Semiconductor Advanced Packaging: Materials Are More Important Than You Think

In recent years, whenever AI, high-performance computing (HPC), or advanced chips are mentioned, advanced packaging inevitably becomes part of the conversation. Yet for many people, terms like CoWoS, CoPoS, Fan-Out, Chiplet, 2.5D, and 3D sound like a string of mysterious spells—concepts seemingly reserved for semiconductor engineers only. Actually, these terms are not about process complexity per se, but about how chips are integrated together within a limited physical space. Once this is understood, the role of materials in advanced packaging becomes much clearer.

Let’s use a simple analogy. Houses come in many forms—high-rises, apartments, townhouses, villas—but the essence is the same: a building with people live inside. What differs is the construction method, appearance, and materials used.

Applied to advanced packaging:

House type = advanced process

People = chips

Construction method / appearance / materials = packaging materials

Advanced packaging is not achieved by relying on a single “high-tech material.” Instead, multiple materials work together in a balanced way, enabling chips to operate reliably under high-performance, high-power, and high-density conditions.

 

 

Next, let's introduce the most important part of the entire packaging process: the packaging materials!

 

1. Why Do Chips Need to Be "Packaged"?

Chips are inherently fragile. They are sensitive to moisture, vulnerable to thermal stress, and cannot directly connect to external circuits.

Packaging serves three fundamental purposes:

• Protect the chip from environmental damage
• Establish electrical connections so signals can enter and exit the chip
• Manage heat and mechanical stress to ensure long-term reliability

These three requirements are precisely why packaging materials exist.

 

2. Resins: The Structural Backbone of Advanced Packaging

 

Among all packaging materials, resins are often the most overlooked—yet they are used in the largest quantities.

 

Much like reinforced concrete in construction, resins secure chips, fill gaps, and absorb mechanical stress.

Common resin systems include epoxy resins and polyimides. While they are electrically insulating, they offer excellent processability and environmental resistance.

 

Common Resin Types:

 

• Epoxy
  • ​​The current mainstream choice
  • Used in EMC, underfill, and die attach
• Polyimide (PI)
  • High thermal resistance and flexibility
  • Used in RDL, Fan-Out, and wafer-level packaging
• BT Resin / Modified Epoxy
  • Used in substrates (ABF, BT)

 

• ​Key Performance Requirements
  • Low warpage
  • High reliability (thermal cycling, humidity resistance)
  • Strong adhesion to silicon and metals

 

However, resins have a critical drawback: their coefficient of thermal expansion (CTE) is much higher than that of silicon. When heat is generated, this mismatch can cause warpage or even chip cracking, significantly reducing reliability.

This brings us to the next key player.

 

 

3. Inorganic Fillers: The “Personality Adjusters”

 

To enable resins and silicon to coexist harmoniously, formulation engineers incorporate large amounts of inorganic fillers, most notably silica.

 

Silica effectively lowers the overall CTE of the material, reducing internal stress caused by temperature changes.

In advanced packaging, fillers often account for more than 50% by weight, and in some applications—such as underfill—can reach nearly 90%.

Choosing the right type of silica for each process is often the deciding factor in whether a formulation succeeds.

 

Some applications also use hollow fillers, which maintain stability while enabling lightweight designs and improved dielectric performance.

 

As computing power continues to increase, heat generation rises dramatically. Without effective heat dissipation, even the most advanced chips cannot operate reliably over time.

 

As a result, packaging materials must not only be heat-resistant, but also thermally conductive.

This has made thermally conductive fillers (such as alumina, aluminum nitride, and boron nitride) and thermal interface materials (TIMs) indispensable in advanced packaging.

 

Common Filler Types

 

• Silica (SiO₂)
  • Controls CTE and reduces warpage
  • The most critical and widely used filler
• Hollow Silica
  • Lowers dielectric constant (low Dk)
  • Enables lightweight designs
• Alumina (Al₂O₃)
  • Enhances mechanical strength, wear resistance, and thermal conductivity
• Boron Nitride (BN)
  • Thermally conductive yet electrically insulating
  • Used in TIMs and packaging substrates

 

4. Metals: The Highways for Signal Transmission

 

The most intuitive materials in packaging are metals.

Copper is the dominant choice due to its low electrical resistance and high reliability.

 

In advanced packaging, metal interconnects are becoming extremely fine, and connection points continue to shrink. This places unprecedented demands on material purity, interfacial quality, and oxidation resistance.

 

Key Metals

 

• Copper (Cu)
  • Used in RDL, micro-bumps, and TSVs
  • Low resistance, high reliability
• SAC Solder (Sn-Ag-Cu)
  • Used for micro-bumps
• Low-temperature sintered copper / silver powders
  • Used for die attach and power devices

 

• Material Trends
  • Line width < 2 µm
  • Low-temperature processing (to protect chips and resins)
  • Oxidation resistance and high-reliability interface design

 

5. Interface Materials: The Invisible Determinants of Lifespan

 

Many packaging failures are not caused by poor material properties, but by weak bonding between different materials.

 

To ensure stable adhesion between resins, fillers, and metals, engineers rely on interface materials such as silane coupling agents, which significantly enhance interfacial bonding.

 

Although used in small amounts, these materials often determine whether a package can pass long-term reliability testing.

 

Key Interface Materials

 

• Silane Coupling Agents
  • Strengthen adhesion between resins, fillers, and metals
• Surface-Modified Fillers
  • Improve dispersion and reduce moisture absorption
• Barrier / Adhesion Layers
  • Prevent metal diffusion and delamination

 

Advanced packaging is fundamentally an art of material balance. Rather than pushing a single material to its performance limits, the goal is to achieve the optimal balance among protection, electrical performance, thermal management, and long-term reliability. For this reason, material selection and design have become the true driving force behind the evolution of advanced packaging technologies.

 

We offer a full range of upstream materials for advanced packaging—including resins, fillers, metals, and interface materials. If you have related needs or questions, we are happy to have the opportunity to discuss them with you.

 

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