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Printed circuit board

Development history editor
history
Before the advent of printed circuit boards, interconnections between electronic components relied on direct wires to form complete circuits. In the contemporary era, circuit boards only exist as effective experimental tools, and printed circuit boards have become an absolute rule in the electronics industry.
Printed circuit board
Printed circuit boards (5 photos)
At the beginning of the 20th century, in order to simplify the manufacture of electronic equipment, reduce the wiring between electronic parts, and reduce manufacturing costs, they began to study the method of replacing wiring by printing. For 30 years, engineers have been proposing to add metal conductors on insulated substrates for wiring. The most successful was in 1925, Charles Ducas in the United States printed a circuit pattern on an insulated substrate, and then successfully established a conductor for wiring by electroplating.
Until 1936, the Austrian Paul Eisler published foil film technology in the United Kingdom. He used a printed circuit board in a radio device; in Japan, Miyamoto Kisuke helped spray the wiring method “メ タ リ コ ン” “Blowing wiring method (Patent No. 119384)” successfully applied for a patent. Among them, Paul Eisler’s method is the most similar to today’s printed circuit boards. This type of method is called subtraction, which removes unnecessary metals. Charles Ducas and Miyamoto Kisuke’s method is to add only the required The wiring is called additive method. Even so, because of the large amount of heat generated by the electronic parts at that time, the substrates of the two were also difficult to use together, so that it was not formally put into practical use, but it also took the printed circuit technology one step further.
development of
In the past ten years, China’s Printed Circuit Board (PCB) manufacturing industry has developed rapidly, and its total output value and output have ranked first in the world. Due to the rapid development of electronic products, the price war has changed the structure of the supply chain. China has both industrial distribution, cost and market advantages, and has become the world’s most important printed circuit board production base.
Printed circuit boards have evolved from single-layer to double-sided, multilayer, and flexible boards, and have continued to develop in the direction of high precision, high density, and high reliability. Continuously reducing the volume, reducing the cost and improving the performance, so that the printed circuit board will still maintain a strong vitality in the future development of electronic products.
The development trend of printed circuit board manufacturing technology in the future is to develop in the direction of high density, high precision, fine aperture, fine wire, small pitch, high reliability, multi-layer, high-speed transmission, light weight and thinness in performance.
Category editor
Single panel
On the most basic PCB, parts are concentrated on one side, and wires are concentrated on the other side. Because the wires only appear on one side, this type of PCB is called Single-sided. Because the single panel has many strict restrictions on the design circuit (because there is only one side, the wiring cannot cross and must go around its own path), only early circuits used this type of board.
Double panel
This type of circuit board has wiring on both sides, but to use the wires on both sides, you must have a proper circuit connection between the two sides. This “bridge” between circuits is called a via. A via is a small hole filled or coated with metal on the PCB. It can be connected to the wires on both sides. Because the area of ​​the double-sided board is double that of the single-sided board, the double-sided board solves the difficulty of wiring interleaving in the single-sided board (through the via hole to the other side), and it is more suitable for more complicated circuits than the single-sided board.
Multilayer board
In order to increase the area that can be wired, multilayer boards use more single or double-sided wiring boards. A printed circuit board with one double side as the inner layer, two single sides as the outer layer, or two double sides as the inner layer, and two single sides as the outer layer. The conductive pattern is alternately connected together through a positioning system and an insulating bonding material. The printed circuit boards that are interconnected according to design requirements become four-layer and six-layer printed circuit boards, also known as multilayer printed circuit boards. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, an empty layer is added to control the thickness of the board. Usually, the number of layers is even, and it includes the two outermost layers. Most motherboards have a structure of 4 to 8 layers, but technically it can achieve a PCB of nearly 100 layers. Large supercomputers mostly use fairly multilayer motherboards. However, because such computers can already be replaced by clusters of many ordinary computers, ultra-multilayer boards have gradually become unused. Because the layers in the PCB are tightly coupled, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.
Data editor
composition
The current circuit board mainly consists of the following
Circuit and Pattern: The circuit is used as a tool for conduction between the originals. In the design, a large copper surface is additionally designed as the ground and power layer. The lines and drawings are made at the same time.
Dielectric layer (Dielectric): used to maintain the insulation between the circuit and the layers, commonly known as the substrate.
Through hole / via: A via hole can make two or more layers of wires communicate with each other, a larger via hole is used as a component insert, and a non-via hole (nPTH) is usually used as a surface mount For positioning, for fixing screws during assembly.
