Laser‐Enhanced Electrodeposition of Lead‐Tin Solder

Abstract

Localized, maskless electrodeposition of lead-tin solder from a sulfonate electrolyte has been achieved by means of laser enhancement. Well defined spots and lines with good surface morphology have been deposited on copper and nickel substrates. This is possible because the laser is found to reduce the deposition overpotential on these substrates.Electrodeposited lead-tin solder alloys are used in a number of electronics applications (1, 2). Through-mask plating is typically employed to deposit the solder onto geometrically defined areas. We report here the results of a study to examine the feasibility of utilizing laser enhancement as a means of achieving maskless electrodeposition of solder alloys. The use of laser-enhancement to produce maskless, localized electrodeposition of gold (3) and copper (4) has previously been investigated. It has been shown that sufficient thermal enhancement of transport and kinetics can be achieved for these metals that localized deposition, often at very significant rates, can be obtained with no significant background plating outside of the illuminated area. Laser enhancement has also previously been applied to alloy electrodeposition, primarily for hard gold alloys. The deposit compositions are found to differ significantly from those obtained under normal, nonlaser plating conditions. The laser enhancement favors only one of the alloy components (5). In fact there are no reports of laserplated alloys containing more than a few percent of the alloying element.A methane sulfonate lead-tin plating electrolyte was employed in the present work. Preliminary studies indicated that the application of laser enhancement to electrolyte compositions typical of those used for conventional 60 Sn/40 Pb plating gave deposits that were primarily tin. For this reason we employed an electrolyte with 20 g/liter each of lead and tin (added as methane sulfonates) for the alloy deposition. This tin concentration represents half of that used in a typical 60/40 plating bath. The electrolyte also contained 81 ml/liter of methane sulfonic acid (70%). The as-supplied tin methane sulfonate concentrate contained < 1% of a proprietary anti-oxidant, identified as a dihydroxy aromatic. Two additives, 5 ml/liter of the surfactant octylphenoxypolyethoxyethanol (Triton-X-100) and 0.25 g/liter of 2-4, dimethoxybenzaldehyde (brightener) were used. These additives had been found to be effective in other studies by us on lead-tin electrodeposition from methane sulfonate electrolytes (6). In particular the Triton X-100 was necessary to prevent dendritic growth.A cw argon ion laser (wavelength 488 nm) was focused to a spot on a glass slide substrate coated with approximately 500 A Cr and 2000 A Cu or Ni. The specimen was immersed vertically in the unstirred electrolyte adjacent to the end quartz window of a glass cuvette. Initial experiments involved electrochemical polarization measurements, both with and without laser illumination. Polarization measurements were conducted on electrodes that were covered with photore...

Experimental Investigation on Laser-Induced Electrochemical Silver Plating Technology

“…Currently, many studies have focused on laser-enhanced electrodeposition to improve coating quality and laser-selective electrodeposition on semiconductor substrates. − Less research has been done on laser-induced localized electrodeposition of silver coatings on metallic substrates. Unlike the previous laser-induced electrodeposition preparation of gold coating by Guo et al, the localized silver coating experiment consisted of three processes: preplated silver, laser-induced electrodeposition silver, and deplated silver.…”