Keywords: Printed Circuit Board, Circuits Board

The substance that supports the traces and parts that form the structure of a printed circuit board is known as a PCB substrate. The result and success of a high-quality Printed Circuit Board project depend greatly on the choice of substrate material.

It has frequently been said that making PCB substrates is like making a sandwich. The strata are often denoted as follows:

• The printed circuit board's core, a hard foundation material that acts as its principal insulating layer and is often wrapped with copper foil as an internal ground plane, is located in the middle of the board.
• Prepreg, a dielectric material binding agent that coats the core, is used to cover it.
• The surface is covered with an outer layer of foil, creating the region where component components will be joined and traces will be etched.
• Next, the solder mask is put to the board's surface. This is done largely to avoid solder bridges, shield the copper traces from oxidation, and aid in visual inspections.
• While believed to be a layer of their own, silkscreen is used to identify which pieces are located where on a board and offers no practical advantage.
• Prepreg and core material are typically referred to when we talk about the PCB substrate. The possibilities that substrates provide can be tailored to the needs of the end-user.

When and how is PCB substrates made?

As was already discussed, during production, PCB substrates are arranged by layers. They can be layered in multi-layer PCB layouts or be as basic as one-sided PCBs. Metal foil and dielectric material are alternated in these layers.

Because to improved electrical performance brought on by lower dielectric constants and loss tangents compared to other materials, the bulk of PCB substrate materials are blended with epoxy. Due to growing environmental concerns about lead-based printed circuit boards, resin chemistry has developed throughout time to accommodate the higher temperatures of lead-free soldering.

When we examine the different substrate materials employed in the production of printed circuit boards, it's critical to keep in mind that as performance increases, so do costs. As compared to a phone that could be thrown out in a few years, printed circuit boards used in telecommunications, military gear, and aerospace engineering need to operate at significantly higher rates. So, when reviewing the list, place the end-use before optimum performance.

PCB substrates types

FR-4

The great majority of printed circuit boards on the market are made of FR-4 material. This is intentional because FR-4 boards, which are constructed of woven glass reinforced by epoxy resin, are inexpensive, effective, lightweight, and have exceptional moisture resistance.

To be clear, FR-4 is a categorization that denotes a substance's flame resistance rather than a material itself.

Although FR-4 is excellent for consumer electronics, it is not appropriate for high-speed or high-frequency applications because to its significant dielectric loss. Printed Circuits Board designers choose to FR-4 to get excellent outcomes at a low cost when money is the deciding issue.

Flex PCB Materials

One of the most significant advancements in consumer electronics is wearable technology. It demonstrates how far we have gone in the past ten years and how much further we still have to go by combining the usability and functionality of smart devices with the ease of fitting around a wrist. Without flexible printed circuit boards, these gadgets would not be conceivable.

Many uses for flexible printed circuit boards exist outside of clothing. Flex PCBs can fit a significant amount of surface area into small or oddly shaped places due to their ability to bend. They may now be found in anything from calculators and video gaming consoles to satellites and medical equipment. They can even operate in hazardous environments.

Flex PCB substrates' greatest strength is their flexibility. As a result, they are made of soft materials and are often produced with an epoxy that is curved like a glass weave. Some typical substrates are:

• Polytetrafluoroethylene (PTFE), sometimes known as Teflon, is the material of choice for flexible PCBs. They are used in telemetry, antennas, power amplifiers, and cruise control because of their low dissipation and strong temperature stability.
• Polyimide - Polyimide possesses strong conductivity qualities as well as a wide operating temperature range and great chemical resistance. Little consumer items like calculators, cameras, and gaming gadgets are well suited for this material.
• PEEK is unrivaled for use in the most difficult circumstances. It has a high melting point, excellent chemical resistance, and can withstand significant radiation exposure. This printed circuit board substate's characteristics allow for its application in both aircraft and medical equipment like gamma and X-ray machines.

Substrates for Rigid PCBs

Rigid printed circuit boards cannot be moved, as opposed to flexible printed circuit boards. They become less corrosion-resistant, waterproof, and shockproof as a result. Nonetheless, inflexible PCBS are resilient, economical, and strong despite these drawbacks.

Substrates with a ceramic basis typically make up rigid printed circuit boards. These boards operate at high temperatures and have strong thermal conductivity. These are the simplest sorts of boards to fix and are small, which allows them to occupy less space than some of their competitors.

The three most common ceramic-based materials for printed circuit boards are:

• Aluminum is the most often used material for ceramic printed circuit boards because it has a high thermal dielectric and little expansion. It offers exceptional high-frequency performance in even the hardest high-temperature situations and can function up to 350 C before melting. These printed circuit boards' thermal conductivity, however, falls short of what high-power components like integrated circuits require. It is typically utilized in sensors, LEDs, medical circuits, and heating and cooling.
• Aluminum Nitride - Aluminum nitride substrates are used in printed circuit boards for high-power devices like LEDs, integrated circuits, and sensors. The heat conductivity of aluminum nitride substrates is over 10 times greater than that of aluminum printed circuit boards.
• The prospective uses of beryllium oxide are considerably more advanced since it has an even better heat conductivity than aluminum nitride. Its severe toxicity during the machining process is one issue, though. High voltage integrated circuits and commercial microwave ovens both make use of it.

Substrates for Flex-Rigid PCBs

Both types of materials are combined in flex-rigid Printed Circuit Board, which are typically utilized in aerospace, medical, and military applications.

Due to their ease of fabrication and low dielectric loss at microwave frequencies, they generally use polytetrafluoroethylene components like RO3000 and RO4000.