PCBA Tech - The importance of smt printing and X-ray in smt processing

According to statistics, more than 60% of poor patch soldering is caused by poor solder paste printing, so solder paste printing is very important. The quality of solder paste printing determines the efficiency of the entire line production and the pass-through rate of good products, in order to improve the efficiency of the entire line To reduce soldering defects, the engineers of SMT processing plants need to analyze and improve the printing defects, and reduce the problems of soldering defects caused by poor printing.

SMT solder paste printing common defects and improvement measures

1. Solder paste collapse

The solder paste cannot maintain a stable shape and the edges collapse and flow to the outside of the pads, and are connected between adjacent pads. This phenomenon is likely to cause solder short circuits.

Causes and improvement measures

1. The pressure of the squeegee is too high, the solder paste is squeezed, and the solder paste flows into the adjacent pad position after passing through the holes of the steel mesh. Improvement measures: reduce the pressure of the squeegee

2. The viscosity of the solder paste is too low to maintain the fixed printing shape of the solder paste. Improvement measures: use a higher viscosity solder paste

3. The tin powder is too small, the tin powder is too small, the solder paste performance is better, but the solder paste molding is insufficient, the improvement measure: choose the solder paste with large tin powder particles

Second, the solder paste offset

Solder paste misalignment means that the printed solder paste is not completely aligned with the specified pad position, which may cause bridges, or may cause the solder paste to be printed on the solder mask, thereby forming solder balls

Causes and improvement measures

1. The PCB board is supported or not clamped, which may cause the alignment of the stencil and PCB pad holes when the solder paste squeegee is printed, and the solder paste printing appears to be offset. Improvement measures: use multi-point clamping to fix the PCB board

2. There is deviation between the PCB incoming material and the mold opening of the stencil. The quality of the stencil opening may be poor, and there is a deviation from the specified position of the PCB pad. Improvement measures: re-open the mesh accurately

Third, the solder paste is missing

Solder paste leakage means that the solder paste coverage area of the solder pad is less than 80% of the opening area, resulting in insufficient solder on the solder pad or no solder paste printed on the solder pad

Causes and improvement measures

1. The squeegee speed is too fast and the squeegee speed is too fast, resulting in insufficient filling of the solder paste vias, especially PCBs and steel meshes with small pads and tiny holes. Improvement measures: reduce the speed of the scraper

2. The separation speed is too fast. After the solder paste is printed, the separation speed is too fast, which causes the solder paste on the pad to be taken away, resulting in missing print or sharpening.

Improvement measures: adjust the separation speed to a reasonable range

3. The viscosity of the solder paste is too strong, and the solder paste is too viscous, and the solder paste printing is not enough to flow into the pad position of the corresponding hole. Improvement measures:

Choose the right viscosity solder paste

4. The stencil opening is too small, the stencil opening is small, and the scraper speed is fast, resulting in insufficient tin removal and solder paste leakage. . Improvement measures: precision steel mesh opening

The importance of X-ray in smt processing industry

X-ray, the full name is X-ray non-destructive testing equipment. Similar to the X-ray machine for chest x-rays in hospitals, it mainly uses X-rays to scan and image the inside of the product, especially for the detection of components such as BGA QFN with pins, to detect whether there are cracks, foreign objects, virtual welding, and Defect detection such as false welding.

With the development of electronic technology, PCBA is everywhere, every electronic product must have fast PCBA, so the application of SMT patch has become more and more popular, intelligence and miniaturization have made the size of the chip smaller and smaller. There are more and more pins. Especially some core BGA and IC components are widely used.

Ordinary manual inspection cannot fundamentally determine the quality of solder joints. AOI testing equipment can only detect soldering components on the surface of the PCBA, and cannot detect the soldering quality inside the pins through the board. High-precision electronic products require very high reliability. High, such as military industry, aviation, automotive electronics, then the best choice is to pass X-ray inspection.

In terms of application, X-ray can not only identify welding defects (such as empty welding, virtual welding) inside the BGA, but also scan and analyze microelectronic systems and sealing components, cables, fixtures, and plastic interiors.