Printed circuit board {PCB circuit board}, also known as printed circuit board, is the provider of electrical connections for electronic components. It has been developed for more than 100 years; its design is mainly layout design; the main advantage of using the circuit board is that it greatly reduces wiring and assembly errors, and improves the automation level and production labor rate.

According to the number of circuit boards, it can be divided into single-panel, double-panel, four-layer, six-layer and other multi-layer boards.

Since the printed circuit board is not a general terminal product, the definition of the name is slightly confusing. For example, the motherboard for the personal computer is called the motherboard, and cannot be directly called the circuit board. Although there is a circuit board in the motherboard, It’s not the same, so when you evaluate the industry, you can’t say the same thing. For example, because the integrated circuit parts are mounted on the circuit board, the news media called him an IC board, but in essence he is not equivalent to a printed circuit board. We usually say that the printed circuit board refers to the bare board – that is, the board without the upper components.


Single panel

On the most basic PCB, the parts are concentrated on one side and the wires are concentrated on the other side. Since the wire only appears on one side, this PCB is called a single-sided. Because single-panel has many strict restrictions on the design line (because there is only one side, the wiring can not cross and must be around the path), so only the early circuit used this type of board.

Double panel

This type of circuit board has wiring on both sides, but to use the two sides of the wire, it is necessary to have proper circuit connection between the two sides. The “bridge” between such circuits is called a via. The via hole is a small hole filled or coated with metal on the PCB, which can be connected to the wires on both sides. Because the area of ​​the double panel is twice as large as that of the single panel, the double panel solves the difficulty of wiring interleaving in a single panel (can pass through the via hole to the other side), and it is more suitable for circuits that are more complicated than a single panel.

Multilayer board

In order to increase the area that can be wired, the multilayer board uses more single or double-sided wiring boards. Using a double-sided inner layer, two single-sided outer layers or two double-sided inner layers, two single-sided outer printed circuit boards, alternating between the positioning system and the insulating bonding material and conductive patterns Printed circuit boards that are interconnected according to design requirements become four-layer, six-layer printed circuit boards, also known as multilayer printed wiring boards. The number of layers of the board does not mean that there are several layers of independent wiring layers. In special cases, empty layers are added to control the thickness of the board. Usually the number of layers is even and the outermost two layers are included. Most of the motherboards are 4 to 8 layers of structure, but technically they can achieve nearly 100 layers of PCB. Large supercomputers mostly use quite a few multi-layer motherboards, but because such computers can already be replaced by clusters of many common computers, super-multilayer boards have gradually disappeared. 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.


The current circuit board is mainly composed of the following

Pattern and Pattern: The line is used as a tool for conducting conduction between the originals. In the design, a large copper surface is additionally designed as the grounding and power supply layer. The line and the drawing are made at the same time.

Dielectric: used to maintain the insulation between the circuit and the layers, commonly known as the substrate.

Through hole / via: The via hole can make the two levels above the line conduct each other, the larger via hole is used as the component insert, and the non-via hole (nPTH) is usually used as the surface mount. Positioning and fixing screws for assembly.

Solder resistant /Solder Mask: Not all copper surfaces should be tinned. Therefore, non-tin-stained areas will be printed with a layer of copper-free material (usually epoxy) to avoid Short circuit between lines that are not tinned. According to different processes, it is divided into green oil, red oil and blue oil.

Legend /Marking/Silk screen: This is a non-essential structure. The main function is to mark the name and position frame of each part on the circuit board to facilitate post-assembly maintenance and identification.

Surface Finish: Since the copper surface is easily oxidized in a general environment, it is impossible to apply tin (poor solderability), so it is protected on the copper surface where tin is to be eaten. The protection methods include spray coating (HASL), gold (ENIG), silver (Immersion Silver), tin (Immersion Tin), and organic solder resist (OSP). The methods have their own advantages and disadvantages, collectively referred to as surface treatment.


