The success of any creation often depends on the foundation upon which it is built, whether it be the strength of character, the depth of a building's foundation or the extent of a tree's roots. Likewise, the success of any electronic device depends on its foundation. The motherboard of any electronic device can act as a playground and host, receiving various forms of electrical signals to perform a certain function for the device. Whether it's a communication signal between the Northbridge and a computer processor, or a simple switch signal in a regular school project, the effectiveness of the design depends on the functionality provided by the substrate itself.
Printed circuit boards not only connect electronic components with etched copper traces, but also provide mechanical strength. Printed circuit boards, or rather, printed circuit boards are found in almost all commercial products, serving as the building blocks of packaging media.
A PCB is a composite of organic and/or inorganic dielectric materials with multiple layers of wiring interconnects that also house components such as inductors and capacitors. There is no standard printing plate, and each is unique, often a function of the product itself. There are industry standards for nearly every aspect of PCB design, controlled by IPC, such as IPC-2221, "Common Standard for Printed Board Design."
PCBs evolved from electrical connection systems developed in the 1850s. The first patents for printed wiring were issued in 1903. Albert Hansen explains a layered structure of foil conductors laminated to insulating boards. In 1913, Arthur Berry patented the "print-etch" method, and Max Scoop patented the spraying of metal onto a board through a mask. Thomas Edison experimented with chemicals for electroplating conductors on linen paper as early as 1904, but the method of electroplating circuit patterns was finally successfully patented by Charles Duques in 1927. Charles Ducasse, who had filed a patent as early as 1925, invented a technique for making circuits directly using stencils and conductive inks.
World War II saw the invention of circuit boards that could withstand gunfire. However, Paul Eisler invented the first PCB in 1943 by inventing a method of etching conductive circuits on copper foil bonded to a non-conductive substrate reinforced by glass. This approach remained dormant until the late 50s when the transistor was introduced into commercial applications. The wires on electronic components have led to the development of "through-hole" technology, where holes are drilled in the PCB and the components are soldered to the board at these points. In 1961, the American company Hazeltyne applied for a patent. However, this process is slightly expensive and wasteful as the extra wires are cut and not used much. Today, "surface mount" technology is gaining momentum as the demand for smaller, higher density circuits continues to increase.
Types of PCBs
A PCB can have four types: rigid board, flexible and rigid-flex board, metal core board and injection molding board, among which rigid board is the most popular. Also, these may be single-sided, double-sided or multi-layered. When manufacturing PCBs, the mechanical, electrical, chemical and thermal properties of the material should be considered, otherwise the reliability of the board will be affected. At present, copper clad laminates with various reinforced resin systems are mainly used for rigid boards. For example, flame retardant fr-4 epoxy resin, PTFE, cyanate ester, polyimide, etc. The most commonly used reinforcement material is continuous filament electronic glass. Flexible and rigid flex boards have a random arrangement of conductors on a flexible base, with or without an overlay. Here, wiring is restricted to select areas of the aircraft. In the case of limiting metal core technology, standard materials can be used for the PCB, but the core material must have a low thermal expansion coefficient and strength to limit the PCB. Copper-invar-copper and copper-molybdenum-copper are two common materials in this regard. Molded sheets have resins containing fillers that are molded into the mold to form the desired shape.
Before anything can be drawn onto a PCB, it must first be designed and verified by means of simulation. The design process is hierarchical in nature and can take either of two approaches:
1. Top-down design. 2. Bottom-up design
top-down design
Designers start with a higher level of abstraction and start with its general functionality before creating a lower-level building block for that layer. This creates an organized design as the overall structure is drawn first and complexity is dealt with at a later, lower stage. It's like building a car body and then customizing parts for it.
Figure 2: Diagram explaining the top-down PCB design hierarchy
bottom-up design
In this approach, designers first develop the smallest modules, and then design larger modules from the smaller modules. This enables a modular approach to design and increases the reusability of design fragments. This approach is like building a standard car in a factory, first making the parts and then putting them together.
Figure 3: Bottom-up PCB Design Hierarchy Diagram
Regardless of the approach the designer chooses, the PCB must meet specific signal integrity requirements such as crosstalk, single point selection, noise, delay and reflections, electromagnetic compatibility, EMI specifications and susceptibility requirements, thermal requirements, strength, etc. Designing a PCB is part of a broader design process. Netlist generation is an important step not only for the PCB designer, but also for circuit simulation. Netlist contains a net, or a complete set of interconnects and components used. Once the circuit simulation is successful, the PCB designer sets out to create the simplest and most effective circuit pattern or drawing. The size of the board is known by placing the components on the board in the software. There are various automated component placement software that can speed up design work and have different algorithms working on their backend. However, an experienced designer should be aware that such software does not always give satisfactory results, and orderly placement of component designs is rarely the right design. The final step involves the placement of interconnect traces. This can also be an automated step, using software based on popular algorithms such as Lee's algorithm, Hightower routers, pattern routers, tunnel routers, and meshless routers, but designer caution is necessary. Once this step is complete, the integrity of the board is verified by using a design rule check to check that all rails, vias and pads have been placed according to the design rule set. The length of the interconnects can cause severe signal distortion. Therefore, signal integrity, EMI compliance and other checks are carried out as the next step.
