The basic principles of solder and welding, you will understand after reading this.
Release time:
2022-06-09
【Summary Description】 The first intermetallic compound formed at the solder substrate interface can be predicted from the calculation of the metastable equilibrium between the substrate and the liquid solder phase, and the comparison of the driving forces for the formation of each phase.
InSolderThe formation of the first intermetallic compound at the substrate interface can be predicted from the calculation of the metastable equilibrium between the substrate and the liquid solder phase, and the comparison of the driving forces for the formation of each phase.
This facilitates the diffusion of the solder, which forms a free energy about two orders of magnitude higher in the formation of intermetallic compounds between the liquid antimony, cadmium, tin and the base metal copper. Therefore, the wettability increases as the formation rate of the intermetallic compound increases, which is determined by the formation rate of the intermetallic compound. Similar to the dissolution of the base metal in the solder, the formation rate of the intermetallic compound is also a function of time, temperature, class of the substrate metal layer, and class of solder.
Generally speaking, the melting temperature of the intermetallic compound is higher than the welding temperature used in the electronics industry, and it remains in the solid state during the welding process. For many systems, the intermetallic compound forms a continuous layer between the molten solder and the solid metal, and the formation of the IMC reduces the diffusion rate of the base metal atoms through the intermetallic layer. This phenomenon is due to the fact that solid-state diffusion processes are roughly two orders of magnitude slower than solid-liquid reactions. As a result, the dissolution rate of the base metal into the solder decreases very slowly.
In general, the wettability of a metal coating increases as its rate of dissolution in solder increases. Although this phenomenon is related to chemical reaction factors, which will be discussed in the section on intermetallic compounds, it may also be due to entropy factors, because the dissolution of the base metal in the solder will cause the entropy to increase. Because the dissolution rate increases with increasing time and temperature, it allows for process parameters to control the dissolution rate. On the other hand, the strong influence of base metal class and solder class on the dissolution rate is pointed out in the engineering design stage of the material.
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