Bare boards (with no parts on the top) are also often referred to as “Printed Wiring Boards (PWB).” The substrate of the board itself is made of a material that is insulated and heat-insulating and is not easily bent. The thin circuit material that can be seen on the surface is copper foil. The original copper foil is covered on the whole board, and part of the manufacturing process is etched away, and the remaining part becomes a mesh-like small line. . These lines are called conductor patterns or wires and are used to provide electrical connections to the 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 protects copper wires and prevents short circuits caused by wave soldering, and saves solder usage. A layer of silk screen is also printed on the solder mask. Text and symbols (mostly white) are usually printed on this to indicate the position of each part on the board. The screen printing surface is also referred to as the legend.

In the final product, integrated circuits, transistors, diodes, passive components (such as resistors, capacitors, connectors, etc.) and various other electronic components are mounted. By connecting wires, electronic signal connections and organic energy can be formed.


The main advantages of using printed boards are:

1. Due to the repeatability (reproducibility) and consistency of the graphics, wiring and assembly errors are reduced, saving equipment maintenance, debugging and inspection time;

2. The design can be standardized and facilitated interchangeability; 3. High wiring density, small size and light weight, which is conducive to miniaturization of electronic equipment;

4. Conducive to mechanization, automated production, increased labor productivity and reduced the cost of electronic equipment.

The manufacturing method of the printed board can be divided into two major categories: subtraction method (reduction method) and addition method (addition method). At present, large-scale industrial production is mainly based on the method of reducing the corrosion of copper foil in the method.

(Overview image)

5. Especially the bending resistance, precision and better application of FPC flexible board to high precision instruments. (such as cameras, mobile phones, cameras, etc.)



The substrate is generally classified by the insulating portion of the substrate. Common raw materials are electric wood, fiberglass, and various plastic plates. Manufacturers of PCBs generally use an insulating part composed of glass fiber, non-woven material, and resin, and then press it into a “prepreg” with epoxy resin and copper foil.

The basic substrate and main components of the Xgs game circuit design are:

FR-1 ─ phenolic cotton paper, this substrate is commonly known as bakelite (higher economy 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 ─ matte glass, polyester

G-10 ─ glass cloth, epoxy resin

CEM-1 ─ cotton paper, epoxy resin (flame retardant)

CEM-2 ─ cotton paper, epoxy resin (non-flame retardant)

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 wiring on the substrate, the metal coating is where the substrate wiring is soldered to the electronic components. In addition, because of the different prices of different metals, it directly affects the cost of production. In addition, each metal has different solderability, contact properties, resistance values, etc., which will directly affect the performance of the component.

Commonly used metal coatings are: copper, tin (usually 5 to 15 μm thick), lead-tin alloy (or tin-copper alloy, ie solder, thickness usually 5 to 25 μm, tin content about 63%), gold (generally only Will be plated in the interface), silver (generally only plated on the interface, or alloyed with silver as a whole).

Line design

The design of the printed circuit board is based on the circuit schematic and realizes the functions required by the circuit user. Printed circuit board design mainly refers to the layout design, which requires internal electronic components, metal wiring, through-hole and external connection layout, electromagnetic protection, heat dissipation, crosstalk and other factors. Excellent circuit design can save production costs and achieve good circuit performance and heat dissipation. Simple layouts can be implemented manually, but complex circuit designs typically require computer-aided design (CAD), and well-known design software includes OrCAD, Pads (also known as PowerPCB), Altium Designer (also known as Protel), and FreePCB. , CAM350, etc.

Basic production

According to different technologies, it can be divided into two major categories of processes.

Subtraction method

Subtractive is the removal of unwanted areas on a blank circuit board (ie, a circuit board covered with a complete piece of metal foil) using chemicals or machinery. The remaining convenience is the required circuit.

Screen printing: The pre-designed circuit diagram is made into a mesh screen. The unnecessary circuit parts on the screen are covered with wax or impervious material. Then the screen mask is placed on the blank circuit board and then on the wire. The protective agent that will not be corroded on the oil on the net will put the circuit board into the corrosive liquid. The part not covered by the protective agent will be eroded away, and finally the protective agent will be cleaned.

