PCB Manufacturing

Understanding PCB Classification: Types, Materials, and Applications

PCB Classification

PCBs are the base where the components are fixed or wired together with a conductive layer to form a circuit. As technology is growing rapidly, the use of a variety of boards for several applications has become indispensable. Therefore we end up having several PCB categories, which are chosen based on the applications and requirements.

PCBs can be classified based on

  1. Layers of conductivity
  2. Flexibility and Hardness
  3. Substrate Material

For simple electronics, PCB with a single layer is used. When there is a requirement for more complex hardware, multilayer PCBs are used.

Although PCBs were associated with computers earlier, they can be found in cell phones, digital cameras, consumer electronics, and other applications.

1.  PCB Classification Based on Layers of Conductivity

  • Single-sided/single-layer
  • Double-sided/double-layer
  • Multilayer PCB

1.1 Single-sided/ Single Layer

  • Single-side PCB is a low-cost PCB, used for simple applications. It has a single layer of substrate made up of fiberglass, copper, or aluminum.
  • The conductive layer used here is copper, for wiring and interconnection.
  • The electronic components are usually placed on one side and the interconnections/wiring is done on the other side.
  • The complexity, space required, and cost involved in these types of PCBs are very low. It is used in mobile phones and calculators.

Single-Layer-Double-Layer-PCB

1.2 Double-sided/Double-layer PCB

  • When the conductive layer is 2, it is called Double-sided PCBs.
  • On the contrary to the Single layer PCBs, double-sided PCBs can hold components on both sides of the PCB.
  • The conductive layers are sandwiched between two base layers, and the base substrate can be chosen based on the flexibility required for the application- rigid base or flexible base substrate.
  • The conductive area is more in these types of PCBs and hence more components, SMD can be soldered onto the PCB. The traces mustn’t overlap in the PCB, to avoid design issues.
  • It is used in applications where a little more complex circuits than single-layer PCBs.
  • The costs involved in double-layer PCBs are less compared to multi-layer PCBs.

Multi-layer PCB

1.3 Multilayer PCB

  • Multi-layer PCBs are PCBs which has more than 2 conductive layers in the PCB. The copper conductor layers are laminated and fused and this forms the inner core layer.
  • Multilayer is a combination of both single and double-layer PCB types, where the top and bottom layer has single-layer PCBs and double-layer PCBs in between.
  • These types of PCBs are mostly rigid PCBs, as multilayer flexible PCBs are highly complex to manufacture.
  • Both through-holed components, SMD, can be soldered on these PCBs
  • The layers are interconnected by through-hole, blind via, and buried via.
  • The multilayer PCBs are hard to manufacture due to the number of layers and complexity. The maximum number of layers is around 100.
  • Multilayer metal core PCB has metal in the inner layer or on the bottom of the PCB.

This helps in heat dissipation.

  • LED lighting and photovoltaic applications use this type of PCB.
  • These PCBs are used in laptops, microwaves, and home automation products.

 

2. PCB Classification Based on the Flexibility

Rigid PCBs are manufactured when the application requires rigidity in the design and in domains where ruggedness and robustness of the material are required. Flexible PCBs are typically made of flexible substances as substrates. The design is complex and hence the cost is on the higher end. When a combination of both types of PCBs is required, then rigid-flex PCBs are manufactured.

  • Rigid PCB
  • Flex/flexible PCB
  • Rigid flex PCB/Rigid flexible PCB

Multi-layer PCB

2.1 RIGID PCBs

  • Rigid PCBs are constructed with rigid substrate materials like FR4, commonly consisting of fiberglass.
  • A common example is the rigid computer/laptop motherboard,
  • Rigid PCBs are commonly designed and used, where the stiffness of the material should last long.
  • Rigid PCBs are traditional PCBs, the most cost-effective, and like all other PCBS, there are single-layer rigid PCBs and multi-layered rigid PCBs.
  • Rigid PCBs are used in aerospace and military applications, database servers, and satellite communications.

2.2 Flex-PCBs

  • Flex PCBs or flexible PCBs are built upon flexible materials, like plastic.
  • Advantages are flexibility, folded over edges, and wrapped around corners, which can lead to weight savings.
  • They occupy less space as they can be rolled and folded. The extra flexible space in any device can be occupied with flexible PCBs, thereby reducing the size of the product.
  • With advancements in technology and considering user preference, flexible PCBs are preferred and can be used in wearable and foldable mobile phones.
  • While there are design constraints and they are prone to damage due to improper manhandling, the fact that they can be used in modern lighting technologies like LED cubes and matrices and other sophisticated applications, makes them unique and preferred.
  • They are shockproof, waterproof, corrosion-resistant, or resistant to high temperatures.

