Characterization of Interface Strength as Function of Temperature and Moisture Conditions

Since Moisture Sensitivity Level (MSL) tests are part of the international reliability qualification standards, all the microelectronics components/products have to pass these specifications. Therefore, it is important to be able to efficiently and accurately characterize and predict the moisture related material and interface behavior in the real manufacturing, processing, testing and application conditions. The success of interfacial fracture mechanics approach to analyze moisture-induced failures in IC packaging strongly depend on accurate characterization of the critical adhesion strength, Gc. However, its measurement is complicated by the fact that adhesion depends not only on moisture concentration, C, but also temperature, T, and mode mixity, ψ. This paper described our research to develop a reliable methodology for interface toughness evaluation as function of temperature, humidity and mode mixity. Our methodology includes using the four-point bending test and shaft-loaded-blister method. Dedicated specimens consisting of various types of moulding compounds bonded onto leadframe are manufactured. Besides temperature, moisture content and mode mixity effects, also the influences of surface treatment (leadframe oxidation and contamination) and production process on the interface fracture toughness are evaluated. Multi-physics-based numerical methods are used to transfer the experimental critical loads to an interface strength parameter. These analysis covers mechanical, moisture diffusion, vapor pressure, hygro-swelling and CTE-mismatch modeling. To test and improve the methodology, various effects are evaluated, such as crack-length dependency, material properties, specimen- width, displacement-rate of the upper support/shaft, etc. The results of the proposed methodology indicate, as expected, a change in interface toughness by mode mixity, moisture content and temperature. It is found that Gc decreases with increasing moisture content and temperature. The presence of moisture at the given interface is observed as the important factor in the reduction of interfacial strength (>>20 %～45%). Furthermore, Gc increases by a factor 3～4 when the mode mixity shifts towards mode II.

Since Moisture Sensitivity Level （MSL） tests are part of the international reliability qualification standards, all the microelectronics components/products have to pass these specifications. Therefore, it is important to be able to efficiently and accurately characterize and predict the moisture related material and interface behavior in the real manufacturing, processing, testing and application conditions. The success of interracial fracture mechanics approach to analyze moisture-induced failures in 1C packaging strongly depend on accurate characterization of the critical adhesion strength, Go. However, its measurement is complicated by the fact that adhesion depends not only on moisture concentration, C, but also temperature, T, and mode mixity, ψ. This paper described our research to develop a reliable methodology for interface toughness evaluation as function of temperature, humidity and mode mixity. Our methodology includes using the four-point bending test and shaft-loaded-blister method. Dedicated specimens consisting of various types of moulding compounds bonded onto leadframe are manufactured. Besides temperature, moisture content and mode mixity effects, also the influences of surface treatment （leadframe oxidation and contamination） and production process on the interface fracture toughness are evaluated. Multi-physics-based numerical methods are used to transfer the experimental critical loads to an interface strength parameter. These analysis covers mechanical, moisture diffusion, vapor pressure, hygro-swelling and CTE-mismatch modeling. To test and improve the methodology, various effects are evaluated, such as crack-length dependency, material properties, specimenwidth, displacement-rate of the upper support/shaft, etc. The results of the proposed methodology indicate, as expected, a change in interface toughness by mode mixity, moisture content and temperature. It is found that Gc decreases with increasing moisture content and temperature. The presence of moisture at the given interface is observed as the important factor in the reduction of interfacial strength （〉〉20 %-45%）. Furthermore, Gc increases by a factor 3-4 when the mode mixity shifts towards mode II.