PCB News - Electroplating process of PCB connector

PCB Process Introduction to Electroplating Process of PCB Connectors

Since the 1980s, the rapid development of 4C electronic products such as computers, mobile phones, and televisions has promoted the growth of electronic connectors. Electronic connectors that connect electronic circuits also tend to be diversified, such as: electronic connectors for sleeves, electronic connectors for interfaces, electronic connectors for internal assembly, gold fingers, etc. These connectors are positive in terms of practicality. The development of miniaturization, complexity, light weight, multi-function, high reliability, long life, and high reliability has led to the emergence of the fourth generation of assembly technology, namely surface mount technology (SMT). The most basic performance of electronic connectors is the reliability of electrical contact. For this reason, the materials used for connectors are mainly copper and its alloys. In order to improve its corrosion resistance/high temperature/wear resistance/plug resistance/conductivity, etc., The necessary surface treatment must be carried out.

The representative surface treatment method of the electronic connector is the gold plating process with nickel plating as the base, or the solderability plating process with the copper plating as the base. The corrosion resistance of silver coating is poor, and it is used less now; palladium and palladium-nickel alloy coating have been developed for nearly ten years as a substitute for gold coating, as a wear-resistant coating, used for the surface of electronic connectors with a large number of insertions and removals. The treatment has been applied.

The following is a brief introduction to the continuous electroplating process, plating solution and coating performance of electronic connectors.
1 Electroplating process of electronic connectors

According to the different functions of electronic connectors, different electroplating processes need to be selected. Most of them use roll-to-roll automatic lines (mostly made in Taiwan and Hong Kong) (most of the additives are imported from the United States/Germany). The electroplating process is essentially the same as general electroplating. However, the processing time of each process is much shorter than that of ordinary electroplating, so various processing solutions and plating solutions must have the ability of rapid electroplating.

1.1 Gold plating process based on nickel plating
Discharging - chemical degreasing - yin and yang electrolytic degreasing - acid activation - sulfamate Ni plating - partial Au plating - partial Sn plating (or flash gold plating) - post-treatment - drying - sufficient water washing must be provided above the material collection. A brief introduction to the process:
1.1.1 Degreasing Different from ordinary chemical degreasing, the degreasing time is only 2~5s. In this way, the degreasing of ordinary immersion methods can no longer meet the requirements, and multi-stage electrochemical degreasing under high current density is required. The requirement for the degreasing liquid is: if the degreasing liquid is brought into the washing tank or pickling tank in the downstream, it should not be decomposed or precipitated.
1.1.2 Pickling
Pickling is to remove the oxide film on the metal surface, and sulfuric acid is often used. Due to the strict size requirements of electronic connectors, the pickling solution must not corrode the substrate.
1.1.3 Nickel plating (palladium nickel)
As the bottom layer of Au and Sn plating, the Ni plating layer not only improves the corrosion resistance, but also prevents the solid phase diffusion of Cu and Au, Cu and Sn in the matrix. The nickel plating layer should have good flexibility. Because the plating layer should not fall off during the cutting and bending of the electronic connector, it is best to use the sulfamate nickel plating solution. The (palladium nickel) layer can save part of the gold cost.
1.1.4 Partially gold-plated
There are various methods for partial Au plating, and many patents have been applied for at home and abroad. The specific method: 1. Cover the unnecessary parts, and only make the parts that need electroplating come into contact with the plating solution, so as to achieve partial electroplating; 2. Use brush plating, and the parts that need to be electroplated are in contact with the brush plating machine to achieve partial electroplating; 3. Use Spot plating machine can also achieve partial plating. The issues that need to be considered for partial Au plating are: from a production point of view, high current density plating should be used; the thickness of the plating layer must be evenly distributed; the location to be plated must be strictly controlled; the plating solution is versatile for various substrates; maintenance and adjustment are simple. (5) Local solderable electroplating Local solderable electroplating is not as harsh as local gold plating, and more economical electroplating methods and equipment can be used. Immerse the part that needs to be electroplated into the plating solution, so that the part that does not need to be electroplated is exposed to the liquid surface, that is, partial electroplating can be achieved by controlling the liquid level. In order to reduce pollution, tin methanesulfonate plating solution can be used, and the thickness of the plating layer is 1 to 3 μm. The appearance should be bright and smooth. The above process is generally applicable to products that require conductivity and resistance to plugging and friction in one section of the terminal, and soldering in the other section.
1.2 Sn plating (or Au flash plating) electroplating process with a copper plating layer as a primer Process flow:
Discharging - chemical degreasing - yin and yang electrolytic degreasing - acid activation - copper plating (cyanide or acid copper can be used) - sulfamate Ni plating - partial Sn plating (or flash Au) - post-treatment - drying -There must be sufficient water washing above the material. The copper coating mainly acts as a barrier to prevent the solid phase diffusion of zinc in the substrate (mainly brass) and tin in the solderable coating. In order to improve the thermal conductivity of the parts after welding, the copper plating layer is generally 1 to 3 μm. Pure tin plating is easy to produce whiskers from the surface of the plating (mostly tin plating). Tin plating is generally 1 to 3μm. Since tin is easily oxidized in the air, necessary post-treatment is necessary to slow down its oxidation rate. The above process is generally applicable to products that require soldering tin on terminals.
1.3 Pd/Au electroplating process based on nickel plating
Process flow:
Discharging - chemical degreasing - yin and yang electrolytic degreasing - acid activation - sulfamate Ni plating - (partial palladium nickel plating) - partial Au plating - post-treatment - post-treatment - drying - sufficient water washing must be performed above the collection A palladium plating layer is inserted between the nickel plating layer and the gold plating layer, and the thickness of the palladium plating layer is controlled to be 0.5-1.0 μm. Due to the high hardness of the palladium coating, if the thickness is too large (more than 1.5μm), the coating is prone to cracks during bending or cutting. Since palladium is more expensive, partial plating is often used. Palladium plating solution is generally weakly alkaline. In order to improve the bonding strength of nickel and palladium, it is necessary to flash palladium plating on the nickel surface. After electroplating palladium nickel, flash plating 0.03-0.13 μm gold plating can stabilize the contact resistance, and the gold plating has a self-lubricating effect when plugging and unplugging, thereby improving wear resistance.
The above process is generally applicable to products that require soldering tin on terminals.
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