As demand for high-performance semiconductors continues to grow, driven by AI and HPC(high-performance computing), semiconductor packaging technologies are also advancing rapidly. To process larger volumes of data with greater stability, circuits inside semiconductor packages must become finer and be stacked in increasingly sophisticated multilayer structures.

This is where BUF(Build-Up Film) plays a critical role. As an insulating film material used to form insulating layers between circuit layers, BUF helps prevent interference among wiring layers and enables fine circuits to be formed with stability.

In this interview, we spoke with LG Chem’s BUF development team to learn more about the role BUF plays in the era of high-performance packaging and the technologies the team is preparing for the future.

Hello! Could you briefly introduce your team and the work you are currently responsible for?

Hello. Our team is responsible for developing BUF(Build-Up Film) materials for semiconductor packages.

We develop BUF applied to high-performance semiconductor package substrates used in AI servers, HPC systems, and other advanced applications. Our key role is to design BUF performance so that fine wiring can be formed with stability and high-speed signals can be transmitted with minimal loss.

To achieve this, we combine various resins, inorganic fillers, and catalyst systems to secure electrical properties, dimensional stability, adhesion, and reliability. We also review key factors required in actual package substrate manufacturing processes, such as laser processability and plating adhesion, to develop BUF solutions optimized for customer processes.

What kind of material is BUF (Build-Up Film), and what role does it play in semiconductor package substrates?

BUF is an organic-inorganic composite insulating film material used to form insulating layers between circuit layers in semiconductor package substrates. It provides electrical insulation between multiple wiring layers, preventing signal interference.

Simply put, for the dense wiring inside semiconductor packages to function properly without affecting one another, a material is needed to reliably separate and support the layers. BUF serves as that foundation.

Electrically, BUF helps prevent signal interference and short circuits between wiring layers. Structurally, it supports fine wiring layers with stability. At the same time, it enables uniform thickness and surface quality, allowing circuits to be formed with precision.

In this way, the role of BUF is expanding beyond that of a simple insulating material that separates layers. It is now becoming a material that supports both fine circuit implementation and package structural stability.

How are the performance requirements for BUF changing as package structures evolve?

Performance requirements for high-performance semiconductor packages vary depending on the application and package structure. LG Chem’s BUF is being developed into a range of product lines to meet these requirements, including low dielectric constant and low loss(Low D_k/D_f), low coefficient of thermal expansion(Low CTE), and fine-patterning solutions.

Accordingly, the key performance requirements for BUF can be summarized as follows.

1. Low D_k/D_f properties to reduce signal loss
These properties help prevent high-speed electrical signals from being lost or distorted.

2. Low CTE properties to reduce thermal deformation
These properties help effectively suppress warpage in large-area and highly integrated substrate environments, providing excellent dimensional stability and high reliability.

3. Fine-patterning performance to enable fine circuitry
Based on thin and uniform insulating layers as well as precise laser processability, BUF enables denser circuits and high-density multilayer structures.

Ultimately, BUF is evolving into a material that supports stable signal transmission, reduces thermal deformation, and enables fine circuits to be formed with precision. What matters most is designing multiple properties to work together in alignment with each package structure and customer process.

What differentiates LG Chem’s BUF from other solutions?

The key differentiator of LG Chem’s BUF lies in its resin formulation technology, which is optimized for customer requirements. Since required performance varies by package structure and application, the key is to precisely combine resins, catalysts, and fillers to achieve the target material properties.

In particular, we are enhancing crack resistance through high-toughness design. This enables the material to maintain stability even in environments where thermal and mechanical stress are repeatedly applied.

In addition, we have overcome the technical limitation that higher filler content makes thin coating more difficult. By simultaneously implementing high nanofiller loading technology and ultra-thin coating technology of less than 10μm, we have improved fine-patterning capability. This allows the formation of thin and uniform insulating layers, contributing to ultra-fine circuit implementation and improved production efficiency.

In other words, LG Chem’s BUF goes beyond material design alone. It is differentiated as an integrated solution that also takes into account the processability, adhesion, and reliability required in actual substrate manufacturing processes.

Warpage is considered an important issue in AI semiconductor substrates.
What is warpage, and how does BUF help reduce it?

Warpage refers to the deformation or bending of a substrate caused by heat or stress. AI semiconductor packages are becoming larger and more highly integrated. Since substrates are composed of multiple stacked materials, each material expands differently when heat is applied. When these differences become significant, substrate deformation can occur.

LG Chem’s Low CTE BUF helps suppress substrate deformation by reducing differences in thermal expansion. Through modulus control and thickness uniformity technologies, we design the material to distribute internal stress more evenly within the substrate and reduce heat-induced distortion.

