HDI PCB vs Microvia PCB
- HDI PCB is a high-density-interconnected printed circuit board. On the two sides of an HDI PCB, the number of electrical connections on average is 20/cm² or 130/in². And the trace width and space are equal to or smaller than 100µm or 0.004".
- A microvia has an aperture equal to or smaller than 0.15mm or 0.006" and penetrates only one PCB layer. An HDI PCB typically has microvias in SMT pads. For this reason, microvia PCB is another name for HDI PCB.
- Besides, the microvias of an HDI PCB can stack to form blind or buried vias. A blind hole penetrates from the external layer to an external layer, while a buried hole penetrates from an external layer to another.
- Microvias are laser drilled. In HDI PCBs, microvias can be single, staggered, stacked, or skipped. The smaller the microvia aperture, the smaller the parasitic capacitance, which is practical for high-speed circuits.
HDI PCB Lamination
HDI PCB manufacturing requires sequential lamination. For example, 3+N+3 means the HDI PCB requires three times laser drilling and laminations. The number of microvia pairs stands for how many times of lamination in HDI PCB manufacturing.
The internal layers without microvias are laminated in the standard lamination way under high temperatures and high pressure. Prepreg melts, fills in gaps between adjacent copper layers, and cures so that the copper layers are bonded and insulated.
Lamination to external layers with microvias is more difficult than internal layers. Microvias are laser dilled before lamination, and after lamination, microvias on different layers may overlap to form stacked vias or stagger to form staggered vias. Positioning for laser drilling and lamination should be highly accurate. Otherwise, the board defects. So HDI PCB manufacturing costs more than normal PCBs.
Advantages of HDI PCBs
- HDI PCBs are suitable for products where electrical performance and noise rejection are of utmost importance. The advantages of HDI PCBs include:
- ● HDI technology decreases products' overall size and improves electrical performance.
- ● HDI PCBs have great impedance control and impressive high-frequency transmission capabilities.
- ● HDI PCBs offer a perfect solution for fine pitch packages, flip-chip assemblies, and complicated BGA designs.