Thermal Profiling – Importance in Reflow Ovens

Reflow oven profiling can be a tedious, expensive, and time-consuming process. Reflow is a single-step procedure. If the oven is built correctly, planned, and maintained, the entire assembly will be subjected to the same oven settings regardless of where a thermal couple (TC) is positioned. The thermal inertia of the various heating zones in an oven with a conveyor belt does not affect the PCB because it physically moves through them. Because a change in the parameter for one zone often affects the characteristics of the other zones, calibrating a profile for a conveyor belt oven can be challenging. As the actual temperature curve deviates
from the theoretical temperature profile. Hence, it is crucial to anticipate the effect of thermal inertia on the temperature profile.

An ideal soldering process temperature profile has four zones: –

1. Preheat: Preheating is done to get the flux going and to let the solvents evaporate.
2. Soak: All board areas and component areas are heated to the same temperature in the soak zone. Components do not heat up at the same rate due to variations in thermal inertia;this is particularly true for infrared heating because components absorb infrared energy unevenly.
3. Reflow Zone: In the Reflow zone, solder paste wets the pads and component pins better and merges with the copper better when it is hotter; better joins are made when the reflow zone’s peak temperature is at least 25 °C above TAL(temperature above liquidus).
4. Cool Zone: Cooling via natural convection is sufficient although cooling rate must not induce thermal stress on the soldered joints.

The ideal solder profile should be given by the soldering paste manufacturer. Hence, It is vital to get the actual temperature profile of the soldering process in the drying oven. Often temperature of the material is monitored via the heat zone temperature of the dryer. However,this assumption of the solder temperature from the heat zone is wrong. Due to convection, radiation, and some heat losses, the actual temperature of the solder jointcomponents on the PCBs varies with the dryer’s temperature, which will lead to inaccurate monitoring of the soldering process resulting in poor quality of soldered joints.

Solution Provided by Tempsens:

These problems can be resolved if we closely monitor the curing temperature for a specific time interval. Here, comes the role of our indigenously designed and developed in India Smartack 10 data logger and Thermal barriers. With these temperature profiling systems, one can closely monitor and optimize their soldering process duration and temperature. One can get a temperature profile of the soldering process by attaching a thermocouple to the PCBs. The data logger needs protection from the prevailing temperature in the drying oven, which is done by keeping the data logger in the thermal barrier.

After the completion of the process, one can download the data from the data logger and convert it to meaningful information in SmartLog Software developed by TEMPSENS. After analyzing the information one can take quick and accurate decisions to solve the Soldering problems leading to increased quality and productivity.

For more details, visit at https://tempsens.com/catalog/thermal-profiling-system.html