Many of today's PCBs adhere to a high-density interconnect (HDI) design, which incorporates a higher wiring density than traditional PCBs. HDI circuit boards require less space and can accommodate more components. The design also makes it possible to create more compact PCBs, which weigh less and require fewer materials. The HDI design is well-suited for use cases where space ... http://hycxpcba.com/blogs/What-is-PCB.html