Hi Guys! Hope you’re well. Happy to see you around. In this post today, I’ll walk you through PCB (Printed Circuit Board) in detail.
PCBs are commonly used in simple electrical circuits and advanced electronic devices. They ensure compact and concise designs where electronic components are placed for the electrical connection in a secure fit. PCB designs have evolved and changed in so many ways since their inception. You cannot compare the heavy PCBs installed in old TVs with the sophisticated and lightweight boards used in supercomputers and nano boards used in the development of pacemakers. Earlier end-to-end wiring was used that was costly and would cover more space. PCBs not only removed the need for this erratic wiring but with the more advanced technology they went through significant development. Now you can produce different types of boards including rigid PCB, flexible PCB, rigid-flex PCB, aluminum-backed PCB, high-frequency PCB, and more. PCB Panelization is a normal practice, used for design products and handheld devices in bulk.
I suggest you read this post all the way through as I’ll be covering each and everything related to PCB including definition, types, material, manufacturing process, price & applications.
Let’s jump right in.
PCB (Printed Circuit Board) is a board that provides mechanical support and electrical connection to the electronic components placed on the board. The board comes with conductive copper traces that are laminated on the non-conductive substrate.
PCBs are categorized into three different types based on the number of conductive layers used to manufacture the board.
Single-sided boards, also known as single-layer boards, are PCBs that contain conductive copper tracks on one side of the board. In these boards, the electronic components are inserted from one side (non-conductive substrate) to the other side that contains copper tracks. The electrical connection is established when components pins are soldered with conductive copper tracks.
Double-sided boards, also known as the double-layer board, are PCBs that contain conductive copper tracks on both sides of the board. Two techniques are used to mount electronic components on these boards: Surface mount technology and Through Hole. Know that these boards come with a single layer of base substrate but conductive copper tracks are added on both sides of the substrate.
Multilayer PCB boards contain multiple double-layered PCBs. These boards are then combined with glue by inserting the pieces of insulation between them to prevent the boards from the excessive heat that can hurt the boards. The number of double-layered PCBs in Multilayer boards varies from 4 layers to 16 layers or more. These boards are more complex in composition than the standard PCBs and are employed in applications like weather equipment, satellite equipment, data storage, GPS technology, and x-ray equipment.
The six components of the PCB include:
- Copper foil
- Solder mask
- Final finish
Prepreg is a substrate material made up of fiberglass and is plated with resin. Know that the most common resin that we use as a substrate is FR4. Laminates, also known as copper-clad laminates, are composed of substrate sheets laminated together with heat and pressure. Next, copper foil is coated on the board that serves as a conductive path for the electrical components we mount on the board.
The solder mask sits on the copper foil. This solder mask layer is used to provide insulation to the copper layer. Nomenclature, also known as silkscreen, is the ink-jet writing on the top of the solder mask, indicating critical board information. To guard the exposed copper holes and to ensure a smooth solderable finish, a metallic coating of nickel, gold, or silver is commonly used.
PCBs are made up of conductive copper laminated on the non-conductive substrate material. PCB comes with multiple layers that are glued together to ensure a compact structure.
The printed circuit board’s manufacturing process includes the following steps.
To start the PCB manufacturing process, first, you need to have the PCB design. In this step, the designer makes the blueprint for the PCB based on the requirements. The computer software is normally used to make the PCB design. Commonly used PCB design software include Protell (Altium Designer), OrCAD, PADS, Eagle, EasyEda, and Extended Gerber.
Know that PCB designs are not printed out on the traditional 8.5x11 sheet as we use for architectural designs. Instead, a Plotted printer, a special kind of printer, is used to print out the PCBs. This printer produces PCB film which is nothing but a transparent negative of the board showing details and layers of the board.
The PCB inside layers come with two ink colors:
- Black Ink: that exhibits the conductive copper traces and PCB circuits
- Clear Ink: that exhibits the non-conductive PCB areas The inner layers follow this trend but for the outer layers, this trend is reversed i.e. blank ink shows the non-conductive PCB areas and clear ink shows the conductive copper traces. ### Printing the Inner Layers
The design is printed out onto a laminate which is the basic structure of the board. Next, the resist covers the laminate panel; the resist is a photosensitive film composed of photo-reactive chemicals that turn to hard material when exposed to UV light. The resist helps align the PCB blueprints with the actual PCB print. To make sure the laminate and resist are perfectly aligned, holes are then drilled onto the board.
