How to Tin Litz Wire: 5 Methods and Why a Plain Iron Won't Cut It

Key terms

The five methods — overview

The methods work on different sizes and in different production settings. Below is a detailed look at each: temperatures, solders, fluxes, equipment, and common mistakes.

Why a plain iron won't tin litz wire

The fine copper wire in litz is coated with enamel. The basic current range in Russian magnet-wire production is polyurethane (ПЭВТЛ-1, ПЭВТЛ-2, self-fluxing), polyesterimide (ПЭТВ-2), polyesterimide-polyamide lacquer (ПЭТД-200), and polyimide (ПИ). In Western terms — polyurethane, polyester, polyamide-imide, polyimide. The insulation thickness is 5–15 microns on each side of the wire. Older vinyl-acetal enamels (ПЭВ-1, ПЭВ-2) are now hardly produced in series and show up only in repairs of Soviet-era equipment built to old design documentation.

Magnet-wire enamel is rated to withstand a working temperature of 105, 130, 155, 180, or 200 °C depending on the thermal class. It does not dissolve in most fluxes, is not broken down by rosin, and does not melt at the standard 320 °C soldering temperature used for electronic components. If you press an iron tip with ordinary flux against the end of litz wire, the solder may wet one or two strands right at the surface of the bundle — the ones that touched the tip and where the enamel was damaged during rewinding. The rest of the strands inside the bundle stay insulated.

A poor connection on litz wire is not a warning, it is essentially a design failure: there was no point in choosing litz otherwise. Litz wire is used to reduce losses from the skin effect and the proximity effect in coils operating at high frequencies. If current flows through only two strands out of a hundred, those two strands are overloaded, they heat up, they melt the neighboring insulation, and the coil fails within days or weeks of operation. You have to tin every strand of the bundle at once.

Method 1. Mechanical stripping

The enamel is removed physically: with a scalpel, P600–P1000 grit sandpaper, or a rotating nylon or steel brush. Each strand individually. After stripping, the litz wire is soldered like ordinary multi-strand wire — with ЛТИ-120 flux or rosin, using an ordinary 320 °C iron and ПОС 61 solder.

In industry this method is automated — the manufacturer Eraser Company in the US makes brush machines that strip enamel evenly from a wire bundle without damaging the copper. The Russian counterpart is the typical brush machines for stripping enamel from magnet wire used in coil-winding shops.

The method is applicable only to large constructions — litz wire with a small strand count (up to 7–10) and a single-wire diameter from 0.3 mm. This is typical for low-frequency applications or for single magnet wire such as ПЭТВ-2 with a diameter of 0.5–1.0 mm. On fine 0.071 or 0.1 mm wire, sandpaper grinds through the strand — copper cross-section is lost and the remnants tear during soldering. Nobody strips a hundred strands one by one with a scalpel under a loupe either — it is not economically justified.

The most common mistake with this method is trying to strip fine litz wire with a file or coarse sandpaper. Half the strands tear, the rest are damaged, and the connection comes out weak and uneven. Use this method only when every strand in the bundle is thicker than 0.3 mm.

Method 2. Active flux with phosphoric acid

The enamel dissolves or breaks down in active fluxes. On the Russian market the basic and most available option is the flux Ф-38Н per ОСТ 4Г 0.033.200. Composition: phosphoric acid, glycerol, ethylene glycol, diethylamine hydrochloride. The working temperature of maximum activity is 300–350 °C. At this temperature the flux reacts with the enamel and destroys it — and that is what sets an active flux apart from an ordinary rosin flux, which only removes oxides from the copper surface.

Procedure. The end of the litz wire is dipped in the flux for 3–5 seconds. Press the iron tip at 320–350 °C against the bundle and hold for 10–20 seconds. The enamel blackens and peels off, and the solder wets the copper across the whole cross-section. Immediately wash the solder joint with alcohol or water — Ф-38Н is corrosive and, on prolonged contact, causes additional corrosion. You cannot skip the cleaning.

