Optimization of PCB Board to Improve Thermomechanical Reliability of Lead-Free Solder Ball Joint

Plastic package are widely applied in the field of consumer electronics and other microelectronic packaging because of its advantages including small size, light weight, low cost and outstanding mechanical properties. Due to significant differences of properties among components within the package, especially the coefficient of thermal expansion (CTE) mismatch, extensive internal stresses and strain exist during switching on and off operation of the components. This paper proposed a novel PCB substrate with cavity or inner compliant layer beneath the SMT component package to reduce the stress and strain of corner solder joints in order to enhance the package reliability. Finite element method was applied to analyze the thermomechanical performance of solder balls. Cavity area and thickness are optimized to achieve the minimum strain or stress of solder balls. Material choice filled in the cavity as inner compliant layer is also analyzed by adjust the key material properties. Simulated switching on and off operation process was conducted to analyze the thermomechanical performance of solder ball joints reflowed on the optimized PCB structure. By comparison with the simulation results between the new substrate and traditional substrate, the performance of the new substrate is proved to be excellent. Compared with the traditional substrate, when the component was attached on the optimized PCB board, the viscoplastic stain of corner solder joints could be reduced from 0.0108 to 0.0064 while the deformation of PCB board remained almost unchanged, thus the reliability of solder improved a lot.