Hot-dip Tin Coated Strips

For decades, tin coatings produced by the process known as "hot-dip tinning" have ensured the reliable performance of billions and billions of connectors in industrial, automotive and communication electronics.

Additional information

Overview Coating Variants Key Benefits Technical Specifications Typical Applications

What hot-dip tinning achieves

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In hot-dip tinning, strip with a cleaned and activated surface passes through a molten tin bath. After leaving the bath, a contactless air stream levels the liquid tin to the target thickness. Inline X-ray fluorescence measures coating thickness on both sides continuously throughout the process.

The result is a two-layer coating structure: an intermetallic phase (IMP) of Cu₃Sn and Cu₆Sn₅ bonds the tin metallurgically to the base material; a free tin layer above the IMP provides the contact surface.

This structure delivers performance characteristics superior to electroplated tin coatings without reflow:

Low contact resistance – the free tin embeds the mating partner over a large surface area, reducing resistance at the contact point
High whisker resistance – IMP formation at elevated temperature relieves internal stresses that drive whisker growth

Good corrosion resistance – a passivating, stable tin oxide forms without pores
Good solderability – the free tin layer remains wettable across standard soldering processes

Coating Variants

SnPUR^® – Pure Tin

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What it is: SnPUR® is a pure hot-dip tin coating. The structure consists of a Cu₆Sn₅ intermetallic phase bonded to the base material, with a free pure tin layer on top.

When to use it: Applications requiring low contact resistance and good solderability at standard operating temperatures (up to 130°C).

Key characteristics:

Very ductile – accommodates stamping and bending without coating separation
Low contact resistance through large, compliant contact surface
Good solderability (improves with increasing coating thickness)
Layer thickness range: 0.7 µm to 10 µm depending on application target

SnTEM^® – Thermal Tin (100% Intermetallic Phase)

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What it is: SnTEM® starts as a standard hot-dip tin coating and is then transformed by a subsequent heat treatment into a fully intermetallic CuSn compound. No free tin remains.

When to use it: Multipole connectors with high mating cycle requirements where insertion and withdrawal forces must be minimized and wear resistance maximized.

Key characteristics:

Significantly lower friction coefficient than pure tin – reduces insertion/withdrawal forces
High surface hardness (approx. 4 GPa nanohardness vs. <1 GPa for SnPUR®) – excellent wear resistance in repeated mating
Layer thickness: 0.7 µm to 2 µm
Not suitable for soldering applications
Note: high hardness limits formability – confirm compatibility with bending radii before ordering

SnTOP^® – Tin-Silver (Sn + SnAg₃)

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What it is: SnTOP® is a tin-silver hot-dip coating containing approximately 4% silver. The silver content causes precipitation hardening of the coating layer.

When to use it: Applications at elevated temperatures (up to 160 °C) where a combination of reduced insertion forces, fretting corrosion resistance, and solderability is required – as a cost-effective alternative to silver-plated surfaces.

Key characteristics:

Operating temperature range: –40 °C to +160 °C
Improved coefficient of friction vs. SnPUR® – lower insertion/withdrawal forces
Good fretting corrosion resistance and abrasion resistance
Good solderability maintained
Good bending properties retained

The Advantage: The Intermetallic Phase (IMP)

The core characteristic of our hot-dip tinned coatings is the formation of a specialized intermetallic phase (IMP) between the base material and the tin layer. Because it is applied under heat, it contains practically no internal stresses, making HDT a completely whisker-free coating.

Superior Bonding: Consisting of Cu₃Sn and Cu₆Sn₅, the IMP ensures an incredibly strong bond to the base material.
Whisker Protection: This process provides a high degree of protection against whisker formation, a critical factor for long-term component reliability.
Optimal Contact: Above the IMP, a ductile free tin layer ensures a large contact surface and low contact resistance, facilitating stable electrical connections.

Technical Specifications

We provide a wide range of dimensions to suit your specific manufacturing needs:

Strip Thickness: Available from 0.1 mm to 2.0 mm.
Strip Width: Available up to 400 mm.
Edge Designs: Standard uncoated edges or specialized tinned edges upon request.
Delivery Forms: Strips can be delivered in standard coils or as MULTICOIL® traverse wound coils for extended production runs.