Breaking down TSMC's glass core substrate slide
On June 11, at JPCA Show 2026 in Japan, TSMC gave a roughly 40-slide presentation titled "Advanced Packaging Technology Essential to the Evolution of AI" (AIの進化に不可欠な先端パッケージング技術). One slide from the deck, titled "Glass Substrate Development for CoWoS," has since leaked online and widespread attention.
Here's a closer read of that slide (see attached image). I'll skip the technical background that is already widely available. One thing to flag: the "COP" on the slide does not stand for Chip-on-Package. It means Coplanarity.
▌ Key conclusions:
1. TSMC has officially announced a partnership with Ibiden and Innolux to develop a glass core substrate. The structure is a three-layer design, a glass core sandwiched between two ABF build-up layers. This is the "oS" in CoPoS.
2. The market underestimates how important the glass core substrate is. It's a must-have capability for TSMC. In other words, within CoPoS the "oS" matters more than the "CoP", which is also why, when it was tested, it was paired with the existing CoW rather than with CoP.
3. The glass core substrate costs several times more per unit than existing ABF substrates. The glass processed by Innolux is very expensive per unit and is the single most critical material. Besides Nvidia, two US-based customers have also expressed strong interest.
▌ Industry checks tied to this slide:
1. The glass core substrate shown on the slide is cut from a full-size 250×250mm one. The ABF build-up layers mainly use Ajinomoto's GL107, mixed with ABF-GCP, and were tested at 24–28 layers, which is the mainstream ABF spec for AI chips in 2027–2028.
2. The CoW used in TSMC's experiment is a test vehicle. It is sufficient to validate the most challenging mechanical-structure issues that arise when working with composite materials. Good results mean TSMC, Ibiden, and Innolux have together broken through the critical technical bottleneck.
3. Ibiden currently handles cutting the 250×250mm glass core substrate. When the 510×515mm format is used for pre-mass-production simulation in 2H27, if Ibiden still wants to reduce production complexity to protect its ultra-high gross margins, it may hand the cutting over to Innolux, which is more familiar with the properties of glass.
▌ The leaked slide shows the validation results of pairing CoW with the "oS" in CoPoS, i.e., the glass core substrate (labeled "glass-SBT" on the slide). This addresses the "Substrate mechanical and electrical Dilemma" raised on the previous slide, and it strongly underscores how important the "oS" is within CoPoS.
1. Within CoPoS, what CoP solves is production efficiency / cutting economics, which ties to cost and price. What the oS solves is warpage and durability, which determines whether the chip can be made at all, and whether it can work.
2. CoP and oS complement each other well when integrated, but looking out over the next few years their technical roles still differ. CoP is a very-nice-to-have optimization, and going without it simply means a more expensive chip. But the oS is a must-have. Without it, even being able to make a usable chip is in doubt.
3. Comparing their roles isn't about elevating oS at the expense of CoP. It comes down to the practical question of which technical piece customers are willing to pay for. Details below.
▌ The real gold here is the power integrity (PI) improvement shown on the slide. This matters a great deal to customers, and it means that once glass core substrate production stabilizes, TSMC's profitability and competitive edge should rise in tandem.
1. How it works: the glass core substrate is thin → the vertical conduction path through TGV (through-glass vias) is short → conduction-path resistance (R) and loop inductance (L) both drop → PI improves.
2. Why it matters to customers: better PI → more stable power delivery → frees up power headroom → room to integrate more transistors, or to push clock speeds higher → more AI compute.
3. For customers, production efficiency is TSMC's basic responsibility, so they won't pay extra for it. But gains in AI compute translate directly into the customer's own competitiveness and profit, so customers are willing to pay for that. This is why Nvidia is so positive on the glass core substrate.
4. For TSMC, the glass core substrate raises yield and lowers cost while also boosting both the compute and the selling price of AI chips. It's both a cost-cutting tool and a pricing lever, a plus for profitability and competitiveness alike.
5. Substrate cost currently accounts for a low single-digit percentage of an AI chip's BOM, while losses from packaging yield run roughly 5–10× the substrate cost. So even if the glass core substrate ends up costing several times more than today's, its share of the BOM stays low, and it can cut the losses from packaging yield. The high unit price is therefore not expected to dampen customers' willingness to adopt it.
▌ In the Q&A after the presentation, an audience member asked about TGV details for the glass core substrate. TSMC declined to answer on the spot, because TGV is the key technology behind the glass core substrate, and the core know-how currently sits with TSMC and Innolux. By contrast, when another attendee asked about integrating IVR, eDTC, and LSI, TSMC answered at length.
▌ According to industry checks, if all goes well, TSMC is aiming to start mass production of the glass core substrate in 4Q28–1Q29, to match the cadence of Nvidia's AI chip iterations. As a side note: the Ibiden earnings presentation slide that many people have been circulating lists the glass core substrate timeline as CY30. My read is this: Ibiden, which has always been conservative and cautious in public, has now formally put the glass core substrate on its roadmap, which further confirms the long-term trend for this technology. That said, some other details on Ibiden's slide don't fully line up with what's known in the market. For example, its reticle timeline is off from TSMC's public claims by about a generation, and the Rubin Ultra substrate size is clearly larger than the 90×90 it marked for CY26–27. It's a reminder to always cross-check across multiple sources when forecasting the future.
