Electroless plating on integrated circuits can, however, be challenging because of the fab-specific variations in materials and processes involved in creating the circuits. Aluminum (or copper) alloy composition, sub-structures under the pad metal, passivation material and quality, pad electrical potential, and energy sensitivity (radiation and grounding effects) all play a role in the plating rates, uniformity, and adhesion of the nickel.
Because the process details (inherent tricks of the trade) are not generally regarded as patentable, developers treat their processes as proprietary. Hence, particulars of electroless nickel plating are not readily available.
The first three steps in the process are critical in determining the overall selectivity of the plating process, nickel morphology, and the adhesion of the nickel to the aluminum (or copper) pad. In general, a process that produces fine grained, uniform, thin layers of the catalyst (zinc or palladium) will produce the best nickel plated structures. The specific chemistries and absolute component ratios are critical in producing this desired structure. In addition to selecting the appropriate plating chemistries, one must also consider availability, place of origin, price, toxicology, bath life, waste treatment/disposal, and environmental issues related to the chemicals when implementing a process in a manufacturing setting.