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Application of Infrared Thermal Imager in Quality Management of Circuit Board
Release time: 2018-06-23

Infrared thermometer case ETG-SH030001

Project organizer: Tianjin FAW Toyota Motor Equipment: NEC TH9100N Time: 2009-1

I. Background Application

As early as the 1960s, the U.S. Air Force began applying infrared technology to electronic equipment.

Research on fault diagnosis; by the 1970s, Hughes Airlines had designed and developed a series of automatic test systems using infrared technology for fault detection and isolation of circuit boards, but could only provide fault areas to testers; up to 80 In the 1950s, the development of high-performance infrared thermal imaging cameras and image processing technology has made great progress in the use of thermal imaging technology for circuit board fault detection and diagnosis, and has a strong ability to diagnose thermal mode faults.

All objects whose temperature is higher than absolute zero in nature radiate infrared radiation with carrier characteristic information every moment. Stefan-Boltzmann's law states that all energy radiated from the surface of an object is determined by the thermodynamic temperature and emissivity of the object. Joule's 2 Lenz's law tells us: Any electronic component with a certain resistance value will consume power when it passes a certain current, causing the component temperature to rise, and a considerable part of the heat will be converted into the form of infrared radiation. Exude. When the IC is supplied with power or excitation through the initial input of the card, the infrared radiation generated by the IC on the board can be seen by infrared thermal imaging. The thermal radiation of the IC characterizes its electrical state and circuit structure characteristics. Once the IC fails, the power consumption of the components on the board will usually change, thereby changing the infrared thermal image of the IC card. By observing and analyzing the change of the thermal image, you can detect and locate the circuit fault.

The faults of electronic circuits are generally divided into short circuit, open circuit and poor contact. The normal working of the circuit is different from the infrared radiation emitted by the electronic components when the circuit is faulty. That is to say, when the circuit is working normally, the thermal imaging of the circuit board is very different from the thermal imaging of the faulty circuit board. When an electronic component fails, there are two situations: one is a short circuit, the current is large during the short circuit, the component is hot, and the amount of infrared radiation is large. At this time, the thermal imaging is more changed than normal and the infrared imaging changes greatly; (Poor contact), the current value flowing through the element is almost zero, so the element temperature is lower than that during normal operation, and there is almost no infrared radiation. At this time, the thermal imaging is significantly different from the normal thermal imaging. Using this principle, it is easy to determine the failure point of the electronic circuit.

Infrared thermal imaging provides testers with a unique IC test method. With one infrared scan imaging, the power consumption value of each IC on the board can be obtained and turned into visual information for testers to diagnose faults.

Infrared PCB image

Infrared PCB image


Infrared PCB image



Second, the thermal imaging detection circuit failure method

Applying stimulus: Within the specified time before thermal image acquisition, apply the power and necessary stimulus signals required for normal operation to the IC board under test to prepare for obtaining a visible thermal image. Thermal image acquisition: When the DUT reaches the required warm-up time, start the thermal image data acquisition program to determine the temperature resolution of the infrared thermal radiation of the DUT in the field of view and collect relevant information such as the environment Temperature, temperature-resolved DUT code, etc.) are written into the thermal image data. Thermal image correction: Due to the unstable imaging of the thermal imaging head, there is often a slight drift in the thermal image acquired each time. In order to ensure the reliability of the data, the thermal image must be corrected for position. Thermal image processing (optional): Although the thermal image signal is amplified and filtered by the hardware circuit, there will still be noise interference in the collected thermal image data. An effective algorithm should be selected for software filtering, and image enhancement can be performed if necessary. deal with.

Thermal image display: During thermal image acquisition, thermal image data can be displayed in monochrome or grayscale in real time. After data processing, up to 256 pseudo-color displays can be performed.

Thermal image storage: Regardless of the original thermal image data or processed data and related information, they can be saved in the form of data files for archiving.

Standard thermal image: After the test object is determined, the thermal images generated when multiple samples work normally must be statistically averaged as the standard thermal image, so that the differences can be found by comparison when a fault occurs.

Thermal image comparison: Display the measured thermal image of the DUT and its standard thermal image at the same time, for testers to observe and compare, and can obtain and display the difference between the two and the thermal image.

Circuit bitmap: It mainly displays the component layout and concise information on the IC board under test, such as chip model, location, normal operating temperature, etc., for reference by testers.

Thermal image analysis: Provides testers with a variety of methods such as single-point temperature, average temperature, and profile temperature measurement. It can also zoom in on the thermal image and display the thermal map, shape, and position of the component directly on the thermal image. Refer to the circuit bitmap data to determine the abnormal part.



Case information

Automotive assembly requires high-speed on-line inspection of products on the assembly line. At the same time, circuit boards account for a certain proportion of modern automobile parts. The quality control of circuit boards has also become an important part of the quality control of the entire automobile.

The two infrared thermal cameras-TH7800N purchased by FAW Toyota this time are used to inspect circuit board components in the FAW production workshop. Improve the quality of circuit boards on the assembly line and during assembly, thereby improving quality

Fourth, the conclusion

The two TH9100s of the customer were successfully applied to production after commissioning and installation, and they have won the customer's affirmation.

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