2.3 Flex-rigid PCBs

  • Flex-rigid PCBs are manufactured, considering the advantages of both rigid PCBs and flexible PCBs. It is used in places where the rigidity of the base is required and the extendable can be a little flexible.
  • It is constructed by fixing or attaching all the flexible PCBs on a rigid substrate or base.
  • The number of PCBs or count required for this application is less, as there are lot of space that can be utilized for wiring the components.
  • As we know the technology is moving towards a reduction in the size of any device, flex-rigid PCBs are used, as they can offer compactness and modularity.

3. PCB Classification Based on the Material

Different Types of PCB Materials

Due to advancements in technology, different materials are being tried and tested, to suit the industrial applications, and match them to the requirements in terms of cost, productivity, performance, and reliability. The types of PCB materials, their advantages and disadvantages are listed below:

3.1 CEM3 Type PCBs

  •  The composite epoxy material (CEM) based PCBs, are very budget-friendly, low-cost, yet efficient PCBs, made of glass cloth.
  • The substrate glass material has reduced the cost of production, hence it is cheaper than other PCBs.
  • It can be efficiently used in hobby projects and common lighting applications.
  •  It is preferred for less critical applications, where the cost incurred should be minimized.
  • CEM3 is used in automotive commercial applications.

3.2 Epoxy Resin PCB

  • A resin PCB is made to improve flexibility and have high resistance to dust, chemicals, and moisture.
  • The core and copper layers are sandwiched with epoxy resin.
  • They are used in bulk productions, as they are simple to manufacture compared to other PCBs

3.3 Ceramic PCB

  • Ceramic PCBs are known for their excellent performance and reliability.
  • They are highly durable and possess a low expansion coefficient.
  • This PCB material is used for applications that require a high level of robustness such as aerospace and military applications, since they can withstand high temperatures.

ceramic pcb

3.4 Teflon PCB

  • The base material of Teflon PCB is a kind of thermo-based synthetic plastic material called polytetrafluoroethylene (PTFE) and it forms the main element.
  • Rogers, Arlon, and Nelco are a few of the Teflon PCB materials available in the market.
  • They are highly expensive because of the PTFE laminates, but they are preferred widely due to their effectiveness in signal transmission with minimal losses.
  • They are also known to have high signal stability and hence used in military applications.
  • Due to moisture absorption capabilities, chemical and UV resistance, and weatherproofing, they are used in most critical applications like automotive cruise control and many others.

3.5. Metal Core PCB or IMS (Insulated Metal Substrate) PCB

  • Metal core PCBs are also known as thermal PCB, which uses a metal base for heat dissipation.
  • The main aim of choosing this PCB is to minimize or mitigate thermal effects.
  • This leads to effective thermal management.
  • These PCBs are made with a metal plate like aluminum, which serves as structural reinforcement or base. This reinforcement is separated between a dielectric layer and the conductors of the circuit.
  • The circuit heat is transferred to the metal substrate via the dielectric layer and the metal base serves as a heat sink.
  • Some of the popular applications include LED lighting, power electronics, and complex circuits.

3.6 Polyimide PCB

  • This is another type of flexible PCB, which is of polymer base.
  • Polyimide materials are highly expensive and hence it is preferred where high durability is required.
  • The high tensile strength is an added advantage to the flexibility of the boards.
  • Good thermal conductivity, heat and chemical resistance, stability, and high durability are the advantages of these PCBs, and hence it is preferred in military and aerospace applications.

Polyimide PCB

3.7. Glass PCB

  • The prime material is the glass substrate and it is the base for optical devices.
  • Glass PCB is used often in LED, LCD, and display devices due to their advantages.
  • The circuit is assembled on the glass surface and it is then transferred onto the copper conductive layer. It is treated with a UV-curable mask.
  • Etching and exposure to light are the other processes involved in the making of glass PCBs
  • They are shockproof and have less attenuation. Hence widely preferred in luxurious lighting devices. 3D printers and solar panels are other applications of glass PCBs.

Glass PCB

3.8 Aluminum PCBs

  • Aluminum, as we know, is one of the most abundant metals on earth, and hence it is the most affordable metal too.
  • The aluminium base offers great strength and rigidity to the device. It is preferred where mechanical strength is preferred in PCBs.
  • It is used in LED and street light applications due to its robustness.

 

There are several categories and sub-categories of PCBs in the market, due to increasing research in the substrate materials. Hence it is important to choose the type wisely, analyzing the cost effects, performance, and compatibility, considering the applications.

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