The Role of Prefluxing in Wave Soldering for PCB Assembly

Prefluxing in Wave Soldering for PCB Assembly

As PCBs became more complex, adding metal inside holes (“plated through-holes”) allowed using both sides of the board for circuitry. Eventually, printing on one side was replaced by laminating the board together. This was a much more practical solution, and also allowed the use of both conductive copper pads and soldering irons. The soldering process had to be adapted accordingly.

The first wave soldering machines used plates (“baffles”) to shape a narrow wave of melted solder. The baffles were positioned so that the front and back of the solder wave formed parallel to each other. The assembled PCB was dipped in a pan of flux and placed on a conveyor which moved it across the solder wave. The conveyor was often tilted (6deg was common) to help the assembly leave the solder wave at the flat crest of the wave where solder would move most slowly.

This worked fairly well and was very efficient. But there were problems. As the solder cooled it would often form oxides which impeded electrical contact between components. Solder globs frequently formed in places where they were not supposed to. Solder bridging shorts were also a problem. These problems were resolved by modifying the machine to stabilize the wave and reduce its speed, which helped reduce oxidation and entrapment. Also, high concentrations of rosin in the liquid flux were introduced to keep the solder wetting better and eliminate oxides.

As the machine was improved and soldering technology continued to evolve, other problems began to appear. For example, shadowing of the solder wave by heat-sensitive parts resulted in long, dark lines on the soldered side of the PCB. This was resolved by a combination of factors including the choice of heat-sensitive materials and optimizing component placement to allow passing the components through the wave soldering process only once.

The Role of Prefluxing in Wave Soldering for PCB Assembly

The choice of preheat temperatures and preheating time is another important factor in the quality of a finished product. Too high a temperature can cause mechanical stress on the PCB, while too low a temperature may not be sufficient to activate the flux and melt the solder paste.

Optimal placement of components is key for successful pcb assembly near me. This will not only make the PCB easier to assemble, but will also produce a more durable and reliable product. The choice of a qualified and experienced EMS provider is also crucial to the success of the project.

The best way to ensure that the quality of your Printed Circuit Board Assembly is optimal is to choose an experienced and reliable EMS provider, like Green Circuits, which specializes in quick-turn PCB assembly and HMLV and HVLM production services. Contact us today to discuss your upcoming projects. We look forward to working with you.

Preheating helps to minimize thermal gradients, which are the temperature differences across the PCB and its components. Sudden temperature changes can cause mechanical stress due to the different expansion rates of materials, leading to warping, cracking, or component misalignment. By gradually increasing the temperature, preheating ensures a more uniform thermal distribution, reducing the risk of thermal shock and mechanical stress.