Six Common Problems in Solder Paste Printing

In SMT chip mounting processing, solder paste printing is an extremely important and complex process. The quality of solder paste printing is not only related to the quality of the solder paste itself, but also directly associated with the printing equipment and parameters. SMT processing manufacturers can improve the quality of solder paste printing by controlling every detail. According to statistics, approximately 60-70% of soldering problems in the SMT assembly process of electronic products are caused by poor solder paste printing. Therefore, the quality of solder paste printing determines the yield of SMT assembly. The key to zero-defect manufacturing is to ensure the quality of solder paste printing and prevent soldering problems caused by poor solder paste printing. Below, Desen Precision introduces the six common problems in solder paste printing. 1. Incomplete Printing It refers to the phenomenon of missing printing on some pads of the PCB. Cause Analysis: • (1) Blocked openings of the steel stencil or partial solder paste adhering to the bottom of the steel stencil; • (2) Unqualified viscosity of the solder paste; • (3) Excessive size of metal particles in the solder paste; • (4) Severe wear of the squeegee. Improvement Measures: • (1) Pay attention to the maintenance of the steel stencil and clean it in a timely manner after use; • (2) Select solder paste with appropriate viscosity; • (3) When selecting solder paste, consider whether the size and particle size of the metal particles are smaller than the opening size of the steel stencil; • (4) Regularly inspect and replace the squeegee. 2. Tailing It refers to the presence of sharp protrusions of solder paste on the pads after printing. Cause Analysis: • (1) Inappropriate viscosity of the solder paste or excessive squeegee gap. Improvement Measures: • (1) Select solder paste with appropriate viscosity and adjust the squeegee gap. 3. Slumping It refers to the solder paste on the pad slumping to both sides of the pad. Cause Analysis: • (1) Excessively high squeegee pressure parameter; • (2) Abnormal fixation of the PCB, resulting in movement; • (3) Inappropriate viscosity of the solder paste or low metal content. Improvement Measures: • (1) Adjust the squeegee pressure; • (2) Re-fix the PCB; • (3) Re-select the solder paste, considering factors such as viscosity and metal content. 4. Insufficient Solder Paste Thickness It refers to the solder paste thickness on the pad failing to meet the standard. Cause Analysis: • (1) The thickness of the manufactured steel stencil does not meet the standard; • (2) Excessively high squeegee pressure parameter; • (3) Poor fluidity of the solder paste. Improvement Measures: • (1) The thickness of the solder paste should be consistent with the thickness of the steel stencil; • (2) Reduce the squeegee pressure; • (3) Select high-quality solder paste. 5. Uneven Thickness The thickness of the solder paste is inconsistent after printing. Cause Analysis: • (1) The PCB is not parallel to the steel stencil, and the solder paste is not uniformly stirred. Improvement Measures: • (1) Ensure good fit between the PCB and the steel stencil as much as possible, and stir the solder paste uniformly before use. 6. Burrs There are burrs on the edges or surface of the solder paste. Cause Analysis: • (1) Low viscosity of the solder paste; • (2) Rough openings of the steel stencil. Improvement Measures: • (1) Consider the viscosity of the solder paste when selecting it; • (2) Prefer steel stencils with laser-drilled openings or improve the precision of etching. To improve the solder paste printing quality in SMT chip mounting processing, it is necessary to start with every detail, including the selection of solder paste, the quality of the steel stencil, and the parameters of the equipment. Every detail will affect the final printing quality. Beijing Zhongke Tongzhi Technology Co., Ltd. is an SMT solder paste printer manufacturer integrating R&D, production and sales of fully automatic solder paste printers and SMT solder paste printers. We provide customization services for fully automatic solder paste printers and SMT solder paste printers. To learn more about solder paste printer knowledge, welcome to visit: www.torch.cc Zhongke Tongzhi, www.torchsemi.com — a professional one-stop PCBA and SMT processing manufacturer, providing electronic OEM processing, PCBA turnkey service and SMT chip mounting processing services.