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52 I-CONNECT007 MAGAZINE I SEPTEMBER 2026 the glass, but due to microbreakage, which typically doesn't appear until after the holes are filled, that is not the case. Germany and Korea have strong play- ers in this field. The cleanliness of the glass prior to lasering is also a significant challenge because every particle on the glass can affect the laser process, creating altered or poor hole shapes that can compromise the etching process and make it difficult to meet hole tolerances. Is the cleaning process for glass similar to other such processes? There are similarities. We are currently investigating the particles on the surface of the glass and deter- mining which particles come from the glass's pro- duction. We are working with glass suppliers who are well-renowned in materials science and glass technology. Most people etch glass using an alkaline-based immersion process, which involves dipping. It typi- cally takes 10 hours or more, which is a very long time. At SCHMID, we prefer to etch with hydroflu- oric acid (HF) solution. So, we have, as an option, a first stage with alkaline etching on a horizontal machine, followed by a second stage with HF, which etches faster. But in a dipping process, which uses a basket, it's easy to get non-uniform etching because the solu- tion cannot flow well through all the holes and the surface. Another problem is creating micro-cracks simply from panel placement in the basket. In our horizontal etching lines, we have a flooding system for better uniformity when processing full panels. This produces greater uniformity during the etching of the glass. Given that microcracks in glass are a critical issue, how are you gauging the quality of glass? Some companies have a system that allows you to detect micro-cracks on the surface at the entrance of the holes. But detecting this type of microbreak- age is difficult. Microcracks are usually an issue after thermal processing, which is primarily when they are detected. The real challenge is the metallization of the through-glass vias (TGVs). There are two ways to fill a glass via. One is with a seed layer, which can be deposited by sputtering or by a metal oxide. Sput- tering can have an aspect ratio of no more than 1:6. For metallization with a metal oxide, the ratio can go up to 1:20, but beyond that, filling the holes will be very difficult. In our work, we see the optimum process at an aspect ratio of 1:6 to 1:8. You get voids beyond that. Given the difficulty of filling the TGV, some companies are now providing an acceptable tolerance for voids in glass vias. You mentioned there is a lengthy processing time for etching glass. What does the plating process look like for glass? Plating time with conformal plating, bridging, and filling can be lengthy as well. Some say four to six hours, but it's more like 12 to 20 hours of total plat- ing time. We have the "bottom/top plating," mean- ing we apply special copper layers on one side and Figure 1: Cross-sections of through-glass vias (TGV) filled with bottom-top technology with different densities that show no voids.