The preheating zone generally refers to an area that rises from room temperature to about 150 °C. In this area, the SMA rises steadily. In the preheating zone, some of the solvent in the solder paste can be volatilized in time, and the components, especially the IC device, slowly heat up to accommodate the subsequent high temperatures. However, due to the different size of the components on the SMA surface, the temperature is uneven, and the rate of temperature rise in the preheating zone is usually controlled at 1.5 ° C - 3 ° C / sec. If the temperature rises too fast, the micro-cracks of the ceramic capacitor, the deformation of the PCB, and the damage of the IC chip due to the thermal stress, and the solvent volatilization in the solder paste is too fast, resulting in the occurrence of flying beads. The preheating zone of the furnace generally occupies 1/4-1/3 of the length of the heating channel, and the residence time is calculated as follows: the ambient temperature is set to 25 ° C, and if the heating rate is calculated at 3 ° C / sec (150-25) / 3 For 42 sec, if the heating rate is calculated at 1.5 ° C / sec, then (150-25) / 1.5 is 85 sec. It is usually best to adjust the time according to the difference in the size of the components to control the heating rate below 2 ° C / sec.
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