Solder resistant / Solder Mask: Not all copper surfaces need to eat tin on parts, so non-tin eaten areas will be printed with a layer of insulation material (usually epoxy resin) to avoid copper. Short circuit between non-tinned lines. According to different processes, it is divided into green oil, red oil, and blue oil.
Silk screen (Legend / Marking / Silk screen): This is an unnecessary structure. The main function is to mark the name and location frame of each part on the circuit board, which is convenient for maintenance and identification after assembly.
Surface Finish: As the copper surface is easily oxidized in the general environment, it can not be tinned (poor solderability), so it will be protected on the copper surface that needs to eat tin. The protection methods are HASL, ENIG, Immersion Silver, Immersion Tin, and Organic Solder Flux (OSP). Each method has advantages and disadvantages, which are collectively referred to as surface treatment.
Exterior
Bare boards (without parts on top) are often referred to as “Printed Wiring Board (PWB)”. The substrate of the board itself is made of insulating material, which is not easy to bend. The tiny circuit material that can be seen on the surface is copper foil. Originally, the copper foil covered the entire board. During the manufacturing process, some parts were etched away, and the remaining parts became small mesh-like circuits. . These lines are called conductor patterns or wiring, and are used to provide circuit connections for parts on the PCB.
Usually the color of the PCB is green or brown, which is the color of the solder mask. It is an insulating protective layer that can protect copper wires, prevent short circuits caused by wave soldering, and save the amount of solder. A silk screen is also printed on the solder mask. Usually text and symbols (mostly white) are printed on it to indicate the position of each part on the board. The screen printing surface is also called the legend surface.
When the final product is manufactured, integrated circuits, transistors, diodes, passive components (such as resistors, capacitors, connectors, etc.) and various other electronic parts are installed on them. Through the connection of the wires, an electronic signal connection can be formed and the energy should be available.
advantage
The main advantages of using printed boards are:

⒈Due to the repeatability (reproducibility) and consistency of the graphics, the errors in wiring and assembly are reduced, and the time for equipment maintenance, commissioning and inspection is saved;
⒉ Design can be standardized, which is conducive to interchange; 3. High wiring density, small size and light weight, which are conducive to miniaturization of electronic equipment;
⒋ It is conducive to mechanized and automated production, which improves labor productivity and reduces the cost of electronic equipment.
The manufacturing methods of printed boards can be divided into two categories, the subtractive method (additive method) and the additive method (additive method). At present, large-scale industrial production is still dominated by the corroded copper foil method.
(Overview picture)
⒌In particular, the flex resistance and precision of FPC flexible boards are better applied to high-precision instruments. (Such as cameras, mobile phones, video cameras, etc.)
Manufacturing editor
Substrate
The substrate is generally classified by the insulating part of the substrate. Common raw materials are bakelite boards, fiberglass boards, and various types of plastic boards. And PCB manufacturers generally use an insulating part made of glass fiber, non-woven fabric, and resin, and then use epoxy and copper foil to make “prepregs” for use.
The common substrates and main ingredients of Xgs game circuit design are:
FR-1 ─ phenolic cotton paper, this substrate is commonly called bakelite (higher economical than FR-2)
FR-2 ──Phenolic cotton paper,
FR-3 ──Cotton paper, epoxy resin
FR-4 ──Woven glass, epoxy resin
FR-5 ──glass cloth, epoxy resin
FR-6 ──Frosted glass, polyester
G-10 ──Glass cloth, epoxy resin
CEM-1 ──Cotton paper, epoxy resin (flame-retardant)
CEM-2 ──Tissue paper, epoxy resin (non-flammable)
CEM-3 ──glass cloth, epoxy resin
CEM-4 ──glass cloth, epoxy resin
CEM-5 ──Glass Cloth, Polyester
AIN-aluminum nitride
SIC-Silicon Carbide
Metal coating
In addition to the metal coating is the wiring on the substrate, that is, where the circuit board and electronic components are soldered. In addition, because different metals have different prices, they directly affect the cost of production. In addition, the solderability, contact, and resistance of each metal are different, which will directly affect the performance of the component.
Common metal coatings are: copper, tin (thickness is usually 5 to 15 μm), lead-tin alloy (or tin-copper alloy, that is, solder, thickness is usually 5 to 25 μm, tin content is about 63%), gold (generally only Will be plated on the interface), silver (usually only plated on the interface, or an alloy that is also silver as a whole).