Alternatives to Ф-38Н:

• ЛТИ-120 — milder, based on rosin (~24 %) and alcohol (~70 %) with activators (diethylamine hydrochloride ~4 %, triethanolamine ~2 %). It handles self-fluxing polyurethane enamels (ПЭВТЛ-1, ПЭВТЛ-2) and old vinyl-acetal, but already struggles on polyesterimide ПЭТВ-2. It is convenient because it does not require mandatory cleaning.
• ФИМ, ФДГ-м — phosphoric active fluxes, for silver, platinum, and hard enamels.
• ТАГС — glycerol with an aniline activator, medium activity.
• Imported: Kester 951, MG Chemicals 8341, Amtech RMA-223 — rosin-based with activators, for self-fluxing enamels.

Abroad, chemical enamel strippers are also used — gels and liquids on a caustic or chlorinated base. The compound is applied to the wire end, after 30–60 seconds the enamel peels off, and all that is left is to wipe and solder. In Russia such compounds are used only to a limited extent: strongly alkaline strippers fall under strict safety and storage requirements, and it is simpler to keep a bath of active flux.

Process parameters:

Active flux works well on litz wire with up to 50–100 strands at a wire diameter from 0.1 mm. For magnet wire such as ПЭТВ-2 at 0.3–0.8 mm it is, in general, the main working method without extra equipment. All you need is a temperature-controlled iron, a bottle of Ф-38Н, and alcohol for cleaning.

On hundreds of strands at 0.071 mm diameter the method breaks down: the flux does not reach the inner strands of the bundle in time, and they stay in their enamel. On top of that, prolonged contact with Ф-38Н partly dissolves the fine strand — copper cross-section is lost and resistance rises. For such cross-sections you need a solder bath.

Safety. Ф-38Н is toxic: at 350 °C the phosphoric acid gives off fumes that strongly irritate the mucous membranes. Work only in a ventilated room or under extraction, wearing gloves and goggles. After soldering, the joint must be washed with water and alcohol, otherwise acid residue will cause corrosion within a few months.

Method 3. Molten-solder bath

The basic industrial method for tinning litz wire. The procedures of New England Wire Technologies (NEWT) and Rubadue Wire in the US, Pack Litz Wire in Germany, and Elektrisola are all built around this method. In Russian terminology it is "bath tinning"; in foreign documentation it is "solder-pot tinning".

Principle. Solder is melted in a temperature-controlled vessel at 320–480 °C. The end of the litz wire is dipped in flux, then into the bath for the required time. The enamel is destroyed, the copper is wetted with solder, and every strand gets an even coating. After removal the wire is wiped with a clean cloth.

Process parameters per the NEWT procedure

Start with the size of the bath. For typical litz wire up to 6 mm in diameter, the minimum is 2 kg of molten solder. If the construction is larger or the batches are big, you need a bath of 10 kg or more. With a small bath everything breaks down at one point: when a cold wire is immersed, the temperature drops locally by tens of degrees, the enamel does not have time to break down, and you get a cold joint.

The standard solder is ПОС 61 (Sn61Pb39) or its imported equivalents Sn60Pb40, Sn63Pb37 — melting point 183 °C, bath working temperature 320–360 °C. For lead-free lines, SAC305 (Sn96.5/Ag3.0/Cu0.5) is used at a working temperature of 350–400 °C. For high-temperature applications (polyimide enamels) — Sn95/Sb5 or silver solders at 450 °C.

The bath temperature and dwell time themselves depend on the enamel type:

The finer the individual wire in the litz, the lower the temperature and the shorter the time — otherwise the copper will start to dissolve in the tin.

Before immersion, the end of the litz wire is dipped in a liquid active flux. For Russian enamels this is Ф-38Н diluted 1:1 with alcohol; for imported ones — Kester 951 or Multicore X32-10I. The flux has to be liquid so it can wick between the strands by capillary action — gels and pastes are not suitable here.

Next comes the mandatory detail on which half of all amateur tinning fails — the heat sink. A copper or brass clamp is fastened to the wire above the tinning zone. Without it, solder wicks up the strands by capillary action 5–10 cm above the immersion zone. Over that length the enamel is partly destroyed, and a section forms in the coil winding where the strands are electrically shorted to one another over the whole climb length. Over that section the litz wire turns into a single solid conductor — the point of transposition and stranding is lost there, local high-frequency losses rise, and the winding heats above its design value. For fine litz wire with hundreds of strands, a heat sink is not optional but an iron-clad requirement.

