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18 PCB007 MAGAZINE I SEPTEMBER 2023 What is Ultra HDI? Feature Article by Happy Holden I-CONNECT007 Ever since high density interconnect (HDI) was created in 1982 by Hewlett-Packard to package its first 32-bit computer powered by a single chip, it has continued to evolve and pro- vide the solutions for miniaturized products. e leading edge of HDI technology became the process used for organic flip-chip packag- ing for the semiconductor industry. e two distinct markets—IC substrates and product- system integration—are now colliding and utilizing the same ultra-HDI manufacturing processes (Figure 1). Introduction ese two markets have different characteris- tics as well as specifications. e middle ground is currently occupied by the very high-density PCBs called substrate-like PCBs (SLPs). e differences lie in that IC packaging is for components of unspecified final applica- tion while an HDI PCB is the result of a sys- tem-integrated product. But time and evolu- tion have introduced a semiconductor com- ponent system integration strategy which the IEEE now calls heterogeneous integration (Figure 2). To meet this construction, a new player called the interposer was created in the substrate arena. SLP vs. Interposer is collision of two different products is where UHDI characteristics and specifications Figure 1: Conventional PCB manufacturing is now entering the domain of advanced IC substrate manufacturing characterized by geometries of equal to or greater than 30 µm. (Source: Inspired by IEEE HI-Roadmap 1 )