In extreme environments such as deep space exploration, ultra-deep oil exploration, and aerospace, electronic devices must endure high temperatures exceeding 200°C for extended periods. Under these harsh conditions, traditional packaged devices are prone to issues such as bonding failure and material degradation. High-temperature packaged devices are widely used in aerospace, oil exploration, deep space exploration, and other extreme environments. Their ultimate temperature cycle reliability is crucial for ensuring long-term stable operation of the devices.
     Different materials (such as chips, solder, substrates, and packaging materials) exhibit varying coefficients of thermal expansion (CTE). During temperature cycling, shear stress and tensile/compressive stress are generated at the material interface due to CTE mismatch, which can accumulate over time and lead to:
     Solder joint failure: Fatigue cracks and void expansion occur in the solder layer, ultimately leading to an open circuit or increased contact resistance.
     Encapsulation delamination: Delamination occurs between the encapsulant and the chip or substrate due to stress concentration, which can lead to moisture ingress or affect heat dissipation.
     Substrate cracking: Ceramic substrates (such as Al₂O₃, AlN) crack due to excessive thermal stress, especially when the chamfer design of the copper layer in the substrate is not optimized.
     The difficulty of high-temperature packaged integrated circuits primarily lies in the reliability of the bonding interface. In temperature cycling tests, addressing the issue of mismatch between the coefficient of thermal expansion (CTE) of the transition piece and the ceramic housing, a micro-transition piece packaging structure was proposed. The actual product successfully underwent 200 temperature cycles ranging from -65°C to 250°C, providing new insights for the reliability design of high-temperature packaging.
     The temperature cycling test was conducted on the product based on the reference temperature cycling test conditions for extreme temperature cycling tests (low temperature of -65℃, high temperature of 250℃, transition time of 1 minute, and dwell time of 10 minutes). After the temperature cycling test, anomalies were found in the electrical test parameters of the product. Further analysis identified the issue as an open circuit in the ground (GND) pin. Upon opening the product for inspection, cracks were discovered on the keys and fingers installed on the transition piece. Slicing of the failed circuit revealed that the transition piece was made of copper with a thermal expansion coefficient of 16PPM/℃, while the ceramic substrate had a thermal expansion coefficient of 7PPM/℃. During the temperature cycling process, due to the significant difference in expansion coefficients between the transition piece and the underlying ceramic substrate, the thermal stress caused the ceramic to crack.
     By establishing a three-dimensional model of the existing packaging structure and conducting finite element simulation analysis, we simulated extreme temperature cycling conditions. The thermal stress at the ceramic bond and fingers is related to the size of the transition piece. The design improvement measure is to reduce the size of the transition piece. At the same time, to ensure the feasibility of bonding, the original transition piece is optimized to a micro-transition piece. After packaging the product using the improved design, we conducted 200 cycles of extreme temperature testing from -65°C to 250°C. After the test, we conducted electrical testing on the product, and both its functionality and various parameters were qualified. To further verify the reliability of the packaging structure, we sliced the circuit after the test. No ceramic cracking or cracks were found at the connection between the bonding fingers and the transition piece, indicating that using a smaller transition piece size has a significant effect on improving the thermal stress at the connection between the bond fingers and the transition piece.
     High-temperature packaged integrated circuits have introduced a transition piece packaging structure to avoid the Au-Al bonding system. Addressing the failure issues under extreme temperature cycling from -65°C to 250°C, failure analysis and finite element simulation calculations determined that the mismatch in thermal expansion coefficients between the copper transition piece (CTE=16ppm/°C) and the ceramic substrate (CTE=7ppm/°C) led to cracking of the bonding fingers. By optimizing the size of the transition piece, the stress on the bonding fingers during temperature cycling was reduced from 275MPa to 153MPa. Testing and slicing verification showed that the improved high-temperature integrated circuit functioned properly and had no cracks inside the packaging structure, verifying the applicability of the micro-transition piece in high-temperature integrated circuits and ensuring their reliability under extreme temperature cycling.

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