Every industrial guide — from NEWT to audio-cable makers — describes the immersion technique the same way: lower the wire slowly and smoothly, without jerks. At the bottom of the bath make a slow horizontal motion — this sweeps dross and charred enamel off the surface so they don't stick to the strands. Raise it just as slowly, vertically. Shake off the excess solder with one sharp downward flick. Wipe immediately with a clean cloth.

The surface of the bath has to be cleaned regularly. Once a shift, oxides and charred enamel are skimmed off the solder mirror with a piece of cardboard or a metal plate. Without this, dross and soot are gradually drawn onto the strands and form a cold joint — the connection works electrically but is mechanically weak and will fail over months of service.

Quality control is a cross-section of the finished tinned zone under a microscope at 100×. The correct picture should be visible: every strand coated with solder, the enamel blackened or gone, the copper shiny, and no oxides between the strands. If the cross-section shows areas with surviving enamel, the temperature or time needs to be increased.

Ferrule + bath

An industrial variation: before immersion, a metal ferrule is slipped onto the end of the litz wire and crimped with force. Then the bundle with the ferrule is lowered into the bath. The ferrule serves two functions:

• it blocks capillary wicking of solder up the strands — a separate heat sink is not needed;
• it simultaneously becomes a terminal ready for connection to a bolt or a board.

The method is used in the production of high-frequency transformers and power electromagnets, where the joint must both withstand vibration and keep solder out of the winding.

The solder bath is the most versatile method in terms of the range of constructions it covers. Litz wire of any geometry, from 7 strands to 2000+ strands, with an individual wire diameter from 0.05 to 0.5 mm — all of it is handled by the same equipment. The main limitation is the equipment itself. A temperature-controlled bath at 350 °C with a thermostat and a controller is not a 2,000-ruble iron. The minimum capital cost for a benchtop model is 30,000–80,000 rubles; a serious industrial bath with automatic immersion and temperature control starts at 300,000 rubles and up. For one-off repairs and single orders it is simpler to find a production shop with a bath and hand over the wire end for tinning.

Method 4. Hot crimping

This is the very technology you see inside industrial welding inverters, traction motors, and large power transformers. There the litz wire is connected to a copper bus or terminal without a trace of solder — just a compact copper ferrule tightly gripping the strand bundle, with no sign of tinning.

Hot crimping is a form of resistance welding. The joint is made without filler material: the terminal and the strand bundle are heated under pressure at the same time by the current passing through them, up to a temperature near the melting point of copper. The enamel on the strands is squeezed out of the contact zone and burns off, and the copper strands fuse to one another and to the terminal material through partial diffusion at the interface.

How it works

The end of the litz wire is inserted into a metal terminal — a ferrule, a lug, a spade terminal, a ring. The terminal is placed between two electrodes of a dedicated machine. Through the electrodes, the following are applied at the same time:

• pressure up to 1000 kgf on the terminal,
• a high-current electrical current passing through the terminal and the litz wire under it.

The resistance in the contact zone causes local heating up to 600 °C. Under pressure and temperature, the enamel on the strands is squeezed out of the contact zone and burns off. Under pressure and at near-melting temperature, the copper strands fuse to one another and to the terminal material through diffusion of copper atoms into the terminal's lattice. The result is a monolithic metallic joint — no solder, no flux, no prior enamel stripping.

The process takes a few seconds.

Hot-crimping machine parameters

Why hot crimping beats soldering

A hot-crimped joint has several fundamental advantages over a soldered one:

• Contact resistance close to zero. The joint is a monolithic piece of metal — there is no transition layer of solder with its own resistance.
• It does not creep under load. Solder is plastic — under mechanical load or vibration a soldered joint gradually weakens. Hot crimping does not have this problem.
• It does not lose strength when heated. Tin melts at 183 °C, and if the coil overheats to 200 °C a soldered joint degrades. Hot crimping withstands temperatures up to 600 °C — the working temperature of copper.
• Copper annealing in the joint zone. Heating to 600 °C relieves internal stresses in the copper structure after crimping. The joint comes out softer and more durable.
• No flux means no corrosion. Active-flux residue, even when washed off, can cause corrosion over time. A hot-crimped contact is contaminated with nothing but charred enamel.

