Thermal Shock in Wave Soldering


#1

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.


#2

To add to this, excess solder placed on a components pad will produce more heat transfer to a component when the solder melts. Using just enough solder with the correct wave process profile to obtain a proper solder fillet on the component may be crucial. If there is too much solder placed on the surface mount pads, this can also attribute to thermal shock to the component. You may want to check the thickness of the solder paste stencil you are using and make sure too much solder is not being placed.