Once resist and laminate lined up, they receive the storm of UV light that hardens the photoresist. The UV light reveals the copper pathways while black ink, on the other hand, stops the light from entering the areas that are not supposed to get hardened, helping you remove those less hardened areas later. Once prepared, the board is then washed out with an alkaline solution to get rid of excessive photoresist.
In this step, we’ll remove the unwanted copper that remains on the board. A more powerful solution, similar to an alkaline solution, is then used to remove the excessive copper, leaving the required copper fully intact under the layer of photo resist.
An inspection is required for the new washed-out layers. The holes drilled earlier help to line up the outer and inner layers. The layers are further passed through the optical punch machine that drills a pin through the holes to make sure layers are lined up. Another machine is then employed to ensure the board carries no defects.
In this step, the board starts taking the shape as the layers are fused together. Metal clamps are used to clutch the layers together as the laminating process starts. A Prepreg (composed of sheets of fiberglass with epoxy resin) is then placed over the alignment basin. The substrate layer sits over the Prepreg before you place the copper sheet. More sheets of Prepreg material are then placed on top of the copper layer. The composition is ready to go through the mechanical press.
A mechanical press is then employed to fuse the layers together. To keep layers properly aligned and secured, pins are punched through the layers; pins can be removed later. The board then goes through the laminating press that applies the pressure and heat to the layers. The applied pressure and the melted epoxy inside the Prepreg then help in fusing the layers together.
A computer-guided drill is then used to drill the holes into the layers that expose the inner panels and substrate. After this step, any leftover remaining copper is removed before the circuit board is ready to get plated. A chemical solution is used to fuse the layers together. The structure is then completely washed out by a series of chemicals. These chemicals then deposit a thin layer of copper on the panel surface. The thin copper layer crawls into the recently drilled holes.
In this step, we apply a layer of photoresist onto the panel, as we did in step 3. The panel then undergoes a blast of UV light that makes the photoresist hard. The unwanted and unhardened resist is then removed by the machine.
In this step, the thin copper layer is coated over the panel, as we did in step 9. After the copper plating, a thin layer of tin is applied on the board that protects the panel section that is supposed to remain covered with copper layer during the following etching stage.
The PCB’s connections are established in this step. The same chemical solution applied before is used to remove the undesired copper beneath the resist layer.
The entire composition is thoroughly cleaned and covered with an epoxy solder mask ink before applying the solder mask. The board then comes under the blast of UV light that removes the unwanted solder mask and the board is then baked in the oven to keep the desired solder mask. Silk screening is applied before the last coating and curing stage. Silk screening applies ink-jet writing on the board’s surface, indicating critical information of the board.
Based on the requirements, the final composition is plated with a solderable finish, increasing the quality of the final structure.
An automated Electrical test is performed on the board to ensure the functionality of the board and its resonance with the initial design.
PCB pricing is mainly dependent on three major factors including the board size, type of the material, and the number of layers. Obviously, the cost of the thicker board with a large size is significantly higher than the cost of the thin board with a small size. Similarly, the multiplayer board is costly compared to a standard single layer and double layer boards.
Other factors that affect the cost of the circuit board include:
Size of hole
- The thickness of the PCB and Aspect Ratio
- Custom and Unique Specs The custom specs may vary depending on the application. Like the circuit boards that come with rounded edges would require more cost to manufacture, especially those that need z-axes routing. Similarly, if you require metal edges, the price of the board will go high. If extra thickness and clearance are required of the solder mask, it will cost more.
The applications of PCBs include:
- PCBs are commonly used for industrial and commercial purposes like in dashboards, power supplies, fuel regulators, heat control systems, satellite navigation, and more. Moreover, they are also a part of many electronic circuits used to join the electronic components together.
- LED-based lighting systems consume lights 90% less than traditional light bulbs and they come with Aluminum backed PCBs, ensuring high efficiency and low power consumption. The main purpose of these boards is to offer economical, compact, and the smallest designs possible; the reason they are the right match for medical equipment like pacemakers, CAT scanners, and x-ray machines.
- Flexible circuit boards are commonly used in the aerospace and automotive industries. The flexibility feature of these boards can endure extreme vibrations, preventing the instruments from accidental damage. Moreover, due to their lightweight, they are widely used in transportation industries for the development of manufacturing parts. That’s all for today. Hope you’ve enjoyed reading this article. If you have any questions, you can approach me in the section below. I’d love to help you in the best way possible. Thank you for reading this post.