A layer of paint on the surface of the PCB is called solder resist ink, that is, PCB circuit board solder resist ink. Solder resist ink is very common and mainly used in PCB circuit boards. Generally, 90% of them are green, but there are also variegated inks: red, blue, black, white, yellow, etc.
The role of solder resist ink is insulation. In the welding process, it prevents short circuit caused by bridging and physical disconnection of conductor circuit, such as insulation deterioration and corrosion caused by external environmental factors such as dust and moisture.
The solder resist bridge is the green oil part between one window of the component pad and the other window, and generally refers to the solder resist strip between the corresponding pads of relatively dense IC pins. The function of the solder resistance bridge is to prevent the flow of solder during soldering, the short circuit between the device and the tin, etc. Usually, in order to prevent the short circuit between the solder and the tin, it is necessary to ensure that the pad has a solder resistance bridge.
PCB solder mask bridge process
The manufacturing capability of the solder mask bridge is related to the color of the ink and the thickness of the copper. The solder mask bridge of green oil is easier to control than the variegated ink, and the solder mask bridge can be kept to a minimum. The thicker the copper, the larger the solder mask bridge needs to be. Thin copper solder mask bridges are easier to control than thick copper.
1. When the base copper ≤ 1oz, the solder mask bridge ≥ 4mil (green and green matte); the solder mask bridge ≥ 5mil (other colors); the solder mask bridge ≥ 8mil (only for the solder mask bridge on the large copper surface of the whole board) .
2. When the base copper is 2-4oz, the solder resist bridge ≥ 6mil (glossy black, matte black, white); solder resist bridge ≥ 8mil (only for the solder resist bridge on the large copper surface of the whole board).
3. Between the tin-sprayed surfaces of the large copper surface area, in order to prevent tin bridging, it is necessary to ensure that the tin bridge is ≥ 8mil.
PCB solder mask bridge design
1. Solder resist bridge on the base material
The size of the solder resist bridge is related to the IC pad spacing of the circuit layer. If the IC pad spacing is too small, it is easy to cause tin short circuit when soldering the device. Taking green oil as an example, the IC pad spacing of the circuit is 8mil, and the single side of the pad window is 2mil, so the solder resistance bridge is 4mil. In the extreme case, in order to keep the solder resist bridge, the IC pad spacing window can be opened by 1 mil on one side, so that even if the IC pad spacing is 6 mil, a 4 mil solder resist bridge can be made.
2. Solder resist bridge on the copper skin
The IC pad on the copper skin also needs to be a solder-resisting bridge. If there is no solder bridge on the IC pad on the copper skin, tinning on the window will lead to the connection of the IC pads, which is equivalent to connecting two IC pads into one pad. Even if the pad on the copper surface is a network, it will not cause a short circuit, but the soldered components will be inconvenient to disassemble due to poor heat dissipation performance.
PCB Solder Bridge Inspection
Here we recommend a domestic free tool: Huaqiu DFM software, through one-click DFM analysis, you can avoid related problems in advance. According to the manufacturing capacity of the conventional process, the gap of the solder mask bridge can be detected, and an error message will be given if it exceeds the manufacturing capacity, so that corresponding processing can be made.
1. Inspection of solder mask bridge
The analysis items of Huaqiu DFM software include solder resist bridges. After one-click analysis, click the solder resist bridge item to view, and you can see the smallest solder resist bridge. If the solder resist bridge exceeds the manufacturing capacity of the board factory, then the spacing of the IC pads needs to be adjusted, and the spacing of the pads can be designed to meet the manufacturing capacity.
2. Situations where solder mask bridges cannot be made
When the pin spacing of components is relatively small, the IC pad spacing is inconvenient to adjust, and exceeds the manufacturing capacity of the solder-resisting bridge, the solution is not to make a solder-resisting bridge. There is no solder resist ink between the two pads, and the base material is between the pads seen in the finished product, which is called an open window. The treatment method of opening the window is not recommended in the industry, because there is a risk of soldering and tin short circuit, it is generally used when the allegro is made and the delivery date is very urgent.
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