As an indispensable device in SMT equipment, reflow soldering plays a very important role in the SMT chip assembly line process. After the placement machine completes the mounting process, the next process is the soldering process, and the reflow soldering process is the entire process. The most important processes in the SMT surface mount technology are common wave soldering equipment such as wave soldering and reflow soldering. Today, I will discuss with you the role of the four temperature zones of reflow soldering, namely the preheating zone. Constant temperature zone, reflow zone and cooling zone, each of the four temperature zones has its important significance.
SMT reflow preheating zone
The first step of reflow soldering is preheating. Preheating is to activate the solder paste and avoid the preheating behavior caused by poor high temperature heating caused by soldering during solder dipping. Target temperature. During the heating process, the heating rate should be controlled. If it is too fast, thermal shock may occur, which may cause damage to the circuit board and components; if it is too slow, the solvent will not volatilize sufficiently, which will affect the welding quality.
SMT reflow insulation area
The second stage-the heat preservation stage, the main purpose is to stabilize the temperature of the PCB board and various components in the reflow furnace, so that the component temperature is consistent. Due to different component sizes, large components require more heat, slow heating, and small components heat up faster. Allow sufficient time in the insulation area to allow the temperature of the larger components to catch up with the smaller components, and allow the flux to fully evaporate. Avoid air bubbles during welding. At the end of the insulation section, the oxides on the pads, solder balls and component pins are removed by the flux, and the temperature of the entire circuit board has reached equilibrium. Tips from the editor of Topco: All components should have the same temperature at the end of this section, otherwise various soldering phenomena will occur due to uneven temperature in the reflow section.
Reflow soldering area
The temperature of the heater rises to the highest in the reflow area, and the temperature of the component rapidly rises to the highest temperature. In the reflow street section, the peak soldering temperature varies with the solder paste used. The peak temperature is generally 210-230 ° C. The reflow time should not be too long to prevent adverse effects on components and PCB, which may cause the circuit board to be baked. Jiao and so on.
Reflow cooling zone
In the final stage, the temperature is cooled below the freezing point of the solder paste to solidify the solder joint. The faster the cooling rate, the better the welding effect. If the cooling rate is too slow, excessive eutectic metal compounds will be produced, and large grain structures will easily occur at the welding point, which will reduce the strength of the welding point. The cooling rate in the cooling zone is generally about 4 ° C / S, and the temperature will be cooled to 75 ° C. .
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