Glass-core substrates are redefining advanced packaging by overcoming warpage and thermal management limits of organic materials. Central to this technology are through-glass vias (TGVs), whose precision and density define performance. We present an innovative alkaline etching technology combined with laser modification, enabling unprecedented control of via geometry with taper angles below 1°. Compared to conventional acidic etching, our process delivers higher selectivity, at advanced throughput, and compatibility with industrial considered glass types. This breakthrough enables the scalable production of ultra-high-density TGV substrates—paving the way for next-generation packaging demands.