Effect of Surface Treatment on the Fatigue Crack Propagation in a TIM/Copper Interface Subjected to High-Temperature Long-Term Exposure
Authors: Lall Pradeep , Zhang Yunli 
Published: November 2023

Abstract
Because of the shrinking of electronic devices, heat dissipation has become a significant concern that threatens device dependability. It is widely known that when two solid surfaces come into contact, the contact area may be limited, with only 1% to 2% of the area in touch in light-loaded interfaces. In this situation, the contact resistance between bare silicon to silicon contacts is on the order of 100mm2/kW. Thermal interface materials, when used to lower contact resistance between two surfaces, are one solution to this type of problem. Microelectronic packages contain numerous bi-material interfaces which influence both device design and reliability. Dynamic mechanical analysis such as 4-points bending test allow study the fatigue failure of bi-layer materials. By applying the cyclic loading stress, fatigue and failure of material could be characterized. Both strain and stress could be controlled in the study. Nowadays, the operational temperature for semiconductor devices is higher than in a traditional environment. As the development of high-power density electronics, semiconductor devices may be subjected to sustained high temperature environment of 125–200C for extended period of time. While, FCGBAs have been previously used in consumer applications where operating temperatures typically range in 55–85°C, relatively little is known on methods to design damage-tolerant packages in automotive underhood environments. The interfacial delamination is a significant reliability issue. However, there is insufficient information on plastic encapsulated electronic components capable of surviving high temperatures for long periods (&gt; 100,000 hours). In this paper, we assess the reliability and stability of grounded lid FCBGA. Thermal interface material (TIM) is prepared and cured. Bi-material specimens are designed and prepared. Low cycle fatigue test vehicle is designed and assembled. 4-point bending instead of 3-point bending setup is used to avoid stress concentration. Strain controlled tests are conducted. The details of the procedure for low cycle fatigue effect measurement are described. Samples are stored in two different high temperatures: 100C and 150C from pristine, 40 days, 80 days to 120 days. Surface treatment of oxygen plasma with different levels of power, 100W and 400W, is applied on the Copper surface. TIM-Copper bi-material interfacial low cycle fatigue properties are investigated. Adhesion strength for fatigue resistance is investigated. Fracture toughness and stress intensity factors as the function of aging time, plasma cleaning power, aging temperatures are calculated and discussed. DIC technology is applied on characterizing the crack growth propagation during the low cycle fatigue. The resulting Paris’ laws are reported. In particular, the impact of mode-mixity on fatigue crack propagation is explored. Paris’ law coefficients and exponents have been seen to be dependent on mode-mixity. The dependency of fatigue behavior on mode-mixity means that some of the properties of fatigue crack propagation can be determined from a bi-material interfaces monotonic fracture behavior.