PCB Fabrication
Artwork is generated by sending a specific format design file to a plotter and transparency for PCB fabrication. After this, the production of printed circuit boards began. Five standard techniques are used in PCB manufacturing:
1. Machining: Including drilling, punching and routing in PCBs, using standard existing machinery, as well as new technologies such as laser and water jet cutting. The strength of the plate needs to be considered when machining the precise hole diameter. Small holes make this method expensive and unreliable, as it reduces the aspect ratio and also makes plating difficult.
2. Imaging: This step transfers the circuit artwork to the various layers. Single-sided or double-sided printed circuit boards can use simple screen printing techniques to create a pattern on a printed and etched basis. But there is a limit to the minimum line width achievable. For fine circuit boards and multilayer boards, using optical imaging technology, it can be used for flood screen printing, dip coating, electrophoresis, roll lamination or liquid roll coating. In recent years, direct laser imaging technology and liquid crystal light valve imaging technology have also been widely used.
3. Lamination: This process is mainly used to manufacture multi-layer boards, or single/double-sided substrates. The glass sheets impregnated with the b-grade epoxy resin are pressed together with a hydraulic press to bond the layers together. Pressing methods can be cold pressing, hot pressing, vacuum assisted pressure cooker or vacuum pressure cooker, providing tight control over medium and thickness.
4. Electroplating: Basically a metallization process that can be achieved by wet chemical processes such as electroless and electrolytic plating, but also by dry chemical processes such as sputtering and CVD. While electroless plating offers high aspect ratios and no external current, thus forming the core of additive technology, electrolytic plating is the method of choice for bulk metallization. Recent developments, such as plasma processes, offer greater efficiency and quality while reducing environmental taxation.
5. Etching: The process of removing unwanted metals and dielectrics from a circuit board, either dry or wet. Etching uniformity is the primary concern at this stage, and new anisotropic etching solutions are being developed in order to expand the capabilities of fine line etching.
Design Flow
The overall design process can be outlined in a flowchart as follows:
Figure 4: A flow chart showing
the PCB design During the entire manufacturing process of a PCB, visual and electrical inspections are done to find any defects that may arise due to process automation, such as tombstoning, when the solder heats up too quickly and one end of the component lifts off the board , unable to contact, or solder excess or bridging. Even after the manufacturing process, the boards are tested at yield levels under different environmental, stress and strain conditions.
In ancient times, when pcbs were just introduced, the military was the main consumer. But as technology improved and demand grew, more and more interest turned to better pcbs, and today they are the basis for a wide variety of components, gadgets, and devices, from ever-innovating computers and cell phones to Basic equipment like TV, radio and children's toys. Soon, there will be more mobile phones than the world's population, and the trend will continue to rise. This may be a convenience for users, but it is not without danger, which provides a lot of space for people in different fields.
challenge
Solder contains lead, which is a toxic substance. When the solder is heated, lead fumes are formed that should not be inhaled. However, for performance reasons, such operations must be carried out in enclosed areas. Before smoke is allowed to enter Earth's atmosphere, it needs to be properly treated and filtered. Due to rapid changes in technology, devices become obsolete in months or even weeks, with more and more older devices growing day by day as progressive populations continue to embrace new technologies. If toxic substances enter the ecosystem through these wastes, it will have a catastrophic impact on the ecosystem, leading to disposal problems. Countries have put in place mitigation measures to deal with the situation, such as e-waste management, electronics recycling, recycling parts from used equipment, recycling and reusing solder, and buyback offers from manufacturers. The development of inexpensive and non-toxic methods to make electrical connections, such as water-soluble conductive molding plastics, is being developed to replace wires and solders. In addition, developments in technologies such as three-dimensional molded plastic sheets ensure that printed circuit board technology will be a very dynamic field for many years to come.
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Mr. Bai Jilong has been engaged in the electronics industry for 15 years. He has developed more than 100 products so far, and most of them have been mass-produced.
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It took 5 years since 2018 to record thousands of practical-level electronic engineer series courses, from components to core modules to complete products
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Lao Bai's original intention is "May the world's engineers not take detours" Among them, there are courses explaining MOS tubes and IGBTs in detail