HDI PCB is defined as high-density PCB with highly dense wiring per unit area. HDI PCB normally consists of finer lines and spacing, tiny vias and smaller components with respect t to conventional PCB designs. With evolution of semiconductor industries, where component packages are smaller and smaller now, compact PCB is being designed using this technology.
In general, there are five types of HDI boards are being manufactured:
1. through vias from surface to surface,
2. with buried vias and through vias,
3. two or more HDI layer with through vias,
4. Passive substrate with no electrical connection,
5. Coreless construction using layer pairs and Alternate constructions of coreless constructions using layer pairs.
HDI PCBs have very high density including laser microvias, superfine lines and high performing thin wires. The increased density is directly proportional to increased number of functions per unit area. HDI PCB is having extremely small micro-vias, which provide several interconnections. HIGH DENSITY INTERCONNECT PCB is important as VLSI which is helping in production of extremely small and large pin count Ics. They are routed on multilayer PCB with complex interconnections.
A micro via maintains a laser drilled diameter of (typically 0.006″ (150µm), 0.005″ (125µm), or 0.004″ (100µm), which are optically aligned and require a pad diameter (typically 0.012″ (300µm), 0.010″ (250µm), or 0.008″ (200µm), allowing additional routing density. Microvias can be via-in-pad, offset, staggered or stacked, non-conductive filled and copper plated over the top or solid copper filled or plated. Microvias add value when routing out of fine pitch BGAs such as 0.8 mm pitch devices and below.
Additionally, microvias add value when routing out of a 0.5 mm pitch device where staggered microvias can be used, however, routing micro-BGAs such as 0.4 mm, 0.3 mm, or 0.25 mm pitch device, requires the use of Stacked MicroVias using an inverted pyramid routing technique. HIGH DENSITY INTERCONNECT PCB manufacturing process is highly dependent upon laser technology. In a PCB design, it can be all the layers which are highly dense, or interconnecting dense layers. HDI PCB applications are widely used in mobile phone designs, computer PCBs, satellites, GPS devices, automobile industries, etc.