PCB, also known as printed circuit board and printed circuit board, is an important electronic component and a support for electronic components, known as the "mother of electronic components". From 1903 to the present, from the perspective of the application and development of PCB assembly technology, the development of PCB circuit board technology can be divided into three stages. What are the three stages, and what are the specific manifestations?
一. Through-hole technology (THT) stage
1.The role of metallized holes:
(1) Electrical interconnection - signal transmission;
(2) Supporting components - the size of the pins limits the reduction of the size of the through holes.
2. Ways to increase density:
(1) The reduction of the device hole size is limited by the rigidity of the component pins and the insertion accuracy, and the aperture is ≥0.8mm;
(2) The line width/spacing is reduced: 0.3mm—0.2mm—0.15mm—0.1mm;
(3) The number of layers increases: single-sided - double-sided - 4 layers - 6 layers - 8 layers - 10 layers - 12 layers - 64 layers;
二. the surface mount technology (SMT) stage
1. The via hole only serves as an electrical interconnection, and the aperture can be as small as possible.
2. Main ways to increase density:
(1) The via hole size decreases sharply: 0.8mm—0.5mm—0.4mm—0.3mm—0.25mm;
(2) The via hole structure undergoes essential changes:
a. Advantages of buried blind holes: increase wiring density by more than 1/3, reduce PCB size or number of layers, improve reliability, improve characteristic impedance control, reduce crosstalk, noise or distortion (due to short lines and small holes) ;
b. The inner hole of the disc eliminates the relay hole and connection.
3. Thinning development: Double panel: 1.6mm—1.0mm-0.8mm-0.5mm;
4. PCB flatness:
(1) Concept: The warpage of the PCB substrate and the coplanarity of the surface of the land on the PCB surface;
(2) The warpage of the PCB is the comprehensive result of the residual stress caused by heat and machinery;
(3) The surface coating of the land: HASL, chemical plating NI/AU, electroplating NI/AU, etc.
