Electroless nickel plating solution

Electroless nickel plating solution (Nickelex) is a type of auto-catalytic plating in which many reactions occur in an aqueous solution without any external power source. Its process includes the catalytic reduction of nickel in an aqueous solution. Nickelex produces an amorphous deposition of nickel in the as-plated condition. It shows properties such as good hardness, corrosion resistance and wear resistance.

Stable electroless nickel plating composition, ready to use, specified for making ohmic contacts to silicon and other semiconductor materials

Advantages

• Stable, ready to use
• Plates without generating ammonia fumes
• Produces quality electrical contacts on p- and n-type silicon
• Does not compensate for p- or n- type conductivity
• Excellent adhesion and solderability
• Plates on silicon, germanium, gallium arsenide, cadmium sulfide

Nickelex is a vastly improved, electroless nickel preparation, formulated specially for semiconductor use. The composition is based upon ions of a nickel complex and hypophosphite together in solution with a catalytic accelerator and a stabilizer. The solution is also buffered at the optimum pH for electroless nickel catalysis. In addition, only high purity chemical materials with trace impurities (such as copper) specifically removed are utilized. NICKELEX, is a very stable product, free of ammonia, and ready for use without the need of any addition or mixing. Fume problems are completely eliminated. Nickelex, furthermore, is not subject to undesirable changes in composition during use.
The chemical reaction during the electroless plating process involves an oxidation-reduction reaction between nickelous and hypophosphite ions. The reaction is essentially a two step process occurring simultaneously.

(1) H₂PO^2- + H₂O --> H₂OPO^3- + H₂
(2) Ni ⁺⁺ (complex) + H₂ --> Ni + 2H⁺

The reaction progresses catalytically with nickel deposition occurring at the operating temperature of 95 °C - 100 °C. The nascent hydrogen evolved insures an oxide free nickel deposit. In addition some NiP formed in a side reaction improves corrosion resistance and solderability. The nickel deposit is highly conductive, remains unstressed, particularly after suitable heat treatment, and shows good adherence.

Nickelex can be deposited on p-type porous silicon for potential usage in light-emitting diodes (LEDs), and organic solar cells.

Use of Nickelex:

• Nickelex provides good mechanical and electrical contacts for semicodonductor devices (silicon rectifers, solar cells, varactors, microwave diodes, transistors, microcircuits, etc.). The quality of the electrical contact is excellent if the surface of silicon is abraded by lapping to increase surface recombination velocity; if the surface is highly doped from diffusion; or if the semicondcutor resistivity is low (0.1 ohm-cm). Nickelex also produces adherent deposits on germanium, gallium arsenide, and cadmium sulfide.
• The Nickelex plate exhibits excellent solderability with lead, tin, and Pb/Sn alloys. Flux can be omitted when furnaced soldered in a hydrogen or non-oxidizing atmosphere.

Instructions

Complete metallization procedures are provided for silicon rectifier and planar device fabrication. These procedures should be followed to obtain optimum adhesion of nickel and quality of the ohmic contacts.