How are PCBs made? A Beginner's Guide to the PCB Manufacturing Process
In the manufacturing of electronic components and devices, a lot is going on behind the scenes and one fundamental part of this process is the Printed Circuit Board (PCB) manufacturing process. From smartphones to laptops to household appliances, the heart of these everyday gadgets lies within this small foundation: the Printed Circuit Board (PCB).
Whether you're a tech enthusiast, an aspiring engineer, or simply interested in the inner workings of your favourite electronics, understanding how PCBs are made is an essential tour into the very essence of modern electronics production. But here's the interesting part: even though PCBs are everywhere, the technology behind them keeps advancing. The wires on PCBs are getting thinner, boards are getting more complex to handle all the electrical connections we need, and the rules for designing them are getting better to work with tiny electronic parts. Even the way they're put together is changing.
The cool thing is, that there are lots of different ways to make PCBs, but they all follow similar steps. So, in this guide, we'll take you through the Printed Circuit Board manufacturing process in a way that's easy to understand.
Background: The Basic PCB Manufacturing Processes
Printed circuit boards, often known as PCB, are found within a broad range of devices, from simple beepers and radios to powerful radar systems and computers. These circuits are created by placing a thin layer of conductive material onto an insulating board, called a substrate material. Tiny electronic parts are then put onto the substrate and connected to these circuits through soldering.
Printed circuit boards, or PCBs, come in various forms. There are three main types of PCBs:
- single-sided boards,
- double-sided boards,
- multilayer boards.
A single-sided board has components on just one side of the substrate. When there are too many components for a single-sided one, a double-sided board is used. The circuits on both sides of the boards are connected by drilling holes in the substrate, and these holes are coated with conductive material. The third type, a multi-layered board, is like a sandwich with layers of printed circuits separated by insulating layers. The components on the surface connect through holes that are drilled down to the right circuit layer. This clever design makes the circuit pattern much more straightforward.
Although they are quite different, the manufacturing process follows different routes only once the initial layer is created, and it is then that the level of complexity truly shows. Depending on the form of the PCB, the manufacturing process might comprise 20 or more separate phases.
The more complex a printed circuit board (PCB) is, the more steps are needed to make it. Think of it like building a puzzle – every piece has to fit just right. In the case of PCB manufacture, if you skip or simplify any of the steps, it can cause big problems with how the finished PCB works. But when each step is done carefully and precisely, these PCBs become the backbone of the electronics.
Parts of a Printed Circuit Board
A standard PCB is made up of the following raw materials:
This is the backbone of the PCB, the core material that creates its primary layers. Fiberglass-reinforced epoxy resin (FR-4) copper foil is the most commonly used substrate because of its strength and durability. Ceramic-filled PTFE composites (e.g., Rogers RO3003) are utilized for high-frequency applications, whereas cyanate ester or polyimide (e.g., Panasonic TR-77) are employed for high-temperature situations. Less costly alternatives, such as paper-reinforced phenolic resin with bonded copper foil, are utilized in some circumstances, particularly in domestic electrical equipment.
This is like the glue that holds everything together. It is made of glass fiber cloth that has been soaked in partially cured epoxy and is used to glue the PCB layers together under heat and pressure. The prepreg is positioned beneath the substrate layer, and then the copper sheet is added.
- Metal Foil
It's a thin copper foil that's shaped into conductive traces and pads. The thickness can vary, usually ranging from 0.5 oz (17 μm) to 3 oz (105 μm).
These act as the PCB's protective coating- its skin. They include a solder mask, which protects the copper from contact with the environment, and a silkscreen, which displays data like as component numbers, logos, symbols, switch settings, and test points.
- Bonding Film
This is similar to the glue used in the lamination of multi-layer PCBs.
- Via Fill
Vias (tiny holes) in high-density interconnect boards are frequently filled with plating resins or conductive pastes. Additionally, PCBs include purchased components like resistors, capacitors, transistors, diodes, and integrated circuit chips, which further enhance their functionality.
Steps in the Manufacturing Process of Printed Circuit Boards
The PCB design process begins with design and continues through the manufacture of the circuit boards.
Step One: Designing the PCB
The printed circuit boards' manufacturing process begins with PCB design, where engineers and designers use specialized software, such as Extended Gerber (IX274X), to create a blueprint that outlines the PCB's layout and requirements. The software not only aids in designing but also encodes essential information like the number of copper layer, solder masks, and component notations. After the initial design, the PCB undergoes a thorough examination to ensure error-free specifications.
