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- November 9, 2022
- PCB knowledge
- (0)
- 06 mins
A practical guide to PCB material and its selection
When it comes to fabricating printed circuit boards in today’s world of cutting-edge electronics, selecting the correct type of PCB material is crucial. In this detailed article learn everything about the composition of PCBs, the most prevalent types of PCB materials, and the most important aspects you should keep in mind when selecting PCB material choices for manufacturing.
Basic composition of PCB
PCB materials are chosen based on their electrical and thermal qualities, which are essential for the board to function according to the design rating. The form factor and the number of layers on the board are both determined by the schematic. A sophisticated PCB, at least, will have following layer composition.
Substrate layer: It is the main insulating and supporting material layer for the whole PCB. The thickness of this substrate layer, which provides a sturdy base for printed circuit boards, varies depending on the intended purposes of the board.
Conductive layer: In most cases, the PCB is fabricated by depositing a very thin layer of a metal such as copper on the surface of the insulating material.
Solder mask layer: It is an additional layer on the top of conductive layer. Contacting pads on PCB need this insulating layer to prevent shorts to other conductive components.
Silkscreen layer: This layer of printing epoxy is used for printing symbols or any informative text on solder mask. A silkscreen can be used to read cautionary signals, identify parts, and determine assembly locations.
Properties of PCB materials
When the high-quality PCB materials are used to fabricate a printed circuit board, not only will it function properly, but it will also survive for the lifetime of the product. Following are some important properties of PCB materials.
Electrical conductivity: Conductive metal normally have high conductivity to reduce the resistance of tracks. Copper is the main used conductive material having good electric conduction properties which do not require any further explanation.
Thermal conductivity: Substrate material should have low thermal conductivity constant. This PCB material should help in NOT spreading the heat of one electrical component to nearby components.
Flexibility and strength: PCB material needs to be rigid and mechanically a little flexible as during operation the material can be prone to effect of thermal elongation and should not develop cracks causing traces to break.
Substrate is the only major PCB material that is considered the backbone of entire PCB as it has to provide support and some extra thermal efficiency. From hereafter, we will focus on the substrate as the main PCB material.
How many types of PCB materials are there?
PCB manufacturing relies heavily on the careful selection and integration of PCB materials. While there are literally hundreds of various materials from which to pick depending on budget and technical needs, some of the most common PCB materials are listed here.
Cellulose based composite materials
- CEM-1
- CEM-2
- CEM-3
- CEM-4
- CEM-5
Glass reinforced epoxy laminate materials
- FR-1
- FR-2
- FR-3
- FR-4
- FR-5
- FR-6
Teflon based materials
- PTFE
Polymer materials
- Polyimide
Metallic materials
- Alumina
Most commonly types of PCB materials
Different materials have different properties and their use depend on the design and environmental requirements. But some of these PCB materials are mostly used due their best and economical properties. Following are some commonly used PCB materials.
FR1 & FR2
These Fire-Retardant materials are utilised only for single layer PCB and is fabricated using paper and phenol chemicals. The glass transition temperature is the only distinguishing feature between FR1 and FR2. FR1’s Tg is greater than that of FR2’s glass transition state.
FR4
The National Electrical Manufacturers Association (NEMA) has established FR4 as the standard for a glass-reinforced epoxy resin laminate.
Polyimide
The temperature endurance of polyimide laminates is superior to that of FR4 materials, and they also exhibit a minor increase in their electrical performance characteristics. Polyimide materials are more expensive than FR4 materials, but this PCB material offers enhanced endurance in hostile and higher temperature conditions. As a result of their improved stability during thermal cycling and reduced tendency towards expansion, these materials are well suited for structures with a greater number of layers.
Teflon – PTFE
Teflon possesses outstanding electrical characteristics for PCB, which makes it well suited for use in high-speed circuits applications. Teflon material is more costly than polyimide. PCBs made of Teflon can also be coated with fabric glass other additives to increase their mechanical strength. In many cases, the production of Teflon based PCBs calls for a workforce with a specific set of skills, specialized equipment, and procedures.
Which material is best for PCB board?
When selecting best PCB material for all sorts of PCBs, whether for household electronics or industrial equipment, quality is of the highest importance. Furthermore, what is most vital is that the PCB material in question provides exceptional levels of excellent performance throughout its planned working life.
FR-4 is the most frequent material used in PCBs. This epoxy-based PCB material is both fire and water resistant. It has a high strength-to-weight ratio. This material has an extremely high tensile strength.
FR-4 PCB material
FR4 is a composite material that is flame resistant. It is made of woven fiberglass fabric that has an epoxy resin acting as the binder. Since its introduction at least fifty years ago, FR4 has undergone significant development, and it is now capable of withstanding continuous temperatures of up to 180 degrees Celsius. FR4 has the benefit of having an excellent resistance to weight ratio, which is a distinct advantage.
It does not absorb water but maintains a high mechanical strength and maintains an excellent insulating capacity regardless of the surrounding conditions, whether they are dry or wet. This PCB material is particularly common for printed circuit boards (PCBs) that have lower layer counts, such as single-sided, double-sided, or multilayered structures that have less than 14 layers.
Considerations when choosing the PCB material
It is critical to carefully select the best type of PCB material to ensure that the PCB has the appropriate electrical, thermal, and mechanical characteristics for durable application.
While selecting appropriate PCB material, consider following characteristics in mind.
Design requirements
Think through the PCB’s intended use, intended environment, signal integrity requirements, and overall design. Do high temperatures need to be tolerated? Is a stiff or pliable board better for your needs? One thing that matters the most is that the PCB material should be insulating.
Heat transfer
When it comes to a PCB’s durability and performance, power and heat are two of the most important aspects. Be sure to check the thermal capabilities of the PCB material you’re considering for the actual design. Overheating is a common problem in many modern devices due to the high-speed impulses.
Mechanical durability & strength
It’s crucial to think about the PCB materials’ mechanical and electrical durability. CTE is also very important in the field of microelectronics. Consider the factor that how long do you think the PCB’s materials will last in your working environment.
Cost
When selecting PCB material, its cost factor is considered to be most crucial. Gold or solder tabs are often used by many designers. The price of gold tabs, however, might be prohibitive for some. Buried vias are often less expensive than blind vias. To sum up, while looking at line and breadth spacing at six mils or greater, there are additional expenditures.
Conclusion
This article provided a practical guide for the selection of right PCB materials but if you want to avoid costly delays and mistakes in the PCB design process, it’s best to acquire some expert advice right from the start.
