Over the years, it has been
evident that integrated circuits are becoming compact and smart with the
increasing demand for the miniaturization of electronic devices. Moore’s law
states that the number of transistors on a chip will double every two years.
These challenges led the scientists to make more sophisticated integrated
circuits and IC substrates. The IC substrate is made up of resin-based
materials and then this substrate is used to create tiny electrical wiring
inside the chip that connects the IC with the PCB or external system. The IC
substrate makes it possible for the microchip to transmit the electrical
signals between the chip and the circuit board.
The advancements in semiconductor
technologies, like the invention of Ball Grid Array (BGA) packages and IC
substrate, make it crucial for design engineers to grasp the fundamental and
core concepts of IC substrate, their manufacturing process, and how and when to
use IC substrate PCBs in their design. This article will help you cover all the
fundamental and core concepts of IC substrate to level up your game!
What is an IC Substrate?
An integrated Circuit, or simply IC, is a circuit that has
transistors, diodes, resistors, and capacitors all fabricated in a small semiconductor
chip. An IC Substrate is a specialized platform that is used as a Base for the
physical and electrical support of integrated circuits. The substrate is a
material that acts as a shield for the IC and establishes the connection
between the IC and the PCB trace. This substrate is a collection of holes and
traces that form the electrical connection for the components inside the IC and
give them a path to communicate with the external world. In simple words, the IC
substrate is nothing but the internal wiring of an IC that connects the chip
with the PCB.
Types of IC Substrate
Different microchips have different sizes, performance, cost,
packaging styles, thermal management, and cost considerations. Based on these
factors, IC substrates can be classified into three main categories:
Classification by Packaging Type
The IC substrate classification by packaging type focuses on the
final structure or packaging style of the IC. Based on the packaging type, the IC
substrate role changes, which divides them into different types.
1. BGA IC Substrate: BGA stands for Ball Grid Array and they use solder balls arranged
in the form of an array to make an electrical connection. This type of IC
substrate is specially designed to handle thermal dissipation. They are used in
applications where better thermal performance and higher densities of pins are
required.
2. CSP IC Substrate: Unlike the BGA packaging type, the Chip Scale Package (CSP) is used
mainly for applications that require a lower pin count. These IC substrate
packages are smart and lightweight, hence suitable for miniaturization products
like consumer electronics, the Internet of Things, and wearable electronics.
3. MCM IC Substrate: MCM stands for Multichip Module, and as its name suggests, these IC
substrates are primarily used to perform multiple tasks. Simply speaking, an
MCM substrate has multiple chips combined in a single module, and each module
serves a unique purpose. As the multiple chips are combined in a single
package, these are suitable for applications that have space and weight constraints.
The disadvantage of MCM IC substrate is that it is not suitable for harsh environments
and extreme temperatures, as the multiple chips are packaged into a single
module, causing heat dissipation.
4. FC IC Substrate: Flip Chip (FC) IC substrate is ideal for applications requiring low
signal interference, better performance, and better thermal management. FC IC
substrates good thermal management capabilities make them ideal for General
processing Units (GPUs), RF communication chips, and machine learning
processors.
Classification by Material Characteristics
IC substrates can be classified based on their material
characteristics. Different material characteristics are utilized to achieve
different functions.
1. Rigid board IC substrates: The IC
substrate used to make rigid circuit boards uses resin and fiberglass material.
The material characteristics of epoxy resin make it rigid and stable. They are
used in traditional rigid boards such as BGA.
2. Flex Board IC
Substrates: These IC substrates are made with
polyimide material. They are used in applications requiring flexibility and
space savings.
3. Ceramic Board IC
Substrate: These IC substrates are made with
aluminum material. These substrates are used in applications where high
reliability is required.
Classification by Bonding Technology
IC substrates can also be classified in terms of bonding
technology.
1. Wire Bonding: The simplest type of
bonding is wire bonding, in which wires are threaded from the microchip using a
machine.
