What is an IC Substrate?

An integrated circuit substrate (or IC package substrate) is a substrate used to package an integrated circuit (IC). In addition to protecting the bare IC, the IC substrate is an intermediate product that connects the chip to the circuit board. Therefore, IC substrates have a significant impact on circuit performance.  

IC substrate is an integral part of the chip packaging process. It features high density, high precision, high performance, miniaturization and thinness. Its main function is to carry the chip. As an important carrier in the IC packaging and testing process, the IC substrate mainly provides support, heat dissipation and protection for the chip. It can realize multi-pin connection, reduce the size of packaged products, improve electrical performance, enhance heat dissipation, and even support multi-chip modularity. 

IC substrates play a key intermediary role by providing the electrical connection between the chip and the printed circuit board.

With the rapid development of servers, 5G, AI, big data and other fields, the demand for high-end chips is rising, driving the rapid growth of the integrated circuit substrate industry. In addition, IC substrates can be embedded with passive and active components to achieve certain system functions.

Classifications of IC Substrate

 Classification by Packaging Type

BGA IC Substrate: This is an IC substrate known for its excellent electrical and thermal properties. It is suitable for IC packages above 300 pins because it radically increases the number of chip pins.

CSP IC Substrates: this is a lightweight, single-chip package type with a smaller design size, primarily used for telecom and storage products with fewer pins. 

FC IC Substrates: Flip chip packaging features low circuit loss, low signal interference, good heat dissipation and high performance.

MCM IC Substrate: MCM stands for Multi-Chip Module. These IC substrates can accommodate chips with various functions in a single package. They are ideal for applications requiring thin, lightweight, miniaturized designs and short connections. However, because multiple chips are packaged in a single package, they tend to perform poorly in terms of heat dissipation, signal interference, and fine wiring.

Classification by Material Characteristics

Rigid IC Substrates: These substrates are mainly composed of ABF resin, BT resin or epoxy resin and have a coefficient of thermal expansion (CTE) of about 13-17 ppm/°C. These substrates are available in a wide range of colors and sizes.

Flexible IC Substrate: These substrates are mainly composed of PE or PI resin, with a CTE ranging from 13-27ppm/°C.

Ceramic IC Substrates: These Substrates contain ceramic materials such as aluminium nitride, alumina or silicon carbide, which have relatively low CTE values, typically in the range of 6-8 ppm/°C.

Classification by Bonding Technology

 --Tape-Automated Bonding (TAB)

 --Wire Bonding

 --Flip-Chip Bonding (FC Bonding)

What does the substrate of an IC usually consist of?

Main Raw Materials of IC Substrates: BT Substrates, ABF Substrates, and Glass Substrates

BT Substrate (Bismaleimide Triazine Resin Substrate)

BT substrate is an IC substrate whose basic material is BT resin, developed by Mitsubishi Gas Chemical Corporation in Japan. It has the advantages of high Tg, good heat resistance and low dielectric constant, which makes it ideal for chips with high reliability requirements. Its downstream applications include memory chips, MEMS chips, RF chips and LED chips.

ABF Substrate (Ajinomoto Build-Up Film Substrate)

ABF substrates use ABF (Ajinomoto Build-Up Film) as a base material. This material was jointly developed by Ajinomoto and Intel, with Ajinomoto having a monopoly on its production. Intel was the first company to use ABF as a substrate material. ABF substrate enables smaller line widths and finer circuitry for package designs with high pin counts and high transmission rates. Downstream applications include CPUs, GPUs, FPGAs and ASICs for high-performance computing (HPC), and as technology becomes increasingly data-driven and intelligent, the precision required of downstream products is increasing. Coupled with the rapid growth of servers and high-performance AI chips, demand for ABF substrates continues to rise.

ABF substrates are characterized by a high number of pins, high transmission rates, precise circuits, good conductivity, and no need for hot pressing processes. They are suitable for ICs with a high number of pins and high transmission rates, and are widely used in flip-chip (FC) packaging for high-performance computing chips such as 5G, artificial intelligence, cloud computing and big data analysis. In terms of packaging material costs, high-end flip-chip IC substrates account for as much as 70%-80% of total packaging costs, making ABF substrates the most valuable material in advanced packaging processes. As computing performance continues to improve rapidly, there is a constant need to develop ABF insulating resins with different properties. These resins must be refined to meet the processing technology needs of emerging customers, while also being tested and validated repeatedly.

As smartphones become more complex and 5G high-frequency communication transmissions become more demanding, the thermal stability, heat dissipation, and low dielectric properties of ABF insulation materials are becoming increasingly important. However, ABF materials are currently susceptible to thermal expansion and contraction issues, leading to reduced reliability. Increasing substrate area and processing complexity are expected to drive future growth.

Glass Substrates: A New IC Substrate Material

Glass substrates are a newly developed substrate material for IC with excellent mechanical stability and superior physical and optical properties. These substrates can withstand higher temperatures and reduce pattern distortion by up to 50 per cent, thereby increasing the depth of focus for lithography. They also increase through-hole density by a factor of about 10. In addition, the improved mechanical properties of the glass greatly increase the yield of very large packages.

According to Intel's analysis, glass substrates enable manufacturers to achieve performance and density gains with greater flexibility, lower overall cost and lower power consumption.

IC Substrate vs. PCB

1. Basic definition

An IC substrate is a technology that integrates microelectronic components onto a circuit board. It is widely used in consumer electronics such as smartphones, tablets and TVs. IC substrates require precise wiring to connect various components in an organized manner so that the circuit operates efficiently.

A PCB is a circuit board that integrates electronic components, connectors and circuit structures. It is widely used in fields such as computers, communication equipment and medical devices. A PCB consists of metal conductors printed on a circuit board to connect and control electronic components.

2. Design features

IC substrates must adhere to precise dimensional standards and routing rules to meet the requirements of miniature components. Designers face challenges such as limited circuit capacity, heat dissipation and noise interference. IC substrate design often involves 3D modelling and detailed animation techniques to simulate and optimize circuit performance.

PCB design must take into account factors such as materials, process costs and manufacturing techniques, as well as the specific needs of the application. Designers must address issues such as electromagnetic compatibility, circuit noise, static resistance and noise reduction. PCB designs are often optimized using CAD technology and circuit simulation software.

3. Manufacturing processes

IC substrate manufacturing uses advanced semiconductor processes such as deposition, exposure, etching and moulding. It requires precise laser cutting and pre-fabrication techniques. IC substrates are usually manufactured in batches or customized according to specific requirements.

The manufacturing process of PCB involves a number of processes including board-cutting, CNC drilling, chemical plating, printing, routing, testing and packaging. Production requires high precision machines and tools, including drilling machines, routing machines and static elimination devices. The production of PCB is usually categorized into high volume and low volume to meet a variety of needs.

Despite their differences, IC substrates and PCBs share similarities in manufacturing processes, principles and applications. Both use modular design concepts that allow for common circuit functionality and optimization. The equipment and tools used in the manufacture of IC substrates and PCBs are also similar, such as modelling software, simulation software and product test instruments. Both adhere to the same circuit design principles and process standards.

Applications of IC Substrate PCB

--Consumer Electronics - Smartphones, laptops and tablets, wearables

--Automotive Industry - ADAS, infotainment system, EVs

--Telecommunications - 5G infrastructure, networking equipment

--Medical Devices - Implantable devices, diagnostic equipment

--Aerospace and Defense - Satellite systems, radar and surveillance system--Industrial Applications - Robotics, automation system

--AI sensor

 (Original:：Chip News)