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IC substrate materials affect routing density, signal performance, thermal reliability, warpage, and manufacturing cost. The three materials getting the most attention are ABF, BT resin, and glass core.
ABF is mainly a build-up dielectric film used for high-density organic package substrates. BT is a mature resin system used in a wide range of semiconductor packages. Glass core is a structural core platform being developed for large, high-density advanced packages.
These are not three identical material categories. ABF and BT mainly describe organic material systems, while glass core describes the structural core of a substrate. The right choice depends on package size, I/O count, routing density, electrical requirements, thermal behavior, reliability targets, manufacturing capability, and cost.
ABF vs BT vs Glass Core: Quick Comparison
| Factor | ABF | BT Resin | Glass Core |
|---|---|---|---|
| Main role | Fine-line build-up dielectric | Organic resin system | Structural core |
| Typical use | High-density package substrates | CSP, BGA, memory and other packages | Large advanced packages |
| Main strength | Fine-line routing and dense build-up | Mature manufacturing and balanced performance | Dimensional stability and flatness |
| Microvia integration | Strong | Application dependent | Application dependent |
| Package scaling | High | High | Strong potential |
| Manufacturing maturity | High | High | Emerging |
| Main challenge | Process complexity and cost | Limited fit for the most demanding routing | Brittleness and TGV processing |
Actual performance depends on the material grade, substrate stackup, package design, process conditions, and reliability requirements. Final material selection should use supplier data and package-level simulation rather than a material name alone.
What Are IC Substrate Materials?
IC substrate materials form the dielectric and structural foundation of a semiconductor package substrate.
An IC substrate sits between the semiconductor die and the PCB. It provides electrical connections while also handling mechanical and thermal stress.
A typical package substrate can contain:
- A structural core
- Build-up dielectric layers
- Copper routing layers
- Microvias
- Solder pads
- BGA connections
- Fine-line circuitry
Important material properties include dielectric constant (Dk), dissipation factor (Df), coefficient of thermal expansion (CTE), glass transition temperature (Tg), moisture absorption, dimensional stability, thermal conductivity, and mechanical strength.
These properties must be considered together. A material with good electrical performance may still create problems with warpage, thermal expansion, or manufacturing yield.
What Is ABF Material?
ABF stands for Ajinomoto Build-up Film.
ABF is a thermosetting dielectric film system used mainly in high-density organic package substrates. It is normally used as a build-up dielectric rather than as the entire substrate by itself.
ABF build-up layers allow manufacturers to create fine-pitch copper routing and microvia structures around a substrate core.
This makes ABF particularly useful when a package needs:
- High I/O density
- Fine-line routing
- Small microvias
- Multiple build-up layers
- Tight interconnect spacing
- Flip-chip package structures
ABF is strongly associated with advanced package substrates used for CPUs, GPUs, AI accelerators, networking ASICs, and other high-performance devices.
Its value comes from the combination of material properties and its compatibility with fine-line build-up manufacturing.
What Is an ABF Substrate?
An ABF substrate is not simply a sheet of ABF film.
A finished substrate can combine a core, ABF dielectric layers, copper circuits, microvias, solder pads, and external connections.
A simplified structure can look like:
Core → ABF build-up → Copper routing → ABF build-up → Copper routing → Package connection
This distinction matters when comparing ABF with BT.
ABF mainly describes the build-up dielectric material. The finished package substrate is a complete multilayer interconnection structure.
In 2026, ABF remains an important material platform for high-density organic substrates. Industry data also shows strong growth in the global IC substrate market, driven by AI servers, GPUs, high-end memory, and other advanced computing applications.
What Is a BT Substrate?
BT stands for Bismaleimide Triazine.
BT resin is a thermosetting resin system widely used in semiconductor package substrates. It offers a balance of thermal stability, electrical insulation, dimensional reliability, and process compatibility.
BT-based substrates can contain:
- BT resin cores
- BT prepregs
- Copper foils
- Build-up dielectric layers
- Microvias
- Fine copper circuitry
BT substrates are used in many package types, including:
- CSP
- BGA
- Memory packages
- RF devices
- Consumer electronics
- Automotive electronics
- Industrial electronics
BT is therefore not one single universal material specification. Different BT grades can have different dielectric, thermal, mechanical, moisture, and processing characteristics.
BT Resin vs BT Laminate vs BT Substrate
These three terms should not be treated as synonyms.
| Term | Meaning | Role |
|---|---|---|
| BT resin | Bismaleimide triazine resin system | Material chemistry |
| BT laminate | Cured BT-based reinforced material | Structural material |
| BT substrate | Finished package substrate | Complete electrical interconnection |
This distinction is useful when reading supplier datasheets or preparing an IC substrate RFQ.
