Each preheating process must be checked physico-chemically in holistic coordination with the neighbouring components, soldering surfaces, heat sinks, solder penetration and quality requirements for the process sequence, as each heating process can trigger an additional ageing process for the assembly to be processed. It is therefore important to pay just as much attention to this process as to the actual soldering process. For this reason, preheating is always integrated into our evaluations for customer projects.
Depending on the duration and level of preheating, three-dimensional mechanical stress states, oxidation surfaces and thus possible pre-damage to the process environment occur in the assembly. Basically, preheating has the task of preparing the environment to be soldered for the actual soldering process and thus also the temperature jump from room temperature to 120 °C and to the soldering process temperature of e.g. typically 300 °C. To protect the assemblies, the typical preheating temperature gradient of approx. 3 °C /sec must be observed.
Does too high a preheating temperature affect the flux?
The peaks of the preheating temperature should also not destroy the flux characteristics. This is because only the balanced interaction of process expertise, flux preheating and solder processing with the thermal characteristics of the assembly reduces or prevents unnecessary stress factors on the overall assembly.
What are the effects of too long a preheating time?
A preheating time that is too long reduces the reaction of the solids in the flux and thus reduces the overall effect of the fluxing process. Increased stress due to preheating can also be caused by thermal pre-processes such as reflow soldering.
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