Professional Soldering 101
If you look inside virtually any piece of electronic equipment, you should find at least one circuit board. Look closely at the circuit board, and you may notice solder, a soft metallic substance that appears to glue things together. Solder helps secure electronic components to circuit boards, but more importantly, it allows electrical signals to flow between components.
In a way, solder is what glues our entire electronic world together.
Solder and Flux
Working with solder means working with flux. Bare metal develops surface oxidization that repels molten solder—preventing it from flowing neatly and taking hold. When molten solder is laid down, adding flux clears the oxidation to ensure the solder flows and sticks. Once the solder cools, any remaining flux residue should be cleaned.
Traditional flux is a hard rosin paste, often embedded in the solder itself. Water-based fluxes and special no-clean fluxes which leave very little residue are also common.
Types of Solder Alloys
The two broad categories of electronics solder alloys are leaded and lead-free.
Until recently, most solder was a simple alloy made from tin and lead. Lead works well in solder because it has a low melting point, flows nicely, and is malleable. Lead is also toxic.
The electronics industry is transitioning to lead-free solder alloys made from less harmful blends of tin, silver, copper, and nickel. Different types of metals in different amounts produce alloys with different melting points, so understanding the melting point of the solder alloy you use and maintaining precise temperature control are the most critical parts of electronics soldering.
With an understanding of the chemical processes and metal alloys associated with solder and flux, the next question is how to apply solder to electronic components.
Solder Wire and Soldering Stations
Solder wire uses the familiar process involving a skilled professional wielding a handpiece with a hot iron tip. The tip is used to heat up the components to be soldered. As solder wire is applied, it quickly melts and flows into position. In the electronics industry, solder stations are ideal when precision is more important than speed, such as prototyping, quality control, rework, or repair. The process is too slow for mass production.
Solder Paste and Reflow Soldering
Solder paste contains powdered solder and flux which can be applied much like glue, loosely securing electronic components to a circuit board. When heated in an oven, the now-molten solder flows into place and leaves a firm solder joint once cooled. This method, called reflow soldering, is easier to mechanize and automate on a production line but can also be prepared and processed by hand.
Solder Bars and Wave Soldering
As the name suggests, solder bars are solid bars of solder which are melted in a pot. Flux-treated components are dipped into these pots of molten solder—or skimmed across the surface of a small wave produced by a pump in a process called wave soldering. Wave soldering is ideal for producing circuit boards with through-hole solder connections.
Smarter, Safer Soldering
Caution: High Temperature
Soldering means high temperatures and burn risks. Soldering stations should have a stand where the handpiece can be holstered when not in use. Use caution near active soldering stations, reflow ovens, and anywhere molten solder is exposed. Always wear Personal Protective Equipment (PPE) when appropriate.
Danger: Toxic Fumes
Soldering produces toxic fumes, mostly from vaporized flux. People exposed to solder fumes for extended periods have reported nosebleeds, bronchitis, and respiratory problems. Most fumes from your soldering work will come from vaporized flux.
When soldering, make sure you do it in a well-ventilated area, which typically means your facility should have ventilation hoods. You can also use a fume extractor at your workstation, which does not require professional HVAC installation.
Attention: Electrostatic Sensitive Devices
Remember the safety of the work itself. Circuit boards can become damaged by electrostatic discharge (ESD). There are lots of ways to protect against ESD. For example, you can wear an antistatic wrist strap, use an ESD protective mat and ionizer, protect sensitive items in antistatic bags, ground yourself with heel grounders, and more.
The Cool Down
Soldering is a critical process that assures PCBs work correctly so that the electronics that power our modern world can function.
Visit TestEquity to explore the largest inventory of solder and electronics production supplies in the industry or contact their staff for brand-agnostic product expertise.