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Principle and detection of 3D SPI in SMT equipment
Principle and detection of 3D SPI in SMT equipment

Principle and detection of 3D SPI in SMT equipment


SPI (SolderPaste Inspection) refers to the solder paste inspection system for SMT equipment. Its main function is to detect the quality of solder paste printing, including volume, area, height, XY offset, shape, and bridging. How to detect extremely tiny solder paste quickly and accurately, generally adopts the detection principle of PMP (Chinese translated as phase modulation profile measurement technology) and Laser (Chinese translated as laser triangulation technology).

1. Laser Triangulation Technology

The detection light source used by the SMT equipment is a laser. The laser beam produces distortion at different height planes. The detection head moves continuously in a certain direction, and the camera takes pictures at a set time interval to obtain a set of laser distortion data, and then perform calculations to obtain the test results. Way (as shown below).

Advantages: faster detection speed

Disadvantages: 1) The laser resolution is low, generally only 10-20um.

           2) Single sampling, low repeatability accuracy.

             3) Sampling during exercise, external vibration and transmission vibration have a greater impact on detection.

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             4) The monochromatic light of the laser has weak adaptability to the color of the PCB board.

 Market status: Laser technology has gradually withdrawn from the SPI industry. Currently South Korea Parmi is still using laser technology (dual laser technology)

2. PMP phase modulation profile measurement technology

1. Use a white light source to measure the solder paste through the phase change of the structured grating

2. Using the gray change measurement of the structured grating to obtain a high-precision height value

3. The phase change is adopted to sample each solder paste 8 times to ensure the high repeatability accuracy of the inspection

4. PMP technology is divided into two detection methods: FOV stop-and-go and Scan scanning

4.1 FOV stop-and-go

When the detection is in progress, no sampling is performed during movement, and no movement is performed during sampling. Minimize the impact of vibration on detection.

Advantages: 1) The PMP principle has high detection resolution, 0.37um. 2) Stable multiple sampling, high detection repeatability accuracy. 3) Not picky about PCB color.

Disadvantages: The speed is relatively slow.

Market: It is determined by the industry as the best solution for SPI with stable detection effect, and a foreign brand represented by KohYoung in South Korea.

4.2 Scan

The continuous movement of the detection head is used to form the phase change of the structured grating. Sampling while moving.

Advantages: 1) The PMP principle has high detection resolution, 0.37um. 2) Not picky about PCB color. 3) With multiple sampling, the repeatability of detection is higher than that of laser-type equipment. 4) The detection speed is faster than the FOV stop-and-go type.

Disadvantages: the impact of external vibration is greater, and the repeatability of detection is low.

3. Programmable structure grating (PSLM)

Programmable structure grating (PSLM): It realizes the software control of the structure grating movement, avoiding the mechanical device necessary for the traditional piezoelectric ceramic motor (PZT) to drive the glass moiré grating, reducing mechanical wear and customer maintenance costs.

The use of advanced phase profile modulation measurement technology (PMP), 8-bit grayscale resolution, and a detection resolution of 0.37 microns, which is 2 orders of magnitude higher than laser measurement accuracy, greatly improving the detection capability and scope of SMT equipment .