Fabrication and analysis of through-glass vias for glass-based electronic packaging using an ultrashort pulsed laser

We report on a comprehensive study of through-glass via (TGV) drilling for glass-based core packaging using a multi-path scanning strategy with a rotating start point and an ultrashort pulsed laser emitting in the green spectral range . In order to optimize the laser drilling quality in a 200 μm thick Borofloat (BF) 33 glass substrate , processing parameters such as laser pulse duration , laser pulse energy , number of passes and TGV hole diameter are studied in detail. After laser drilling, through-holes are evaluated for the hole diameter, taper angle and crack formation using optical microscopy and scanning electron microscopy. Although small taper angles down to 6 ± 0.3° are obtained using a femtosecond pulse duration, microcracks and backside ablation of the glass substrate are observed. Using a laser pulse duration of 5 ps, a laser pulse energy of 25 μJ and 600 passes for TGV fabrication with a hole diameter of 125 μm, a minimum taper angle of down to 7.3 ± 0.1° is obtained without the formation of cracks. Minimum hole pitches of 180 μm are realized for a hole diameter of 125 μm. To meet industrial requirements for temperature resistance in electronics manufacturing, laser-drilled TGV arrays are tested for thermal sensitivity using a furnace for both thermal cycling and shock at temperatures up to 950°. After thermal tests, no crack formation is observed for a minimum hole pitch of 180 μm and maximal laser-induced stresses is reduced by 37.4% down to 8.2 MPa on average, demonstrating the great potential of the applied scanning strategy for glass-based core packaging.