For enamelled wire, another question comes first: can the insulation be removed during solder dipping, or does the wire need a separate stripping operation? A higher-melting solder will not automatically remove a difficult enamel coating or produce a more reliable termination.
Understand the three temperatures involved
The solder's melting temperature describes when the alloy changes from solid to liquid. A eutectic alloy has a single melting temperature; other alloys melt over a range.
The solder-bath temperature is the process temperature used for dipping. It must allow adequate heat transfer and wetting and, for suitable solderable wire, removal of the enamel from the termination area.
The finished joint's operating temperature is the temperature it experiences in service. Joint strength, creep and thermal fatigue must be assessed at that temperature. Staying below the solder's melting point does not by itself establish an acceptable service life.
Confusing these values can lead to the wrong material choice. A process requiring a relatively hot solder bath does not necessarily require a solder alloy with a correspondingly high melting point.
Typical melting temperatures of common solder alloys
The following values describe the alloys, not recommended solder-pot settings. Composition percentages are by weight.
| Alloy | Nominal composition | Typical melting temperature or range | Selection considerations |
|---|---|---|---|
| Sn63Pb37 | 63% tin, 37% lead | 183°C | Eutectic tin-lead solder; use depends on the product's material restrictions |
| SAC305 | 96.5% tin, 3% silver, 0.5% copper | 217 to 220°C | Common lead-free electronics solder |
| Sn99.3Cu0.7 | 99.3% tin, 0.7% copper | Approximately 227°C | Silver-free solder used in suitable wave and dip processes |
| Sn95Sb5 | 95% tin, 5% antimony | Approximately 232 to 240°C | Higher melting range than the other alloys shown; suitability requires application review |
These representative values follow Kester's alloy chart. Use the selected supplier's product data sheet when setting the purchasing and process specification.
For an alloy with a melting range, the lower value is the solidus, where melting begins. The upper value is the liquidus, above which the alloy is fully liquid. Neither value specifies the temperature needed to tin a particular wire.
When does a higher-temperature solder make sense?
A higher-melting alloy may be worth evaluating when a joint must tolerate a later heating operation or operate under demanding thermal conditions. The decision also depends on mechanical load, joint geometry, thermal cycling and compatibility with the surfaces being joined.
For wire-end pretinning, consider the later assembly step. The pretinned wire may subsequently be soldered into a terminal or onto a PCB using another solder. The final joint contains material from both operations, so its properties cannot be established from the pretinning alloy alone.
Changing to a higher-melting alloy may also require changes to the soldering process. More heat or a longer heating period can affect nearby insulation and connector components. Those effects belong in the material review.
Start with the enamelled wire specification
Wire intended for direct soldering
Some enamel systems allow the termination area to be stripped and tinned through controlled immersion in molten solder. Certain polyurethane wires are designed for this process, but the precise wire grade, coating thickness and conductor diameter still matter.
Manufacturer solderability data may specify test conditions around 390°C. For example, Elektrisola publishes a 390°C solderability test for a particular fully insulated wire construction, with a defined specimen size and time requirement. That is a test condition for the stated wire, not a universal production setting.
Use the wire supplier's data to establish a trial process, then check whether it removes the coating completely without damaging the conductor or the insulation that must remain.
Wire requiring separate enamel removal
Where the coating is not suitable for direct solder stripping, select a removal method appropriate to the wire. Mechanical stripping, laser processing or a specified chemical process may be options, depending on the insulation and conductor dimensions.
The stripped surface must then be clean and suitable for wetting. Increasing bath temperature to compensate for incomplete stripping can create damage without resolving the underlying problem.
The wire's thermal class alone does not determine solderability. Some formulations combine relatively high thermal resistance with solder-strippable insulation. Obtain the exact product designation rather than relying only on descriptions such as "polyurethane wire" or "high-temperature wire."
What controls tinning quality?
Conductor material and diameter
Confirm whether the conductor is copper, copper alloy, aluminium or another material. A process developed for copper cannot automatically be transferred to aluminium wire.
Fine copper conductors need particular attention to immersion time. Copper can dissolve into molten solder, and dissolution depends on time and temperature. Excessive exposure can therefore reduce conductor cross section even though the copper has not reached its melting point.
Flux and surface preparation
The flux must suit the conductor, solder alloy and process temperature. It must remain effective long enough for wetting without leaving unacceptable residue.
Flux activity is not a substitute for a suitable enamel-removal process. Residue removal should follow the flux supplier's instructions and the cleanliness requirements of the finished assembly.
Bath condition and temperature control
Measure the actual bath temperature with suitable calibrated equipment. Check temperature recovery during repeated dipping; the displayed setting alone does not show whether the process remains stable under production load.
Keep the bath surface and alloy condition under control. Dross, coating residues and dissolved metals can change process behavior. Avoid mixing unidentified solder bars into an established bath.
Tinned length and thermal exposure
Define the immersion depth, dwell time and acceptable tinned length. Heating too far along the wire can damage insulation beyond the termination area. In stranded constructions, excessive solder penetration can also create an unwanted stiff section near a bending point.
A termination that accepts solder easily still needs adequate mechanical support in the finished product.
Applying the process to pogo pin and magnetic connector assemblies
For custom connector work, the wire preparation and termination geometry should be reviewed together. A small solder cup, closely spaced PCB pads or a compact molded housing may impose limits on tinned length, solder volume and heating time.
We can work from customer drawings to develop pogo pin or magnetic connector assemblies with the wire termination, contact layout and cable support considered as part of the complete connection. Where enamelled wire is specified, sample validation should include coating removal, conductor condition and the final solder joint.
Before releasing a process, inspect solder coverage around the intended termination, the insulation boundary and any conductor thinning or nicks. Check joint strength and electrical performance using acceptance criteria suited to the assembly. A bright surface alone is insufficient evidence of a sound termination.
Provide local exhaust for flux and enamel-decomposition fumes, and use protective measures appropriate to handling molten solder.
FAQ
Does a high-temperature solder bar remove enamel more effectively?
Not automatically. Enamel removal depends on the coating formulation, bath temperature, exposure time and preparation method. The solder's melting point does not establish its ability to strip insulation.
Can conventional solder be used in a relatively hot tinning bath?
Potentially, if the alloy, equipment and process are suitable. The bath temperature can be well above the alloy's melting point, but oxidation, copper dissolution and wire damage must remain controlled.
Is Sn95Sb5 always a better choice than SAC305 for enamelled wire?
No. Sn95Sb5 has a higher melting range, but the choice should follow the wire's tinning requirements and the finished joint's service conditions. A higher melting point does not guarantee better wetting or longer life.
What information is needed before selecting a solder bar?
Provide the wire manufacturer and grade, conductor material and diameter, insulation construction, stripping method and required tinned length. Also specify material restrictions, the final termination process and the joint's expected operating conditions.
