The printing process of solder paste PCB circuit board and PCBA circuit board mainly solves the problem of consistency of solder paste printing volume (filling and transfer), rather than the demand for solder paste volume at each solder joint. In other words, the printing process of solder paste PCB circuit board solves the problem of fluctuation of welding pass through rate, rather than the problem of high and low pass through rate, The key lies in the solder paste distribution. Through the optimization and matching design of pad, solder resist and steel mesh window opening, the amount of solder paste is distributed as required for each solder joint. Of course, the consistency of solder paste amount is also related to the design. Different PCB solder resist designs in PCB Factory provide different process capability indexes.
1. Area ratio. Area ratio refers to the ratio of steel mesh window opening area to window opening hole wall area.
2. Transfer rate. Transfer rate refers to the ratio of solder paste deposited on the pad in the steel mesh window during printing, which is expressed by the ratio of the actual amount of solder paste transferred to the steel mesh window volume.
3. Influence of area ratio on the transfer rate. The area ratio is an important factor affecting the transfer of solder paste. In engineering, the area ratio is generally required to be greater than 0.66, and PCBA can obtain more than 70% of the transfer rate under this condition.
4. Requirements for area ratio design. The area ratio has requirements for the design of steel mesh, which mainly affects the fine spacing elements. In order to ensure the area ratio requirements of steel mesh window opening of micro pad, the thickness of steel mesh must meet the requirements of area ratio, so for the elements requiring a large amount of solder paste, It is necessary to increase the amount of solder paste by increasing the steel mesh window area - which requires space for deformation around the pad, which is a main consideration in the design of element spacing.
When PCBA is used, PCB circuit board needs to carry out component layout. There are certain requirements for component layout. Only in strict accordance with the requirements can PCBA give full play to its role Then, what are the basic operation requirements for PCBA in component layout.
1. Components on PCB shall be evenly distributed and arranged as regularly as possible For similar packaged components, the orientation, polarity and spacing shall be consistent as far as possible Regular arrangement is convenient for inspection, which is conducive to improve the speed of patch / plug-in, and uniform distribution is conducive to the optimization of heat dissipation and welding process.
2. Power components shall be evenly placed on the edge of PCB or the ventilation position in the chassis to ensure good heat dissipation.
3. Valuable components should not be placed at the corners and edges of PCB, or close to connectors, mounting holes, slots, cutting of panels, gaps and corners. These locations are high stress areas of PCB, which are easy to cause cracking of solder joints and components.
4. A certain maintenance gap shall be reserved around large components (the size that the heating head of SMD repair equipment can operate shall be reserved).