3.1.1 HDI/SBU PCB

The abbreviation HDI stands for “high-density interconnect”. It is used to describe printed circuit boards that have a high packing density and so enable optimum miniaturization to be achieved. Blind vias, microvias, and buried vias are typically used within this context, along with thin conductor widths and narrow conductor spacing. To achieve the HDI properties, the SBU construction method is often used because of its special capabilities. For this reason, both abbreviations – HDI and SBU – frequently appear together.

SBU stands for “sequential buildup”. With this method, multilayer PCBs are built up layer by layer (sequentially) in several pressing cycles. In contrast to multilayer PCBs that only undergo pressing once, the SBU approach allows components to be connected to each other in a more complex way, as buried vias (of various designs) can be additionally incorporated as part of the process. As the SBU method generally involves the creation of HDI (high-density interconnection) PCBs, both abbreviations – SBU and HDI – usually appear together.