About the setting procedure of the temperature curve
The first parameter to consider when making the temperature curve is the speed setting of the conveyor belt, which will determine the time that the PCB spends in the heating channel. Typical solder paste manufacturing factory parameters require a heating curve of 3min~4min. Divide the total heating channel length by the total heating temperature sensing time, which is the accurate conveyor speed. For example, when the solder paste requires a heating time of 4 minutes and a heating channel length of 6 inches is used, the conveyor belt speed is 1.5 feet/min, which is 18 inches/min. (1 foot = 0.3048m, 1 inch = 0.0254m).
Then determine the temperature settings for each zone. It is important to understand that the actual zone temperature is not necessarily the displayed temperature of the zone. The displayed temperature only represents the temperature of the thermocouple in the zone. If the thermocouple is closer to the heating source, the displayed temperature will be higher than the interval temperature. The closer the thermocouple is to the direct channel of the PCB, the more the displayed temperature will reflect the zone temperature. . It is wise to consult the manufacturer of the reflow soldering furnace to understand the relationship between the displayed temperature and the actual temperature in the range. What is considered here is the zone temperature rather than the displayed temperature. Table 5.11 lists the interval temperature settings used for typical PCB assembly reflow.
SMT patch processing 3
After the speed and temperature are determined, they must be input to the furnace controller. Other parameters that need to be adjusted include cooling fan speed, forced air impulse, and inert gas flow. Once all the parameters are entered, start the machine, and when the furnace is stable (that is, all the actual displayed temperatures are close to meeting the set parameters), the curve can be started. The next step is to place the PCB on the conveyor belt and trigger the thermometer to start recording data. For convenience, some thermometers include a trigger function to automatically start the thermometer at a relatively low temperature. The typical starting temperature is slightly higher than the human body temperature of 37X3 (98.6°F). For example, the automatic trigger of 38P (100T) allows the thermometer to start working almost when the PCB is put on the conveyor belt and enters the furnace, so that the thermocouple does not trigger falsely when it is handled by human hands. Once the initial temperature profile is generated, it can be compared with the ideal profile recommended by the solder paste manufacturer.