![]() ![]() After reaching the maximum temperature (above 217☌), the temperature starts to drop and falls below the return line, after which the solder solidifies. The high temperature zone is where the complete melting and wetting reaction takes place where the intermetallic layer begins to form. It is necessary to retain the flux during the reflow phase as it facilitates the solder wetting process and prevents re-oxidation of the soldered surface. Due to the importance of this part of the process, soak time and temperature must be well controlled to ensure that the flux completely cleans the soldering surfaces and that the flux is not completely consumed before it reaches the reflow soldering process. This ensures that the molten solder wets the soldering surface well. Another important effect of this stage is that the flux in the solder paste begins to react aggressively, increasing the wettability (and surface energy) of the weldment surface. This helps reduce the effects of thermal stress in the reflow area and limits other soldering defects such as larger volume component lift. The first is to achieve a uniform temperature for the entire PCB board. The setting of the constant temperature zone is mainly controlled within the parameters of the solder paste supplier and the heat capacity of the PCB. This is especially true for solder pastes with high flux content. Another side effect of too high a heating rate is that the solder paste can collapse and cause short circuits. Excessive heating rates can thermally stress the component, which can damage the component or reduce its performance/lifetime. The preheating zone needs to volatilize the solvent, but the temperature rising slope must be controlled. The role of the solvent is mainly as a carrier for the resin, with the additional function of ensuring sufficient storage of the solder paste. The main components of flux in solder paste include resins, activators, viscosity modifiers and solvents. The purpose of the preheat zone is to volatilize the low melting point solvents in the solder paste. ![]()
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