Printed Circuit Boards play a vital role in electronic devices. Many people feel they are in the dark when they hear this term.
What Is a Printed Circuit Board?
The printed wiring board is also known as PCB. PCB is a professional term that refers to the carrier used for electrical connections of electronic component. It can also be the support for electronic components. PCB, in simple terms is a board that holds electronic components to connect them to form a complete circuit.
PCBs Classified
The PCBs can be classified into different types based on their characteristics.
The rigid PCB (printed-circuit board) can be classified according to its strength. its flexibility. its rigid-flex circuitry.
The PCBs can be classified into two types according to the base material: Metal core PCB (also known as FR4 PCB) and FR4 base material.
According to layer it can be classified into single-layer, double-layer, multi-layer, and high density interconnect board (HDI).
1) Single-Layer PCB
The simplest board is a single-layer board. The circuit board is routed on one side, while the other side is used to print and install logos and electronic components.
Single-layer boards are best suited for circuits with simple connections, as it is hard to wire just one side. Single-layer boards are characterized by their low cost and easy manufacturing process.
2) Double-Layer PCB
On both sides of the insulating board you can route double-layer boards, one as the top and the other the bottom. Electrical connections are made between the top and bottom layers through vias.
In general, electronic components are placed on the top layer. Components can be placed on either layer to reduce the size.
Double-layer boards have a low price and are easy to wire. Double-layer boards are the most common type of circuit board used today.
3) Multilayer PCB
Circuit boards with two or more layers.
4) High-Density Interconnect Board
Circuit board with a high density, using the micro blind buried technology. HDI compact product is designed for users with small capacities.
Structure of PCB
PCB is mainly composed of copper-clad laminates (CCL), prereg (PP sheets), copper foil and solder masks. To protect the copper foil exposed on the surface, and to ensure the welding effects, the PCB must be surface-treated, and characters marked (also known by the name silk screen printing).
1) Copper-Clad Laminate
The copper-clad lamination (CCL) material is used to manufacture printed circuit boards. This composite material is composed of a dielectric (resin or glass fiber) layer and a high purity conductor (copper). FR4 is most commonly used on the market.
2) Prepreg
Prepreg is also known as PP Sheet and is one of primary materials used in multi-layer boards. The main components are resin and reinforcing material. Prepreg softens under heat and pressure, and then solidifies after cooling.
3) Copper Foil
The copper foil is a thin metal foil that covers the base layer on the circuit board. The PCB is made of copper foil. It can be easily bonded to the insulating layers and then etched into a circuit pattern.
4) Solder Mask
Copper is protected by printing ink onto the surface of the panel. Ink is typically green so we see green PCB boards. We can also print inks other than green, including red, black and blue.
5) Silkscreen Printing
This is the top layer on the PCB and it is used for printing text notes etc. This is the same as making a PCB Label.
What Are the Steps Involved in PCB Production?
PCB fabrication begins with the design of the blueprint and continues through several stages to produce a finished PCB. Each step is important because they are interconnected.
1) Design PCB
PCB designers use software called Extended Gerber. This program not only aids in the design, but also encodes data about the number and type of copper layers.
PCB design is not required by our PCB manufacturer. The PCB design is supplied by the customer. Before production begins, the factory will perform a secondary inspection for defects, also known as manufacturing design inspection. The next step is to review the design and address engineering issues.
2) Design Review Issues and Engineering Issues
The next step is to verify the design for errors and omissions. After the engineer has confirmed that the design is free of defects and potential errors, the PCB can then be printed.
3) Print PCB Design
A plotter is used to print the PCB designs. The PCB design is printed on a plotter that looks like film. Use two colors of ink to show the inner and outer layers.
• Black Ink
The black ink on outer layers of PCB represents areas that have been copper-free.
• Transparent Ink
Use on the outer layer of the copper vias.
Each layer of the PCB has its own solder mask. Eight sheets of black film are required for each layer on the PCB. The film also needs to be punched with a hole puncher.
4) Copper Printing
The PCB fabrication process begins with this step. The PCB is printed onto a laminate that has copper foil on both sides. The copper foil is then etched off to reveal the original design.
Then, clean the copper. To make sure the printed panel is free of dust. It may lead to a PCB short or an open circuit.
On the board, a light-sensitive film called photoresist is applied. A chemical in photoresist hardens upon exposure to ultraviolet light.
The film and the circuit board are then aligned and exposed to ultraviolet light in order to harden the resist. The circuit board is then cleaned using an alkaline solution, and dried.
5) Remove Any Excess Copper
In the same way, we dissolve excess copper on the inner layer with an alkaline liquid, so that the copper required under the hardening photoresist layer is not affected. The weight and size are a positive feedback on the time and solvent required for dissolution.
6) Alignment Between Inner and Outer Layers
Align the inner layer to the outer layer after cleaning. The technician usually places the circuit boards on an optical puncher and then passes pins through the holes to align the inner layer.
7) Automatic Optical Examination
This step is important. The inner layers cannot be changed once the layers have been assembled. Technicians will perform AOI testing to ensure that the PCB does not have any defects. The AOI machine compares the PCB with the original design. On the display, some problems will be shown. At this stage, failure circuit boards are no longer used.
