The heat preservation stage has three functions. The setting of the heat preservation stage should mainly refer to the recommendations of the solder paste supplier and the heat capacity of the PCB board. At this stage, the temperature rises slowly. Slowly heat the entire board to 170 so that the circuit board reaches a uniform temperature, which is called the soak or equilibrium phase. Another reason is that a too high heating rate will cause the solder paste to collapse and cause the danger of short circuits, and a too high heating rate will cause the solvent to evaporate too quickly, and it is easy to splash out metal components and cause tin beads. Too high a heating rate will cause thermal stress impact of the component, damage the component or reduce the performance and life of the component, the latter brings greater harm. The preheating stage needs to volatilize too much solvent, but the heating rate must be controlled. The role of the solvent is mainly to act as a carrier of rosin and to ensure the storage time of the solder paste. The main components of flux in solder paste include rosin, activator, viscosity improver and solvent. The purpose of the preheating stage is to volatilize the lower melting point solvent in the solder paste. The PCB temperature is heated to 150 and the heating rate is less than 2 T/s, which is called preheat. Therefore, this temperature curve is required when the size of the components on the PCB is uneven and the assembly density is relatively high. This kind of temperature profile has a heat preservation time during heating, so the surface temperature of SMA is relatively uniform, even if the PCB components are not uniform in size and assembled When the density is relatively large, the surface temperature of the SMA is still relatively uniform. The conventional temperature curve is divided into four main stages: preheating zone, heat preservation zone, reflow zone and cooling zone. ![]() Take the lead-free solder paste Sn96.3 Ag3.2Cu0.5 with a melting point of 217 ☌ as an example to introduce two typical temperature profiles. Generally, solder paste suppliers can provide a reference reflow profile, and users can optimize based on their product characteristics on this basis. Due to the different chemical composition of alloy solder powder and flux, different solder pastes have different requirements for temperature and reflow temperature curve due to their chemical changes. ![]() The characteristics of the solder paste determine the basic characteristics of the reflow temperature profile. About PCBA factory reflow soldering temperature profile and soldering process settings
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