Wave Soldering is a common soldering process during PCB assembly. It exposes components to considerable levels of heat and may cause a thermal shock. Thermal Shock occurs when a component structure absorbs excessive changes of temperature in a short time, often causing mechanical cracking. Multilayer Ceramic Capacitors (MLCC) are a commonly used part which are very prone to thermal shock.
Wave soldering requires the highest heat transfer rate and the largest temperature changes in a short period of time, which can easily cause visible and micro-cracks if any improper processing occurs. This micro crack can propagate through the component’s structure and may cause opens, intermittents or excessive leakage currents.
To minimize this issue, preheating in wave soldering is necessary to steadily bring up the components on PCB to the required temperature and avoid the rapid temperature changes that induce thermal shock. Each component has a soldering profile with a specified preheating area. Below as an example is the soldering profile of Kemet’s ArcShield Series X7R MLCC, which shows the preheating area.