Gold plating is a method of depositing a thin layer of gold on the surface of other metal, most often copper or silver.
Gold plating is often used in electronics, to provide a corrosion-resistant electrically conductive layer on copper, typically in electrical connectors. With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer.
A layer of a suitable barrier metal, usually nickel, has therefore to be deposited on the copper substrate, forming a copper-nickel-gold sandwich.
- MIL-G-45204 Type II Grade D
- ASTM-B488 Type I Class A
For less demanding applications in electronics, silver is often used as a cheaper replacement for gold. (Although silver is a better conductor than gold it does oxidize and so gold is better for contacts. However, variable capacitors are considered of the highest quality when they have silver plated plates. In this application there is no make and break contact so gold would not offer any advantage over silver).
Care should be used for parts exposed to high humidity environments. When the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion, flaking off the plating and exposing the copper itself; a process known as red plague.
Historically, silver plate was used to provide a cheaper version of items that might otherwise be made of silver, including cutlery and candlesticks.
- QQ-S-365A Type II
With a higher current, hydrogen bubbles will form on the item to be plated, leaving surface imperfections. Often various other chemicals are added to improve plating uniformity and brightness. Without some form of additive, it is almost impossible to obtain a smooth plated surface. These additives can be anything from dish soap to proprietary compounds.
Copper is an active metal and so difficult to plate onto a passivated surface, making direct plating of iron based metals difficult. Such surfaces often require a nickel strike base coat for the copper to adhere to.
We use a copper cyanide-based solution to ensure a high level of copper remains in solution.
- Copper plating is the process in which a layer of copper is deposited on the item to be plated by using an electric current.
- QQ-N-290A is the Federal standard
- Mil-STD-808, TYPE I, Finish P-103
Benefits of Nickel Plating
In general, electroplating improves a wide range of characteristics not inherently present in the base material.
Some of these benefits include:
- Increased resistance to corrosion
- Improved hardness
- Superior strength
- Resistance to wear
- Improved ductility
Nickel is considered useful for plating metal because it provides superior ductility, corrosion resistance, and hardness. Nickel plating can also improve a product’s brightness and external appearance. Different nickel-plating chemicals incorporated into the process deliver anything from a semi-bright and fully bright cosmetic effect, to matte, pearl, or satin finishes.
The Nickel Plating Process
Nickel plating, also known as nickel electro-deposition, is becoming an increasingly popular process for a variety of different manufacturing applications. Electro nickel plating is a process that uses an electrical current to coat a conductive material, typically made of metal, with a thin layer of nickel. Other metals used for electroplating include stainless steel, copper, zinc, and platinum.
Strike Nickel Plating
Another solution to the current density issue involves incorporating a strike layer to the initial nickel plating process. A strike layer, also known as a flash layer, adheres a thin layer of high-quality nickel plating to the base material. Once up to 0.1 micrometers of nickel coats the product, a lower quality current density is used to improve the speed of product completion. When different metals require plating to the product’s base material, striking can be used. In cases where nickel serves as a poor adherent to the base material, for example, copper can be a buffer prior to the electro nickel-plating process.
Pre-treatment Process for Electro Nickel Plating
Proper pre- and post-treatment of the base product has a direct correlation to the quality and deposition rate of electro nickel plating. To help ensure uniform and quality adhesion, chemical or manual preparation includes the following three steps:
- Pre-treatment surface cleaning: Surface cleaning entails eliminating contaminants through the use of solvents, abrasive materials, alkaline cleaners, acid etch, water, or a combination thereof.
- Surface modification: Modifying the exterior of the base product improves adhesion through processes such as striking or metal hardening.
- Post-treatment surface cleaning: Performing finishing operations, such as rinsing, end the electroplating process.
Once pre-treatment cleaning is complete, testing the level of cleanliness in the base material prior to beginning the electro nickel plating process is a good idea. To do this, the waterbreak test is recommended. In this test, the treated substrate is rinsed and held vertical. If contaminants such as oils are absent, then a thin sheet of water remains unbroken across the entire surface of the base material.
Electroless Nickel Plating
Yielding excellent wear and corrosion resistance, electroless nickel is an autocatalytic plating process resulting in a reflective layer of nickel-phosphorous. The total build up plating process provides uniformity on all surfaces, making post machining unnecessary when dimensions are accurate. The surface treatments to increase hardness, lubricity and corrosion resistance.
In terms of ductility, a 0.001″ foil of electroless nickel can be bent 360° around an 18″ mandrel without cracking.
Other benefits include its natural lubricity, which provides excellent release properties, an infinite throw (which eliminates auxiliary anodes), a solderable hard coat for light metals and a self-polishing effect when used in molding operations.
Electroless nickel provides a sound base coating for subsequent finishing operations and has anti-galling characteristics for mating metallic finishes. The process can salvage worn or mis-machined parts and provides excellent wear resistance as an alternative for hard chrome plating.
- MIL-C-26074 Type II
- Grade A, B & C
- Class 1, 2, 3 & 4
- TYPE III
- Excellent abrasion and corrosion resistance
- Uniform plating, no edge build up
- Excellent natural surface lubricity
- Perfect for tight tolerance work
- Can be applied to different substrates including aluminum, steel, stainless steel, brass and copper.
- Well-suited for salvage work
The Electroless Nickel Process
Electroless nickel is a very useful and versatile tool when understood and properly applied. Because of the unique characteristics and physical properties of our processes we can upgrade your existing finishes for stainless steel, aluminum and brass.
Should there be scratches, tool marks or blemishes, they will be duplicated in the finish. Masking for selective plating is possible because the solution will deposit upon contact. The edge definition will be slightly uneven, depending on the thickness of the plate. Allowance should be made for blending in the plate by grinding or stoning, if required. Tapped holes or threads may be plugged or fixtured if they are standard size.
Design consideration should be given to dimensioning parts for overall plating. Joined parts of the same or different materials may be plated. An approved silver solder or a carbon-free weld should be used for joining. Soft solder is usually not platable without special pre-treatment.