Simulation on equivalent stress in soldered joints of QFP devices with different leads

Finite element method was used to simulate residual stress in soldered joints of QFP devices with different leads.Results indicate that the PCB is warped outward, but the distortion is small.The ceramic plate is warped upward and the distortion of its integral structure is obvious after thermal cycle.At the same time, the expending of the crack in soldered joint will be aggravated for the pull stress from ceramic plate to the lead. The largest strain value emerges in outside of the soldered joints.The equivalent stress is relatively large in the root and toe of the soldered joint of QFP gull wing lead that the stress is larger in the root than that in the toe, but that in the middle area of the soldered joint is the least.The simulating results show that the largest stress was endured by the soldered joint of QFP with 32 leads, larger stress endured by the soldered joint of QFP with 48 leads, and the least stress endured by the QFP with 100 leads.The tensile test shows that the soldered joint of the QFP device with 100 leads possesses the biggest tensile strength than that of the QFP with 48 leads and the QFP with 32 leads, which is concordant with the numerical simulation results.