Ensure Proper Dwell Time in Wave Soldering for SMT Assembly
The soldering process used in electronic assemblies has a significant impact on the long-term reliability of your finished product. Many of the factors that determine whether a solder joint is strong or weak are not immediately obvious, but will influence the performance and longevity of your finished assembly for years to come. Wave soldering is one of the most commonly used techniques to produce solder joints, and ensuring proper dwell time is critical in preventing common wave defects from occurring.
Modern wave soldering machines have automated the entire soldering process, ensuring accurate and consistent results. This method involves passing a PCB assembly over a wave of molten solder, which ensures the correct placement and connection between components.
As the conveyor system slowly moves the assembly over the molten solder, the components are exposed to the wave of heat in an evenly distributed manner. If the proper preheat temperature and profile is used, this method provides superior soldering quality and consistency for both through-hole and surface mount smt assembly components.
The most common issue seen in wave soldering is bridging, where solder bridges are created between conductors. This can be caused by a number of factors including component, design, tooling and the soldering process. However, a simple fix to this defect is by ensuring the preheat temperature and profile are matched with your specific component type and design.
How to Ensure Proper Dwell Time in Wave Soldering for SMT Assembly
Another common issue is component lifting, most often experienced on axial and radial leads. This can be avoided by proper component lead pre-forming and pallet hold downs which mechanically hold the components in place. Using a longer preheat duration and ensuring the optimum profile are also helpful in eliminating this problem.
Finally, thermal stress warpage can occur during the wave soldering process due to the high temperatures involved. This can be minimized by ensuring the appropriate PCB design is selected for use with this soldering method, utilizing the right type of pallets and hold downs, as well as preheating and cooling techniques that take into account the assembly’s thermal properties.
Insufficient preheat and profile temperatures are the leading cause of this issue, especially when a large portion of the board is covered by small SMTs. Insufficient pre-heat prevents the solder from coming to its optimal melting point, which can lead to a poor soldering outcome. This can be addressed by ensuring the preheat temperature and optimum profile are set for your specific assembly, or by using a hot-gas reflow system, which dispenses solder at the point of contact and heats it to its optimal melting point. This can be much slower than the wave soldering process, but can improve the quality of your final assembly. This type of reflow soldering is quickly becoming the preferred soldering technique for electronic manufacturers. FS Technology can provide both wave and reflow solutions for your next project, so be sure to reach out for more information.