From 1903 to the present, from the perspective of the application and development of PCB assembly technology, it can be divided into three stages
1 Through-hole technology (THT) stage PCB
1. The role of metallized holes:
(1). Electrical interconnection---signal transmission
(2). Support components---pin size limits the reduction of through-hole size
a. Pin rigidity
b. Requirements for automated insertion
2. Ways to increase density
(1) Reduce the size of device holes, but limited by the rigidity of component pins and insertion accuracy, the hole diameter ≥ 0.8mm
(2) Reduce line width/spacing: 0.3mm-0.2mm-0.15mm-0.1mm
(3) Increase the number of layers: single-sided-double-sided-4 layers-6 layers-8 layers-10 layers-12 layers-64 layers
2 Surface mount technology (SMT) stage PCB
1. The role of the via: only serves as electrical interconnection, the hole diameter can be as small as possible, and the hole can be blocked.
2. The main way to increase density
①. The size of the via is drastically reduced: 0.8mm-0.5mm-0.4mm-0.3mm-0.25mm
②. The structure of the via has undergone essential changes:
a. Advantages of the buried blind hole structure: increase the wiring density by more than 1/3, reduce the size of the PCB or reduce the number of layers, improve reliability, improve characteristic impedance control, and reduce crosstalk, noise or distortion (due to short lines and small holes)
b. Hole in pad eliminates relay holes and connections
③ Thinning: double-sided board: 1.6mm-1.0mm-0.8mm-0.5mm
④ PCB flatness:
a. Concept: PCB board substrate warpage and coplanarity of the connection pad surface on the PCB board surface
b. PCB warpage is the result of residual stress caused by heat and mechanics
c. Surface coating of connection pad: HASL, chemical plating NI/AU, electroplating NI/AU…
3 Chip-scale packaging (CSP) stage PCB
CSP has begun to enter a period of rapid change and development, driving PCB technology forward. The PCB industry will move towards the laser era and nano era.
