Effects of Lead Widths and Pitches on Reliability of Soldered Joints and Optimum Simulation for QFP Devices

Abstract- The FEM method was used to analyze the effects of lead widths and pitches on reliability of soldered joints. The optimum simulation for QFP devices was also researched, the results indicate that when the lead pitches are the same, the maximum equivalent stress of the soldered joints increases with the increase of lead widths, while the reliability of the soldered joints reduces. When the lead widths are the same, the maximum equivalent stress of the soldered joints doesn’t decrease completely with the increase of lead pitches, and a minimum value of the maximum equivalent stress values exists in all the curves. Under this condition the maximum equivalent stress of the soldered joints is relatively the least, the reliability of soldered joints is high and the assembly is excellent. The simulating results indicate that, as the best parameter setting, the lead width is 0.2mm and lead pitch is 0.3mm (the distance between two leads is 0.1mm). This parameter setting is beneficial to the micromation of QFP devices now. The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25mm and lead pitch is 0.35mm (the distance between two leads is 0.1mm). In such a setting, the devices can serve for a long time, the reliability is the highest, and the assembly is excellent. The simulating results also indicate that the limit of QFP occurs when the lead width is 0.15mm and lead pitch is 0.2mm. This is significant for the high lead count and micromation of assembly. Key words: QFP; maximum equivalent stress; soldered joints; assembly optimization; finite element metho