abf film

Ajinomoto Build-Up Film (ABF) for HDI, UHDI, and Substrate-Like PCBs

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UHDI PCBs need materials that can support increasingly complex designs and higher interconnection densities, and this is achieved with very thin buildup films in the UHDI PCB stackup. One such material that has become the market-leading buildup film used in UHDI PCBs is Ajinomoto buildup film (ABF).

ABF is a specialized thin-film material that has everything from ultra-fine pitch packages to high-performance components like FPGAs, ASICs, processors, and graphics chips. Its material properties, including a low Dk value and rigidity, allow it to meet the stringent demands of today’s electronics. This article will look into the unique attributes of ABF and how it continues to shape the direction of HDI, UHDI, and UHDI PCBs.

Overview of ABF

ABF is not a new material, but it remains a cutting-edge material for use in UHDI PCBs, where it serves as a buildup layer to support advanced circuit fabrication. This thin-film material is laminated onto a rigid core, such as organic FR4, BT epoxy, or stiffened polyimide, creating a platform for microvia formation and transmission line routing. ABF is compatible with both subtractive and additive circuit fabrication processes, making it highly versatile for modern electronic designs.

Applications of ABF

High-Performance Computing (HPC)

ABF is extensively used in UHDI PCBs for high-performance computing systems, including CPUs, GPUs, and multi-core processors. These devices require high pin count interconnections and exceptional signal integrity, both of which are supported by ABF's low dielectric constant and low loss tangent. The material's ability to support high layer counts and fine-line circuit patterns makes it ideal for the dense interconnects needed in HPC applications.

 

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GPU packages with high-density routing require an advanced thin-film material like ABF.

 

Consumer Electronics

In consumer electronics, such as smartphones, tablets, and laptops, ABF plays a critical role in enabling compact designs without compromising performance. Its thin film thickness and compatibility with HDI features allow manufacturers to integrate more features into smaller packages. This is particularly important in devices where space is at a premium, and high-speed data processing is essential.

Telecommunications and Networking

The telecommunications industry relies on ABF for its ability to maintain signal integrity in high-frequency applications. Its low dielectric constant and high thermal stability make it suitable for substrates used in 5G infrastructure, data centers, and other networking equipment. These applications demand materials that can handle high-speed signals and operate reliably under thermal stress.

Advanced Packaging Technologies

ABF is also a key enabler of advanced packaging technologies, such as flip-chip substrates and multi-chip modules. These packaging methods require materials that can support fine-line patterning, high aspect ratio vias, and precise circuit formation. ABF's compatibility with both subtractive and additive fabrication processes makes it a preferred choice for these cutting-edge designs.

 

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Typical package structure involving ABF. Source: Ajinomoto Fine-Techno USA Corporation.

 

Emerging Applications

Innovative companies are exploring alternatives to ABF, but its dominance in UHDI PCBs and HDI PCBs remains strong. As new technologies emerge, ABF is expected to continue playing a significant role in applications requiring advanced material properties and HDI design features.

Advantages of ABF

ABF offers a range of advantages that make it a preferred material for HDI and UHDI PCBs. Its unique properties contribute to improved performance, reliability, and manufacturability in advanced electronic systems.

HDI Design Capability

ABF's thin film thickness enables the creation of high layer count substrates, which are essential for compact and high-performance devices. This capability supports the formation of fine-line circuits and microvias, allowing for dense interconnections in modern UHDI PCBs. The material's compatibility with laser drilling and sequential lamination processes further enhances its suitability for high-density designs.

Superior Electrical Properties

ABF provides excellent electrical performance due to its low dielectric constant (Dk as low as 3.1) and low loss tangent (Df as low as 0.014). These properties ensure minimal signal loss and high signal integrity, which are critical for high-speed and high-frequency applications. This makes ABF an ideal choice for devices requiring reliable and efficient data transmission.

ABF provides excellent electrical performance due to:

  • Low dielectric constant (Dk as low as 3.1)
  • Low loss tangent (Df as low as 0.014)

These properties ensure minimal signal loss and high signal integrity, which are critical for high-speed and high-frequency applications. This makes ABF an ideal choice for devices requiring reliable and efficient data transmission.

Thermal and Mechanical Stability

With a high glass transition temperature (Tg of ranging from 165 °C to 198 °C) and low water absorption (<0.6 to 1.1 wt% at 100 °C for 1 hour, depending on specific ABF material), ABF exhibits excellent thermal and mechanical stability. These characteristics ensure reliable performance in demanding environments, such as those encountered in high-performance computing and telecommunications applications.

Versatility in Fabrication Processes

ABF is compatible with both subtractive and additive circuit fabrication processes, making it highly versatile for various manufacturing techniques. Its ability to support advanced copper deposition and precise circuit/via formation ensures flexibility in design and production. This versatility allows designers to optimize their processes for cost, performance, and manufacturability.

Low Moisture Absorption

ABF's low water absorption rate enhances its reliability by reducing the risk of moisture-related defects, such as delamination or electrical failures. This property is particularly important in applications where the substrate is exposed to varying environmental conditions.

Use of ABF in HDI and UHDI PCBs

ABF plays a critical role in the fabrication of HDI, UHDI, and substrate-like PCBs. Its unique properties and compatibility with advanced manufacturing techniques make it an essential material for achieving the high performance and miniaturization required in modern electronics. The low thickness of ABF also allows very high layer counts in PCB stackups, as well as PCB analogues of standard IC substrate stackup approaches (e.g., CSP and corelss).

 

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High-density copper traces on ABF film. Source: Ajinomoto Fine-Techno USA Corporation.

 

Enabling High Layer Count Stackups

ABF's thin film thickness is ideal for creating high layer count stackups, a key requirement in HDI and UHDI PCBs. This property allows designers to pack more interconnects into smaller spaces, enabling compact and high-performance designs.

Supporting Fine-Line Circuitry

The low dielectric constant and low loss tangent of ABF make it suitable for fine-line circuitry in HDI and UHDI PCBs. These properties ensure signal integrity and low dielectric signal loss in high bandwidth channels. Furthermore, copper-dominated losses may be tunable by deposition processes such that insertion loss can be further controlled.

Compatibility with Advanced UHDI Fabrication Techniques

ABF is compatible with laser drilling processes, enabling the formation of microvias and other fine interconnect features. This capability is essential for HDI and UHDI PCBs, where precise via formation is required to achieve HDI features.

ABF supports additive copper deposition processes, which are commonly used in UHDI PCB manufacturing to achieve higher densities. This compatibility allows for the creation of intricate circuit patterns and small diameter vias, meeting the stringent demands of modern UHDI PCBs and substrate-like PCBs.

 

Whether you're designing high-speed PCBs for mil-aero embedded systems or a complex RF product, you should work with a design and development firm that can ensure your product will be reliable and manufacturable at scale. NWES helps aerospace OEMs, defense primes, and private companies in multiple industries design modern PCBs and create cutting-edge embedded technology, including power systems for high reliability applications and precision control systems. We've also partnered directly with EDA companies and advanced ITAR-compliant PCB manufacturers, and we'll make sure your design is fully manufacturable at scale. Contact NWES for a consultation.

 



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