SUMMARYThe properties of anodic films produced by anodising aluminium in aqueous solutions of organic acids at room temperature at commercially interesting current densities were investigated with particular emphasis on the wear index, micro hardness, surface roughness and pore structure. Voltage time curves obtained using 10% w./v. solutions of the pure acids showed a rapid rise in voltage at commercially realistic current densities of 1–2 A dm−2 but this problem could be overcome by the addition of 1–2% v./v. sulphuric acid. The films obtained under these conditions using sulphosuccinic acid (SSA), sulphosalicylic (SCA) or sulphophthalic acids (SPHA) had properties closely resembling those obtained under hard anodising conditions in 10% sulphuric acid at 0–4°C. Films were not formed using para-toluenesulphonic acid (PTSA) and the use of maleic acid (MA) resulted in the formation of substantial quantities of fumaric acid. The oxide films exhibited a structure made up of densely packed columns suffused by narrow pores. The films fall into two categories. On the one hand films produced using sulphur containing organic acids have very narrow pores of less than 10 nm diameter resembling those produced by the conventional low temperature sulphuric acid process, and on the other hand films produced using maleic or citric acids exhibit much larger pores with diameters of the order of 20 nm. Attempts to incorporate PTFE particles from aqeous dispersions of this polymer into the films were unsuccessful due to their large size (~200 nm). Duplex films with a highly porous outer layer (~100 nm diameter) on top of a dense hard layer were produced and evidence is presented which shows that some of the smaller PTFE particles can enter the mouths of these pores.

Aluminium oxide films may be electrolytically treated in order to modify or enhance their physical characteristics, with electrocolouring being the common application. This research has shown that the incorporation of a metallic deposit into the porous oxide film can also improve the tribological properties of the film using methodology similar to electrocolouring. Performance of this coating system has been evaluated for two common aluminium alloys using standard mechanical tests, LIMA surface analysis and electron microscopy. Such films treated with In, Sn or In-Sn have shown improved abrasion resistance and reduced coefficient of friction compared to a 'standard' film making them especially suited to applications requiring low friction properties and good sliding wear resistance.

A new throwing power cell is described in detail; it has the virtue of being usable as a small fixture that can be positioned in an electroplating tank, This so-called Assaf Cell is particularly useful for simulating small recesses, typically through-holes found in printed circuit boards (PCBs).This paper demonstrates how a Throwing Power Index, given by the ratio of metal thickness on the front and rear faces of the Assaf-Cell test panel, may be used to evaluate/optimize electrodeposition conditions. Data are presented from work using various electrolytes, including high-throw acid copper solutions, thereby illustrating its usefulness and application.

Parmi les procédés de finition des métaux, l'électrodéposition du chrome et l'anodisation de l'aluminium sont deux techniques qui nécessitent une agitation importante. Pour différentes raisons, c'est l'agitation par air qui est habituellement préconisée. Cette agitation produit un fluide diphasique qui a été peu étudié.

The contribution of N.T. Kudryavtsev (and later his son V.N. Kudryavtsev) to the development of electrodeposition science and technology, and especially to that of chromium, is inestimable. It is a privilege on this occasion to present some considerations of the two-phase nature of chromium electroplating solutions, caused by the generation of hydrogen gas and the use of vigorous air agitation, and to discuss its influence on fluid conductivity and consequent power consumption during electrodeposition.

The necessity for agitation of anodising solutions is well known but is particularly acute in the case of production of hard anodised surfaces. Throughout metal finishing agitation is widely practised for a number of reasons, only two of which are appropriate to anodising:1. To remove heat from the electrode-electrode interface.2. To dissipate aluminum ions and any oxygen gas at the anode/solution interface.The use of eductors, which are available in many proprietorial forms, is in principle old technology but has recently been adapted for use in electroplating applications.The paper will discuss results for eductor agitation and show that they are of importance in the context of surface heat dispersal, the effectiveness of which can be assessed in terms of anodic film hardness and porosity which are the two properties most sensitive to temperature rise beyond specified values.Limitations of the analogy will also be considered, notably that anodic film formation is not usually solution mass transfer controlled and so the opportunities for process rate-enhancement may be limited, unlike electrodeposition.

The effects of air agitation on electrolyte conductivity have been considered. Experimental data obtained from a conductivity probe was found to be comparable to theoretical models for conductivity which show that localized reductions of 20–30% are quite normal in an acid copper electrolyte. Such nonuniformity within an electroplating tank could be one cause of the throwing power/metal distribution variations which are normally attributed to surface irregularities or poorly designed agitation systems. These aspects have particular bearing for printed circuit board (PCB) manufacture where consistency in electrodeposition is paramount to ensure low defect or failure rates, especially within high aspect ratio through-holes.

SummaryMetal distribution on printed circuit boards exhibits two main problems: over-board thickness variations and through-hole thickness uniformity. A novel electrolyte agitation method involving eductors has been fully characterised using both three dimensional mass transport mapping of agitation patterns within a process tank and by measuring copper thickness distribution on stainless steel panels. Results indicate that improved thickness distribution across boards and enhanced deposition rates are possible using this technology.