignment on the PCB and ensures the quality of the soldering process.
Opening handling directly affects the quality of soldering, once the opening is not properly designed, may lead to poor soldering, thus affecting the performance of the entire circuit board,
in the design needs to ensure that the opening is in the correct position. Unreasonable window design may lead to problems such as solder bridging,
which may lead to short circuits and other undesirable phenomena when soldering components.
Generally speaking, the size of the opening will be larger than the pad, to take into account the PCB manufacturing tolerances, to avoid soldermask ink covering the pad.
If the opening area is the same as the pads' area, it may lead to the problem of ink on the pad. In the PCB production process, the area and position of the soldermask opening will usually be
adjusted according to customer needs and circuit design requirements
Common PCB soldermask opening problems are:
1. Ignoring the pad opening setting
In the design of PCB packages, there may be a setup error resulting in the package does not open the soldermask of the case.
2. Improper matching of opening area and pads
To avoid the production process of soldermask ink covered to the pad, the area of the opening should be slightly larger than the pad. If the opening design is the same or too
small as the pad area, it will result in poor soldering. It is recommended that the opening width be increased by approximately 4 to 6 mils to accommodate production tolerances.
3. Wrong opening holes' position
The relative positions of component pins and opening holes should be considered to avoid soldering difficulties due to improper hole placement.
4. Neglecting DFM inspection
5. Soldermask opening size is not reasonable
6. Soldermask dam too small
7. Defective soldermask processing
Defective handling of the soldermask in the production process can also lead to windowing problems. For example, improperly set thickness of the soldermask layer,
too small spacing between openings, etc. will affect the quality of the weld.
Common types of opening are:
1. Holes' opening on pads : for plug-ins, pin soldering
2. PAD opening: for SMD soldering components
3. Large copper surface opening: to meet the actual needs of the product.
Soldermask opening in the PCB design and production process are of great significance, reasonable soldermask opening design can ensure the welding quality and circuit performance.