Electroless Deposition of Gold

Abstract

The term electroless plating was originally used by Brenner and Riddell [1], inventors of the well-known autocatalytic nickel and cobalt plating processes using hypophosphite as the reducing agent. A literature survey indicates, however, that this term is currently being used to describe three mechanistically different, nonelectrolytic processes for depositing metals and alloys: (1) galvanic displacement plating (also called immersion plating or cementation), (2) substrate-catalyzed plating, and (3) autocatalytic plating. In this chapter only autocatalytic gold plating processes are reviewed.The first autocatalytic, electroless gold plating bath was developed in 1970 at Bell Laboratories [1a] to plate thick, pure soft gold on semiconductors and circuit boards without employing an external source of electric current. The bath contained potassium cyanoaurate (I), KAu(CN) 2 , as the source of gold, potassium borohydride, KBH 4 , or dimethylamine borane, (CH 3 ) 2 NHÁBH 3 , as the reducing agent, potassium cyanide, and potassium hydroxide. Typical bath compositions are given in Table 21.1. The original baths did not contain stabilizing additives, and they were sensitive to minute amounts of impurities, which tended to lead to spontaneous decomposition. Nevertheless, those baths were employed successfully with sufficient stability under carefully controlled conditions [2-5], yielding highly pure, soft gold useful for the purpose of bonding semiconductor devices [6]. Other successful applications documented in the open literature include (1) metallization of GaAs microwave field-effect transistors [7], (2) formation of ohmic contacts consisting of Pd/Sn/Au films on n-GaAs [8], (3) metallization of polyvinylidene fluoride (PVDF) films used for making piezoelectric devices [9], (4) deposition of a conducting layer on the interior surface of waveguide tubes made of an aluminum alloy [10], and (5) deposition of a gold layer on tungsten-metallized ceramics for packaging semiconductor devices [11].More recently the accelerating trend of miniaturization and the need for greater reliability of electronic components have resulted in the development of new technologies for mounting devices on circuit boards, which in turn created new requirements for compatibility of the plating process with substrate materials and also for properties of gold films to be deposited on semiconductors and circuit boards. Quite generally, the method of electroplating has inherent advantages over that of electroless plating in terms of the ease of maintaining the bath and controlling the film thickness and properties. On the other hand, electroless plating has, in principle, a distinct advantage over electroplating in its capability of minimizing the number of processing steps when gold is needed in areas which are electrically isolated from each other. Under these circumstances, efforts have been made to improve the original borohydride and dimethylamine borane (DMAB) baths, especially in their stability and plating rate, and such improved baths are...

Development of Hybrid Electro-Electroless Deposit (HEED) Coatings and Applications

“…The choice of Ni as the substrate for the formation of the Co/Au tri-layer deposit was based on past successful electroless deposits of Au on Ni from the electrolyte as well as the document success of similar Au electrolytes. The specific Au electrolyte chosen for this work, Table II, was modified from one used by Paunovic and Sambucetti 14,15 as it demonstrated exceptional stability in the presence of CoSO 4 . The base electrolyte is composed in two parts, 'Bath A' and 'Bath B', which are mixed slowly at a 1:1 ratio.…”

“…13 Additionally, the Au electrolyte does not contain a typical reducing agent, such as sodium hypophosphite {NaH 2 PO 2 }, but rather makes use of the mixed ligand structure as a means of reduction with SO 3 − acting as the main reducing agent. 15 In order to allow surface-on analysis, the sample was raised for each of 3 stages of deposition creating single, bi-layer, and tri-layer deposits on a single surface. In stage 1 electroless deposition of Au occurred on the immersed portion of the Ni substrate surface for a deposition time of 20 minutes.…”

A Practical Approach in Glycerol Oxidation for the Development of A Glycerol Fuel Cell

“…The change may be possibly related to copper oxidation [41]. Also, it may result from displacement of copper ions for the more noble gold ions [40]. The effect of cyclic voltammetry cycling is presented in Figure 13.…”

“…A Zn-Au electrode was prepared using the same procedure for the GC-Au electrode. The electrode was checked visually before and after been in the aqueous solution of AuBr 2 and it was observed a change in color on the surface of the zinc electrode, the change may be related to zinc oxidation [39] and also, to a displacement of zinc ions for gold ions [40]. In order to observe if gold is presented on the surface of the zinc electrode voltammetry was used.…”

Selective Laser Sintering with Gold Nanoparticles on Stainless Steel for Electrical Components

“…Besides, the surface requires a middle layer formed by strike electroplating with nickel or gold to obtain firm adhesion. [8] From an industrial point of view, cost-effective measures ought to be taken in electroplating, including the reduction of gold consumption and a short processing time; an ecofriendly process is also desirable. To meet with these requirements, a novel process for electrical contact forming, which combines dispensing a silver nanoparticle paste with laser sintering, has been proposed.…”