Improved method for determining the shear strength of chip component solder joints

In this paper an improved method has been presented to determine the solder joint shear strength of passive discrete surface mounted (SMD) chip components (like resistors and capacitors). To calculate the stress in a solder joint in the case of shear loading, the force applied should be measured and the amount of joined surface (wetted area of the component metallization) calculated. Using the method we suggest, we first measured the exact position of the chip component after soldering according to the guidelines set out in standard IPC 9850 (Institute for Interconnecting and Packaging Electronic Circuits). To determine the accurate value of the joined surface, a 3D profile calculation was carried out taking into account the exact position of chip components after soldering. The calculation of the profile was based on the principle of minimum energy. Then, the next stage was to determine the maximum force experimentally that the solder joint was able to withstand before failure in shear. The evaluation of the shear load results verified that the standard deviation coefficient of the results was lower when the shear strength of the solder is characterized by the maximum stress instead of maximum force. It was proved by our experiments and by simulations that the shear strength of misaligned components solder joints depends on the degree of component misalignment after reflow soldering.