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3D SPI Principle and Test Method

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SPI is solder paste inspection system. The main function is to detect the quality of tin paste printing, including volume, area, height, XY offset, shape, bridge and so on. The detection principle of how to detect very small solder paste quickly and accurately is generally PMP( phase modulation profile measurement technology) and Laser( laser triangulation technology).

Laser triangulation technology

The detection light source used is laser, the distortion of laser beam in different height plane, the detection head moves continuously in a certain direction, and the camera takes pictures at a set time interval, so as to obtain a set of laser distortion data and calculate it. The way to get the test results (see below).

Advantages: faster detection speed

Disadvantages :

1) low laser resolution, generally only 10-20 um.

 2) single sampling, low repeatability.

 3) motion sampling, external vibration and transmission vibration have a great impact on the detection.

 4) laser is less adaptable to the color of the PCB plate.

Market conditions: laser technology has gradually withdrawn from the SPI industry. At present, the Korean Parmi is still using laser technology (dual laser technology)

PMP Phase Modulation Profile Measurement Technology

1.Using a white light source, the solder paste is measured by the phase change of the structural grating (see below)


2. Measuring the gray-level variation of the structural grating to obtain high-precision height values (see below)

3.The phase change is used to sample each solder paste 8 times to ensure the high repeatability (see figure below)

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

4.1FOV stop

When the detection is carried out, no sampling when moving, and no moving when sampling. The impact of vibration on detection is minimized.


1) PMP principle high resolution ,0.37 um.

2) stable multiple sampling, the detection repeatability is very high.

 3)Not picky about PCB colors.

Disadvantages: relatively slow speed.

Market: A stable detection effect is identified by the industry as the SPI best solution.

4.2 Scanning Type

The continuous motion of the detection head formed the phase change of the structural grating. sampling while moving.


1) high resolution um.0.37

2) not picky about PCB colors.

3) multiple sampling, the detection repeatability is higher than that of laser equipment.

4) detection speed is faster than FOV stop type.

Disadvantages: external vibration has a greater impact and low repeatability.

Programmable Structure Grating

Programmable structural grating : the software control of the structural grating motion, avoids the traditional piezoelectric ceramic motor (PZT) to drive the glass molar grating necessary mechanical devices, reduces mechanical wear and customer maintenance costs.

By using the advanced phase profile modulation measurement technology (PMP), the gray order resolution of 8 bits can reach the detection resolution of 0.37 microns, which is 2 orders of magnitude higher than the laser measurement accuracy, and greatly improves the detection ability and application range of the equipment.

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