What is PCB
PCB is short for Printed Circuit Board,also called for Printed Wire Board, which is the core component of an electronicproduct,it is the basic support body for electronic components,and a provider of electrical connections for electronic components. As the circuits and the the relative pattern (soldermask and silkscreen) generated and transferred to the board by the printing way so it is called as “printed” circuit board.
The role and function of PCB in various electronic devices
- PAD: Providing mechanical support for fixing and assembling IC and all kinds of electronic components.
- Track: Realize track route and electrical connection (signal transmission) or electrical isolation between various electronic components such as integrated circuits. Providing the required electrical characteristics, such as characteristic impedance, etc.
- Solder-mask and silkscreen: Providing the soldermask graphics for automatic assembly, Provide identification texts and graphics for component insertion, inspection and maintenance.
PCB Technology Development Stages Summary
Since 1903, it can be simply summarized 3 stages by the application and the development of the PCB assembly technology
- Through-hole technology (THT) stage:
1-1. The function of through metalized holes (PTH) :
(1). Electrical connection and Signal transmission
(2). Supporting components-Pin size determine the hole size smaller and smaller:
a. Rigidity feature of the pins
b. Requirements of automatic mounting technology.
1-2. The way of improving the density
(1). Minimizing the components holes size, but the hole size must be not less than 0.8mm due to the restriction from the rigidity feature of the component lead pins and the mounting density of the components.
(2). Minimizing the track width/spacing:0.3mm-0.2mm-0.15mm-0.1mm
(3). Increasing the PCB layer counts: single side-double sides-4L-6L-8L-10L-12L-64L
- Surface mounting technology (SMT) stage PCB.
2-1: The through via holes function: only for electrical interconnection, hole size to be as small as possible, via holes plugged is well.
2-2: The way of improving the circuit interconnection density
(1). The via holes size reduced mostly smaller and smaller: 0.80mm->0.50mm->0.40mm->0.30mm->0.25mm->0.20mm->0.15mm
(2). Essential change occurring in the via holes structure.
a. The advantage of blind & buried via: increasing track path and layout density above 1/3,reduce PCB size or reducing the circuit board layer counts, improve reliability, impedance controlling improved, reduce signal interference, noise or distortion(because track short hole small).
b. Via hole in pad eliminates relay holes and wiring
(3). Thinning: 2L PCB:1.6mm-1.0mm-0.8mm-0.5mm
(4). PCB flatness:
a. Concept: The warpage of the PCB base material and the coplanarity of the pads surface on the PCB board.
b. PCB warpage is the combined result of thermally and mechanically induced residual stress.
c. PAD surface coated finish: HASL,ENIG,plated(electronic)Ni/Au
- Chip Scale Package (CSP) Stage PCB
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 the nano era.