8) Lamination of PCB Layer
The PCB board will be formed at this stage. The layers with no defects are pressed. The following steps are involved:
• Riveting
To avoid deviations during processing, it is best to join multiple inner core boards (prepregs), and film together.
• Lamination
In preparation for pressing, pre-laminated board are stacked as multi-layer boards.
The heated boards are then pressed under vacuum conditions into multi-layer board.
• Post-Processing
Initial profile treatment involves grinding, milling, and targeting of the laminated boards.
9) Drilling
PCB drilling is a highly precise process because even a slight error can result in a large economic loss. You can use an X-ray to find the location of the drill hole.
To ensure a clean drilling, it is necessary to place buffer material underneath the target before drilling. The PCB is fixed in the hole. The computer will control the drilling bit and determine the correct drilling position using the Gerber file as the target. After drilling, remove any copper that remains on the edge.
10) PCB Plating
A thin layer of copper is then deposited onto the wall of the hole after a series chemical reactions.
11) External Imaging
Use yellow light to illuminate the photoresist, since it hardens when exposed to UV light. Pins can be used to align the black transparent film with the panel.
In the same way as in step 4, we use ultraviolet light to harden the photoresist on the outer layer. The panel is then placed into the machine, which removes the photoresist that has not been hardened and protected by black ink.
12) Outer Layer Etching
Photoresist must be dissolved to remove excess copper. In preparation for AOI and soldering, excess copper foil is dissolved with an alkaline solution.
13) Outer Layer AOI Inspection
The outer layer must also be subjected to automatic optical inspection in order to verify that it meets the design requirements. The inspection can also be used to check if the copper from the previous layer has been removed.
14) Solder Mask
Clean the circuit board first to remove any impurities and excess copper.
The surface of the board is covered with a soldering mask and ink. The PCB is then exposed to ultraviolet light in order to harden and remove any unhardened components.
The board is then placed in an oven for the solder mask to be cured, creating a protective film on the copper.
15) Silkscreen Printing
A silk screen is a label or business card attached to a circuit board. Inkjet printers are used to print the information directly onto the circuit board. Information such as company ID, symbol and component number are included.
16) PCB Electrical Testing
PCB testing checks the routing of the circuit board and the through-hole connections to make sure there are no open or short circuits. There are several different testing methods.
• Online Test ICT
The most reliable test is the in-circuit testing (also known as bed-of-nails testing). It is also expensive.
ICT is a leader in determining PCB component failures such as circuit open, shorts and other defects. It also provides clear guidance on how to handle defective PCBs.
• Automated Optical Inspect (AOI)
This method is ideal for PCB inspections that are performed in high volumes. Automatic optical inspection machines use a high-performance digital camera to detect and observe any welding problems from different angles.
• X-ray Inspection
Infrared rays are used to detect potential problems within the inner layers.
17) Analysis
The PCB production process ends with the analysis. The printed circuit board was a panel before this step. It had to be divided into individual boards and compared with the original design. You can cut the printed circuit board using several different methods:
• V-Groove
This method uses a CNC machine to make a V-shaped cutting along the side of pcb board.
• Laser Cutting
This method is ideal for PCBs that have complex shapes and require high precision.
• Mechanical Cutting
Cut PCBs using knives, cutters, etc. This method is ideal for PCBs in large quantities.
PCB Terminology
Many professional terms will be used during the PCB manufacturing or PCB Assembly processes. Take a look at this!
• Substrate: The most basic material in PCB and is made from glass fiber. Glass fiber is the basis for PCB rigidity and also has anti-breakage properties. It is the equivalent of the human skeleton.
• Copper foil: A thin layer of copper is applied to the functional surfaces of PCBs. Copper foil is an electrolyte cationic material. Copper foil is used as a conductor for the PCB, and to transmit electrical information. This is the same as our central nervous system, which transmits movement commands via the spinal cord and the peripheral nerves. The brain then sends the commands to the muscles.
• Slots: Any hole on the PCB which is not circular. Slots may be unplated or plated. Slots can increase the price of the board, because they take more time to cut.
Angle ring: The copper ring that surrounds the hole on the PCB.
• Drilling Hit: This indicates the deviation between required drilling position and actual drilling position. Computers control the drill bit today to ensure accuracy in the drilling position.
• Pad: A portion of metal that is exposed on the PCB surface and used to attach soldered components.
• Trace: Refers to the continuous copper track on the circuit board.
Panelization is a large circuit board that consists of several smaller circuit boards. Panelization can increase production efficiency when mass producing PCBs.
• Picking: The process of placing electronic parts on a circuitboard. There are both machine and manual pickers.
• Wave soldering: A method for soldering component pins and exposed pads together. The circuit board is passed at a constant rate through a solder molten furnace to create a wave crest. This solder wave will then solder together the pins of the components and the exposed pads.
• Surface mount: A PCB assembly method whereby the machine places the electronic components directly on the circuit board, and then fixes them firmly on the pads using steps such as printing solder paste and reflowing soldering.
• Reflow soldering: Melts the solder to connect the pads and pins of the device.
• Solder bridge: Two pins are connected on a component, a printing mistake.
