Reliability testing and failure analysis of blind buried hole circuit boards
2026-02-02 16:28【Q】Blind buried hole circuit boards are mostly used in high-end electronic products, with extremely high reliability requirements, as a PCB engineer, what core reliability indicators do you need to pay attention to? What are the commonly used testing methods?
The core reliability indicators include conduction reliability, temperature resistance reliability, humidity and heat resistance, and vibration resistance reliability, which directly determine the life and stability of the product in actual use. Common test methods should be selected based on the characteristics of the indicators to ensure that the test results are suitable for actual application scenarios.
The on-reliability is the basic index, which mainly evaluates the on-performance and stability of the copper-plated layer of the blind buried hole, and the core test items include DC resistance test, on-continuity test, and copper thickness test. DC resistance test uses a microresistance tester to measure the on-resistance of blind buried holes, the standard value is generally ≤ 0.05Ω, if the resistance is too large, it means that the copper plating layer is too thin or there are problems such as virtual welding and residual glue; The continuity test adopts a continuity tester to detect the energization of all blind buried holes to ensure that there is no open circuit or short circuit. The copper plating thickness test uses a metallographic microscope or X-ray thickness gauge to measure the copper plating thickness of the hole wall, and the standard value is generally not less than 20μm. During the design, it is necessary to optimize the copper plating process parameters to ensure that the copper plating thickness is uniform; After production, 100% of the continuity test is required to check for defective products.
The reliability of temperature resistance evaluates the stability of blind buried hole circuit boards in high and low temperature environments, and the core test items include high and low temperature cycle tests and high temperature aging tests. The high and low temperature cycle test adopts a high and low temperature test chamber, the test conditions are generally -40°C~125°C, 500 cycles, each cycle is maintained for 30 minutes, after the test detects the change of the conduction resistance of the blind buried hole, if the resistance change rate ≤ 10%, it means that the temperature resistance reliability is qualified; The high-temperature aging test adopts a high-temperature test chamber, which is placed at a constant temperature of 150°C for 1000 hours, and after the test, check whether the blind buried hole has problems such as the copper plating layer falling off and the hole wall cracking. The temperature resistance reliability of blind buried holes mainly depends on the bonding force between the copper plating layer and the sheet metal and the heat resistance of the sheet, and the design should choose a sheet with good heat resistance (such as FR-4 sheet with a glass temperature of Tg≥150°C) to optimize the hole wall treatment process and enhance the bonding force between the copper plated layer and the hole wall. Avoid dense blind buried holes in high-temperature areas to reduce the impact of high temperature on interconnection reliability.
The reliability of moisture and heat resistance evaluates the corrosion resistance and conduction stability of the product in humid and high-temperature environments, and the core test item is the damp-heat cycle test. The test adopts a damp heat test chamber, the test conditions are generally 85°C/85%RH, constant temperature and humidity placed for 1000 hours, or the damp heat cycle test (40°C/90%RH~85°C/85%RH, 200 cycles), after the test to detect the conductivity and appearance of the blind buried hole, if there are copper plating corrosion, open circuit and other problems, it means that the reliability of humidity and heat resistance is not up to standard. In a humid environment, moisture is easy to penetrate into the inside of the blind buried hole, resulting in oxidation and corrosion of the copper plating layer. Choose sheet materials and solder masks with good moisture resistance to enhance the moisture resistance of the product; Design drainage holes around blind buried holes to reduce water retention.
Vibration resistance reliability evaluates the ability of products to resist blind buried hole failure caused by vibration impact during transportation and use, and the core test items are vibration test and shock test. The vibration test adopts a vibration testing machine, the test conditions are generally 10-2000Hz, the acceleration is 20G, and the vibration time is 1 hour (20 minutes in each of the three directions of XYZ); The impact test adopts an impact testing machine, the test conditions are generally 50G, the impact time is 11ms, and the impact is 3 times (1 time in each of the three directions of XYZ). After testing, the blind buried hole is detected for open circuits, short circuits, or sudden changes in resistance to ensure stable conduction in the vibration and shock environment. During the design, the connection between the blind buried hole and the device pad should be optimized to avoid the blind buried hole being directly located in the vibration-sensitive area (such as under the device pin). Increase the reinforcement design around the blind buried hole, such as arranging grounding via around the hole to enhance mechanical strength.
Q: If the blind buried hole circuit board fails in the reliability test, how should the failure analysis be performed to locate the root cause?
【Answer】The failure analysis of blind buried hole circuit boards should follow the process of "appearance observation→ performance testing→ microscopic analysis→root cause location", combined with professional equipment and process experience, to accurately locate the cause of failure. First, observe the appearance, use a magnifying glass or microscope to observe the appearance of the failed product, check whether the blind buried hole has problems such as cracking of the hole wall, peeling off the copper coating, damage to the solder mask, etc., and preliminarily judge the type of failure (such as mechanical failure, corrosion failure). Secondly, the performance test measures the conductivity of the blind buried hole through the conduction tester and microresistance tester, and determines the failure location (such as a blind hole of a certain order, buried hole); Use an infrared thermal imager to detect the heating of the failure area and check whether there is a local short circuit or poor contact. Thirdly, microscopic analysis, metallographic microscope is used to observe the cross-section of the failed blind buried hole, and check the copper plating thickness, hole wall roughness, hole bottom residual glue, interlayer bonding, etc. Scanning electron microscopy (SEM) and energy spectrum analyzer (EDS) were used to analyze the elemental composition of the failure area and check for corrosion, oxidation or impurity contamination. Finally, the root cause is located, combined with the design parameters, production process and test results, to locate the root cause of failure, if it is a design problem (such as too small hole spacing and insufficient copper plating thickness design), the design scheme needs to be optimized; If it is a production process problem (such as drilling depth deviation, copper plating process parameters are unreasonable), the production process needs to be adjusted; If it is a material problem (such as poor temperature resistance of the sheet and insufficient moisture resistance of the solder mask), the suitable material needs to be replaced. After failure analysis, targeted improvement measures should be formulated and the improvement effect should be verified through secondary testing to ensure that the problem is completely solved.
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