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The reliability of microelectronics components and assemblies it should be considered as expression of solder joints functionality. The functions are in close connection with the microstructure of the solder joints, which are the result of the soldering Process temperature gradient action over the trinomial solder alloy/Paste, electronic components terminals/Pin and PCBs Pads finishes. Consequently the solder joints quality can be correctly evaluated taking into consideration not only the severally intrinsic parameters of the trinomial elements, Pad-Paste-Pin, but also interrelate the complex reaction at the interface between them and interdependence with the soldering Process parameters. Therefore the solder joints can be considered result of a complex function of 4P elements defined before. In the paper, a 4P Soldering Model will be proposed in order to characterize the solder joints quality, emphasizing dynamics of Pad-Paste-Pin-Process elements synergistically interactions. The different pad finishes (NiAu, ImmAg, ImmSn, HASL, OSP) realized on PCBs having different core material, (FR4, Glass, Al, Cu, Al2O3), the components terminals/pins/balls having different finishes, the different solder paste type and the reflow soldering process (infrared-convection/vapour phase/LASER) with their typically parameters are the 4P Soldering Model variables. Practical experiments were designed in order to study 4P Soldering Model elements, Pad-Paste-Pin-Process, interactions.