What Role Does Flux Density Play in Wave Soldering?

Flux Density Play in Wave Soldering

As a long-established soldering process, wave soldering provides certain advantages over reflow. However, it can also suffer from problems if not carefully controlled. One problem occurs when too much flux is used. Another is oxidation of the PCB or component leads. These oxidations can prevent the solder from wetting to them and forming a strong joint.

To address these issues, a high level of sensitivity is required to maintain quality. A quality inspection of the PCBs can identify these defects and fix them before they go out for use. This allows the manufacturer to keep costs down and produce more efficient electronic devices.

The problem is compounded when the assembly contains surface-mounted components (SMDs). Using glue to hold them down to the boards meant that there was more equipment and handling. Plus, the adhesives themselves needed to be heated and cured, adding more steps to the process.

Moreover, the adhesives often degraded over time and needed to be replaced regularly. This added cost and extra handling, increasing production times. A better solution was found with a process called “wave-paste” (wave applied solder paste). This eliminated the need for glue and shortened the assembly process.

But, there were still concerns that the wade-paste method did not meet the quality requirements of some customers. For example, some customers require the use of no-clean or water-soluble fluxes. Others have strict environmental policies that require no lead in the solder.

What Role Does Flux Density Play in Wave Soldering?

In addition to these problems, there were other issues with the wave-paste process itself. For example, the PCBs had to be preheated before the wave-paste process. This heat can cause thermal stress that can warp the board and damage sensitive parts. In addition, the excess heat can contaminate other surfaces of the PCB and create defects.

For this reason, it was necessary to make some adjustments to the wave-paste process to overcome these problems. One major issue was the need to add more heat to the puddle to drive off solvents and activate the flux (to remove oxidation from the surfaces to be soldered).

Other adjustments included changing the size of the puddle and adding baffles to reduce turbulence. In this way, the puddle was kept more flat and the velocity of the solder reduced so that it would drain easily into the wave and not cling to the assembly. Finally, the conveyor was tilted (6deg was common) to improve the way it sat on the wave crest and allowed solder to flow onto it more easily.

The most important factor in ensuring good wave-paste results is the quality of the flux. The best fluxes are low rosin concentration and contain other additives that improve the way it cleans the metal surfaces of the pcb assembly near me and component leads, preventing them from becoming too contaminated with oxides. If these are not removed properly, solder will not wet to the metals and, consequently, bridging can occur. This is a major contributor to poor quality in wave soldering.

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