AI accelerators hit a T-glass bottleneck as Nittobo races to add capacity

A single Japanese company sits between the AI accelerator boom and the factories that build it. Nittobo controls roughly 90% of the global supply of specialist glass-fiber cloth known as T-glass, according to Tom's Hardware, and demand has outrun what the company can ship.

T-glass is a low-CTE glass cloth used in the organic core of IC substrates, the interconnect layer between a chip and its printed circuit board. As AI processors get bigger and run hotter, keeping those packages dimensionally stable stops being a packaging detail and becomes a supply constraint.

Prices up, lead times gone

The numbers show how tight the market has become. Prices have risen between 20 and 30%, and lead times for downstream materials such as copper-clad laminates have stretched from a normal 8 to 10 weeks to beyond 20, per Tom's Hardware.

"With T-glass supply even more constrained now, suppliers are no longer providing lead times," said Bill Ho, an analyst at Yuanta, in comments carried by Tom's Hardware.

Replacing the material is not simple. Bilal Hachemi, an analyst at Yole Group who tracks the IC substrate supply chain, told Tom's Hardware Premium that T-glass "has specific dielectric and CTE values that work better for the AI chips, especially for the organic core." He also pointed to the industry's thin margins, saying that "any increase in demand for build-up materials, ABF material, or T-glass can cause potential shortage, because it's against the basics of this industry."

Nittobo is tripling capacity at its Fukushima plant in Japan, but that supply will not arrive on the market until mid-2027. The material needs specialised electric melting furnaces running between 1,600 and 1,700°C, and the process, melting silica-rich glass, spinning it into yarn and weaving it into ultrathin cloth, takes years of investment to scale.

Bigger packages, more material

What makes this crunch different from a routine cyclical shortage is who is driving it. Hyperscalers keep ordering larger chip packages, and each generation consumes more T-glass per unit. Nvidia data cited by Tom's Hardware puts interposer sizes at 814mm² for Hopper and 1,700mm² for Blackwell, a 109% increase, with the forthcoming Rubin and Feynman generations scaling further.

Bank of America estimates Nittobo's electronic materials segment will nearly double sales from ¥40.9 billion ($266 million) in 2025 to ¥87.7 billion by March 2028, with operating margins approaching 48%. "Demand for T-glass cloth seems likely to grow more than originally expected," said Takashi Enomoto, a research analyst at Bank of America, per Tom's Hardware. He added that attention had been on thick T-glass for GPU and CPU packages, but that ultra-thin T-glass demand is now likely to rise as leading-edge devices shift away from E-glass.

E-glass is the cheaper alternative and is used in lower-end chips such as microcontrollers and older mobile processors. For massive 2.5D and 3D packaging, and therefore advanced AI accelerators, T-glass remains the preferred option.

The scramble for allocation has already produced an unusual sight. Hachemi said Nvidia approaching an upstream material supplier directly is unprecedented. "For the first time, we are seeing Nvidia, the end customer, reaching out to the upstream material suppliers to secure the capacity and make sure they will get it," he told Tom's Hardware Premium. The risk is that once Nvidia locks down its share, rival chip buyers compete for what is left.

Nittobo is not waiting on Fukushima alone. It is doubling raw yarn capacity at its Taiwan plant and importing yarn back to Japan for cloth manufacturing, and it has a collaboration deal with Nanya Plastics to outsource some weaving. Tom's Hardware reports that by 2027 roughly 20% of Nittobo's glass cloth is expected to be woven by Nanya, a competitor, which is a fair measure of how tight the market is.

The wider accelerator pipeline keeps moving. At Hot Chips 2026, Microsoft detailed its second-generation Maia 200, a TSMC 3nm part with 140 billion transistors, 6 stacks of HBM3e, 7TB/second of memory bandwidth and a 750 Watt TDP, according to ServeTheHome's live write-up. d-Matrix used the same event to present Raptor, a 3D-DRAM accelerator that stacks a TSMC N4 logic die on DRAM, with the company arguing that HBM4 packages such as Nvidia's Vera Rubin and AMD's Instinct MI455 face a practical bandwidth ceiling around 20 TB/s.

None of that matters much if the substrate underneath cannot be built. Analysts quoted by Tom's Hardware expect the squeeze to persist until new T-glass capacity lands, which means pricing pressure on AI hardware has a component most buyers have never heard of.