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SMT process monument phenomenon:
Apr 21, 2018

SMT process monument phenomenon

1. The reason of the component itself: The difference in the shape and size of the soldering end is large, the solderability of the soldering end varies greatly, and the weight of the component is too light.

2. Reasons of the substrate: The thermal conductivity of the substrate material is poor, and the thickness uniformity of the substrate is poor.

3, the reason of the pad: the pad's heat capacity is different, the solder pad's solderability is different.

4. Preheating temperature: In the preheating stage of the reflow furnace, the temperature of the holding zone is set low, the time is short, and the melting probability of the two ends of the component is not increased at the same time.

5. Non-uniform heating: The temperature distribution in the reflow furnace is not uniform, and the temperature distribution on the surface of the board is not uniform.

6. Paste: The solder paste has poor uniformity or poor activity. The thickness of the solder paste on the two pads is quite different. The solder paste is too thick and the printing accuracy is poor. The dislocation is serious.

7, component placement offset, and more contact with the components of the solder paste to get more hot melt, melt first and pull the other end to form a vertical.

SMT process monument how to prevent:

1, the pad, component surface without oxidation.

2, select the appropriate substrate material to ensure quality.

3, the correct design and layout of the pad, pad design consistent with no over the top of the pad.

4. Correctly set the process parameters during the warm-up period, and adjust the appropriate temperature profile of the oven temperature according to each different product.

5. Properly increase the temperature in the preheating zone and extend the time to the upper limit, so that the tin at both ends can be fully melted at the same time.

6. Use a higher active solder paste to improve the solder paste printing parameters, especially the window size of the template.

7. Adjust the placement accuracy of the components to avoid large patch deviations. When mounting, ensure that placement accuracy is over 90%.


The above content is about the causes and prevention methods of the monumental phenomenon in the SMT process. I believe we have some understanding. The tombstone in the SMT process is a major defect of the electronic assembly process, and has a great influence on the processing quality, the through-pass rate and the repair cost of the product.

Therefore, we need to understand the phenomenon of erection of the SMT process, its causes, and how to prevent it. In the event of a tombstone phenomenon, it is timely improved and resolved to avoid the occurrence of process defects.

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