Smart chemistry towards highly efficient soldering material formulation

Meanwhile, the fluxing performance has become paramount because of the increasing development and advances in the electronic industry, such as high integration and fine pitch components. Moreover, the demand for halogen-free soldering materials with equal or superior performance compared to their halogenated predecessors makes the design of solder paste, tacky flux and liquid flux formulations even more challenging.Activator choices are critical parameters in the design of paste and flux formula in order to achieve outstanding performance in lead-free and halogen-free soldering processes. For an efficient printed circuit boards (PCBs) soldering operation, the fluxing mechanism requires the right chemistry coupled with a proper initial heat cycle to remove the oxide and surface contamination. A synergetic combination between chemistry and processing will promote a clean and solder-wettable metal surface, which is a prerequisite to achieve good metallurgical bonding. Meanwhile, the activator itself has to remain inert at mild temperatures to guarantee an acceptable shelf-life while leaving non-corrosive and non-conductive residues to ensure a high-reliability in the no-clean categories. Here, we report a systematic study of a series of innovative activator systems applied in new solder paste and liquid flux platforms. Analytical methods such as thermogravimetric analysis (TGA) are applied to characterize the thermal behavior of these activators. Solder pastes are formulated using these activator packages. The solderabilities, physical properties and stabilities of the pastes and fluxes are evaluated. This fundamental understanding may provide some scientific guidance for future formulation work. In summary, five activators were created from standard chemicals A and B commonly used in solder paste formulation. The physical properties, thermal stability and solderability of these activators can be tuned by adjusting the ratios between A and B. We demonstrated that specific entities govern the product performance. The production of these will depend on complex interactions within the formula and will be dependent on formulation and processing parameters. As an example, the tackiness, hot slump resistance and shelf-life of our pastes varied in a nonlinear fashion with the activator stoichiometry. The deviation from linear correlation was also observed in solderability evaluations. In spite that A and B are quite similar in certain aspects, combining them in different ratios may remarkably alter the pastes performance from head to toe. Additional studies on the reaction mechanisms during reflow between these activators and other flux components,solder alloy powders, and surface metal oxide layers are desired to provide further scientific guidanc