Understanding Furnace Temperature in SMT Reflow Soldering
When operating an SMT reflow soldering furnace, the temperature displayed is actually the temperature of the hot air inside the furnace, not the temperature of the PCB or the heating element. To effectively set the furnace temperature, it is crucial to grasp two fundamental laws of heat transfer:
- If the PCB temperature is lower than the furnace temperature, the circuit board will heat up. Conversely, if the PCB temperature is higher, it will cool down. When both temperatures are equal, no heat exchange occurs.
- A larger temperature difference between the furnace and the SMT circuit board results in faster temperature changes on the board.
The setting of furnace temperature typically begins with determining the chain speed, followed by temperature adjustment. A slower chain speed allows for a lower furnace temperature, enabling thermal equilibrium over a longer period. Conversely, a higher furnace temperature may be needed for densely populated PCBs or larger components requiring more heat. It’s important to note that the adjustment range for chain speed is generally limited by the process time and total length of the temperature zone in the reflow soldering furnace.
Temperature setting involves a process of setting, measuring, and adjusting, with a focus on the temperature curve. Temperature measurement methods fall into two categories: contact and non-contact. In reflow soldering, thermocouples are commonly used for contact temperature measurement, offering simplicity, reliability, and high accuracy. Non-contact temperature measurement, based on thermal radiation principles, eliminates the need for direct contact with the measured medium, providing a wider temperature range and faster response times.
