Every time we take our Mobile Phones, Tablets, Laptops we don’t think much about the circuit and the components from which it is made, whether it is the Microcontrollers, the SoC’s, power unit, Cameras, the touchscreen and much more. However, the question comes how do these components are connected? How do they communicate with each other? To answer these questions there must be some conducting surface or wires through which these are connected. Here comes the work of Printed Circuit Board (PCB’s). Anyone who has ever opened up a piece of electronic equipment has seen a printed circuit board, also known as a PCB. They are thin, flat, and often green rectangular substrates that are covered with a maze of fine copper lines and silver pads and are the heart and soul of most electronic equipment.
What are PCBs?
To answer this question let us first see the classical definition –
“A printed circuit board (PCB) mechanically supports and electrically connects electrical or electronic components using conductive tracks, pads, and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.” (Source — Wikipedia)
This Definition clears much about the basic purpose that a PCB serves. Let us see one more definition in a simpler language to know more “Printed circuit boards (PCBs) are the boards that are used as the base in most electronics both as a physical support piece and as the wiring area for the surface-mounted and socketed components. PCBs are most commonly made out of fiberglass, composite epoxy, or another composite material.” (Source — Pcbcart)
But why use PCB, since we can use wires –
But, you might wonder why don’t we connect the components directly through wires like every other device that we use to connect. Before the advent of the PCB, circuits were constructed through a laborious process of point-to-point wiring. This led to frequent failures at wire junctions and short circuits when wire insulation began to age and crack. A significant advance was the development of wire wrapping, where a small gauge wire is literally wrapped around a post at each connection point, creating a gas-tight connection, which is highly durable and easily changeable.
As electronics moved from vacuum tubes and relays to silicon and integrated circuits, the size and cost of electronic components began to decrease. Electronics became more prevalent in consumer goods, and the pressure to reduce the size and manufacturing costs of electronic products drove manufacturers to look for better solutions. Thus was born the PCB.
What PCB’s are made up of?
The PCBs are used in various devices from a small watch to big computers. To provide a sturdy and stable surface to mount all the components as well as to provide suitable circuit tracks for conductivity, the PCBs must be both conductive as well as insulated in specific sections designed by the Engineers. Today, boards are made to be larger and smaller than this standard, but the standard probably remains the most common thickness for designs. It is more accurate to say there is a range of common or standard PCB thicknesses. These include 0.031in (0.78mm ), 0.062in (1.57mm) and 0.093in (2.36mm).
The substrate most commonly used in printed circuit boards is a glass fiber reinforced (fiberglass) epoxy resin with a copper foil bonded onto one or both sides. PCBs made from paper-reinforced phenolic resin with a bonded copper foil are less expensive and are often used in household electrical devices.
The printed circuits are made of copper, which is either plated or etched away on the surface of the substrate to leave the pattern desired. The copper circuits are coated with a layer of tin-lead to prevent oxidation. Contact fingers are plated with tin-lead, then nickel, and finally gold for excellent conductivity.
A PCB is a sort of like a layer cake or lasagna- there are alternating layers of different materials, which are laminated together with heat and adhesive such that a result is a single object.
What are the types of PCBs?
Depending on the application of use, PCBs are broadly classified as follows –
Single Layer PCB — A single-layer or single-sided PCB is one that is made out of a single layer of base material or substrate. One side of the base material is coated with a thin layer of metal. Copper is the most common coating due to how well it functions as an electrical conductor. Once the copper base plating is applied, a protective solder mask is usually applied, followed by the last silk-screen to mark out all of the elements on the board.
Double-layer PCBs — Double-layer or double-sided PCBs have a base material with a thin layer of conductive metal, like copper, applied to both sides of the board. Holes drilled through the board allow circuits on one side of the board to connect to circuits on the other.
The circuits and components of a double-layer PCB board are usually connected in one of two ways: either utilizing a through-hole or with the use of a surface-mount. A through-hole connection means that small wires, known as leads, are fed through the holes, with each end of the leads then soldered to the right component.
Multi-layer PCBs — Multi-layer PCBs consist of a series of three or more double-layered PCBs. These boards are then secured together with a specialized glue and sandwiched between pieces of insulation to ensure that excess heat doesn’t melt any of the components. Multi-layer PCBs come in a variety of sizes, going as small as four layers or as large as ten or twelve. The largest multi-layer PCB ever built was 50 layers thick.
Flexible PCBs — Flexible PCBs are made of materials that can flex and move, such as plastic. Like rigid PCBs, flexible PCBs come in single, double or multilayer formats. As they need to be printed on a flexible material, they tend to cost more for fabrication. Flexible PCBs can also be used in areas that might be subject to environmental hazards. To do so, they are simply built using materials that might be waterproof, shockproof, corrosion-resistant or resistant to high-temperature oils — an option that traditional rigid PCBs may not have.
Aluminum-Backed PCBs — Aluminum-backed PCBs are designed in much the same way as their copper-backed counterparts. However, instead of the usual fiberglass used in most PCB board types, aluminum-backed PCBs make use of aluminum or copper substrate board.
The aluminum backing is lined with a thermally insulating material that is designed to have a low thermal resistance, meaning less heat is transferred from the insulating material to the backing. Once the insulation is applied, a circuit layer of copper, ranging in thickness from one ounce to ten, is applied.
What is in our smartphones?
When we talk about Mobile phones be it a Google Pixel or an iPhone there is a big competition in terms of size, thickness, and weight of the phone. Every smartphone manufacturer wants lightweight circuitry that can perform the functions well as it fits the small and compact body of the phone.
The smartphone you are holding could have about 110 meters or about 360 feet of wires inside of it, that’s what it takes to combine cameras, GPS, wifi, battery, Fingerprint sensors, dozens of microchips and many more components into a single device.
One thing that might amaze you that we do not see many PCBs in a smartphone then how all these are connected. The smartphone PCB could contain 10 conductive layers. It contains a mix of Multilayer and flexible PCBs. In fact, multilayer PCB is stacking several PCBs one over the other and provide a verticle line across the board for wires. Multilayer boards usually consist of at least one or more cores and prepregs. Cores are made up of copper-plated glass-reinforced epoxy laminate sheets. The thickness of the core is in the range from 0.1mm to 0.3mm.