PCB Tech - HDI circuit board manufacturing

HDI circuit board is the abbreviation of English High Density Interconnection, which refers to high-density interconnection board. As large ASICs and FPGAs with smaller device pitches, more I/O pins and embedded passive devices have shorter and shorter rise times and higher frequencies, they all require smaller PCB sizes, which promotes There is a strong demand for HDI/micro via PCB, and HDI is becoming more and more common in PCB design. High-density HDI circuit boards are entering many applications, such as military communications equipment, aerospace, computers, smart phones, medical equipment, and many other applications.

HDI processing and manufacturing
1. Aperture ratio

Both the design of through holes and buried blind holes must consider the aperture ratio. The aperture ratio of the traditional PCB board is usually 8:1, and the limit is 12:1. However, due to the limitation of energy and efficiency in laser drilling, the aperture of the laser hole cannot be too large, generally 4mil, and the depth-to-diameter ratio of the electroplated hole is the largest 1:1.

2. Laminated

HDI board laminate classification is divided by order. The second order is determined by the number of blind holes. For example, L1-L2 is the first order, L1-L2, L2-L3 is the second order, L1-L2, L2- L3, L3-L4 are third-order, and there are several typical stacks:

First-order process 1+N+1
Second-order process 2+N+2
Three-stage process 3+N+3
Fourth-order process 4+N+4
Factors to consider when designing HDI:
Cost-Compared with traditional circuit boards, HDI technology is more costly.
Materials-Higher-end PCB materials are used for HDI circuit boards
Design-requires expertise and experience
Processing-Not all manufacturers have the necessary capabilities for HDI. The small line width and strict tolerances of HDI circuit boards require laser imaging, which requires factories to have advanced equipment and superb process capabilities.