2. FC Bonding: Flip chip bonding is
typically done using the polymer adhesive. This method uses solder balls to facilitate
the interconnections of chip and board contacts.
3. TAB Bonding: Tape automated bonding is
done using pressure-sensitive adhesive by attaching the chip to the flexible
substrate.
Key Functions of IC Substrate
There are several key functions that an IC substrate serves. The
following are some of the important key functions of the IC substrate.
1. The IC substrate
acts as a bridge that connects the microchip and PCB by making electrical
connections.
2. It provides mechanical
support to the chip.
3. IC substrate
plays a key function in managing heat dissipation and preventing overheating.
4. The IC substrate
protects the microchip from external environmental conditions.
5. Their small size
and light weight help designers manufacture smart devices.
IC Substrate Manufacturing Process
The IC substrate manufacturing process is a
complex process that is being done in an extremely clean environment with no
dust particles.
1. Material Selection: The very first step in the IC substrate manufacturing process is to
choose the material. Normally, BT resin, ABF materials, or sometimes polyimide
are used depending on the requirements.
2. Copper Patterning
and Plating: The second and most critical step is
the creation of electrical circuits on the substrate. Ultraviolet light and
photoresist are utilized for the circuit design pattern. The developed pattern
is then passed through the etching process to form the conductive paths.
3. Lamination: The final IC substrate is made by stacking and bonding multiple
layers of materials together.
4. Drilling: Now, the holes and vias are drilled in IC substrate to make the way
for electrical connections. The vias enable the electrical signals to pass
through different layers.
5. Surface Treatment: The IC substrate is passed through the oxidation resistance process
to protect it from environmental conditions such as moisture and temperature.
6. Quality
Inspection: After the fabrication of the IC
substrate, it goes through comprehensive quality testing to ensure that it
performs as per the set specifications.
Applications of Integrated Circuit Substrate PCBs
IC substrates are the fundamental blocks of
IC technology. They are extensively used in all types of applications in which
ICs are used.
1. Consumer
Electronics: The IC substrates are widely used in
consumer electronics products, such as they are used in mobile phone
processors, due to their lightweight and high performance. Similarly, they are
used in other consumer electronic devices, including memory devices and digital
cameras.
2. RF Technologies: The RF technologies require high frequency and high-speed
transmission, e.g., 5G. IC substrates are used in RF modules to meet these
requirements while maintaining signal integrity.
3. Military Industry: Military applications like drones, missiles, and
aircraft are operated in harsh environmental conditions. IC substrates used in
these applications make them fit to withstand environmental conditions.
4. Automotive
Electronics: Modern vehicles are becoming dense
with electronic systems like navigation modules and autonomous driving systems.
The IC substrate provides the way forward for implementing these technologies
in modern vehicles.
5. Medical
Devices: The IC substrate makes it easy for the
designers to make extremely smart and compact devices like pacemakers for heart
patients and other diagnostic equipment.
Design Considerations for Integrated Circuits
When designing the integrated circuits, it is important to consider
important factors that can entirely alter the final results of your design.
1. Material
Characteristics: The material characteristics can
greatly alter the overall performance of the chip. It is important to know the
exact material composition and substrate characteristics for your IC package.
2. Thermal
Management: Thermal dissipation is an important
parameter that must be taken into account while designing the IC substrate.
3. Signal Integrity: Signal integrity is a critical design parameter
that must be considered in the design process of the IC substrate to ensure it
is free from signal loss.
4. Reliability: The IC substrate must be reliable and withstand harsh environmental
conditions.
Conclusion
The world is shifting towards miniaturization, and the IC substrate
provides a way forward to achieve this milestone. The IC substrates are the
fundamental components in integrated circuits. The IC substrates are the
internal wiring of the IC that connects the chip with the PCB. Understanding IC
substrate types, their manufacturing process, and design considerations is
important for engineers to manufacture and design state-of-the-art integrated
circuits.