Where it is used in industry

Abroad, hot crimping is one of the main methods for terminating magnet wire in high-volume series production:

• Starters, alternators, traction motors of traditional design. The joint has to withstand vibration, thermal cycling from –40 to +200 °C, and a machine service life of 15+ years. In modern EV traction motors with hairpin windings, the bar ends are more often joined by laser welding — a different, newer technology; hot crimping remains the baseline solution for classic wound constructions.
• Welding inverters and power supplies. The HF transformers of Miller, Lincoln, and Hypertherm inverters are terminated by hot crimping — at 50–200 kHz, because of the skin effect, a soldered joint heats up more than the winding itself.
• Industrial induction heaters. The zone where the inductor winding connects to the bus carries currents up to thousands of amperes, with an enclosure temperature up to 150 °C. At such loads hot crimping is more stable than any solder.
• Power electromagnets for medical and scientific installations. Stability of joint resistance is required over decades of continuous operation.

Where the technology came from

Hot crimping has been known since the 1960s as a development of resistance welding. The first industrial machines were made for aluminum-to-copper joints in the aerospace industry. In the 1980s the technology was adapted for magnet wire in the production of automotive starters and alternators.

The main equipment makers worldwide:

• Joyal — A Division of Alliance Winding Equipment Inc. (USA) — a long-standing supplier of equipment for coil-winding production.
• Strunk Connect Automated Solutions (Germany) — a European supplier of hot-crimping machines.
• Amada Weld Tech (Japan / Germany) — a major manufacturer of resistance-welding equipment.
• AMR Electronique (France) — hot-crimping equipment for complex wound assemblies, including litz wire.
• TATE Welding (China) — the mass-market segment, affordable machines for series production.

The Russian reality

Hot crimping in series production is still rare in Russia — the equipment is imported and expensive, and it only pays off on large batches. But in practice the problem is not even that. The Russian cable plants that make litz wire as a commodity (Pskovkabel, Kirskabel, Moskabel, and others) do not offer end-termination as a service for the customer's product — it is not part of their process. The customer gets cut-to-length reels and does whatever they want with the ends: tinning with a rosin iron, heating with a hot-air gun, or, at best, setting up their own solder bath.

Because of this, two practices prevail in Russia:

• The customer has in-house production and tins it themselves, with their own means. The quality depends heavily on process discipline: not everyone has a solder bath, the flux is not always the right one, and a heat sink is not always used.
• There is no in-house production, and the ends are tinned with a rosin iron "as best one can". The ends come out unreliable: only the outer strands are wetted, at operating frequencies the winding heats up more than the copper itself, efficiency is below design, and the coil's service life is reduced.

DIADA's design bureau is one of the few in Russia that does end-termination, ferruling, and cut-to-length of litz wire ends for the customer's application: the tinning length, the solder type (ПОС 61, SAC305, Sn95Sb5), the ferrule material and diameter, and the heat-sink point are all agreed. The customer receives wire with prepared ends, ready to install — no need to keep their own solder bath, no need to put up with unreliable improvised terminations.

For series hot crimping (large traction motors, inverters), several players in Russia are still working on an in-house line; on our side a combined approach — a solder bath plus a ferrule — covers the vast majority of tasks from prototypes to medium series.

Induction crimping

A newer variation of hot crimping, developed and patented in the early 2020s. The terminal on the litz wire is crimped with an ordinary mechanical press without current, then placed inside an induction coil. An alternating magnetic field induces eddy currents in the terminal itself, which heats to 600 °C from the inside. The enamel burns off and the copper fuses through diffusion.

The advantage is that there are no contact electrodes and none of the working-surface contamination associated with them. It is used in particularly critical applications (medical equipment, aviation).

