We rarely lay eyes on interconnections.
Hidden deep inside chip packaging,
they pierce silicon wafers and run through glass substrates,
underpinning the three-dimensional expansion of computing power.
Rising complexity in advanced packaging buries yield risks deep within internal structures at an earlier production stage. The later defects are spotted, the steeper the associated costs. Accordingly, X-ray inspection has evolved from merely end-of-line quality screening to frontline checks at critical manufacturing nodes, zeroing in on interconnection units—the core components governing packaging reliability.
01 PTH, TSV, TGV: Interconnections Go Deep
Layer-to-layer interconnection stands as an indispensable foundation for PCBs, packaging substrates as well as 2.5D/3D advanced packaging. Conventional PCBs and packaging substrates rely primarily on PTH (Plated Through Hole) to realize vertical interconnection between top and bottom layers of boards. As packaging evolves toward higher density, shorter routing paths and three-dimensional stacking, vertical interconnects penetrate deep into silicon and glass materials, forming ultra-fine, intricate 3D via architectures represented by TSV (Through-Silicon Via) and TGV (Through-Glass Via).
Bare transparent TGV substrate (pre-copper plating)
Orange-toned TGV after full copper metallization
Both TSV and TGV are vertical interconnection solutions for advanced packaging, differentiated mainly by their base substrate materials.
TSV is silicon-based, widely adopted for silicon interposers, HBM and 2.5D/3D packaging. It delivers ultra-short interconnect routing and superior integration density, ideal for die stacking and high-speed short-reach interconnection.
By contrast, TGV is built on glass substrates or glass interposers. Benefiting from glass’s low dielectric loss, outstanding dimensional stability and capability for large-panel manufacturing, TGV fits applications requiring high-frequency, large-format and low-loss interconnection.
Schematic Cross-Section of TGV
Driven by advanced packaging’s pursuit of larger footprint, higher bandwidth and lower transmission loss, semiconductor packaging platforms are evolving from basic integration toward high-quality, large-scale, low-loss and cost-effective integration. Against this backdrop, glass substrates stand out for their inherent material merits and compatibility with large-panel production, pushing TGV into a spotlight as a promising vertical interconnect technology.
02 What Inspection Challenges Does TGV Bring to X-Ray Testing?
Rising market demand and stringent yield control requirements are fueling technical upgrades for X-ray inspection toward finer resolution, stable imaging and multi-angle tomography analysis. TGV poses primary inspection challenges stemming from miniaturized geometry and ultra-high via density. Vias are densely arrayed inside glass substrates with tiny diameters and tight pitch spacing. Individual defects often manifest only as subtle grayscale shifts or faint edge irregularities on radiographic images. Consequently, TGV inspection calls for boosted magnification and spatial resolution, alongside stringent standards for image uniformity, contrast optimization and noise suppression.
Image Caption: Cross-Section Schematic of a Single TGV, Demonstrating Miniaturized Interconnect Geometry
As inherently 3D architectures, TGV arrays suffer from structural overlap under conventional single vertical X-ray projection. Vias, metallization layers, bonding pads and routing traces stack on one another in 2D radiographs, blurring via wall contours, interior anomalies and intermittent defective segments. To resolve overlapping features in actual inspection, tilted acquisition, multi-angle imaging and X-ray CT scanning are routinely deployed to decouple superimposed internal structures.
Simply put, TGV inspection hurdles stem not merely from tiny via dimensions, but a compound of compact sizing, ultra-high density, low image contrast and imaging noise. These combined factors make consistent identification of micro-defects far more demanding.
Figure Caption: X-Ray Images of TGV Structures
Regularly arrayed TGV with tiny via diameter and fine pitch
Obscured boundaries and internal features caused by structural overlapping
For miniature 3D architectures such as TGVs, upgrading X-ray inspection performance relies not solely on hardware specifications, but also on coordinated optimization of imaging recipes and image processing algorithms.
Image Caption: TGV X-Ray Radiographs Captured by UniXray AX9600 Microfocus X-Ray Inspection System with Clear outlines of vias, distinct internal defects and superior image contrast
Tilted acquisition, multi-angle viewing and 2.5D/3D reconstruction effectively separate overlapping features among via arrays, bonding pads, metallization layers and interconnect traces, sharpening the visibility of via wall edges, inner anomalies and intermittent faulty segments. Nevertheless, successful image capture does not equate to clear defect identification. Advanced image processing including noise reduction, contrast adjustment, edge enhancement and dynamic range optimization reliably exposes faint borders, low-contrast features and subtle grayscale abnormalities.
Built for ultra-fine interconnect inspection, UniXray AX9600 microfocus X-ray system delivers high-precision imaging performance. Equipped with a 160kV open-type X-ray source, the unit offers magnification over 1500× alongside native 2.5D imaging capability to resolve structural contours and microscopic defects within densely packed via arrays. Powered by UniXray’s self-developed AI large model algorithms for intelligent contrast improvement and noise suppression, the equipment minimizes imaging artifacts and highlights faint low-contrast details. It empowers customers implementing front-end inspection with robust support for accurate defect screening, process validation and full quality control.
Picture Caption: UniXray AX9600 Microfocus X-Ray Inspection System with 160kV Open-type X-ray Source
03 Future Outlook
Market research figures put the global TGV substrate market size at USD 230 million in 2026, with a projected market value of USD 3.72 billion by 2035, corresponding to a CAGR of approximately 34.2% from 2026 to 2035. Driven by accelerated adoption of advanced packaging technologies, the inspection market fueled by stringent yield requirements is poised for explosive expansion.
As yield constraints keep pushing inspection deeper into packaging workflows, a pivotal question emerges: if defects cannot wait to be detected at the packaging interconnection stage, how much further upstream can inspection be shifted?
The answer may lie in an even more microscopic realm…
UniXray has fully progressed into R&D and mass production of dedicated inspection equipment for TSV and TGV applications.
