Tier-1 semiconductor advanced packaging can integrate different types of chips (logic, analog, RF, etc.) interconnected on a shared interposer substrate to achieve high performance without needing monolithic dies. Glass interposers specifically offer crucial physical, electrical, chemical and thermal stability at low cost. Recently market interest has emerged for low-tier manufacturing of customised interposers for high-value, low-volume applications.

This paper discusses advantages and limitations between three different femtosecond laser drilling techniques on 0.3mm thick borofloat33 glass based on 1030nm amplifiers (fibre and solid-state): (i) single-mode percussion or trepanning laser drilling, (ii) percussion GHz-burst drilling and (iii) selective laser-assisted chemical etching. All three techniques find valuable niches for TGV sizes ranging 20-100μm depending on throughput and quality requirements. High power laser drilling rates contrast both, thermal stress management in glass, crucial for achieving high TGV areal density, and post-process surface quality to allow subsequent smooth via filling and RDL metal deposition.

The increasing demand for miniaturized and high-performance consumer electronics has driven advancements in packaging solutions, including the transition to glass interposers. A critical aspect of this development is the fabrication of high-density through-glass vias (TGVs). This study presents the formation of TGVs in various glass substrates using a femtosecond laser FemtoLux 30 operating in MHz/GHz burst modes. By employing burst mode and micromachining methods such as bottom-up milling, TGVs with aspect ratios exceeding 1:80 were achieved, with drilling times as low as 350 ms. The findings demonstrate the potential of GHz burst femtosecond lasers as a high-throughput, precise solution for TGV fabrication.

Through-Glass Vias (TGVs) are crucial for modern microelectronics packaging, enabling high-density interconnections in high power/frequency electronics as well as devices like smartphones, automotive sensors, and Micro-Electro-Mechanical Systems (MEMS). By producing vertical electrical connections through glass substrates, TGVs support device miniaturization and enhanced electronic performance. Femtosecond laser pulses are used to drill glass with minimal thermal effects, though thousands of pulses may be required for well-defined TGVs, driving demand for more efficient methods.

This study compares two approaches for producing TGVs. The ablation-based method splits a single pulse into sub-pulses with 400 ps temporal separation (GHz mode) to drill glass. The second method, selective laser etching (SLE), focuses laser pulses within transparent materials, creating etchable modified areas in aqueous solutions like KOH. Both methods outperform conventional single-pulse micromachining, achieving deeper channels and increased efficiency. These techniques hold potential for applications in advanced optics, biomedical devices, and more.

Ultrafast lasers proved to be a handy tool for the microprocessing of glass. Near-IR and visible wavelengths are commonly used for cutting, drilling, structuring, and complex-shape surface machining. Although ultrafast deep-UV lasers (usually achievable through fourth-harmonics conversion) have been available for some time, their practical use for processing is rarely reported. The main benefits of shorter wavelengths are mainly tighter focal spots and better laser absorption in the material. We present a study of the microprocessing of fused silica using a 258nm 1ps laser in combination with a galvoscanner and F-theta lens. The main aim is finding suitable parameters considering resulting roughness and material removal rate. The results are compared to similar processing using fundamental and second-harmonic wavelengths presented in the past.

We present a study on the modifications induced in fused silica by a femtosecond laser shaped into a Bessel beam, comparing three operation modes: single-pulse, MHz-burst, and GHz-burst regimes. In both the single-pulse and MHz-burst modes, the laser forms elongated, slightly tapered structures within the glass. Post-etching with Potassium Hydroxide reveals high etching rates and selectivity, reaching up to 606 μm/h and 2103:1 in the single-pulse mode, and up to 322 μm/h and 2230:1 in the MHz-burst mode. Remarkably, the GHz-burst regime enables the direct formation of taper-free holes using a single burst of 50 pulses, without any-etching. This breakthrough demonstrates the potential for chemical-free, high-speed drilling of high aspect-ratio holes in glass, opening new possibilities for advanced glass processing techniques.

An advanced laser-based method for form correction of optical elements, known as Laser Beam Figuring (LBF), is being developed by the authors. This technique intends the precise and cost-effective correction of complex surface geometries, such as aspheres and freeform surfaces. LBF allows for selective material removal from fused silica surfaces at the nanometer scale with a removal rate of several mm³ per hour, aiming for a form accuracy of less than 50 nm. Unlike traditional methods, LBF does not require polishing agents, thereby avoiding surface contamination. Additionally, LBF reduces mid-spatial frequency errors (MSFE), bridging an economic and technological gap for spatial wavelengths ranging from 100 µm to 3000 µm. The simplified equipment technology of LBF leads to savings in costs, energy, and resources, making this method an attractive alternative for the precise form correction of optical elements. In the presentation the state of the development will be presented.