These guidelines draw the user’s attention to:
a) If some properties of the tin-lead alloy are not known, it may lead to the incorrect use of this coating;

b) Properties and preparation of the substrate;

c) Electroplating practice.

Performance of D1 coating

ISO 2179-1986 Guidelines for Common National Standards and Specifications for Electroplating

May lead to incorrect use of this coating;

Tin-lead coating is a soft and easy to wear coating, composed of 62sn/38Pb low-eutectic alloy coating melting point as low as 183℃. This relatively low melting temperature of tin – lead alloy can be conducive to automatic welding. Under certain outdoor exposure conditions, especially under high humidity conditions, some corrosion of the tin-lead coating may occur. The thickness specified in Table 1 is the minimum value, and the thickness may be required to be greater than the specified value in Table 1 in actual use. Under normal indoor exposure, if there are no organic vapors such as phenolic compounds and volatile organic acids, and the coating is not discontinuous and porous, the tin-lead coating can protect most metals. The porosity of the coating is affected not only by its thickness, but also by the surface state of the substrate material and the actual electroplating process conditions. These factors should be taken into account when specifying porosity tests (see 10.5). Compared with pure tin coating, tin-lead alloy coating within the composition range specified in this standard is better able to prevent product growth phenomenon or allostatic changes at sub-zero temperatures.

The electroplating layer conforming to this national standard is thinner or thicker than the general hot dip coating.

ISO 2179-1986 Guidelines for Common National Standards and Specifications for Electroplating

D2 matrix material properties and preparation

D2.1 Surface condition

The surface condition of the coating depends in part on the surface condition of the substrate material.

D2.2 Formation of intermetallic compounds

Due to the diffusion process between solid and solid, the coating and copper or copper based alloy will diffuse with each other, the degree of diffusion depends on time and temperature conditions, this diffusion can lead to thin coating black and welding performance deterioration. This deterioration rate varies depending on the release conditions. In poor conditions, the storage period may only be a few months.

D2.3 Diffusion of zinc

Zinc in Zinc-containing alloys such as copper diffuses to the surface through the tin-lead coating, reducing the welding properties, bond strength, and appearance of the coating (see Chapter 9).

ISO 2179-1986 Guidelines for Common National Standards and Specifications for Electroplating

D2.4 “Difficult to clean” substrate material

Some matrix materials, such as phosphorous bronze, bronze plating and nickel-iron alloys, are difficult to perform a good chemical pre-cleaning due to the natural oxide film on their surface. If soldering properties are required for tin-lead alloy coatings, preplating nickel or copper substrates with a minimum local thickness of 25µm will be beneficial to improve soldering properties.

D2.5 Aluminum, Magnesium and Zinc Alloys These alloys are susceptible to damage by dilute acids and/or alkalis and therefore require a special pretreatment prior to electroplating the tin-lead alloy by deposition of a fairly thick (10 to 25µm) copper, copper-tin alloy or nickel substrate.

D3 Electroplating practice

D3.1 Label wash after plating

If the coating is required for welding performance, it should be washed with an appropriate solution, such as 3%(mass ratio) lime acid or tartaric acid solution in the water washing process to ensure the removal of hydrated tin salt. If there is hydrated tin salt on the surface of the coating, it will have a harmful effect on the welding performance of the surface after drying and solidification.

ISO 2179-1986 Guidelines for Common National Standards and Specifications for Electroplating

D3.2 Coating thickness requirements

Unless otherwise specified in GB/T12334, it should be noted that the thickness of the deposition layer specified in this standard is the minimum local thickness and not the average thickness. The AVERAGE THICKNESS TO BE ACHIEVED for a GIVEN MINIMUM LOCAL THICKNESS requirement ON THE MAIN SURFACE WILL DEPEND ON THE GEOMETRY OF BOTH the PLATE and the BATH, AND THE PLACEMENT OF THE CATHODE AND ANODE closely RELATED to BOTH. In the roll plating, especially in the roll plating of small parts, the deviation of the coating thickness conforms to the normal (Gaussian) distribution law.

During hot melt treatment, because the formation of meniscus will affect the thickness of the coating, the coating should only be evaluated for its welding performance requirements.

D3.3 Co-deposition of organic matter

Organic additives are often used in tin – lead electroplating solutions. If the coating is used for welding performance requirements, attention should be paid to the selection of organic additives to minimize co-deposition of organic matter, because organic matter may cause coating skin or blistering during melting or welding. However, if it is a coating on a connector, the mechanical properties of the coating will be improved by co-deposition of some organic matter included.

ISO 2179-1986 Guidelines for Common National Standards and Specifications for Electroplating

D4 Hot melt treatment

The tin-lead coating can easily melt if it is immersed in hot oil, or exposed to infrared radiation or compressed hot steam. The advantage of hot melting is that the poor welding performance caused by the defects of the substrate can be shown in the hot melting of the coating as a non-hole wet area. The effect can be satisfied when the coating thickness is less than 20µm. However, if the molten coating may flow to the edge of the workpiece during the hot melting process, the thickness of the coating should be limited to less than 8µm to avoid the formation of “peak” on the edge of the workpiece. Hot melt treatment is not recommended for very bright electroplating.