AI chips now generate more heat than plastic substrates can handle. The glass substrate market is expected to grow to about USD 4.2 billion (about KRW 6 trillion) by 2034, and BOE has now entered it. BOE started operating the pilot line it invested in during 2024 after two years, and in May it signed a packaging and optical interconnect development agreement with Corning of the United States.
The logic that larger chips raise heat dissipation and flatness requirements for the substrate is essentially the same as the cell upsizing and energy density race in the battery industry. Another common point is that when one material changes, all the equipment that handles it has to be redesigned.
Because of its brittleness, glass substrate carries a far higher risk of breakage during transfer and processing than plastic does. The handling and alignment mechanism know-how needed to solve this problem is likely to overlap with the know-how used to handle thin electrodes in the battery electrode process.
Mechanism-Perspective Impact Analysis (General Principles)
Brittle fracture of glass substrates is explained by the thin-plate bending stress principle of general mechanics of materials. When a thin plate of thickness $t$ (mm) is bent to a radius of curvature $R$ (mm), the maximum bending stress at the surface is approximated as follows.
$$ \sigma_{max} = \frac{E \cdot t}{2R} $$
Here $E$ is the elastic modulus (GPa), $t$ is plate thickness (mm), and $R$ is the radius of curvature (mm). When $\sigma_{max}$ exceeds the allowable stress based on the material’s fracture toughness ($K_{IC}$), cracks propagate. Glass has lower fracture toughness than metals and plastics, so it is more likely to break at the same curvature, and surface micro-defects (scratches, edge chipping) act as stress concentrators that greatly lower the actual fracture stress. This is the same principle as slitting edge quality control for ultra-thin battery electrodes. The actual thickness and target bend radius of BOE’s glass substrate are undisclosed and need to be confirmed.
From a transfer standpoint, tension control is the key. Unlike ductile materials, brittle materials cannot absorb local tension variation through plastic deformation and respond immediately with cracks, so the general R2R design convention is to hold the tension variation limit in roll transfer sections tighter than for metal foil or film. Particle adhesion from electrostatic attraction is also a common control item when handling thin sheets.
Spec Comparison Table
| Item | Glass substrate (general) | Ultra-thin battery electrode (general) |
|---|---|---|
| Failure mode | Brittle cracking (low fracture toughness) | Ductile rupture, pinholes (relatively ductile) |
| Control axis in transfer | Tension variation, bend radius | Tension variation, roll pressure |
| Typical defect causes | Edge chipping, surface scratches | Slitting burr, foreign particles |
| Actual thickness and curvature | To be confirmed (undisclosed) | Varies by product |
Design Reflection Checklist
- Recalculate maximum bending stress after confirming sheet thickness and target bend radius
- Set management criteria for surface defects such as edge chipping and scratches
- Set a narrower tension variation limit for roll transfer than for metal foil or film
- Include measures against particle adhesion from electrostatic attraction
One-line summary: Transfer design for brittle thin sheets starts from a tighter tension variation limit than for ductile materials.