Method 5. Self-fluxing enamel

The simplest approach is to choose litz wire whose enamel is designed from the start to break down at soldering temperature. Then no bath, no active flux, and no hot crimping are needed.

What this enamel is

In international terminology, the class of self-fluxing enamels is called solderable enamel or self-fluxing enamel. The composition is a modified polyurethane to which substances are added in manufacturing that break down at 320–360 °C. In Russian terms these are the magnet wires of the ПЭВТЛ-1 and ПЭВТЛ-2 series (polyurethane solderable, classes A and E respectively).

On heating to 320 °C, the enamel on the wire surface decomposes into volatile components, exposing the copper. If solder is applied to that copper at the moment the enamel decomposes, it wets the surface at once. No active acids, no long dwell, and no special equipment are needed. An ordinary iron at 320–360 °C with rosin flux or ЛТИ-120 is enough.

Litz on ПЭВТЛ-2 (DIADA design bureau)

In the DIADA design bureau catalog, per ТУ ДСГТ.685660.019ТУ (ТУ 27.32.11-019-59596873-2025), the base enamel is ПЭВТЛ-2, self-fluxing polyurethane, class F (155 °C). Accordingly, the entire standard Litz range solders with an ordinary iron at 320–360 °C. No baths, no Ф-38Н, no complications.

For applications that require a 200 °C thermal class, the enamel ПЭТ-200-2 is used — it is not self-fluxing. Only a solder bath at 420–450 °C or hot crimping works with it.

Procedure for soldering self-fluxing litz wire

1. Remove the outer covering (fiber, film, jacket) from the end over 10–15 mm.
2. Apply a little flux to the end. Ordinary rosin or ЛТИ-120 will do.
3. Press with the iron tip at 320–360 °C and feed ПОС 61 solder.
4. Hold for 5–10 seconds. The enamel blackens and evaporates, and the copper is wetted with solder.
5. Remove the iron and let it cool. Inspection — every strand is evenly coated with solder.

For large litz wire (from 200 strands) it is hard to heat the whole area with a tip at once. In that case the "tip with a well" solution is used: a small cup attachment on the iron into which a drop of solder is poured. The end of the litz wire is dipped into this improvised bath. The result is a miniature bath, and the joint is consistent across the whole cross-section.

When self-fluxing is not suitable

• The coil's thermal class is above 155 °C. Then ПЭВТЛ-2 is unsuitable for the heat rating of the winding itself, and you need ПЭТД-200 or polyimide.
• The design documentation is strictly tied to a TU with a different enamel (for example, Soviet design documentation for ПЭВ-2 with silk). Then, formally, that specific enamel is required.
• Very large cross-sections (from 10 mm² of copper). At such cross-sections an iron physically cannot heat the bundle through in time — a bath or hot crimping is needed.

Comparison of the five methods

Common mistakes and how to avoid them

Overheating fine strands during soldering. On a 0.071 mm strand, solder can dissolve the copper within seconds at 380 °C. The sign is that, after soldering, the cross-section in the tinned zone is visibly smaller than in the undamaged part of the wire. The fix: lower the temperature or immersion time; on self-fluxing enamels work at the lower end of the range (320 °C).

Fig. 2. Capillary wicking of solder into the winding

Capillary wicking of solder into the winding. Without a heat sink (a copper or brass clamp above the tinning zone), solder wicks up between the strands by capillary action by several centimeters. The enamel over that section is destroyed and the strands become electrically shorted over the whole climb length. Over that section the litz wire turns into a single solid conductor — the skin effect and proximity effect are no longer compensated, local high-frequency losses rise, and the zone heats above its design value. Breakdown itself usually does not occur — litz operates at low inter-strand voltages — but the coil's efficiency drops, the thermal regime exceeds the design point, and over months it drags along degradation of the impregnation and an eventual failure of the winding. The fix: a heat sink is mandatory on any fine litz wire; in ferrule soldering the heat-sink role is played by the copper ferrule crimped on the end — it physically blocks solder from climbing into the winding.

