Is PCB simple?

What are the layers of the 1. PCB?
Here, the PCB is divided into 7 working layers: signal layer, internal plane, mechanical layer, solder resist layer, silk screen layer, system layer and other layers.

1. Signal layer
The signal layer includes Top Layer, Bottom Layer, Mid Layer1, Mid Layer2…. The signal layer is used to install components and trace wires. It is also called the circuit layer.

copper layer
2. Internal plane layer
The internal plane layer is used to arrange power and ground wires. Each inner plane layer may have two or more power supplies, e.g., 5V, 15V, etc.

3. Mechanical layer
The mechanical layer is generally used to place indicative information about the PCB printing and assembly method, such as circuit board physical dimension lines, dimension marks, data sheets, via information, assembly instructions, etc.

4. Solder resist layer
The solder resist layer includes a top portion and a bottom portion. Solder Paste Layer includes Top Paste and Bottom Paste, and its functions are similar to Solder Mask Layer.

The solder mask can prevent the copper from interacting with air to oxidize, and prevent the PCB from shorting.

For more information about the solder resist layer, welcome to read the following article: What is the PCB solder resist layer? PCB solder resist layer production process summary, with you to fix the PCB solder resist layer

Six solder mask design mistakes have been made by 99% of engineers. Are you the 1% engineer?

Solder mask
5. Screen printing layer
The silk screen layer includes a top cover layer and a bottom cover layer. Used to place text information such as component introduction, component quantity, logo, date, etc. Screen printing is usually mostly white, but also useful in other colors. Screen printing is mainly used to display information and has nothing to do with the circuit connection.

For more information about the screen printing layer, welcome to read the following article: Why is PCB screen printing so important?

screen printing layer
6. Other layers

Keep-Out Layer is used to define the area of the printed circuit board. Drill guide and Drill drawing are used for borehole mapping and borehole positioning. Drill Drawing are commonly used.

PCB solder resist layer
7. System layer
系统层包括 Connections、Pad Holes、Via Holes、Visible Grid 1 和 Visible Grid 2。

PCB
2. PCB Classification-Number of Layers
According to the number of layers, PCB can be divided into three types, namely single-layer PCB, double-layer PCB and multi-layer PCB.

1. Single-layer PCB
A single-layer PCB is a PCB in which electrical material (usually copper) is laid on only one side of the board. Single-layer PCB designs are the simplest, usually contain fewer components and are easier to manufacture.

Single-layer PCB

Single-layer PCB
2. Double layer PCB
Unlike single-layer boards, double-layer boards have conductive materials on both sides. Thus, traces may be etched on both sides of the circuit board. Vias are one of the important factors in double-sided PCB design, which can connect PCB traces from one side to the other.

Double layer PCB
The two sides of the PCB are often referred to as the top and bottom, respectively, and the image below shows an image of a two-layer PCB.

Double layer PCB
3. Multilayer PCB
A multilayer PCB has more than two conductive layers. They essentially consist of multiple double-sided PCBs glued together with an insulating layer attached. Multilayer PCBs can have as many as 12, 16 layers, or even more. Production is more complicated and the price is more expensive.

Multilayer PCB
3. PCB Classification-According to Appearance
Common PCB appearance includes: rigid PCB, flexible PCB and hard and soft PCB

1. Rigid PCB
In everyday electronic devices, rigid PCBs are often seen, composed of solid materials, which can be single-layer/double-layer/multi-layer. The service life is relatively high.

Rigid PCB
2. Flexible PCB
Flexible PCB uses flexible materials, such as polyamide, PEEK (polyether ether ketone) or transparent conductive polyester film as the substrate, which is relatively flexible and can be bent. It can also be single-sided/double-sided/multi-sided.

For more information about flexible PCB, please read the following articles: FPCB process flow explanation, structural diagram stack diagram process flow, a few minutes, easy to handle

Flexible PCB

Flexible PCB

Flexible PCB
Flexible circuits are widely used in organic light-emitting diodes, LCD manufacturing, flexible solar cells, automotive industry, mobile phones, cameras, personal computers and other wearable and complex electronic devices. Flexible circuits are more complex to manufacture and cost more.

3. Rigid-flexible PCB
Because of the size and application requirements, some devices need to be flexible, and the other part is rigid PCB, that is, rigid flexible PCB.

A flex-rigid PCB consists of a multi-layer flex PCB connected to a plurality of rigid PCB layers. In mobile phones, digital cameras, cars have applications

rigid-flexible PCB

rigid-flexible PCB
4. PCB classification-based on component packaging/mounting
Electronic components are usually installed in DIP (dual in-line package)/with leads or SMD (surface mount). Although it is only installed, it can also be used for classification.

Based on this, PCB can be divided into: through hole PCB and surface mount PCB

1. Through-hole PCB
The through-hole PCB is composed of DIP and leaded components. There are drilled holes in the PCB, and the leads of the components are placed in these holes and soldered to the pads usually located on the other side of the PCB.

Through-hole PCB
2, Surface Mount (SMT )PCB
Surface mount PCB, using SMD components, the components are usually small in size and do not need to be punched. Many times, the two installation methods will be combined.

Surface Mount (SMT )PCB
5. PCB substrate material
The most common materials used in PCB manufacturing: FR4, FR-1 and FR-2, CEM-1, CEM-3, polyamide and prepreg

1、FR4
FR4 is based on woven glass epoxy compound, more commonly used PCB substrate material, FR stands for flame retardant, based on FR4 PCB is usually very strong.

2. FR-1 and FR-2
FR1 and FR2 are similar materials made from paper and phenol compounds that are commonly used to make low-cost single-layer PCBs. PCBs made from these materials are generally of poor quality compared to FR4 and are commonly found in consumer electronics.

FR1 has poor moisture resistance and low arc resistance, so it is less used.

3、CEM-1
CEM-1-based PCBs have slightly higher performance than FR4-based PCBs, but are generally more expensive. The CEM-1 material is made of paper and two layers of glass fiber epoxy and phenol compound, and is only used for the development of single-layer PCB boards.

4, CEM-3
The material is a white glass epoxy compound, which is mainly used for double-layer PCB. CEM-3 is less mechanically strong than FR4, but less expensive than FR4.

5. Polyimide
Polyimide is used as a base material for flexible PCBs, a high-temperature polymer made from a variety of materials. It has good electrical properties, wide operating temperature range, high water absorption and high chemical resistance, but the price is more expensive.

6. Prepreg
Prepregs are glass fibers impregnated with resin. The resin is pre-dried so that it flows, adheres and is completely submerged when heated. The prepreg has an adhesive layer with a strength similar to that of FR4.

The material is available in various versions depending on the resin content, SR-standard resin, MR-medium resin and HR-high resin, usually chosen according to the required thickness, layer structure and resistance.