Soldering of components onto a smart tag - an evaluation of the process window

An experiment was designed using optimal design of experiments to identify the most relevant parameters in an assembly step for a smart tag; the soldering of 0402 resistors to a polyimide backplane. The parameter window was set to reflect natural variations in production, and parameter variations were investigated to ascertain whether these variations could lead to unacceptable values of electrical resistance or shear-strength of the soldered joints. All tests were performed before and after exposure to hygrothermal aging, i.e. exposure to 85 °C in combination with 85 % RH, and/or cyclic bending. All test results gave values well within the predefined failure criteria. It could therefore be concluded that all of the tested combinations of parameters spanning the tested process window can be considered as safe variations for the assembly of 0402 resistors in the production of the smart tags. The parameters that influenced the electrical resistance and shear-strength of these assemblies were identified.