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What Is the Use of Solder Paste Inspection?

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Published by Pinsheng Electronics Co., Ltd March 11,2020

Solder Paste Inspection (SPI), commonly refers to SPI machine, as well as this process in PCB assembly. To many buyers, one of the reasons that allow them to work with a PCB assembly house is the factory has equipped with solder paste inspection machine.

SPI Machine
SPI Machine

 

So why solder paste inspection is so critical? What can an SPI machine do? 

The first truth is almost 75% of defects in SMT process are caused by improper printing of solder paste. SMT defects usually means extra plenty of time and money will be spent in rework and remanufacture. 

SPI machine is set before solder paste printing and placement to correctly screen out the poor solder printing, and then trace back to why the solder paste printing has occurred, to avoid 75% of the SMT defects.

In particular, there are more and more parts below 0201 or bottom soldered parts such as BGA, which are very sensitive to the quality of solder paste printing. If the boards with problems can be detected before reflow, It is more effective and cost-effective than detecting after reflow soldering is completed, because the repairing after reflow might also damage the boards.

Solder paste inspection is actually similar to the AOI (Auto Optical Inspection) identification system, which check the boards quality through optical images. So the workflow of SPI machine and AOI machine is almost same: It is necessary to take one of the panel first to make a visual inspection, if it get through, then let the machine take its photo as a standard sample. Obviously, there will be many false positives, therefore, the parameters must be continuously modified until the false negatives rate is reduced to a certain level. 

AOI Equipment

Thus, a new solder paste inspection machine cannot be directly put into use, before which, engineering programming is required. In addition, most SPI machine can read Gerber file and CAD, but usually with some errors, continued adjustments are required.

 

The measurement features of solder paste inspection:

  • Printing volume of solder paste

  • Solder paste printing height

  • Area/volume of solder paste printing

  • Flatness of solder paste printing

  • Make SPC statistics to test process capability

In addition, the solder paste inspection machine can detect the following defects:

  • Whether the solder paste printing is shifted

  • Whether the solder paste printing is highly deviated (tipped)

  • Solder paste printing bridges

  • Whether the solder paste printing is defective

SPI machine contributes so much to SMT quality, but which is not enough. Without experienced operators and quality control, the solder paste inspection is not able to achieve the expected effects. Fortunately, we've got a highly experienced QC and operation team, that's why PS Electronics can always offer high quality boards.

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