AI Chip Packaging Capacity Shifts Outside TSMC

TSMC (TSM) and Amkor Technology (AMKR) both said on their third-quarter 2026 earnings calls, held between October 15 and October 26, that AI chip packaging capacity is short, and that new capacity is being built outside TSMC's own fabs and locked in with long-term contracts and customer prepayments.

Why AI chip packaging capacity is running short

The capacity bottleneck for AI accelerators now reaches past wafer fabrication into packaging, the back-end step. After the circuits are made on the wafer, the back end places the compute die and high-bandwidth memory side by side on a silicon interposer and packages them into one finished chip. The interposer is a slice of silicon covered in fine wiring that lets those dies exchange data. TSMC calls this process CoWoS. It has mostly been done in TSMC's own packaging fabs, with outsourced assembly and test companies, known as OSATs, taking only part of the assembly work.

Packages for a single AI chip keep getting larger, so back-end demand is growing faster than TSMC can add capacity on its own. On October 15, TSMC Chairman C.C. Wei said the company is in volume production of packages at 5x reticle size and is developing 9x and 14x versions [1]. Reticle size is the largest area a lithography tool can expose in one shot; the higher the multiple, the more interposer area and assembly work each chip needs. The overflow goes to outside suppliers: interposer wafers to mature-node foundries, and assembly to OSATs.

TSMC buys interposers outside while Amkor's customers prepay for capacity

TSMC's description of the back-end gap became much stronger within six months. In April it said advanced packaging capacity was "very tight" and that it had to work with its packaging partners [2]. By October, Wei said there is "a big shortage on the back end" and called the deal with GlobalFoundries (GFS) part of TSMC's overall back-end supply strategy [1]. According to Manufacturing Dive, the agreement is worth $2 billion over an initial five years; GlobalFoundries will make silicon interposers for TSMC's CoWoS at its fab in Malta, New York, with volume ramping in the first half of 2028 [3].

Amkor described the other side of the shift: customers are now putting up money for its expansion. On October 26, CFO Megan Faust said that since 2025 Amkor has signed advance payment arrangements with about 12 customers, mainly for advanced packaging capacity in Korea and Arizona, with several more under discussion [4]. CEO Kevin Engel said packaging is becoming one of the key bottlenecks, that customers are securing capacity into 2027 and even 2028, and that Amkor is raising capital spending above historical norms as a result [4]. This practice surfaced only in recent months. The April call carried no prepayment language [5]. In July, Amkor explained the structure of one prepayment for US capacity: the cash arrives in 2027 and is returned to the customer as services are delivered [6]. Faust also said that with this support Amkor may not need incremental debt even through 2028 [4].

One company is a buyer of back-end capacity and the other a seller, yet both describe the same change: back-end capacity is tight enough that customers sign long-term commitments and pay in advance, and expansion is moving outside TSMC.

Who funds packaging expansion, and where it is built, is shifting

As back-end capacity becomes scarce, customers have started to pay for part of the expansion. OSATs used to fund growth mainly from their own cash and debt, while customers paid a per-unit service fee. Prepayments shift part of the capital spending onto customers in exchange for production slots over the next two to three years, which eases pressure on the packager's balance sheet [4]. Mature-node foundries gain a new line of work: as TSMC outsources interposer wafers, a foundry such as GlobalFoundries can take it on with US-based production lines [3].

The shift still has clear limits. ASE Technology (ASX), the other leading OSAT, did not mention prepayments on its July call, and its interest-bearing debt rose by NT$40.9 billion to NT$306.2 billion in the second quarter, so its expansion is still mainly debt-funded [7]. The pricing terms of the GlobalFoundries deal have not been disclosed [3]. TSMC is also building 13 leading-edge and advanced packaging fabs in Taiwan [1], and the outsourced share could fall once that capacity comes online. Most of the outside capacity ramps in 2027-2028. Two things to watch: whether ASE also starts taking customer prepayments [7], and whether the prepayment agreements Amkor is still negotiating get signed [4].

Companies exposed to this change

• United Microelectronics (UMC): A mature-node foundry that already sells 2.5D interposers and raised its 2026 capex to $2 billion for advanced packaging and silicon photonics, while stating it will not do full CoWoS [8]. It is another foundry outside TSMC that could take on overflow interposer work.
• Camtek (CAMT): A semiconductor inspection and metrology equipment maker that gets about half its business from OSATs and has received multi-system orders for 2.5D/3D capacity [9]. Expansion at packagers and interposer fabs ultimately turns into purchases of this kind of inspection equipment.

Sources

[1] Drillr · TSMC · 2026-10-15 · Earnings call

[2] Drillr · TSMC · 2026-04-16 · Earnings call

[3] Manufacturing Dive · GlobalFoundries-TSMC silicon interposer agreement · 2026-10-09 · News report · https://www.manufacturingdive.com/news/globalfoundries-tsmc-silicon-interposes-semiconductors/832537

[4] Drillr · Amkor Technology · 2026-10-26 · Earnings call

"Customer advance payments are expected to provide significant funding support for these CapEx investments. Since 2025, AMCOR has executed advanced payment arrangements with a dozen customers, primarily supporting advanced packaging capacity across both Korea and Arizona, and there are several more customer agreements under discussion."

[5] Drillr · Amkor Technology · 2026-04-27 · Earnings call

[6] Drillr · Amkor Technology · 2026-07-27 · Earnings call

[7] Drillr · ASE Technology · 2026-07-30 · Earnings call

[8] Drillr · United Microelectronics · 2026-07-29 · Earnings call

[9] Drillr · Camtek · 2026-08-10 · Earnings call

This note only aims to surface industry changes and companies that may be overlooked. It is not a stock recommendation.