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💡 Samsung Electronics 、NVIDIA のカスタムメモリ「NVHBM」で先行か | HBM4E 8段・17〜18Gbpsを開発中 $NVDA $MU $TSM $AMZN
Samsung Electronics が NVIDIA $NVDA のカスタムHBM「NVHBM」供給で中核パートナーの座を先に押さえた、とソウル経済が8月28日に報じた。
同社は NVIDIA の要求に合わせ、当初準備していた12段・16段ではなくHBM4E(第7世代)の8段品を開発している。提示された動作速度は17〜18Gbpsで、初期HBM4Eサンプルの14.4Gbpsを2割上回る。積層高さを3分の1削り、その分を速度に振り替える構成になる。
NVHBMは NVIDIA が現地時間8月26日、NVLink Fusion の拡張として公開した独自規格である。従来はXPU側の演算ダイに載っていたメモリコントローラをHBMスタック内部へ移す設計で、標準HBM4E比で帯域が最大30%向上、HBM消費電力が最大15%低下、演算ダイ側で使える面積が最大25%増える。JEDEC規格比でPHYと周辺回路の面積は最大67%削減され、インターポーザ配線が簡素化されることでパッケージ全体では最大80%多くのシリコンを実装できるとする。NVIDIA 自身は製造せず、複数のメモリベンダーが供給できる標準実装を整える形を取り、第1号パートナーは Amazon $AMZN 傘下のAnnapurna Labsとなる。次世代Trainiumでの組み合わせが想定されている。
8段への回帰は、これまでのHBM競争の前提を反転させる。HBMは4段から8段、12段へと積み上げて容量を稼いできたが、段数が増えるほどDRAMダイを薄く削って精密に積む必要があり、後工程の難易度と歩留まり負担が跳ね上がる。8段は製造負荷が軽く、同じウェハ投入量からより多くのスタックを取り出せる。
Samsung と SK hynix は今年下期、NVIDIA 向けHBM4でも8段比率を引き上げる計画で、発熱管理と供給安定性が主因とされる。SK hynix のCEOは27日、米インディアナ州の先端パッケージ工場起工式後の会見で、メモリ不足が2030年末まで続くとの見方を示している。8段回帰は、この供給制約下でHBM搭載GPUの絶対数を確保するための現実解と読める。
代わりに NVIDIA は速度を取りにいく。NVHBMは2027年後半投入のRubin Ultra世代からの適用が有力とされ、同世代はスケールアップ領域を従来の72基から最大576基へ8倍に広げる。GPU単体のメモリ容量が減っても、より速いHBMを載せたGPUを数百基束ねて全体演算性能を積み上げる設計思想である。
Samsung のHBM4Eラインアップは8段32GB、16段64GBの構成で、16スタック実装なら8段採用時のパッケージ容量は512GB、当初示された1TBの半分に落ちる。一方、HBM4Eの2048ビット幅(16Gbpsで4.0TB/s)を前提に17〜18Gbpsを当てはめるとスタック帯域は4.4〜4.6TB/sとなり、NVIDIA が掲げる標準HBM4E比30%増とほぼ一致する。容量と帯域のトレードオフを、帯域側へ振り切った判断だ。
Samsung が優位に立つ理由は組織構造にある。NVHBMはDRAMだけでなくロジックベースのベースダイ設計と製造能力を要求する。Samsung はHBM4で1c DRAMと自社Foundry 4nmベースダイを組み合わせ、JEDEC標準8Gbpsを約46%上回る11.7Gbps(最大13Gbps)を安定確保した。対してSK hynix はHBM4E向けロジックダイにTSMC $TSM の3nm採用を検討し、Samsung は自社4nmで対応する構図にあり、Micron $MU も標準・カスタム双方のHBM4Eロジックダイ製造をTSMCに委ねている。高積層ではなく速度と開発回転数で勝負が決まる局面では、この一貫体制が効く。
最大の未確定要素は初適用世代である。NVIDIA 自身の発表はNVHBMを将来のGPUのメモリ基盤とするに留め、時期を明示していない。海外メディアの一部は2028年のFeynman世代を初適用先と見る一方、韓国側の報道はRubin Ultraを指す。
より本質的なのは主導権の移動である。ベースダイに載るコントローラが NVIDIA 設計になるということは、HBMの付加価値の一部が製造側から設計側へ移ることを意味する。Micron 経営陣は既に、設計と認証にかかる時間とコストを踏まえれば顧客が3社すべてと組むとは限らず、2社あるいは単独調達へ収斂し得ると指摘している。標準品の汎用化と特注品の囲い込みが同時に進み、供給者の交渉力は案件ごとに大きく振れる。
需要側の温度は依然高い。NVIDIA の2027年度第2四半期(7月26日締め)は売上高962億ドルで前年同期比106%増、データセンター部門は890億ドルで同117%増、第3四半期ガイダンスは1,058〜1,101億ドル、上位5社のハイパースケーラー設備投資は2026年の8,000億ドルから来年1兆3,000億ドルへ拡大する見通しが示された。この需要を前に、メモリ供給の物理的制約をどう回避するかという設計解がNVHBMであり、8段回帰である。積層数を競う段階から、速度と実装数を競う段階へ。AIメモリの評価軸が入れ替わる過程を注視したい。
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