Oxides and soot on the surface of the bath. Without regular cleaning they stick to the strands and form a cold joint — a connection that conducts electrically but is mechanically weak and falls apart over time. The fix: skim off the surface layer with cardboard or a metal plate every 10–20 operations.

Crimping a terminal onto a tinned end. If you mechanically crimp a terminal (lug, spade) onto tinned litz wire, the solder "creeps" over time under pressure and the joint weakens. Both foreign litz-wire makers and experienced practitioners on specialized forums warn about this directly. The fix: either crimp before tinning (so the solder fills an already-compressed ferrule) or use hot crimping instead of soldering.

Insufficient cleaning of Ф-38Н. Phosphoric acid residue at 60–80 °C causes corrosion of the solder joint over months. The sign is a greenish-white deposit on the copper after six months. The fix: after soldering, rinse with distilled water, then isopropyl alcohol, and dry.

Soldering non-self-fluxing litz wire with an ordinary rosin iron. The most common amateur mistake. Outwardly everything is shiny, but the solder wetted only the outer strands. At operating frequencies the coil heats up and fails. The fix: either switch to self-fluxing litz wire, or use active flux or a bath.

FAQ

Which solder should I use for tinning litz wire?

The general-purpose choice is ПОС 61 (Sn61Pb39) or the equivalent Sn60Pb40, Sn63Pb37. Melting point 183 °C, bath working temperature 320–360 °C. For lead-free lines — SAC305 (Sn96.5/Ag3.0/Cu0.5), working temperature 350–400 °C. For high-temperature applications (polyimide enamels) — Sn95/Sb5 or silver solders.

What tip temperature should I use to solder self-fluxing litz wire?

320–360 °C. The lower end of the range gives more stable results; the upper end is faster but risks dissolving fine strands. For 0.071 mm and finer series — 320–340 °C, dwell time 5–8 seconds. For 0.15–0.25 mm series — 340–360 °C, dwell time 8–15 seconds.

How does bath tinning differ from soldering with an iron?

An iron heats the wire from the outside; the inner strands of the bundle heat up with a delay and often don't solder properly. A bath of molten solder surrounds the bundle from all sides at once, so every strand heats up evenly. For bundles of 50 strands and up, an iron works poorly — you need a bath or self-fluxing enamel with the right tip.

Can litz wire be soldered with a heat gun?

You can, but poorly. Hot air at 350–400 °C heats the bundle unevenly: the outer strands overheat and can melt, the inner ones don't heat through. It is used only for repair work — reheating an already-soldered joint when reworking it. A heat gun is not suitable for the initial tinning of litz wire.

What is a cold solder joint and how do you recognize it?

A cold joint is a connection in which the solder did not wet the copper properly: an invisible layer of oxides or unreacted enamel remains between the solder and the copper. There is electrical contact, but the AC resistance is above normal and the joint is mechanically brittle. It is recognized by a dull, rough look instead of a shiny one. Under a 100× microscope you can see a dark layer between the solder and the strand. The fix is to reheat it with fresh flux.

What is the smallest litz wire diameter that can be tinned?

Litz wire is produced in series on 0.03 mm wire and finer. It can be tinned in a dedicated bath at 320 °C with a 1–2 second immersion. By hand with an iron it is practically impossible — overheating is guaranteed.

Do you need fume extraction when tinning litz wire?

With active fluxes (Ф-38Н, chemical strippers) it is mandatory. With rosin-based and mildly active fluxes (ЛТИ-120) it is advisable, but in a small workshop an open window will do. When working with a solder bath using active flux and with hot crimping, extraction of vapors and enamel-combustion products is mandatory.

Which standards govern the quality of soldered joints in industry?

In Russia — ОСТ 92-1024-77 "Soldered joints. General technical requirements" and industry-specific ОСТs for civil applications. In international practice — the IPC standards: J-STD-001 "Requirements for Soldered Electrical and Electronic Assemblies" and IPC-A-610 "Acceptability of Electronic Assemblies". For solderless joints (hot crimping, ordinary crimping) — the IEC 60352-2 / DIN EN 60352-2 standard "Solderless connections — Crimped connections".