PCB Tech - PCB process fast continuous electroplating method for electronic connectors

PCB process fast continuous electroplating method for electronic connectors

With the development of the electronics industry, the electronic connectors used to connect electronic circuits tend to be diversified, such as: electronic connectors for sleeves, electronic connectors for interfaces, electronic connectors for internal assembly, etc. These connectors are more practical In consideration, it is developing in the direction of high density, lightness, thinness, miniaturization, multi-function, and high reliability. The most basic performance of electronic connectors is the reliability of electrical contacts. For this reason, the materials used for connectors are mainly copper and its alloys. In order to improve its corrosion resistance and wear resistance, 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 alloy coating have been developed for nearly ten years as a substitute for gold coating. As a wear-resistant coating, it is used for the surface treatment of electronic connectors with a large number of insertions and removals. Has been applied.
The following is an introduction to the processing technology, plating solution and coating performance of the electronic connector for continuous accelerated electroplating.
1 Processing technology of continuous and rapid electroplating
The processing technology of continuous and rapid electroplating is essentially the same as general electroplating, but the processing time of each process is much shorter than that of ordinary electroplating, so various treatment solutions and plating solutions must have the ability to adapt to rapid electroplating.
1.1 Gold-plating process with nickel-plated layer as a primer

The process flow is as follows:
Upper hanger - degreasing - water washing - water washing - water washing - pickling - water washing - water washing - water washing - sulfamate Ni plating - water washing - water washing - water washing - partial pulse Au plating - recycling - recycling - water washing - water washing - water washing - Partial Sn-Pb alloy plating - water washing - water washing - water washing - deionized water washing - deionized hot water washing - drying - lower hanger - inspection (thickness, bonding strength, appearance, solderability, local plating position, etc.) The main procedures in the process are briefly explained.
(1) Degreasing Unlike ordinary chemical degreasing, the degreasing time is only 2 to 5 seconds. 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.
(2) Pickling Pickling is to remove the oxide film on the metal surface, and sulfuric acid or hydrochloric acid is often used. Due to the strict size requirements of electronic connectors, the pickling solution should not dissolve the substrate.
(3) Nickel-plated Ni-plated layer is used as the bottom layer of Au and Sn-Pb alloy plating, which not only improves the corrosion resistance, but also prevents the solid phase diffusion of Cu and Au, Cu and Sn-Pb alloy in the matrix. The plating layer of electronic connectors should not fall off during cutting and bending, so it is better to use nickel sulfamate plating solution.
(4) Partial gold plating There are various methods for partial Au plating, and many patents have been applied for at home and abroad. Most of the methods are to cover the unnecessary parts, and only make the parts that need electroplating come into contact with the plating solution, thereby realizing partial electroplating. The issues that need to be considered for local Au plating are: 1. From the perspective of production, high current density plating should be used; 2. The thickness of the coating should be evenly distributed; 3. Strictly control the location to be plated; 4. The plating solution should be universal for various substrates; 5. Maintenance and adjustment are simple.
(5) Local solderability electroplating Local solderability 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, organic acid salt plating solution can be used. The composition of the plating layer is about Sn:Pb=9:1, and the thickness of the plating layer is 1 to 3 μm. The appearance should be bright and smooth.
1.2 Solderability electroplating process based on copper plating layer The typical process flow is as follows:
Upper hanger - degreasing - water washing - water washing - water washing - pickling - water washing - water washing - water washing - KCN activation - cyanide copper plating - water washing - water washing - water washing - pickling - water washing - electroplating Sn-7%Pb alloy - water washing - Washing - Washing - Anti-tarnishing - Washing - Washing - Deionized water washing - Deionized hot water washing - Drying - Lower hanger - Inspection (thickness, bonding strength, appearance, solderability)
The copper plating layer mainly acts as a barrier layer to prevent the solid phase diffusion of zinc in the substrate (mainly brass) and tin in the solderable plating layer. In order to improve the thermal conductivity of the parts after welding, the thickness of the copper plating layer is 1 to 3 μm. In addition to cyanide plating solutions for copper electroplating, in recent years, organic acid systems such as alkyl sulfonic acid or alkanol sulfonic acid have been used.
Pure tin coating is easy to produce whiskers from the surface of the coating. If more than 5% of lead is co-deposited in tin to form a Sn-Pb alloy coating, the generation of whiskers can be prevented. When Sn-Pb alloy is co-deposited, Pb is easier to deposit than Sn. Therefore, when [Sn4+]/[Pb2+]=9:1 in the plating solution, an alloy plating layer with a lead content of more than 10% can be obtained. As the electroplating progresses, the Pb2+ in the plating solution gradually decreases. Periodic analysis of the plating solution is required to supplement Pb2+.
The solderable coating will slowly oxidize in the air. In order to slow down its oxidation rate, it can be immersed in a phosphate aqueous solution at 50-80°C after plating to form a dense phosphate film on the surface of the coating.
1.3 Pd/Au electroplating process with nickel plating as a primer The representative process flow is as follows:
Upper hanger - degreasing - water washing - water washing - water washing - pickling - water washing - water washing - water washing - sulfamate Ni plating - water washing - water washing - water washing - activation (flash Pd) - partial Pd plating - recycling - water washing - Water washing - water washing - partial pulse Au plating - recycling - recycling - water washing - water washing - water washing - electroplating Sn-7%Pb alloy - water washing - water washing - water washing - deionized water washing - deionized hot water washing - drying - hanging tools - inspection ( Thickness, bonding strength, appearance, solderability, location of partial plating, etc.)
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 neutral to alkaline. In order to improve the bonding strength of nickel and palladium, it is necessary to flash palladium plating on the nickel surface.
After the palladium is electroplated, the gold plating layer of 0.03-0.13μm can be plated to stabilize the contact resistance, and the gold plating layer has a self-lubricating effect when plugging and unplugging, thereby improving the wear resistance.

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