Molybdenum, by buffering silicon against damaging thermal expansion whilst providing a contact of low electrical and thermal resistance, has an important part to play in determining the reliability of semiconductor devices. By selecting appropriate surface coatings, the bulk properties of molybdenum can be used to full advantage without the problems associated with the chemistry and metallurgy of its surface.

Within H.C. Starck`s electro-plating processes are finely tuned to ensure consistent and high quality results. Adhesion and integrity are vital to the reliability of semiconductor devices, and all coatings are diffusion bonded to the molybdenum by sintering under selected time - temperature cycles. The inter diffusion of substrate and coating then guarantee the adhesion of the surface layer, interracial and intergranular oxides are dispersed, the surface layer is annealed and consolidated and the exposed surface is cleaned and degassed. These are all ideal preparations for solder-wetting, electrical contact or corrosion protection. For soldering and alloying applications, excellent wetting and adhesion can be obtained with any hard or soft solder, eliminating the need for expensive and capricious special solders which are highly sensitive to conditions and can require unnecessarily high temperatures.

Pressure contact devices benefit from the use of discs coated to optimise tribiological and electrical contact properties, and modern techniques permit 100% adhesion of these coatings whilst providing less than one micron flatness deviation.

Coatings can be supplied on one, both, or all sides of the product and our technical staff are always available to advise the best coating for your application.

Example coatings and applications for Molybdenum

Nickel 1-2 microns Pressure Contact (or light duty soft soldering). May be base layers for precious metal in these applications.
Nickel 5 microns Solder wetting A firmly bonded base layer whose resistance to passivation may be enhanced by further layers (see below).
Nickel 25 microns Solder wetting and etch resistance an economically applied layer, it retains a solderable surface after heavy etching and also facilitates re-work of failed devices.

Nickel 5 microns +

Gold 1-2 microns

A) solder wetting     B) Electrical contact
C) Etch resistance   D) Au-sieutectic bonding

Nickel 5 microns +

copper 5 microns

Solder wetting for soft soldering
Nickel 5 microns +
gold 0.5 microns +
silver 5 microns
Solder wetting An intermediate gold layer enhances adhesion at high temperature.
Nickel 1-2 microns +
Copper 50-100 +
Nickel 3-5 microns
Superior multi layer system to Cu-Mu-Cu composites used for PCB heatsinks and hybrid ciruit substrates. Offering high integrity diffusion bond avoiding the problems of interfacial contaminant leaching.
Gold (alone) Excellent protective layer which can be applied without heat treatment to produce extremely flat discs for pressure-assembly applications.
Rhodium 0.3 microns A) Electrical contact Very low, stable electrical contact resistance and excellent tribological properties make Rhodium an ideal pressure-contact coating.
B) Solder wetting Wetted by both aluminum-based and silver-based solders.
Ruthenium 0.3 microns Same application as Rhodium with the advantage of being significantly cheaper
Platinum 0.5 microns +
silver 5 microns
Spacecraft Solderable non-magnetic coating with excellent electrical properties
Electroless Nickel* High uniformity of thickness with excellent chemical and physical properties. Particulary beneficial when coating complex parts.
*Not an electrolytic process. Deposition is dependant on autocatalytic effect.