PCB concept
PCB can be said to be common or uncommon in our lives. It is an important electronic component and a support for electronic components. All electronic products in our lives contain PCB boards. The full name of PCB is Printed Circuit Board, which is called “printed” circuit board because it is made by electronic printing.

The role and function of PCB in various electronic devices
1. Pad: Provide mechanical support for fixing and assembling various electronic components such as integrated circuits.​​
2. Wires: wires used to connect various electronic components, which can help circuit boards achieve wiring and electrical connection (signal transmission) or electrical insulation between components. Provide the required electrical characteristics.
3. Green oil and silk screen: Provide solder mask graphics for automatic assembly, and provide identification characters and graphics for component insertion, inspection, and maintenance.

Development history of PCB technology
Since the advent of PCB, if we look at the development of PCB assembly technology,FS TECH has divided it into three stages

THT-Through Hole Technology Stage

The role of metallized holes:

(1). Electrical interconnection—signal transmission
Literally, the electrical appliances are directly connected or indirectly connected through transformers and the like
(2). Supporting components—pin size limits the reduction of through hole size
a. Rigidity of the pins
Pin, also called pin. It is the wiring from the internal circuit of the integrated circuit (chip) to the peripheral circuit, and all the pins constitute the interface of this chip. A segment of the end of the lead, which is formed by soldering to form a solder joint with the pad on the printed board. Pin can be divided into bottom, toe, side and other parts.
b. Requirements for automated instrumentation

There are three ways to increase density
(1) Under the regulations (aperture ≥ 0.8mm) to reduce the size of the device hole, why is there a regulation? This is because of the rigidity of the component Pin pins and the limitation of the insertion precision.
(2) Control line width/spacing: 0.3mm—0.2mm—0.15mm—0.1mm
(3) Increase the number of layers of the circuit board: the better the technology, the more layers can be added, FS technology can achieve all the layers, 64 layers – 12 layers – 10 layers – 8 layers – 4 layers – double-sided – single noodle,

SMT-Surface Mount Technology Stage PCB

1. The role of the via hole: it only plays the role of electrical interconnection, the aperture can be as small as possible, and the hole can also be plugged.
2. The main way to increase the density
①. The size of the via hole decreases sharply: 0.8mm—0.5mm—0.4mm—0.3mm—0.25mm
②. The structure of the via has undergone essential changes:
a. Advantages of buried blind hole structure: increase wiring density by more than 1/3, reduce PCB size or reduce the number of layers, improve reliability, improve characteristic impedance control, reduce crosstalk, noise or distortion (due to short lines, small holes )
b. Hole in pad eliminates relay holes and connections
③ Thinning: Double-sided: 1.6mm—1.0mm—0.8mm—0.5mm
④PCB flatness:
The warpage of the PCB board substrate and the coplanarity of the land surface on the PCB board.

PCB warpage is the combined result of residual stress due to mechanical, thermal, etc.

Surface coating of connection pad: PCB surface coating (plating) coating technology The surface coating (plating) coating technology described in this article refers to the solderability for electrical connections other than solder resist (solder mask, solder mask) Or contactable coating (plating) coating. These surface coatings protect the fresh copper surface. Mainly ASL, electroless NI/AU, electroplating NI/AU…

CSP – Chip Scale Packaging Stage
Compared with traditional packaging, advanced packaging improves the integration density and interconnection speed of chip products, lowers the design threshold, and optimizes the flexibility of function matching. For example, flip-chip interconnects the chip and the substrate, shortens the interconnection length, and realizes the enhancement of chip performance and the improvement of heat dissipation and reliability. CSP has begun to enter into a drastic change and development, promoting the continuous development of PCB technology, and the PCB industry will move towards the laser era and nano era.

FS Technology’s PCB surface coating technology
In order to ensure that the copper surface of the solder pad on the PCB is not oxidized and polluted before soldering, the circuit boards produced by FSPCB must be protected by a surface coating (plating) layer, and the surface coating (plating) layer must meet the necessary and sufficient conditions to achieve the purpose.

Copper is second only to silver as an excellent conductor and a metal with good physical properties (such as ductility, etc.). In addition, the reserves are quite abundant and the cost is not high. Therefore, copper is selected as a conductive material for PCB. However, copper is an active metal, and its surface is easily oxidized to form an oxide layer (copper oxide and cuprous oxide). This oxide layer often causes solder joint failures and affects reliability and service life. According to statistics, 70% of PCB failures come from the solder joints. The main reasons are: (1) due to the surface contamination of the pad, oxidation and other components of incomplete soldering, virtual soldering, etc.; (2) due to the mutual between gold and copper For diffusion, a diffusion layer is formed or an intermetallic compound is formed between tin and copper, thereby causing failures such as interface looseness and embrittlement. Therefore, the copper surface of the PCB used for soldering must be protected by a solderability protective layer or a solderability barrier layer in order to reduce or avoid failure problems.