Step two: Design Review and Engineering Considerations
Engineers rigorously assess the PCB design in this stage to look for any potential defects, missing components, or structural difficulties. The printing phase begins when the engineering team approves the design.
Step Three: Printing the PCB Design
In this step, engineers review the PCB design meticulously to check for any potential errors, missing components, or structural issues. Once the design is approved by the engineering team, it proceeds to the printing phase.
The PCB design is printed using a special type of printer known as a plotter printer. This printer creates a "film" of the PCB design, somewhat resembling transparencies. The inner layers of the PCB are represented using two ink colours: black ink for copper traces and clear ink for non-conductive areas. On the outer layers, clear ink denotes copper pathways, while black ink represents areas where copper will be removed. Registration holes are punched through the printed films to aid alignment in subsequent steps.
Step Four: Creating the Printed Circuit Pattern
The next phase is to create the printed circuit pattern, which is done by copper plating the conductive pattern, and then a layer of positive photoresist material is vacuumed onto the foil surface. The printed circuit pattern mask is placed on top and exposed to Ultraviolet light, causing the photoresist material within the circuit design to become soluble. The circuit pattern mask is removed, and the board is treated with an alkaline developer, revealing the exposed copper foil circuit design.
Step five: Chemical Etching Process of the internal layers
Before proceeding, extra copper on the PCB's inner layers must be removed. The board is etched by exposing it to a chemical solution that eliminates exposed copper while keeping just the needed copper traces intact. Depending on the design, the time and intensity of the treatment may vary.
Step Six (For Multilayer PCBs only): Inner Layer Processing
In this step, the inner layers of multilayer PCBs undergo a series of processes. This includes imaging, etching, resist stripping, post-etch punching, automated optical inspection, oxide application, layup, and lamination. These procedures ensure proper layer alignment, etching, and insulation for a functional multilayer PCB.
Step Seven: Align the Layers
The layers of the PCB are perfectly matched using registration holes. This is aided by an optical punch machine.
Step Eight: Automated Optical Inspection
A machine performs automated optical inspection (AOI) to detect defects. AOI compares the printed circuit boards to the Extended Gerber design, serving as a quality checkpoint.
Step Nine: Laminating the PCB Layers
Layers are bonded together using epoxy resin-soaked fiberglass sheets and copper foil. These are pressed together and heat-laminated.
Step Ten: Drilling process
Drilling into the PCB is guided by X-ray for accuracy. Registration holes are used, followed by deburring and removing excess copper. When producing a double-sided or multi-layered PCB, holes must be drilled to electrically connect the circuits on each of the different layers. To accomplish this, holes are drilled and deburred in the circuit boards in the determined pattern, and these holes are then lined with a layer of copper to create a conductive connection.
Step Eleven: PCB Plating process
Once it's been cleaned, the PCB undergoes a chemical treatment. During this process, a very thin layer of copper, just a few microns thick, is applied to cover the uppermost layer of the board and fill the recently drilled holes. These holes initially reveal the fiberglass substrate within the panel.
Step Twelve: Outer Layer Imaging and Etching
After imaging the outer layer with photoresist, a protective layer of tin is plated over the copper. Following that, the etching procedure eliminates any excess copper and residual resistance, leaving just the required copper design.
Step Thirteen: PCB Surface Treatment and Finishing
In this step, the PCB undergoes a series of surface treatments and finishes. Initially, a solder mask is applied to safeguard the copper from corrosion, followed by curing in an oven. Next, important information is printed on the board's surface, and a surface finish is applied to prevent oxidation. The specific finish used is determined by design specifications.
Step Fourteen: Final Quality Assurance and Delivery
During this last process, the PCB is subjected to a variety of quality tests and inspections. An electrical reliability test, for example, evaluates circuit continuity and isolation to guarantee adequate operation and design conformity. Then, profiling and routing out methods are used to neatly isolate specific boards. A CNC machine or router is utilized to cut out each board from the panel, shaping and sizing it according to the desired specifications. A thorough final check confirms hole sizes, dimensions, cleanliness, and overall quality. Finally, before being supplied to consumers for integration into electronic products, the PCBs are rigorously packed to protect them during storage and transportation.
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