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Slightly Unusual, But Necessary, Soldering Methods
November 26, 2013 | Pete Starkey, I-Connect007Estimated reading time: 2 minutes
“Most of us use conventional wave or reflow soldering techniques and such automated soldering technologies apply to the vast majority of soldered products. But what if you have a soldering requirement that needs a different approach? For example, you may need to solder battery terminations inside a housing in high volume or you may need to solder a connection without damaging a temperature sensitive device or plastic housing nearby. Conventional methods will probably not apply.”
This was Altus Group's Sales and Applications Manager and long-standing stalwart of the SMART Group Technical Committee Peter Grundy’s introduction to an extremely informative SMART Group webinar. The session was moderated by SMART Group Technical Director Bob Willis and was sub-titled “Joining electronic items beyond the scope of reflow and wave soldering.” The webinar set out to investigate alternative soldering techniques including light-beam, laser, inductive-coil, robotic soldering irons, and high temperature inert atmosphere systems. Grundy showed many examples of specific soldering challenges, explained how they could be tackled, and suggested what methods were best suited.
Light-beam soldering is characterised by contactless low-energy heating with precise power control, and is often used for rework as well as for production. Typical applications are the secondary mounting of temperature-sensitive LEDs, soldering flex cables to PCBs, and soldering components onto polyester-based printed electronics. A variation is light-beam-line soldering, which enables multiple joints to be made simultaneously.
Inductive-coil soldering wi another contactless heating technique, capable of operation at high power density, useful for soldering inside housings too deep for light-beam, or soldering cable terminations without damage to insulation or temperature-sensitive substrates, or, alternatively, for soldering on to high thermal mass substrates to overcome heat-sinking effects. Only metallic elements near the inductor and with chosen frequency characteristics become heated. Solder can be applied as paste, preform, or wire, and some systems have automatic wire feed.
Laser soldering, using 30 to 60-Watt diode laser sources, gives contactless heating with the ability to focus extremely accurately with high power density, making tiny joints possible. It can be used with solder paste or wire feed. A typical application is to solder in areas inaccessible to light-beam or inductive-coil.
Robotically-controlled hot-iron soldering offers single-point soldering with tin-lead or lead-free solder wire feed and automatic tip cleaning. Joints can be formed more quickly than with inductive-coil. Even quicker are microflame techniques, capable of very high temperatures, and good for metallic applications where temperature is not an issue.
High temperature reflow under vacuum is a means of achieving void-free soldering for power electronics applications, and can also be used with inert gas. Heating is by conduction and temperatures up to 450°C are possible, although the whole product is heated so the process cannot be used selectively.
Grundy explained that all of the processes described are capable of being automated and can be built into work-cells or operated as stand-alone units.
His presentation raised many questions, which gave him and Bob Willis the opportunity to respond with a wealth of intelligent and practical advice on individual soldering problems. Asked what were his opinions of what techniques would dominate the future, Grundy believed that all the processes he mentioned would continue to be used, but laser soldering would be progressively replaced by light-beam, and the use inductive-coil soldering would remain about the same.