Thermo-mechanical analysis and design for small-outline packages (SOP) based on finite element method

Because of the increased use of computers and electronics in all aspects of our lives, increasing performance of electronic packaging configurations without increasing cost is becoming a major trend of the electronics industry. On the other hand, small size and low profile with high power density are becoming more critical design parameters for portable electronic products. Electronic packaging products have to keep shrinking in size and achieving higher packing density, packages are preferred to be low-cost and easy-manufacturing at the same time. The small-outline packages (SOPs), which saving significant board space and having a direct metal thermal path from die to the outside circuitry, fairly meet these requirements. On the other hand, due to the increasing demands of functionality and miniaturization in portable consumer electronics, the reliability of the electronic packages becomes a major concern in product design. Moreover, thermo-mechanical failures of electronic packages are actually the major failure mechanisms. Thus the thermo-mechanical reliability represents a primary and perpetual concern in the electronic packaging industry. In fact, thermo-mechanical performance has become the critical path of nearly every design and process in this industry. In addition, since the finite element method has been proved as a very effective and reliable approach to design and analyze the electronic packages in many aspects, this method was employed to investigate the thermo-mechanical behavior of SOPs in the present research. Based on such method, two types of SOP with relatively simple structures (SOD923 and SOT1263) have been modeled and studied as examples. The residual thermal stresses accumulated in two cooling processes during production, which are the cooling after die bonding and after PMC (Post-mold Curing), were considered as the indicator of thermo-mechanical behavior of the packages. Then the results of the simulation were presented and discussed. Subsequently, the impacts of both material properties and geometric parameters of the package to the residual thermal stresses were investigated. Based on this parametric study, the optimal design for SOPs has been obtained for the sake of reducing thermal stresses. Besides, in order to make the finite element analysis more efficient and accurate in electronic packaging, an optimized design procedure on the aspect of thermo-mechanical performance has been established. Furthermore, die cracking is one of the crucial problems in electronic packaging industry that certainly influences the reliability of electronic devices. During cooling processes, the temperature loading could also cause the occurring of die crack especially when there are defects in the Silicon die. In this work, the possibility of slanting corner cracking in Silicon die during the cooling process after die bonding was taken into account, and the strain energy release rate in fracture mechanics at the crack tip was employed to evaluate the impact of several package parameters to the risk of die cracking. Similar to the previous part, parametric studies and optimal design have been conducted with the purpose of reducing the risk of die cracking. In fact, the section of studying die crack issue was also a demonstration of the design procedure published in the former section, all the analyses were followed the proposed process flow, which could be validated by this part. Besides, the results of the latter section were basically the same as the one obtained from the last section, which means that the die cracking could also be categorized into the thermo-mechanical performance of electronic packages during the cooling processes