Selective Laser-induced Etching of Borosilicate Glass In Hydrofluoric Acid

In recent years, with the continuous development of 2.5D/3D packaging, glass interposers that can achieve vertical interconnection have been widely used due to their excellent high-frequency electrical characteristics. However, one of the main difficulties restricting the development of glass interposers is vias formation technology. The through glass via (TGV) technology has become a research hotspot due to its advantages such as low cost, small size, fine spacing, and simple process flow. This paper introduces a method of selective etching borosilicate glass substrate by laser modification. In this method, the borosilicate glass substrate was modified with an infrared ultrashort pulse laser, and then the modified substrate was etched with hydrofluoric acid. In this paper, a hydrofluoric acid wet etching model was established, and an electromagnetic simulation of TGV was conducted using the HFSS software. Ultimately, the process was optimized based on the wet etching model and electromagnetic simulation results. Through the experiments in this paper, the validity of the established wet etching model has been confirmed, and the optimization results based on the wet etching model and HFSS simulation show that a vertical through-hole (~85 °) with a diameter of about 100 μm can be obtained on borosilicate glass. A low-cost and small-size TGV formation technology has been realized.