Glass Through Hole (TGV) Technology: Breaking the Bottleneck of Micromachining and High Density Interconnection Revolution

In the evolution of semiconductor packaging towards high-density, high-frequency and three-dimensional integration, glass substrate has become the core carrier of a new generation of advanced packaging by virtue of its excellent high-frequency characteristics, coefficient of thermal expansion (CTE) matching with silicon and ultra-high flatness. However, the glass through hole as its core interconnection channel（ TGV ）Technology, in the process of realizing micron level through-hole machining and metallization, it still faces a series of severe challenges. The breakthrough of these technical bottlenecks is quietly reshaping the performance boundary and industrial ecology of electronic devices.

1、 Through hole forming: dual challenges of precision and integrity

The hardness and brittleness of glass make it easy to produce microcracks and thermal stress damage in micro hole processing. Traditional mechanical drilling leads to substrate damage due to stress concentration. Although wet etching can avoid mechanical stress, its isotropic characteristics make it difficult to break through the limit of 1:1 depth width ratio, which cannot meet the requirements of high-density interconnection.

Innovative solutions:

Ultra fast laser induced deep etching (LIDE) technology : The femtosecond/picosecond laser is used to induce controlled phase transformation in the glass, and the rate of the modified area in the subsequent wet etching is significantly improved (for example, the KOH etching rate can reach 50 µ m/h). This technology can be used in Achieving a depth to width ratio of 50:1 to 100:1 at an aperture of 20-100 μ m The side wall roughness (Ra) is ≤ 0.08 μ m, and microcracks are completely avoided. Germany LPKF’s Vitrion system has realized high-speed machining of 5000 holes per second, laying the foundation for mass production.
Bessel beam shaping technology : Lengthen the focal depth through non diffracting beam, realize flexible control of inclined hole wall and vertical through hole, and support microfluidic chip, three-dimensional capacitor and other complex structure processing.

2、 Metallized bottleneck: reliable filling under high aspect ratio

Through hole metallization needs to solve two problems: seed layer covering and no cavity filling. When the pore diameter is less than 10 μ m, it is difficult for the traditional sputtering process to form a continuous seed layer on the inner wall of the deep hole, while the filling of electroplated copper is prone to generate voids due to diffusion restrictions, resulting in decreased conductivity and thermo mechanical failure.

Key technical breakthroughs:

Nano seed layer optimization : Ion enhanced magnetron sputtering (such as titanium/copper composite layer), combined with plasma activation treatment on the glass surface, improves the coverage uniformity and adhesion of the seed layer in the deep hole. The nano compressive stress layer technology developed by Kunshan Dongwei has increased the bending strength of glass by 300%.
Non single-sided copper electroplating process : Through the coordinated control of pulse reverse electroplating and additives, the filling of deep holes can be realized from bottom to top. Dongwei Technology has realized through hole with depth width ratio of 5:1 No cavity copper filling The resistance is lower than 10m Ω. For ultra micro holes (<10 μ m), metal conductive adhesive filling combined with ultrasonic vibration can improve the fluidity, but the formula needs to be optimized to reduce the resistance.

3、 Mass production and cost: key barriers to industrialization

The high cost of TGV mainly comes from special glass materials, high-end equipment investment and low yield constraints. For example, the unit price of laser etching equipment is more than one million dollars, while the environmental treatment cost of wet etching accounts for 15%.

Cost reduction and efficiency increase path:

Panel Level Processing : Upgrade the processing size from wafer (12 inches) to 600 × 600mm or even 1500 × 800mm panel, and increase the number of chips processed at a time by more than 5 times. Intel predicts that panel level TGV can reduce the cost of sensor packaging from $0.8 to $0.3.
Vertical integration of industrial chain : Glass manufacturers (such as Corning and AGC) directly provide pre drilled substrates to reduce downstream processing steps. Corning’s melt molding technology can produce>2m × 2m ultra-thin glass (<50 μ m), and the through hole metallization yield reaches 99.8%.
Intelligent closed-loop control system : Introduce real-time optical detection (such as precision measuring electronic seal equipment) and AI parameter optimization to control the position accuracy of mass production through-hole within ± 2 μ m, and compress the yield fluctuation rate to below 1%.

4、 Cross domain application: technology breakthrough drives scene innovation

The maturity of TGV is promoting the evolution of high-performance equipment in many fields:

Medical Electronics : WaferPlus’s borosilicate glass based DNA sequencing chip integrates micro channels and electrodes through TGV, which increases detection flux by three times and reduces reagent consumption by half.
Photon integration : Intel glass based CPO (co packaged optics) module, which uses TGV to realize millimeter level coupling between the optical engine and the chip, with data transmission power consumption as low as 1.2pJ/bit.
Automobile radar : The 77GHz antenna module adopts low dielectric glass (Dk=5.4), and the TGV vertical interconnection makes the beam pointing accuracy reach 0.1 degree, and the detection distance increases by 70 meters.

5、 Future trend: flexibility and multi-function integration

The next generation TGV technology focuses on two major directions:

Application of flexible glass substrate For example, Schott 30 μ m ultra-thin glass combined with polyimide substrate has a bending radius of<5mm, providing neuron level signal acquisition capability for brain computer interface electrode (aperture 3 μ m).
Integration of structure and function : Thermoelectric materials (such as Bi ₂ Te ≮) are integrated in the TGV through-hole to supply power for implantable equipment by temperature difference; Or it can be filled with ferrite to realize embedded inductance and reduce the proportion of surface passive components.

epilogue

From the radical cure of microcracks by laser induced deep etching technology to the subversion of cost by panel level process, TGV technology is crossing the final gap from laboratory to mass production. With the deep collaboration of equipment, materials and processes, glass substrate is no longer just an alternative to silicon based packaging – it is opening up a new track in millimeter wave communication, implantable medical treatment, optoelectronic integration and other scenes by virtue of its unique optical, electrical and thermal characteristics. When the copper filling resistance in the micropores drops to the milliohm level, and when the brittleness of the glass is tamed by the nano compressive stress layer, this technology has become an indispensable “invisible skeleton” for high-density electronic systems.