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Experimental Validation of Fatigue Life of CCGA 624 Package with Initial Contact Pressure of Thermal 时间:2018-10-09 22:24   来源:未知   作者:admin   点击: 次 Abstract:Thermal gap pads are widely used for effective heat transfer from high-heat-dissipating components to a heat sink. The initial contact pressure of thermal pads is an important parameter for enhancing the heat transfer capability of thermal design during the assembly process of the heat sink. However, this causes stress on the solder joint of the component as a result of the pad’s inherent resistance to deformation. In this study, we investigated the effect of thermal pad on the fatigue life of the solder joint of CCGA 624 package for space usage. A random vibration fatigue test for several specimen assembly sets with various pressurization levels of thermal gap pads was performed, and their fatigue lives were compared with that of the package without the initial pressure of thermal gap pads.
1. Introduction
  Highly integrated electronic packages such as a ball grid array (BGA), small outline package, and column grid array (CGA) offer several advantages for space applications owing to a drastic reduction in size and weight and efficient utilization of accommodation area of a printed circuit board (PCB) [1–3]. These packages are subjected to various forms of mechanical loads during the launch phase, such as a quasi-static load due to the engine thrust, a sine vibration due to the main engine cut-off (MECO) and pogo oscillation, a random vibration due to the noise of the exhaust, turbulent flows along the launcher, and shock loads induced by the activation of the pyro-device [4]. In addition, these packages are also subjected to thermal stresses due to a mismatch between the thermal expansion coefficients of the different materials of the electronic equipment, induced by the on-orbit thermal cycling environment. Among these, random vibration is a main cause of failure in electronics [5] because a relative displacement between the package and PCB due to the repetitive bending behavior of the PCB incurs a fatigue fracture on a solder joint, which connects the package to the PCB.
  Several previous studies have focused on securing the mechanical safety of a solder joint under vibration excitation by applying mitigation techniques to the package, such as applying an underfill or dummy solder balls [6–8]. Kim and Hwang [6] investigated the effect of underfill on the fatigue life of a plastic ball grid array (PBGA) package for space usage under random vibration excitation of the launch. Fatigue test results indicated that the underfill remarkably improved the structural safety of the solder joint by reducing its stress under random vibration. Jang et al. [7] investigated the effect of dummy solder balls on the fatigue life of a solid-state drive (SSD) under harmonic vibration excitation. The dummy solder balls replaced the functional solder balls at the outmost corners of the package that were vulnerable to the vibration environment. The results of the fatigue test under harmonic vibration showed that applying dummy solder balls improved the fatigue life of the given SSD by 4.5 times by reducing the stresses on the functional solder balls. Uppalapati et al. [8] investigated the sensitivity of three critical PCB design factors on the mechanical safety of the solder joint of a flip-chip ball grid array under vibration during shipping. The results showed high sensitivity with respect to the location of the package on the PCB, trace routing orientation of the PCB under the package, retention mechanism design, and mass of the heat sink.