Hot-dip tinned copper alloys （Stamped Fire-tinned system carrier & Leadframe)
In almost all branches of industry, the treatment of surfaces is crucial to the use of metallic materials.
Increasing requirements in the reliability of connectors and lead frames, like good solderability, high corrosion protection and moderate low insertion/extraction forces can be met by applying a surface finishing on the metallic materials. One special combination is the treatment of copper-based alloys with tin.
The hot-dip tinning of copper alloys is an alternative to the treatment with semi-precious and precious metals due to the different properties and cost factors. Hot-dip tinned strip reduce the contact resistance in electromechanical and electronic components. In addition to providing protection against corrosion, the treatment ensures reliable contact in plug connections and easier wetting during automated soldering.
The thickness of the intermetallic phase can be precisely controlled and adjusted to the requirements of downstream processing and the intended application of the tin-coated strip by means of targeted heat treatment. This also has a favourable effect on the insertion and extraction forces, surface hardness and solderability.
In the electrical engineering and electronics sectors, electrotinning and hot-dip tinning are well established processes.
While electrotinning can be used to apply coatings with an outstanding degree of accuracy, the system-inherent formation of intermetallic phases makes hot-dip tinned surfaces largely resistant – even without post-treatment – to the formation of whiskers, the occurrence of which is difficult to control and can cause electrical component failures due to short circuiting.
Hot-dip tinning allows higher temperature applications, is resistant to abrasion and reduces mating forces. All layers are lead-free. Solderability requirements are met over several months.
Application in the automotive, electrical and electronic industry:
Connectors, lead frames, contact parts, electromagnetic shieldings, cable lugs and conductive planes in current distributors of vehicles and battery clamps.
XIANDUAN recommends the following alloys for hot-dip tinned strip based on copper and copper alloys:
Brass: CuSn6 (C5191), MB10 (CuZn10) to MB37 (CuZn37), bronze BB01 to BB95, high-performance alloys SB01, SB02 and SB92, special alloys SB23 and SB69, nickel-silver NB10 to NB18 and CuNiSi-materials.
Process steps - hot-dip tinned copper alloys
1. Mechanical degreasing
2. Chemical degreasing
6. Liquid tin bath