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SPI is the abbreviation for Solder Paste Inspection. The widespread use of SPI in SMT (Surface Mount Technology) manufacturing is largely due to the development of the current electronics manufacturing industry. Those working in the SMT manufacturing industry know that many defects in SMT occur due to solder paste printing issues. To better control the quality of printed solder paste, SPI was developed within the SMT industry.
80% of defects in the SMT manufacturing process come from improper solder paste printing.
If approximately 80% of the defects in SMT are due to improper solder paste printing, do you think setting up a solder paste inspection (SPI) checkpoint after solder paste printing and before component placement can help improve the yield of SMT soldering? The answer should be affirmative. The key is how to use the solder paste inspection machine to correctly screen out boards with poor solder paste printing, and then trace back to find out why solder paste printing had defects.
Especially now, with more and more components below 0201 or bottom soldering components like BGA, the quality of solder paste printing is very sensitive. If we can detect boards with solder paste printing issues before they go into the reflow oven, it will be more effective and cost-saving than detecting them after reflow soldering is complete, as post-reflow repairs usually require soldering irons or complex repair tools and may also damage the boards.
This type of solder paste inspection machine is actually similar to the commonly seen AOI (Automated Optical Inspection) systems placed after the SMT reflow oven, which also uses optical imaging to check quality. The difference is that the solder paste inspection machine has added a laser device for measuring solder paste thickness. Therefore, the problems that SPI may encounter are similar to those of AOI: first, take a sample board that has no visible issues and let the machine photograph it as a standard sample (Golden Sample). The subsequent boards will be judged based on the images and data of the first board. This will naturally lead to many false positives, so the parameters must be continuously adjusted until the false positive rate is reduced to an acceptable level. Thus, simply purchasing an SPI machine does not suffice; engineers must also be able to write programs and maintain it.
Solder paste printing and SPI solder paste inspection
What role does SPI play in SMT manufacturing?
1. SPI is generally placed after the SMT solder paste printing machine. When the PCB solder paste is printed and transmitted through the conveyor to the SPI for inspection, can this improve SMT yield? The answer is affirmative. More importantly, how to use SPI to screen out PCBs with poor solder paste printing and then trace back to the reasons for the poor solder paste printing, thereby solving the root problem.
2. Due to the precision and miniaturization of current electronic products, many SMT-manufactured electronic components have very high precision requirements. Therefore, the quality of the solder paste printed on the PCB surface is very critical during component placement. If solder paste printing quality can be detected before component placement, it will certainly be more effective than detecting it after component placement and reflow soldering, as post-reflow defective PCBA boards require soldering irons or more complex tools for repairs, and a slight oversight may damage the PCBA. Therefore, SMT manufacturers with SPI inspection equipment can avoid a series of problems.
3. The content of SIP inspection includes: solder paste printing volume, solder paste printing thickness, solder paste printing area, solder paste printing flatness, solder paste printing offset, solder paste printing pulling, and solder paste printing bridging.
SPI is a quality control measure in the SMT manufacturing process. When used effectively, it can significantly enhance product quality and thereby reduce manufacturing costs.
If SPI is merely a decoration in the SMT workshop, it will only impact production efficiency. When an SPI alarm occurs, the quality of PCB solder paste printing must be investigated to control the defect rate to a minimum.
SPI in SMT manufacturing not only prevents the quality of solder paste printing but also plays a crucial role in controlling and preventing later repair costs, helping to increase productivity and additional profits. With the precision of electronic products increasing, the quality of printed solder paste becomes increasingly important. SPI can effectively ensure good solder paste printing quality and significantly reduce potential quality risks.
(The images and text in this article are not directly related)
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