Circuit design
The design of the printed circuit board is based on the circuit schematic diagram to achieve the functions required by the circuit user. The design of the printed circuit board mainly refers to the layout design, which requires various factors such as the layout of internal electronic components, metal wiring, through holes and external connections, electromagnetic protection, heat dissipation, crosstalk, and so on. Excellent circuit design can save production costs and achieve good circuit performance and heat dissipation performance. Simple layout design can be realized by hand, but complex circuit design also generally needs to be implemented with the aid of computer-aided design (CAD), and well-known design software includes OrCAD, Pads (also known as PowerPCB), Altium designer (also known as Protel), FreePCB CAM350, etc.
Basic production
According to different technologies, it can be divided into two types of processes: elimination and addition.
Subtraction
Subtractive method is to use chemicals or machinery to remove the unnecessary places on the blank circuit board (that is, the circuit board with a complete piece of metal foil), and the remaining space is the required circuit.
Screen printing: Pre-designed circuit diagrams are made into screen masks. Unwanted circuit parts on the screen will be covered with wax or water-impermeable material. Then place the screen mask on the blank circuit board, and then place it on the silk screen. The protective agent that will not be corroded on the oil on the net, put the circuit board in the corrosive solution, and the part that is not covered by the protective agent will be etched away, and finally the protective agent will be cleaned.
Photosensitive plate: Pre-designed circuit diagram is made on a transparent film mask (the simplest way is to use a printer-printed slide), and the required part should be printed in opaque color, and then the blank circuit Apply photosensitive pigments on the board, place the prepared film mask on the circuit board and illuminate the light for several minutes, remove the mask and use a developer to display the pattern on the circuit board, and finally use the screen printing method. Corrosion of the circuit.
Marking: Use a milling machine or laser engraving machine to directly remove the unnecessary parts on the blank line.
Additive method
Additive method is now commonly used on a substrate pre-plated with thin copper, covered with a photoresist (D / F), exposed to UV light and then developed, exposing the required areas, and then plating the circuit board The thickness of the copper on the formal circuit is increased to the required specifications, and then a layer of anti-etching resist-metal thin tin is plated, and finally the photoresist is removed (this process is called film removal), and then the copper foil under the photoresist is added. The layers are etched away.
Lamination
The lamination method is one of methods for manufacturing a multilayer printed circuit board. After the inner layer is made, the outer layer is wrapped, and the outer layer is processed by the subtractive method or the additive method. Continuously repeating the operation of the lamination method, a multilayer printed circuit board that can obtain multiple layers is a sequential lamination method.
1. Inner layer production
2. Layering (ie the action of bonding different layers)
3. Lamination is completed (the outer layer contains the metal foil film of the subtractive method; the addition method)
4. Drilling
Panel method
1. Full PCB plating
2. Add a resist on the surface where it is to be kept (to prevent it from being etched)
3. Etching
4. Remove the barrier layer
Pattern method
1. Add a barrier layer on the surface where it should not be kept
2.Plating required surface to a certain thickness
3. Remove the barrier layer
4. Etching until the unnecessary metal foil film disappears
Full addition
1. Add a barrier layer where no conductor is needed
2. Make lines with electroless copper
Partial addition
1. Cover the entire PCB with electroless copper
2. Add a barrier layer where no conductor is needed
3. electrolytic copper plating
4. Remove the barrier layer
5. Etching until the original copper disappears under the barrier layer
ALIVH
ALIVH (Any Layer Interstitial Via Hole, Any Layer IVA) is a layering technology developed by Matsushita Electric of Japan. This is using aramid fiber cloth as the base material.
1. Dip the fiber cloth in epoxy to become a “prepreg”
2. Laser drilling
3. Fill the hole with conductive paste
4. Stick the copper foil on the outer layer
5. Circuit pattern is made on copper foil by etching
6. Stick the semi-finished product that completed the second step on the copper foil
7. Laminated into
8. Repeat steps 5 to 7 again and again until complete
B2it
B2it (Buried Bump Interconnection Technology) is a layering technology developed by Toshiba.
1. Make a double-sided or multilayer board first
2.Print cone silver paste on copper foil
3. Put the adhesive sheet on the silver paste, and make the silver paste penetrate the adhesive sheet
4. Stick the adhesive sheet from the previous step on the board of the first step
5. Circuit pattern of the copper foil of the adhesive sheet by etching
6. Repeat steps 2 to 4 again and again until complete
function test
Dense PCBs, higher bus speeds, and analog RF circuits all pose unprecedented challenges to testing. Functional testing in this environment requires careful design, well-thought-out testing methods, and appropriate tools to provide


Post time: Mar-17-2020