ABF vs BT Substrate: What Is the Difference?
ABF and BT are often compared because both are used in organic semiconductor package substrates. However, they do not describe exactly the same material role.
| Factor | ABF Build-Up | BT-Based Substrate |
|---|---|---|
| Material role | Build-up dielectric film | Resin system used in substrate construction |
| Routing density | Very high | High, depending on design |
| Fine-line build-up | Strong | Application dependent |
| Microvia integration | Strong | Application dependent |
| Advanced FC-BGA | Common fit | Application dependent |
| Manufacturing maturity | High | High |
| Cost structure | Generally higher for demanding builds | Often more economical for suitable designs |
| Main selection driver | I/O density and routing complexity | Package requirements, maturity and cost |
ABF is often associated with packages that need very dense routing and fine-line build-up structures.
BT can be a better fit when the package does not require the highest routing density and a mature manufacturing platform is important.
Neither material should be treated as universally better.
The final choice depends on:
- Package size
- Die size
- I/O count
- Bump pitch
- Routing density
- Signal speed
- Thermal requirements
- Warpage target
- Reliability requirements
- Manufacturing capability
- Cost target
When Should You Choose ABF or BT?
Start with the package requirements instead of choosing the material first.
Choose an ABF-based build-up when:
- The package has very high I/O density.
- Fine-line routing is required.
- Multiple build-up layers are needed.
- Microvia density is high.
- The design uses demanding flip-chip or FC-BGA structures.
- Package routing space is limited.
Consider a BT-based structure when:
- The package uses a mature architecture.
- Routing density is demanding but does not require the most aggressive build-up process.
- Cost and production maturity are important.
- The package falls into established CSP, BGA, memory, RF, or similar applications.
The material decision should always be reviewed together with the substrate stackup, via structure, copper geometry, package assembly, and reliability requirements.
What Is a Glass Core Substrate?
A glass core substrate uses engineered glass as the structural core of an advanced semiconductor package.
This is different from ABF.
ABF is mainly a build-up dielectric material. Glass core is mainly a structural core platform.
A glass core can be combined with build-up dielectric layers and copper routing. In other words, glass and ABF do not necessarily compete directly.
A possible architecture is:
Glass Core → Build-Up Dielectric → Copper Routing → Build-Up Dielectric → Package Connection
Glass substrates are attracting attention because large semiconductor packages require tighter control of flatness, dimensional stability, registration, and warpage.
For more background on glass substrate technology, see our Glass Substrate guide.
TGV and Glass Core
Through-Glass Via (TGV) technology can create vertical electrical connections through a glass core.
A glass-core manufacturing flow may therefore require:
- Glass preparation
- Via formation
- TGV metallization
- Dielectric build-up
- Copper routing
- Layer registration
- Package assembly
TGV is one of the major process differences between glass-core structures and conventional organic cores.
Why Is Glass Core Attracting Attention?
Glass offers several properties that are attractive for large advanced packages:
- High dimensional stability
- High rigidity
- Excellent flatness
- Controlled thermal expansion
- Potential for large-format processing
- Good electrical characteristics
These properties become more important as package dimensions increase.
Glass core technology is therefore being investigated for AI processors, HPC devices, chiplets, and other large high-density packages.
However, glass is not a universal replacement for organic substrates. Brittleness, TGV processing, handling, metallization, reliability, equipment, and manufacturing yield remain important challenges.
Glass Core vs Organic Core Substrates
The most useful comparison is not simply “glass vs ABF.”
The better comparison is:
Glass core vs organic core.
ABF can still be used as a build-up dielectric on top of a glass core.
| Factor | Organic Core | Glass Core |
|---|---|---|
| Core material | Organic resin system | Engineered glass |
| Dimensional stability | Good | High potential |
| Flatness | Good | High potential |
| Warpage control | Application dependent | Strong potential |
| TGV | Not applicable | Required for many architectures |
| Handling | Mature | More difficult |
| Manufacturing maturity | High | Emerging |
| Large package potential | High | Very high potential |
Glass substrate technology is still developing, so specific performance depends heavily on glass composition, thickness, TGV design, metallization, build-up materials, and the complete package architecture.
How to Choose an IC Substrate Material
Material selection should start with the package requirements.
1. Check Routing Density
Very dense routing and fine microvia structures can favor an ABF-based build-up architecture.
A less demanding package may be well suited to a BT-based substrate.
2. Check Signal Requirements
For high-speed packages, review:
- Dk
- Df
- Copper roughness
- Trace width and spacing
- Reference plane structure
- Insertion loss
- Crosstalk
The material should be evaluated together with the complete stackup.
3. Check Thermal Expansion
CTE mismatch between silicon, copper, substrate materials, solder connections, and the PCB can create mechanical stress.
