Thermal shock test: the key link to ensure PCB reliability

In the field of electronic equipment manufacturing, the quality and reliability of printed circuit board (PCB) directly determine the performance and life of the final product. Among many test items, thermal shock test has become one of the important means to evaluate PCB reliability because of its harsh conditions and efficient screening ability.


Core value of thermal shock test

Thermal shock test simulates the extreme environment that the product may encounter in the process of actual use, transportation or storage by making the PCB sample experience sharp temperature changes in a very short time. This test not only tests the tolerance of PCB substrate, but also comprehensively tests the manufacturing process level.

Electronic products often face an environment with rapid temperature changes, such as the transition from an air-conditioned room to an outdoor high-temperature environment, or the sudden drop in temperature from indoor to outdoor in winter, which may cause potential damage to the internal PCB.

Thermal shock test simulates and amplifies the temperature stress in a short time by laboratory means, so as to find the potential defects of the product in advance.


Purpose of thermal shock test

1. Material tolerance evaluation

PCB is composed of many materials, including base material, copper foil, solder mask and so on, and the thermal expansion coefficient of each material is different. When encountering sudden temperature changes, these materials will expand or contract at different rates, resulting in internal stress. If the thermal stability of the substrate is insufficient, it may lead to delamination or warping. In the actual test, we often observe that the substrate with substandard quality will have tiny cracks or bubbles after repeated thermal shocks, and these changes may become hidden dangers of circuit failures.

2. Welding reliability verification

Solder joint connects electronic components and PCB, and its quality is very important. Under the temperature change, due to the difference of thermal expansion coefficient of materials, periodic stress occurs in the solder joint. Long-term stress will lead to solder joint fatigue, cracking or virtual welding. There are differences in physical characteristics between lead-free solder used in modern electronic products and traditional lead-containing solder, which makes thermal shock test more important in the evaluation of new welding process.

3. Interlayer adhesion test

For multi-layer PCB, the bonding strength between layers directly affects the integrity of the overall structure. Thermal shock test can effectively check the quality of lamination process and prevent interlayer separation caused by insufficient resin adhesion. This delamination phenomenon will not only affect the signal transmission quality, but also significantly reduce the mechanical strength of PCB.

4. Strict and standardized test standards

In industrial practice, IPC-TM-650 and other related standards provide clear technical specifications for thermal shock tests. These standards not only stipulate the basic parameters of the test, but also specify the requirements for setting the test conditions in detail to ensure the comparability and reliability of the test results conducted in different laboratories and at different times. The importance of following uniform standards is self-evident. It not only ensures the fairness of test results, but also establishes a common language foundation for technical exchange and quality evaluation in the industry.

Process of thermal shock test

1. Sample selection

The first step of the experiment is to select representative PCB samples. These samples must come from the normal production process, and before testing, it is necessary to confirm that their appearance and electrical properties meet the requirements. Proper sample selection is the premise of obtaining effective test results.

2. Equipment calibration

The accuracy of thermal shock test equipment is directly related to the reliability of test results. The test equipment must be strictly calibrated to ensure the accuracy and uniformity of temperature control. In general, the temperature deviation between the high-temperature box and the low-temperature box should be controlled within 2℃, and the temperature conversion time needs to be accurately controlled to ensure the rigor of the test conditions.

3. Test method

In the actual testing process, samples need to be quickly converted between high temperature and low temperature environment. Typical test conditions may include: high temperature of 125℃, low temperature of -55℃, holding at each temperature point for about 15 minutes, and the conversion time does not exceed 10 seconds. This cycle will be repeated dozens or even hundreds of times, depending on the application requirements of the product. During the whole testing process, the tester will monitor the electrical performance of the sample at a specific time point and record the change of resistance value or conduction state. This real-time monitoring can help engineers understand the performance degradation process of products under temperature stress.

4. Conduct sample inspection after inspection, analysis and testing, including appearance inspection and function inspection.

Visual inspection to observe the surface of PCB, looking for physical damage, such as solder joint cracking, copper foil tilting, substrate delamination or solder mask damage. Functional inspection evaluates the electrical performance, compares the electrical parameters before and after the test, and judges whether the product still meets the use requirements. Usually, the change of resistance value over 5% is considered as unqualified. Microscopic analysis of damaged samples, such as metallographic section, can understand the damage mechanism and degree, and provide information for improving product design and manufacturing process.


As an important part of PCB reliability test, thermal shock test has been widely recognized in electronic manufacturing industry. Through this test, manufacturers can find potential defects before leaving the factory and avoid on-site failures.

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