In the production process of PCBA patch processing, some processing defects sometimes appear. Short circuit is one of the more common ones, and it can also be said to be a relatively primary processing defect. For PCBA factories, this kind of short-circuit phenomenon cannot be tolerated. FASTPCBA will give you a brief introduction to some of the reasons and solutions that easily lead to short-circuit phenomena during processing.

1. Steel mesh

The occurrence of bridges in PCBA patch processing will cause short-circuits and other defects. Most of the bridges occur on boards with small IC pin spacing, such as 0.5mm or less.

Solution: For the case where the IC pin spacing is less than or equal to 0.5mm, the length of the stencil opening method can be kept unchanged, the opening width is 0.5~0.75 pad width, and the thickness is 0.12~0.15mm. Choose to use when stencil processing The laser stencil processing method and polishing treatment will perform better for the precision PCBA patch, which can better ensure that the opening shape is inverted trapezoid and the inner wall is smooth.

2. solder paste printing

In PCBA processing, solder paste printing is also a very important link. To avoid short circuits due to improper printing, the following issues need to be paid attention to:

2.1. Type of squeegee: There are two types of squeegee: plastic squeegee and steel squeegee. For IC with PITCH≤0.5mm, steel squeegee should be used when printing to facilitate the formation of solder paste after printing.

2.2. Adjustment of the squeegee: The operating angle of the squeegee is 45° for printing, which can significantly improve the imbalance of the opening directions of the different templates of the solder paste.

2.3. Printing speed: fast printing speed is beneficial to the rebound of the template, but at the same time it will prevent the solder paste from being printed. If the speed is too slow, the solder paste will not roll on the template, causing the resolution of the solder paste printed on the pad. Bad, usually the printing speed range for fine pitch is 10~20mm/s.

3. solder paste

The selection of the solder paste type has a relatively large impact on the short-circuit phenomenon. When using solder paste for ICs with a pitch of 0.5mm and below, the particle size should be 20~45um and the viscosity should be around 800~1200pa.s. The activity of the solder paste can be based on The surface cleanliness of the PCBA board is determined by the RMA level.

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