CO2-laser drilling of TGVs for glass interposer applications

Glass as a substrate material for interposer application has many benefits compared to conventional packaging materials like silicon, ceramic or polymer based laminates because of its excellent dielectric and transparent properties. Furthermore, the integration potential of glass is superior because of the dimensional stability under thermal load and the coefficient of thermal expansion (CTE) matching to that of silicon ICs. A small pitch size of conductor traces, small scale through-vias and high alignment accuracy are the key requirements that will be achieved from glass based packaging. Also the transparency of glass has benefits for photonic packaging. Glass substrates are available in wafer and large scale panel formats. Very fast CO₂-laser drilling of holes and thermal post-treatments for reducing mechanical stress are very promising for fast processing and high reliability. Holes with a diameter smaller 100 μm in different glasses with thicknesses between 145 and 500 μm have been achieved by CO₂-laser drilling. The holes have been metallized by sputtering a seed layer and galvanic copper platting. The CO₂-laser drilling in combination with copper metallization has high potential for through glass via forming in glass substrates for interposer applications.