In addition, multifunctional curing agent design helps lower thermal expansion itself. Through these technologies, LG Chem’s BUF contributes to improving manufacturing process stability and package structural reliability, even in large-area AI packages.

Beyond warpage, what is the most challenging technical issue in BUF development?

The most challenging aspect of BUF development is balanced design that satisfies multiple performance requirements at the same time. Because improving one property can affect another, we must consider electrical properties, adhesion stability, structural reliability, and process compatibility together.

For example, when materials with low dielectric constant(Low D_k) and low dissipation factor(Low D_f) are applied to reduce signal loss, adhesion to copper(Cu) can decrease. This may affect the reliability of plating interfaces or interlayer bonding.

In addition, as packages become larger and more complex with multiple layers, heat and stress can accumulate more easily inside the package. This can lead to issues such as substrate deformation, cracking, and delamination. At the same time, customer requirements for low dielectric properties and fine-patterning continue to rise, making it difficult in some cases to meet all required performance levels with conventional materials alone.

Ultimately, BUF development is not about improving a single material property. It is a sophisticated material design process that requires balancing multiple interdependent properties.

* Low D_k (Low Dielectric Constant): A property that reduces signal transmission delay by storing less electrical energy.
* Low D_f (Low Dissipation Factor): A property that minimizes signal attenuation by reducing energy loss during signal transmission.

As BUF is an ultra-precision material, what are the areas your researchers pay the closest attention to in the lab? Are there any ‘occupational habits’ unique to your team?

Because BUF is an ultra-precision material used to implement fine wiring, our team places the greatest emphasis on particle control and ensuring uniformity in both the material and film. Even small particles or uneven dispersion can lead to defects in fine circuits, so we strictly manage cleanliness and dispersion conditions throughout the entire process, from material synthesis to coating and evaluation.

To verify performance and secure quality, we focus on evaluating dielectric properties(D_k/D_f) related to signal loss, copper(Cu) adhesion, coefficient of thermal expansion(CTE), warpage, cracking and delamination, fine-pattern formation capability, and reliability under high-temperature and high-humidity conditions. We also optimize process conditions such as lamination, laser drilling, and plating to support actual application.

Because of this work, our researchers often find themselves naturally noticing dust or subtle differences in surface conditions even in everyday life. The habit of not overlooking even the smallest defect has become deeply embedded throughout the R&D process.

The R&D process likely requires collaboration among team members with diverse academic backgrounds and experience. Could you introduce the collaboration culture or problem-solving approach unique to the BUF R&D team?

BUF development closely connects many different areas, including raw materials, formulation, reliability and product commercialization. Even when a single issue arises, we need to examine the cause from multiple perspectives, such as material composition, process conditions, and evaluation methods. This makes collaboration that connects each team member’s experience and expertise essential.

Our team values a culture where members can freely share opinions and translate those discussions into actual verification. The verification results are then organized and standardized so they can be accumulated as team assets. This growing base of data and know-how becomes the foundation for solving complex issues more quickly and reliably.

Finally, what role do you expect LG Chem’s BUF to play in the semiconductor packaging materials market going forward?

The semiconductor packaging market is expected to continue growing, driven by AI, HPC, and other high-performance applications. As semiconductors become faster and more highly integrated, the role of package substrate materials will become even more important.

Amid these changes, LG Chem’s BUF aims to establish itself as a material that supports the realization of next-generation semiconductor packages. Our goal is to proactively secure the performance required in line with customers’ technology roadmaps and provide material solutions that can be validated in actual process and mass production environments.

Going forward, LG Chem will support customers in developing next-generation packages as an integrated solution partner that goes beyond simple material supply, offering both advanced material design and process compatibility. Through these efforts, we will continue to strengthen our differentiated competitiveness in the high-performance semiconductor packaging materials market.

As this interview shows, as semiconductor packaging technologies become more advanced, the role of substrate materials that support them is also becoming increasingly important.

Based on its accumulated expertise in material design and process optimization, LG Chem will continue to advance BUF solutions tailored to evolving package structures and customer requirements.

 
[Explore More from LG Chem’s Advanced Materials R&D Interview Series👉]
1) CCL R&D Team: Driving Semiconductor Performance in the AI Era: An Interview with LG Chem’s CCL R&D Team

2) DAF R&D Team: The Hidden Enabler of Advanced Semiconductor Packaging: LG Chem’s DAF(Die Attach Film) R&D Team

3) PID R&D Team: Pushing the Boundaries of Next-Generation Semiconductor Packaging: LG Chem’s PID (Photo Imageable Dielectric) R&D Team