Printed Circuit Board (PCB) manufacture involves an electrolytic copper deposition stage for consolidation of conductive circuit paths. Miniaturisation trends requiring increased circuit densities and high aspect ratio through-holes are restricted by the phenomenon of non-uniform copper electrodeposit thickness which can affect electrical impedance properties of the circuitry, cause electrical discontinuity between adjoining circuit layers and inhibit component-lead insertion. This thesis considers means of enhancing the electrodeposition process to alleviate the aforementioned problems. Following a comprehensive review of process technology, both a novel electrolyte agitation method utilising eductors and a Periodic Pulse Reverse (PPR) current technique were investigated experimentally within a pilot tank containing 350 litres of electrolyte. Eductor agitation was analysed/optimised using high-speed photography and a mass transport mapping technique. Data for agitation configurations were verified by statistical analysis of thickness distributions across high surface-area panels. PPR current was initially studied with a small-scale pulse unit and Assaf Cell throwing power test, followed by pilot tank trials using a full-size pulse rectifier in conjunction with eductor agitation and a proprietary electrolyte containing additives. Through-hole throwing power, deposit morphology and microstructure were investigated under various low-frequency pulse conditions and anodic-to-cathodic current density ratios. Eductor agitation and PPR current were compared against the more widely used air agitation and direct current techniques. The effects of air agitation on electrolyte conductivity and commercially produced PCBs were also considered. Optimum agitation conditions were achieved using eight eductors inclined at 37.5° from the horizontal and spaced equidistantly along longitudinal tank walls. Such conditions decreased the standard deviation of copper thickness measured on high surface area panels and lessened edge-effects. Consistent agitation levels up to ten times greater than static solution were recorded, providing enhanced deposition rates; by comparison, air agitation achieved levels of around seven times in uniform regions. Conductivity data showed good correlation with a theoretical approach; air agitation was found to reduce conductivity in proportion to the voidage fraction of gas bubbles and by 20-30% in electrolyte adjacent to air sparge pipes. PPR current provided superior deposits compared to direct current. Through-hole throwing power ratios between 1:1 and 1.3:1 (hole-thickness: surfacethickness) were recorded at mean cathodic current densities between 3.3-4 A/dm2 using pulse timings of 15,1,20,1,25,1 and 30,1 ms (cathodic: anodic) and current density ratios between 2.6:1 and 3:1 (peak-anodic: peak-cathodic); optimum conditions for boards produced in the pilot tank were provided by the 20,1 ms timing. The 25,1 ms timing exhibited high throwing power between 2.5-3.5 A/dm2 under Assaf evaluation but was unable to maintain a uniform thickness distribution in through-holes across a PCB surface. Deposit microstructure and microhardness recorded using PPR current varied according to pulse parameters. Controlling factors and their influence upon results were discussed. Parameters critical to optimisation of agitation and PPR current were attributed to electrochemical effects during deposition. The merits, limitations and potential application of these techniques were examined in relation to PCB manufacture and future priorities were considered.

Thesis (Ph. D.)--Columbia University, 1932. / Vita.

( i) A linear circuit is shown not to explain the behaviour of a conductivity cell towards a long rectangular pulse of amplitude less than the decomposition potential of the solution in the cell. (ii) It is shown that the flow of current through the cell is governed by diffusion to the electrode. The diffusion current expression is the familiar one used in the case of diffusion up to a plane micro-electrode, except that in this case the concentration in the layer next to the electrode is not zero, but only somewhat less than the bulk concentration. (iii) Except during a short initial period (less than 10 seconds), the resistance of the electrolytic cell varies directly with the square root of the time for which an e.m.f. (less than the decomposition potential) is applied to the cell, and inversely with the concentration difference between the electrode surface and the bulk of the solution.

The subject of this thesis was chosen originally as a result of a suggestion made by a manufacturer of lactic acid. Lactic acid is made by a fermentation process from molasses and the acid is extracted from the fermentation liquors as calcium lactate. The conversion of the calcium lactate back to lactic acid is a tedious process from an industrial point of view. It was therefore suggested that the conversion may be more easily accomplished by electrolysis. The first experimental work was conducted with this object in view, but it soon became apparent that it was unlikely that lactic acid could be produced in suitable quantities for industrial purposes by this means. There was no reference in the literature to the electrolysis of calcium lactate, and little reference to the electrolysis of lactates in general, and what there was appeared to be conflicting, so it was decided to continue the investigation into the subject in order to determine what are the products of the anodic oxidation of calcium lactate. Intro., p.1.

[No abstract submitted] / Science, Faculty of / Chemistry, Department of / Graduate

The effect of stress on the electrode potential of copper in aerated cupric sulphate and in aerated cupric chloride solutions was studied. The influence of the variables time, temperature, concentration, magnitude of stress, mechanical condition of the metal, and pH was considered. The potential difference between two size #22B&S copper wires was continuously recorded on a type G speedomax automatic recorder. Weights were added to one of the wires and the change in the potential difference between the two wires from the pre-stress potential difference value was taken as the strain potential. At least six runs, using fresh pairs of wire for each run, were carried out to illustrate each specific point and to show the results have statistical significance and are reproducible. The following results were obtained: (A) Electronegative strain potentials have been obtained for copper metal in copper sulfate solution; these changes achieve a maximum at the instants of stressing and then decay with time. The magnitude of the electronegative strain potential for a given stress increased exponentially with the absolute temperature and decreased significantly for concentration changes from 0.0005 N to 0.500 N. (B) Experimental evidences were obtained to support the postulate that strain potentials of copper metal in copper sulfate solution and their time dependence parallel film rupture and repair. (C) Both electronegative and electropositive strain.potentials were obtained with size #22B&S soft copper wire in cupric chloride solution; the sign of the strain potential was negative for a concentration of 0.500 N and the sign of the strain potential was positive for concentrations of 0.100, 0.050, and 0.005. The magnitude of the strain potential did not vary with concentration as for the case of copper wire in copper sulfate solution. The electronegative change, obtained in 0.500 N cupric chloride lasted for less than three seconds whereupon the change in the potential difference between the two wires shifted rapidly to a positive value. An attempt was made to explain these results on the basis of the stability of Cu₂O and CuCl films using potential-pH diagrams. The magnitude of the strain potential for a given stress was found to vary exponentially with the absolute temperature between the range 298°K to 338°K. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Call number: LD2668 .T4 1951 M377 / Master of Science

Vita. / Digitized by Kansas Correctional Industries

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references.