Furnace Temperature Profile Design and Solutions

Furnace temperature profile design is a complex and critical process, which directly affects product quality and production efficiency. In the design of the temperature curve, the following aspects need to be noted:

1. the encapsulation body characteristics limitations Thermal capacity: the thermal capacity of the encapsulation body as well as the device carrier board fixtures determine the ability to absorb and store heat. For large heat capacity of the package body (such as copper substrate / thick fixture / large substrate chip, etc.), even if there is no limitations on the rate of warming, to reach a higher peak temperature will take longer. Heated area and thermal conductivity: the heated area affects the rate of heat absorption, while the thermal conductivity determines the rate of heat transfer inside the package. These two factors together determine the temperature response of the package in the heating process.

2.  the process and equipment limitations Warming rate limitations: From the process point of view, the rate of warming can not be too fast, in order to avoid excessive thermal stress and damage to the package. This limits the possibility of reaching high temperatures in a short period of time. Equipment Limitations: Heating equipment such as reflow ovens are designed to have a suitable temperature range and chain speed range. These constraints make it difficult to achieve a specific temperature profile on existing equipment.

3. the challenges of the temperature profile design Target peak temperature and time conflicts: in a limited time (such as within 20s), to achieve a high peak temperature (such as not more than 230 ℃) for some packages is not possible, especially when their heat capacity is large, even if there is no limitations on the rate of heating, to achieve a certain peak temperature, there must be enough time, the most typical significance of the example is the soldering of copper substrates. This is shown in the figure below:

Difference between oven temperature and PCB target peak temperature: The difference between oven temperature and PCB target peak temperature may lead to uneven temperature distribution inside and outside the component package. Even if the test curve shows a temperature rise rate that meets the requirements, it may not be possible to ensure that the temperature inside the package also meets the requirements.

4. Solution Optimise the design of the encapsulant: If possible, consider optimising the design of the encapsulant to reduce its heat capacity or improve its thermal conductivity. Adjustment of process parameters: Within the range allowed by the equipment, try to adjust the process parameters (e.g. preheating temperature, holding time, etc.) to better meet the temperature profile. Use advanced heating equipment: If the existing equipment cannot meet the requirements, consider using advanced heating equipment with higher heating rates and wider temperature ranges. Make use of the analogue temperature measurement function: Use the analogue temperature measurement function of the pyrometer for virtual setting and debugging to improve the setting efficiency. Note, however, that simulation results may differ from actual conditions, so actual testing is required to verify. Consider alternatives: If it is really impossible to achieve the target temperature profile under the existing conditions, you can consider using alternative solutions, such as changing the welding material, adjusting the structure of the package body.

5. Summary

Debugging the temperature profile is a complex process that requires comprehensive consideration of a number of factors, such as the characteristics of the package body, process and equipment limitations. When encountering difficulties, the causes should be carefully analysed and multiple solutions should be tried. At the same time, it is also necessary to recognise that in some cases it may not be possible to fully meet all the requirements, and compromises need to be made within an acceptable range.