Fine hole drilling of alkali-containing silicate glass substrate using preferential penetration of etchants around silver precipitates

Abstract

Solid-state ion exchange is a metal doping method used for alkali-containing glass materials. When an additional voltage is applied to the silver-doped glass surface, it yields nanometer-sized dendritic precipitates in the doped area. The silver precipitation is accompanied by crack formation, which causes the formation of a network of micro-cracks in the glass substrate. These crack networks can be a penetration path for the etchants in removal processes. In this study, we evaluated the effect of etching conditions on the dissolution characteristics of silver-precipitated and un-precipitated areas. Furthermore, fine hole drilling of glass with a higher aspect ratio was performed. When hydrofluoric (HF) acid was used as an etchant, the etching rate of these areas increased with an increase in the etchant temperature and concentration. However, there was no significant change in the etching rate ratio (etching rate of silver-precipitated area per that of un-precipitated area). Similarly, the effect of the etchant concentration on the etching rate ratio was small in the case of potassium hydroxide (KOH) solution. However, the etching rate ratio in the KOH solution was more than three times higher than that of the HF solution. This demonstrates that the KOH solution was suitable for the preferential removal of the silver-precipitated area. Additionally, fine hole drilling of the glass substrate was performed using patterned silver plating film as a silver ion source. Consequently, through-glass hole array was successfully formed.