Photosensitive plate: The pre-designed circuit diagram is made on a light-transmissive film mask (the simplest method is to use the printer to print the slide). Similarly, the required part should be printed as an opaque color, and then in the blank line. The board is coated with photographic pigment, and the prepared film mask is placed on the circuit board to illuminate the glare for a few minutes. After removing the mask, the pattern on the circuit board is displayed with the developer, and finally, as with the screen printing method. Corrode the circuit.

Marking: Use the milling machine or laser engraving machine to directly remove unwanted parts of the blank line.

Addition method

Additive, now commonly used on a substrate pre-plated with thin copper, covered with photoresist (D / F), exposed to ultraviolet light and then developed, exposed where needed, and then used to plate the circuit board On the official line, the copper thickness is thickened to the required specifications, and then an anti-etching resist-metal thin tin is applied, and finally the photoresist is removed (this process is called film removal), and then the copper foil under the photoresist is applied. The layer is etched away.

Laminated method

The laminate method is one of the methods for producing a multilayer printed circuit board. The outer layer is wrapped after the inner layer is made, and the outer layer is treated by subtraction or addition. By repeating the operation of the lamination method, it is possible to obtain a multilayer multilayer printed circuit board which is a sequential lamination method.

Inner layer production

2. Layered (ie, the action of bonding different layers)

3. The completion of the layering (subtracting the outer metal foil film of the method; addition method)

4. Drilling

Panel method

1. Full block PCB plating

2. Add a barrier layer to the surface where it is to be retained (resist)

3. Etching

4. Remove the barrier layer

Pattern method

1. Add a barrier layer to the surface where it is not to be retained.

2. Electroplating required surface to a certain thickness

3. Remove the barrier layer

4. Etching to unwanted metal foil film disappears

Complete addition method

1. Add a barrier layer to the place where the conductor is not needed.

2. Composition line with electroless copper

Partial addition method

1. Cover the entire PCB with electroless copper

2. Add a barrier layer to the place where the conductor is not needed.

3. Electrolytic copper plating

4. Remove the barrier layer

5. Etching until the original electroless copper disappears under the barrier layer


ALIVH (Any Layer Interstitial Via Hole, Any Layer IVA) is a layer-adding technology developed by Matsushita Electric Industrial Co., Ltd. This is based on the use of an aramid fiber cloth.

1. Dip the fiber cloth into epoxy resin to become a “prepreg”

2. Laser drilling

3. The hole is filled with conductive paste

4. Sticking copper foil on the outer layer

5. The copper foil is etched to form a line pattern.

6. Sticking the semi-finished product that completes the second step to the copper foil

7. Layered

8. Repeat steps 5 through 7 until you are finished


B2it (Buried Bump Interconnection Technology) is a layering technology developed by Toshiba.

1. Make a double or multi-layer board first

2. Printing a cone of 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 to the board on the first step.

5. Etching the copper foil of the adhesive sheet into a circuit pattern

6. Repeat steps 2 through 4 until you are finished

function test

More intensive PCBs, higher bus speeds, and analog RF circuits present unprecedented challenges for testing. Functional testing in this environment requires careful design, well-thought-out testing methods, and appropriate tools to provide credible Test Results.

When dealing with fixture suppliers, keep these issues in mind while also thinking about where the product will be manufactured, a place that many test engineers will ignore. For example, we assume that the test engineer is in California, USA, and the product is manufactured in Thailand. Test engineers will consider the product to require expensive automated fixtures because of the high price of the plant in California, requiring as few testers as possible, and the use of automated fixtures to reduce the need to hire high-tech, high-paying operators. But in Thailand, these two problems do not exist, so it is cheaper to solve these problems manually, because the labor cost here is very low, the land price is also very cheap, and the big factory is not a problem. Therefore, sometimes state-of-the-art equipment may not be popular in some countries.

techinque level

In high-density UUTs, if calibration or diagnostics are required, it is likely to be manually probed because the needle bed contact is limited and the test is faster (using the probe to test the UUT can quickly acquire data instead of feeding back information to the edge) For reasons such as connectors, it is required that the operator probe the test points on the UUT. Wherever you are, make sure that the test points are clearly marked.

Probe types and general operators should also be aware that issues to consider include:

Large probe