The manufacturing of electronic devices is a sequence of essential steps from design, fabrication and assembly of printed circuit boards (PCBs) and components, up to the final electronics assembly. Each stage requires thorough planning and development to achieve a functional device. The PCB holds together the components to enable them to perform according to requirements. It starts as a bare PCB, with pads and traces, intricately designed to accommodate succeeding assembly processes.
In this blog article, we will have a wider understanding of what a bare PCB is, as well as its structure, types and applications.
What is a Bare PCB?
A bare PCB is a blank printed circuit board consisting of conductive and dielectric layers, without the electronic components yet. Production of bare circuit boards often comes as a separate set of processes referred to as “PCB fabrication”, whereas the mounting process of the electronic parts on the PCB is referred to as “PCB assembly”. The bare PCB is a vital component in electronics manufacturing as it provides electrical and physical connections between electronic parts.
What is the Structure of a Bare PCB?
A bare PCB can be visualised as a sandwich with layers of conducting and non-conducting materials. The biggest thickness in a bare PCB is the insulating layer, which can be made from fibreglass and epoxy resin. Let’s further break down the different layers of the PCB:
- Copper Layer: The conductive part of a bare PCB is made of a layer of copper. The copper layer is where the circuit pattern is etched to form the pads and traces, allowing electrical connection between components.
- Prepreg: Prepreg is the layer of interwoven glass impregnated with epoxy resin that is cured partially in its initial state. This is pressed together with the other layers to achieve a final cured state with the application of heat and pressure.
- Core: The core or copper clad laminate is a stack of pre-preg and copper foil that is bonded together using adhesive. Copper clad laminate can be categorised as rigid and flexible types.
- Vias: Not exactly a layer, but still an essential part of the bare PCB, are the vias. The vias are the drilled holes which are later plated with metal to provide electrical connections across the layers.
- Solder Mask: The copper which needs not need to be soldered must be covered with solder masking. This is the green material that is commonly seen on PCB, which isolates and protects the pads.
- Solder Mask: The exposed copper pad needs to be protected from factors such as heat, moisture and contamination. As copper easily oxidises, a metallic solderable surface finish must be applied. This surface finish can be made of gold, Nickel, palladium and silver. Other cheaper alternatives include Organic Solder Preservative (OSP) and Hot Air Solder Levelling (HASL)>
What are the Different Types of Bare PCBs?
Printed Circuit Board types vary according to the number of layers, which can be broadly classified as follows:
- Single Layer PCB. The single-layer PCB is the least complex and cheapest type of bare PCB, as it consists only of one layer of conductive material. The electrical components can only be mounted on one side, limiting the functionality of the PCB. It is the easiest to design and manufacture among the other types.
- Double Layer PCB. A double-layered PCB has two layers of copper material, on the top and bottom sides of the PCB. Vias or holes are drilled into the bare PCB to provide an electrical path between the layers.
- Multi-layered PCB. A multi-layered PCB has more than two layers of conductive material laminated together with substrate and prepreg layers. It has a compact design, offering high component densities for high-speed applications.
Another classification of PCB is based on the type of substrate used. See below the major types:
- Rigid PCB: The oldest type and most frequently used type of PCB is the rigid PCB. It is also the most readily available, providing enhanced mechanical support for electronic components.
- Flex PCB: Popularly used in medical and consumer electronics, flex PCB is a type of PCBs that can conform to various surfaces and shapes due to its flexibility.
- Rigid-Flex PCB. With the combined advantages of flex PCB’s flexibility and rigid PCB’s structural strength, rigid flex PCB offers good reliability and performance for applications requiring versatile 3D configurations.
What are the Applications of Bare PCBs?
Bare PCBs can later be used for vast industries and applications. We need to know the function of the bare circuit boards and apply them to the end product. Below are some of the sectors that utilise the benefits of PCBs.
- Automotive Electronics. Vehicles have upgraded in capabilities with the proliferation of PCBs of all sorts—rigid, flexible, and rigid-flex to enable important functions such as infotainment, safety and operation.
- Medical Devices. Comfort, reliability and biocompatibility are crucial attributes that PCBs for medical applications should exhibit. The rise of flex PCBs is well evident in medical applications due to their ease of assembly.
- Commercial Electronics. The devices that we typically use daily, such as laptops and mobile phones, have internal parts mounted on tiny PCBs. The PCBs inside these gadgets are designed for high-speed performance and good memory and storage space.
- Aerospace. Bare PCBs for aerospace applications demand high reliability performance. This means that the PCB must be able to withstand extreme stress from temperature changes and mechanical impact. Reliability tests, such as burn-in and thermal cycling tests, are applied to printed circuit boards to
- Industrial. Industrial machines have mechanical and robotic systems that require PCBs, rigid, flex, and rigid-flex types. The bare PCB needs to be able to tolerate multiple cycles and dissipate heat generated from high-power industrial devices.
Conclusion
Bare PCB is the fundamental component of PCB assembly. If we don’t manufacture the Bare PCB as the substrate for the components, then this PCB won’t be able to achieve the functionality we want. The application fields of Bare PCB are becoming increasingly wide, and novel PCBs are emerging one after another. Therefore, new Bare PCB technologies should also be put into use to meet the production of special PCBs. The future of Bare PCB manufacturing will only become increasingly complex. Manufacturers and designers should keep abreast of relevant trends and changes to make timely communication and produce better products.
