MicroTech Systems, Inc. Engineering Wet Process Solutions

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Electroplating Tutorial

There are basically three types of plating:

  1. Electrolytic (often call electroplating) that uses electrical current to reduce metal ions,

  2. Electroless (autocatalytic) that uses a chemical reaction to induce the ion reduction, and

  3. Immersion (displacement), where the metal ion is reduced from solution by exchange with a metal ion from the substrate.

There are several components to a Plating Bath that are critical to plating success:

  • Metal salt: the source of the plating metal, for example, copper sulfate

  • Acid, base additive: provides ionic conductivity, e.g., sulphuric acid

  • Carriers: help increase throwing power into holes, e.g., polyethers

  • Levelers: improve plating thickness uniformity, e.g., organic N2 compounds

  • Brighteners: control deposit brightness and hardness, e.g., sulphur containing compounds

  • Wetters: decrease surface tension, e.g., surfactants.

Filling Vias

In microelectronics, plating is very effective in filling high aspect ratio open or blind vias. This creates different plating environments in distinct regions of the substrate by manipulating the surface concentration of the organic additives. Agitation is crucial to remove any brighteners from the surface of the substrate. In-via agitation can disrupt the required brightener concentration in via holes. Of course, the plating bath must be specially designed for this purpose.

The via size must be wide enough to sputter a minimum of 1000 angstroms of seed metal along the wall of the via. Once the wall is plated, a low current density cycle followed by a higher current cycle can also help with this situation.

Copper Plating

Copper is often used as a plated layer of plated via substance. Its role can be as a:

  1. Electrical conductor

  2. Thermal conductor

  3. Ductile layer

The typical key properties of copper plating include a thick deposit and a dense via fill to avoid trapping of plating impurities.

Nickel (die attach, diffusion layer and wirebond applications) and gold (die attach and wirebond applications) can also be used to plate substrates.


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