Dwell Time in Wave Soldering for Board Assembly

The success of a printed circuit board (PCB) assembly depends on the quality and reliability of its solder joints. There are many factors that contribute to this, from proper component placement to ensuring a high-quality wave or reflow soldering process. Both processes are critical for achieving a solid connection between components, but each has its own unique set of challenges. The most important of these is controlling the length of time that a circuit board is exposed to heat during the soldering process. This is particularly challenging for reflow soldering, which requires careful control of the preheat, soak, reflow and cooling phases to avoid thermal shock or overheating, which can lead to insufficient solder and poor connections.

When a board assembly is placed in the soldering machine, it will be subjected to a preheating phase known as a thermal soaking. During this period, the PCB and components are heated to a specified temperature. While the exact temperature will depend on the type of reflow process and the board’s configuration, it should be above the melting point of solder so that it can melt during the reflow stage. This step also helps eliminate solvents and volatile material in the solder paste, activates the flux and ensures that all areas of the PCB are properly heated.

Once the preheat is complete, the soldering machine will introduce a wave of hot solder to the PCB. The duration and height of this wave will depend on the type of reflow system used. The wave is designed to provide a uniform distribution of heat throughout the PCB, and this even heating can help prevent thermal stress from damaging components. As the solder reaches a high temperature, it will begin to melt and form a metallurgical bond with the connections on the PCB. The temperature of the solder will also depend on the reflow system and the type of paste being used, but it is typically in the range of 260-250°C.

How to Ensure Proper Dwell Time in Wave Soldering for Board Assembly

After the solder has melted, the circuit board will enter a soak or dwell phase where it remains at the reflow temperature for a short period of time. This step is essential for the reflow process because it allows the solder to fully saturate the connections and reduce the likelihood of defects such as tombstoning or insufficient soldering.

Insufficient dwell time can be caused by a number of things, from contaminants to improper reflow chemistry. A thorough inspection of the reflow process can identify these issues and help you make corrections to improve the quality of your boards.

If you are struggling with soldering defects in your production line, it’s important to contact a trusted manufacturer that can assist you. TRW’s expert engineers can help you optimize your wave and reflow processes to minimize defects and maximize the life of your boards. We use the latest tools and technologies to offer our customers unparalleled support and quality service. Our dedicated team of experts can provide guidance for both the initial setup and ongoing maintenance of your reflow or wave soldering equipment.