About reflow soldering temperature curve and its settings
In the limited welding time, the temperature of the welded product cannot reach thermal equilibrium with the heat source, so infrared and convection reflow welding is a non-equilibrium process. Therefore, the reflow soldering process parameter settings must be suitable for each product design to ensure that the specific PCB component obtains the optimal time/temperature curve. Early reflow soldering furnaces with radiation-based heat transfer have been gradually replaced by modern infrared convection-combined heat transfer reflow soldering furnaces. This kind of reflow soldering can reach a higher level of heat exchange and reduce the temperature profile between different products and the difference in temperature distribution within a single product, thereby enhancing the applicable scope of the reflow soldering process. However, the rapid development of lead-free soldering process has reduced the scope of application of the process, so attention should be paid to the reflow temperature curve optimization technology.
The common method of establishing the reflow soldering temperature curve is to paste a certain number of thermocouples on the assembled product samples. The selection of the thermocouple position is determined based on the comprehensive consideration of the comparison of similar products and component packaging forms and the comprehensive consideration of experience. Next, the product passes through the reflow oven at the initial temperature setting, while the data logger records the temperature measured by the thermocouple. Then, modify the initial process parameter settings until the desired curve is obtained. Before obtaining the required temperature profile with this method, new product samples and necessary test tools must be used for initial reflow soldering process experiments.
The increase in assembly density and the decrease in the size of components and their pin spacing make the welding process of SMA more difficult, the setting range of welding temperature curve parameters narrows, and welding quality problems are extremely prone to occur. The correct design of the welding process, especially the accurate setting of the welding temperature curve, has become one of the key contents to ensure the quality of SMA assembly.
