The Role of Flux Density in Wave Soldering for Board Assembly
Flux Density in Wave Soldering for Board Assembly
The right soldering process is essential for assembling a board. It ensures a strong bond and prevents corrosion. However, it’s important to know that the smallest details can impact the outcome of the finished product. A jiggling component, a dangling coil or a loose screw are just a few examples of potential defects. These can be easily avoided by selecting the correct process. Sierra Circuits uses a variety of inspection techniques, including AOI (Automated Optical Inspection) and X-ray inspection to detect the most minor errors.
Before a PCB goes through the reflow oven, it’s transported on a conveyor belt to different zones with specific temperature profiles. These include preheat, soak and reflow zones. The preheat zone heats the assembly to the ideal temperature and evaporates any moisture in the components. This also activates the flux in the solder paste. The soak zone maintains the assembly at the proper temperature for a set period, which ensures that any areas of the PCB that weren’t heated properly due to shadowing are brought up to the optimal temperature. This step is also known as thermal soaking.
In the reflow zone, the flux breaks down any oxides on the metal surfaces to promote good wetting. It also reduces surface tension at the metal junctions to facilitate a strong metallurgical bond. The type of flux used depends on the composition of the metals in the assembly. For example, some fluxes are designed for copper, while others are suitable for a wider range of applications. Some are designed to be low-activity, while others are more active and can remove larger amounts of oxidation.
The Role of Flux Density in Wave Soldering for Board Assembly
Once the reflow phase has ended, the assembly enters a cooling zone to minimize thermal shock and excessive intermetallic compounds. Cooling also helps the solder solidify and prevents stress on the components.
Flux density is another crucial factor in the wave soldering process. High flux density means the reflow flux can flow more easily and cover a greater area of the surface of the assembly, improving solder wetting. This can help eliminate problems with voiding, under-soldering, and shorting out at the joints.
The most common soldering methods use liquid or dry rosin-based flux. Both require rigorous cleaning and disposal procedures to avoid contamination of the board assembly. This process can be time-consuming and labor-intensive, especially in large production runs. It is also possible to use a no-clean flux, which doesn’t require the same level of cleanup. However, a no-clean flux may not be appropriate for sensitive through-hole components and might interfere with testing and conformal coating processes.
When choosing a CM, it’s important to choose one that follows environmental policies on the handling and application of solder and flux. A CM that follows strict guidelines will be able to provide consistent quality and reduce costs. Additionally, a CM that stores and handles their flux correctly will preserve its chemical properties over time. This is important because open containers of flux can degrade faster than those kept in airtight conditions.