What reliability test items are included in PCBA lead-free solder joints?

Date：2021-09-16 16:15:23Views：1254

PCBA lead-free solder joint reliability test mainly refers to the thermal load test (temperature impact or temperature cycle test) for electronic assembly products; Carry out mechanical stress test on the junction of electronic devices according to the fatigue life test conditions; Use the model for life assessment. As the carrier of various components and the hub of circuit signal transmission, PCBA has become the most important and key part of electronic information products. Its quality and reliability level determine the quality and reliability of the whole equipment. In order to verify the reliability of PCBA lead-free solder joints in the actual working environment, it is necessary to test the reliability of PCBA lead-free solder joints.

First, what is reliability testing? Reliability test is an activity to ensure that the product maintains functional reliability in all environments of expected use, transportation and storage during the specified service life. It is to expose the product to natural or artificial environmental conditions and undergo its action, so as to evaluate the performance of the product under the environmental conditions of actual use, transportation and storage, and analyze and study the influence degree and action mechanism of environmental factors. By using various environmental test equipment to simulate the high temperature, low temperature, high temperature water humidity and sudden change of humidity in the climatic environment, accelerate the reaction of the product in the service environment to verify whether it meets the expected quality objectives in R & D, design and manufacturing, so as to evaluate the overall product to determine the reliability life of the product.

The reliability test methods of PCBA lead-free solder joints mainly include appearance inspection, X-ray inspection, metallographic section analysis, strength (tensile and shear), fatigue life, high temperature and humidity, drop test, random vibration, reliability test methods, etc. Here are some of them:

1. Visual inspection

PCBA solder joints without lead and with lead are different in appearance, and will affect the correctness of AOI system. The stripes of PCBA lead-free solder joints are more obvious and coarser than the corresponding lead solder joints, which is caused by the phase transition from liquid to solid. Therefore, this kind of solder joint looks more rough and uneven. In addition, due to the high surface tension of lead-free solder in PCBA processing, it is not as easy to flow as lead solder, and the fillet shape is also different.

2. X-ray inspection

In the spherical solder joint of PCBA lead-free welding, the number of false soldering increased. PCBA lead-free welding has high welding density, which can detect cracks and false welding in welding. Copper, tin and silver should be "high-density" materials. In order to characterize excellent welding characteristics, monitor PCBA assembly process and analyze the structural integrity of PCBA solder joints, it is necessary to recalibrate the X-ray system and have high requirements for testing equipment.

3. Metallographic section analysis

Metallographic analysis is one of the important means of experimental research on metal materials. In the reliability analysis of PCBA solder joint, the metallographic structure of the solder joint profile is often taken for observation and analysis, so it is called metallographic slice analysis. Metallographic slice analysis is a destructive inspection, with long sample making cycle and high cost. It is often used for post weld failure analysis, but it has the advantages of intuitive and speaking with facts.

4. Automatic solder joint reliability testing technology

Automatic solder joint reliability detection technology is an advanced technology that uses photothermal method to detect the solder joint quality of circuit board point by point. It has the characteristics of high detection accuracy, good reliability and no need to contact or damage the tested solder joint. During the detection, the determined laser energy is injected into the welding points of PCBA board point by point, and the thermal radiation generated by the welding points irradiated by the laser is monitored by infrared detector. Because the thermal radiation characteristics are related to the quality of the solder joint, the quality of the solder joint can be determined.

5. Perform temperature related fatigue tests

In the reliability test of PCBA lead-free solder joints, the more important is the temperature related fatigue test for the different thermal expansion coefficients of solder joints and connecting components, including isothermal mechanical fatigue test and thermal fatigue test.

When evaluating the reliability of PCBA lead-free solder joints, the most important thing is to select the test method with the strongest correlation, and clearly determine the test parameters for a specific method. In the reliability test of PCBA lead-free solder joints, the more important is the temperature related fatigue test for the different thermal expansion coefficients of solder joints and connecting components, including isothermal mechanical fatigue test, thermal fatigue test and corrosion resistance test. According to the test results, it can be confirmed that different lead-free materials have different mechanical stress resistance at the same temperature. At the same time, some studies show that different lead-free materials show different failure mechanisms and failure modes.

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