Considerations For Choosing a Selective Soldering Process
Selective soldering has become a crucial process in electronics manufacturing, automating the soldering of assemblies that would otherwise require hand soldering. When selecting a selective soldering machine, several parameters need to be considered to ensure an effective and efficient soldering process. In this blog post, we will explore the key factors that should be taken into account when choosing a selective soldering process.
PCB Size: The size of the PCB being processed plays a significant role in machine selection. Smaller PCBs can be processed using compact machines with the option of dual conveyors to increase throughput. Larger PCBs may require in-line machines with board handling capabilities for higher volume production.
Floor Space: The available floor space must be considered when selecting a selective soldering machine. Machines range in size from compact units to larger in-line systems, and the available space should align with the chosen machine’s dimensions.
Maintenance: The level of maintenance required can vary based on the technology employed within the solder pot. Machines using impellers to drive the solder may generate more dross, requiring regular removal. Opting for machines with electromagnets to drive the solder reduces maintenance needs and ensures a more stable wave for accurate soldering.
Solder Type: Selective soldering machines can accommodate various solder alloys. While some companies still use leaded solder, most prefer lead-free alloys. The pot temperature typically ranges between 270°C and 300°C for lead-free solder, although newer alloys are available that operate at lower temperatures, around 250°C.
Solder Pots: To optimise the selective soldering process, manufacturers often offer the option to add solder modules to the system. Machines may use multiple solder pots per module, allowing different solder alloys, variable Z-axis configurations, and variable Y-axis positions for simultaneous soldering of multiple PCBs.
Nozzles: The versatility of selective soldering lies in its ability to reach areas that are challenging to solder manually. A wide range of nozzles is available, varying in diameter and length. It’s important to consider the process time and nozzle wear when selecting the appropriate size and type of nozzle.
Nitrogen Supply: To prevent oxide formation and maintain solder quality, a high-purity nitrogen atmosphere is required. Nitrogen can be supplied through pressurised bottles, liquid nitrogen tanks, or locally generated sources. While each method has associated costs and safety considerations, locally generated nitrogen is often preferred due to its long-term cost-effectiveness and reduced safety concerns.
Flux: Flux is essential for cleaning metal surfaces and creating acceptable solder joints. Different flux types are available, categorised based on activity, solids content, and material type. Low-solid/no-clean fluxes are commonly used in selective soldering processes. Sufficient flux application is necessary for optimal solder hole fill and reliable soldering.
Pre-heating: The preheating stage serves several purposes, including activating and drying the flux, facilitating solder flow, minimising the effect of large copper planes, and reducing the risk of thermal shock to components. Infra-red preheating is often used, and closed-loop control with a pyrometer ensures accurate temperature control.
PCB Handling: For larger volume production using in-line selective soldering systems, PCB handling becomes essential to manage the flow of assemblies. Depending on the requirements, a combination of magazine PCB line loaders and unloaders can be integrated into the process.
Machine Options: Various machine options are available to enhance process repeatability, simplify machine operation, and improve overall efficiency. These options include visual inspection modules, automatic conveyor width adjustment, automatic wave height checks, automatic nozzle cleaning, automatic solder level checks, PCB warp compensation, and closed-loop control of heating elements.
Machine Configuration: The type and mix of assemblies being processed dictate the machine configuration. High-volume, low-mix production may prioritise speed, while low-volume, high-mix production requires flexibility. Choosing a machine configuration that aligns with the specific production requirements is crucial.
In conclusion, by carefully considering these parameters, electronics manufacturers can achieve accurate, repeatable, and efficient soldering processes, resulting in high-quality assemblies and a positive return on investment. Gelco EMS, as a trusted leader in selective soldering processes, offers tailored solutions that ensure accuracy, repeatability, and efficiency for electronics manufacturers. With advanced technology, expertise, and a commitment to excellence, Gelco EMS delivers high-quality assemblies and a positive return on investment. Choose Gelco EMS for reliable and optimised selective solder.