Electroplating Process: Methods and Metals

Introduction

A crude metal will likely corrode due to environmental conditions. In order to protect it, manufacturers can use the process of electroplating.

In this post, we’ll help you understand what is electroplating, the different methods of electroplating, and several common metals used in the process.

Table of Contents

What is Electroplating?

Electroplating is a process by which metal ions migrate via a solution from a positive electrode to a negative one. An electrical current passing through the solution causes objects at the cathode to be coated by the metal in the solution.

Electroplating Makes Use of an Electrical Current

Many products have electroplated parts; the most popular items are electroplated jewelry. A car has numerous electroplated parts, including its bumpers, hubcaps, grilles, door handles, and other decorative trimmings. The body of the car and its various automotive parts are electroplated to prevent rust, protect it from heat and other potential damage.

The aerospace industry also uses electroplated parts similar to cars, but they use electroplating to increase the hardness and thickness of the airplane’s body to make it resistant to atmospheric and other environmental conditions or to use lighter materials and have functional coatings with specific properties. Electronic devices, including computers and smart phones, also have electroplated parts that allow for better conductivity of electrical current as well as prevent overheating during charging.

Electroplating Methods

Barrel Plating

The primary function of barrel plating is to provide an economical means to electroplate manufactured parts that also meet specific finishing requirements. This method is best for high-volume plating with uniform coverage.

The parts that need to be plated are placed inside a barrel and immersed in the metal plating solution. The barrel slowly rotates and electrical contact is achieved through the use of danglers or centerbars located inside the barrel. The mechanical energy of the rotation produces a burnishing action that helps to clean and descale the parts to a greater degree than rack plating. The tumbling action is also responsible for the high degree of plating uniformity which can be achieved in the barrel.

Rack Plating

Rack plating is used for coating large, complex or fragile parts where they are hung on a “rack” and then submerged in the plating solution in a tank. For electrical contact, metal bands or hooks are used to hold the parts that need to be plated.

In this method, damage to delicate parts are lessened, intricate contours and deep crevices are evenly plated, and the finishes are generally of higher quality than barrel plating. With this method and by using specific masking products and techniques, it is possible to produce selective deposits.

Reel-to-reel Plating

Reel-to-reel plating is an efficient and economical method to plate strips of manufactured products or reels of raw material before they are used for parts. Electronics and semiconductor components are the primary parts that are plated using this method. Typical examples of these parts include connector contacts, lead frames, connecting devices, leads, headers, or the solid strip materials from which contacts and components are subsequently formed.

The process starts by loading the reels onto a de-reeling station. Thereafter, the material is fed through various electroplating processes using a capstan system. At the end of the line is a take-up system that re-spools the material once the desired metal finish is achieved.

The process can be summarized in 3 stages:

Key Stages of Reel-to-reel Plating

Inspection

Finished products in electroplating are subjected to a number of tests to ensure good plating quality. Typically, these tests may include:

  • Adhesion: By twist, bend bake and/or tape
  • Appearance: Visual and microscopic (to the level of magnification contractually agreed on)
  • Solderability
  • Bondability: E.g. ultrasonic wire bonding
  • Porosity: Can include nitric acid vapor or immersion, electrolytic or gas techniques
  • Thickness: X-ray Fluorescence (XRF) or microsection

Common Types of Metals Used for Plating

Copper Plating

Copper layers are very decorative and are good electrical conductors. Depending on the additions, hardness can vary between 90 HV and more than 200 HV. For functional applications, a copper layer is often covered by another metallic layer.

Advantages

  • Copper layers have excellent heat and electrical conductivity
  • A very wide range of properties are achievable by changing the deposition conditions
  • A large number of metals and plastics can easily be plated with copper
  • Copper plating is an essential step in the fabrication of printed circuit boards

Limitations

  • Copper may tarnish in air or when touched; this necessitates a metallic or organic top layer

Nickel Plating

Nickel layers are not only decorative, but also corrosion and wear-resistant. Depending on the organic additions, the deposit can exhibit hardness values between 150 and 500 HV. The metal layer may have varying levels of internal stress and ductility. Bright nickel looks yellowish in daylight and tarnishes easily; for this reason, it is commonly covered with a top layer such as chrome or gold.

Advantages

  • Attractive-looking decorative layer
  • Corrosion and wear-resistant
  • Different bath compositions can be used for vastly differing applications
  • Can be applied on a wide variety of substrate materials
  • A good underlayer for other surface coatings

Limitations

  • Discoloring of nickel in air necessitates the use of a top layer; for electronics, a final coat of gold may be necessary
  • Nickel could cause allergic skin reactions

Tin Plating

Tin offers a good level of conductivity, making it extremely useful in the manufacturing of various electronic parts. It is also widely used in the food production industry.

Advantages

  • Corrosion and adhesive wear resistant
  • Good solderability
  • Resistance welding is possible after deposition of tin
  • Good electrical properties
  • Approved for use in food industry (FDA-approved)

Disadvantages / Limitations

  • High-strength steel is sensitive to hydrogen embrittlement
  • For some substrates, heat treatment is necessary in order to prevent brittleness
  • Under certain conditions, whisker growth could appear from the tin layer which could cause short circuits in electrical contacts

Gold Plating

Gold layers have many technical applications, related to their excellent corrosion resistance, low electrical contact resistance and good electrical and heat conductivity.

Gold layers can be deposited on a large variety of substrates such as metals, plastics, ceramics and natural materials (such as leather and wood), in all cases using an intermediate copper or nickel layer.

Advantages

  • Outstanding electrical conductivity
  • Excellent heat conductivity
  • Good solderability
  • Good corrosion and chemical resistance

Disadvantages

  • High cost, which can fluctuate during the year
  • Softness of the unalloyed metal

Silver Plating

Due to its good electrical conductivity, silver is very often used in electrical and electronic applications.

Advantages

  • Outstanding electrical and heat conductivity

Disadvantages

  • Tarnishes readily in air under certain conditions and in the presence of sulphur-containing compounds

Palladium Plating

Palladium is well suited to plating applications where the prevention of oxide formation is required. It has a high melting point of 1554°C and costs less (per ounce troy) than gold. In most general electronics applications, palladium is an excellent substitute for gold.

Advantages

  • Cost-effective plating; relatively inexpensive compared to other precious metals
  • Corrosion-resistant; it is about as resistant to corrosion as gold, with a natural resistance against oxidation
  • Relatively hard; despite being considered a softer metal, it is still harder than gold, which helps against impact and denting
  • Diffusion-resistant; copper diffuses rapidly through gold but not palladium, making palladium an excellent coating for copper objects
  • Very good solderability

Disadvantages

  • Reduced heat resistance; Palladium has a lower melting point than gold, making it easier to deform under extreme heat
  • Not resistant to acid; Vulnerability to strong acids limits the types of applications where palladium can be used
  • More prone to cracking; when placed under stress, palladium is more prone to cracking than gold because of its hardness

 

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