Thermal cycling and warpage should therefore be considered during substrate design.
4. Check Package Size
Large packages create greater demands on:
- Flatness
- Registration
- Warpage
- Thermal expansion
- Mechanical stability
This is one reason glass core technology is being investigated for next-generation large packages.
5. Check Manufacturing Capability
The selected material must support the intended:
- Laser drilling
- Fine-line imaging
- Copper plating
- Lamination
- Layer registration
- Via formation
- Inspection
- Assembly process
A material with excellent theoretical properties is not useful if the required process cannot be controlled at production scale.
6. Balance Performance and Cost
The highest-specification material is not automatically the right choice.
A mature BT-based structure can make sense when the package does not need extreme routing density.
An ABF build-up can make sense when I/O density and fine-line routing become the main constraints.
Glass core may become attractive when package size, flatness, and dimensional stability become major design limits.
IC Substrate Materials for AI and HPC
AI accelerators and high-performance computing are increasing the requirements placed on package substrates.
Typical requirements include:
- Very high I/O density
- Large package size
- High-speed interconnects
- High power delivery
- Multiple dies or chiplets
- HBM integration
- Tight warpage control
- Fine-pitch connections
These requirements are increasing demand for advanced substrate technologies.
Current industry projections put global IC substrate output value at about $19.5 billion in 2026, with AI servers, GPUs, high-end memory, and other advanced computing applications driving much of the growth.
ABF remains important for high-density organic substrates, while glass core is being developed for future large-package architectures.
Material development and package architecture therefore need to evolve together.
IC Substrate Materials in 2026
The IC substrate market is becoming more divided by package requirements.
ABF is closely linked to high-density organic substrates and advanced FC-BGA applications.
BT remains important across established package architectures.
Glass core is moving from research toward process and manufacturing validation for future large packages.
The supply chain is also becoming more important. ABF film, low-CTE glass fabric, BT materials, copper foil, and other substrate inputs are under pressure from stronger AI-related demand. Industry reports in 2026 have also pointed to higher ABF material costs and tighter supply conditions.
This means material selection is no longer only a technical decision. Material availability, approved suppliers, lead time, and production capacity can also affect package planning.
IC Substrate Assembly and Packaging
Material selection is only one part of the complete package process.
The substrate must work with:
- Die attachment
- Flip-chip bonding
- Wire bonding
- Underfill
- Reflow
- BGA connections
- Inspection
- Reliability testing
For example, substrate warpage can affect fine-pitch flip-chip alignment and downstream assembly yield.
Our IC Substrate Assembly guide covers the main assembly and reliability considerations.
FAQ
What is an ABF substrate?
An ABF substrate is a multilayer package substrate that uses ABF dielectric film in its build-up layers. The finished structure also includes a core, copper routing, microvias, pads, and package connections.
What is a BT substrate?
A BT substrate is an IC package substrate that uses a bismaleimide triazine resin system in its construction. BT-based substrates are widely used in CSP, BGA, memory, RF, and other semiconductor packages.
What is the difference between ABF and BT substrates?
ABF is mainly used as a fine-line build-up dielectric, while BT describes a broader organic resin system used in package substrate construction. ABF is closely associated with very high routing density, while BT supports a wider range of established package architectures.
Is ABF a substrate or a substrate material?
ABF is primarily a build-up dielectric material. A finished ABF substrate is a complete package interconnection structure that combines ABF layers with copper circuits, microvias, a core, and external connections.
When should you use ABF instead of BT?
ABF is worth considering when the package requires very high I/O density, fine-line routing, dense microvias, and advanced build-up structures. BT may be suitable when the package has less demanding routing requirements and manufacturing maturity and cost are important.
What is a glass core substrate?
A glass core substrate uses engineered glass as the structural core of a semiconductor package. It can use build-up dielectric layers and copper routing around the glass core.
Does a glass core substrate still use ABF?
It can. Glass core and ABF describe different parts of the substrate architecture. A glass core can be combined with ABF or another build-up dielectric system.
Why are glass core substrates being considered for AI packages?
Large AI and HPC packages require high dimensional stability, flatness, fine-pitch interconnection, and warpage control. Glass has properties that may help address these requirements, although manufacturing maturity and TGV processing remain challenges.
Conclusion
ABF, BT, and glass core are not interchangeable material categories.
ABF is mainly a fine-line build-up dielectric used in high-density organic package substrates.
BT is a mature resin system used across a broad range of semiconductor packages.
Glass core is an emerging structural platform for large and highly dense advanced packages.
The right material depends on the complete package architecture. Engineers should consider I/O density, routing, electrical performance, thermal behavior, warpage, reliability, manufacturing capability, material availability, and cost before selecting a substrate system.
