SPI Testing Principle and Application

SPI detection purpose

The SPI testing principle is widely used in SMT patches to check whether the solder paste printing on the pad is correct.

SPI testing helps to find the following defects in solder paste printing：

• Solder paste voids: This means the soldering paste does not fill the pad, which may result in loose soldering.

• Solder paste bridging: This means the solder paste creates a bridge between pads that shouldn't be connected, which may cause short circuit problems.

• Solder paste offset: It means the soldering paste is not printed correctly on the pad, which may cause poor solder joints.

SPI testing is adopted in the following ways

• Optical SPI inspection: Use a camera to check the shape and size of the solder paste and generate a three-dimensional image by taking an image of the solder paste on the pad.

• X-ray SPI inspection: Use X-rays to inspect the internal structure of solder paste to check for problems such as voids and bridging in solder paste.

• 3D SPI inspection: Use phase modulation profilometry (PMP) or laser triangulation technology to create a three-dimensional image of the solder paste.

Optical SPI testing principle

• Place the PCB on the SPI inspection machine.

• The camera shoots the solder paste on the pad from different angles.

• Overlay these images to generate a three-dimensional image of the solder paste.

• Use image processing technology to detect defects in solder paste.

X-ray SPI testing principle

• Place the PCB on the SPI inspection machine.

• X-rays pass through the solder paste on the pad.

• The detector receives the X-rays.

• Use image processing technology to detect defects in solder paste.

3D SPI testing principle:

• Place the PCB on the SPI inspection machine.

• PMP or laser triangulation technology is used to create a three-dimensional image of the solder paste.

• Use image processing technology to detect defects in solder paste.

Advantages and disadvantages of SPI testing

The advantages of SPI inspection include improving the quality of SMT assembly, reducing the defect rate, thus saving costs, and improving production efficiency.

It helps detect and correct problems early, ensuring the reliability and performance of electronic equipment.

However, the disadvantages of SPI testing are that it requires professional personnel to operate, some SPI machines have high maintenance costs, and high requirements for the PCB surface flatness.

Summary

In short, SPI testing is a crucial step in the SMT assembly process, which helps to improve product quality, reduce defective rates, reduce costs, and thus improve production efficiency.