Improvement of Thermo-Mechanical Reliability of Wafer-Level Chip Scale Packaging

Author:

Shi Lei1,Chen Lin1,Zhang David Wei2,Liu Evan3,Liu Qiang45,Chen Ching-I6

Affiliation:

1. State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China

2. State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China e-mail:

3. Tongfu Microelectronics Co., LTD, Nantong 226006, Jiangsu, China

4. Tongfu Microelectronics Co., LTD, Nantong 226006, Jiangsu, China;

5. School of Microelectronics, Tianjin University, Tianjin 300072, China e-mail:

6. Mechanical Engineering, Chung Hua University, Hsinchu 30012, Taiwan

Abstract

Due to low cost and good electrical performance, wafer-level chip scale packaging (WLCSP) has gained more attention in both industry and academia. However, because the coefficient of thermal expansion (CTE) mismatches between silicon and organic printed circuit board (PCB), WLCSP technology still faces reliability challenges, such as the solder joint fragile life issue. In this paper, a new WLCSP design (WLCSP-PN) is proposed, based on the structure of WLCSP with Cu posts (WLCSP-P), to release the stress on the solder joints. In the new design, there is a space between the Cu post and the polymer which permits NiSn coating on the post sidewall. The overcoating enhances the solder–post interface where cracks were initiated and enlarges the intermetallic compounds (IMC) joint area to enhance the adhesion strength. Design of experiment (DOE) with the Taguchi method is adopted to obtain the sensitivity information of design parameters of the new design by the three-dimensional (3D) finite element model (FEM), leading to the optimized configuration. The finite element analysis results demonstrate that compared to WLCSP-P, the proposed WLCSP-PN reduces the package displacement, equivalent stress, and plastic strain energy density and thus improves the fatigue life of solder joints.

Publisher

ASME International

Subject

Electrical and Electronic Engineering,Computer Science Applications,Mechanics of Materials,Electronic, Optical and Magnetic Materials

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