How to Choose and Set Up Induction Soldering Equipment

Soldering joins two metals with a filler that melts below 450 °C (840 °F), while brazing uses fillers above that line. That threshold decides which process belongs on which joint, so thin wires, cable shoes, PCB end connectors, and copper tube assemblies sit in the soldering range while thick structural joints move into brazing.

The heat source matters as much as the filler, and induction wins where the joint count is high and heat has to stay local.

With a torch, the operator controls heat by eye, while induction repeats the same power and time on every cycle, so the joint passing at nine in the morning still passes at five.

Every solder alloy has a working window, and guessing costs parts. Tin-lead eutectic melts at 183 °C, tin-silver-copper families flow near 217 °C to 220 °C, and lead-free grades sit in a similar band. You need superheat so the filler wets both surfaces, without so much that flux burns off before the joint forms.

Melting points do not set a recipe on their own. A thermocouple on a scrap part shows what the work actually reaches, and that reading is what a recipe should be built around.

Alloy choice deserves its own decision. Tin-lead stays easiest to run, tin-silver and tin-copper grades answer lead-free rules and higher service temperatures, and the flux chemistry has to suit both the alloy and the base metal.

Frequency decides how shallow the heat sits. Ultra-high frequency units run from 100 kHz to 1 MHz and concentrate energy in a thin surface layer, which suits fine wire and small connectors. High frequency covers 10 kHz to 100 kHz for mid-size parts, and medium frequency handles heavier sections at 1 kHz to 10 kHz.

The 6KW ultra high frequency induction brazing machine we build runs at 800 kHz from a single-phase 220 V supply at 25 A, and it joins tin, silver, and copper on wire as fine as 0.1 mm. That is the class to reach for when the joint is measured in millimeters.

Those rows are starting points rather than datasheet values, because part mass, coupling distance, and coil shape shift the answer, which is why we run a sample before quoting.

The coil is the only part of the system that touches the process, so it earns the most attention. A single turn couples tightly and heats small parts in a second or two, while a multi-turn coil spreads the field along a longer joint.

Coupling distance behaves like a volume control, since a closer coil heats faster and a wider gap spreads the heat. On repeating work, the coil should sit in a fixture so that distance never changes. Custom coils shaped to one joint do more for consistency than any tuning at the panel.

Access matters too, since a split or hairpin coil reaches joints that a closed loop cannot, which happens on tube assemblies fixed in a frame.

Cold joints come from three causes, and each has a control. The part never reached flow temperature, the filler did not wet the surface, or the joint moved while the solder solidified. Induction answers the first because heat is generated inside the metal instead of delivered from outside.

Time and power settings hold the cycle, yet position holds repeatability. Fix the coil and the part, and the heating curve stops drifting between shifts.

Temperature feedback closes the loop. A pyrometer reading the joint lets the controller stop on temperature rather than on time, which matters when incoming parts vary in mass. On sensitive assemblies, a shielding gas keeps the surface clean enough to wet without aggressive flux. Where a part needs a brazed joint instead of a soldered one, the physics changes.

Looking at soldering defects across a production batch can help identify problems with the heating process. If similar defects keep appearing, it’s worth checking the induction coil position, fixture alignment, and heating settings before making further adjustments. Coil design and operating frequency also affect how heat is distributed across the joint.