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24 DESIGN007 MAGAZINE I JANUARY 2023 Feature Article by Lee Ritchey SPEEDING EDGE As the aerospace industry has been tasked with fitting increasingly complex electron- ics in existing airframes the demands on PCB substrates have begun to overtask the existing state of the art in PCB fabrication. Recently, I was called in to troubleshoot some reliability problems with a very dense PCB that had components on both sides and required the use of stacked blind vias and bur- ied vias. e usual name for this kind of design is "build-up fabrication," requiring many trips through the lamination, drilling, and plating operations at a fabricator. e designers decided to reach down from the outer layer to the third layer below the sur- face using stacked blind vias, much like that shown in Figure 1. e process used to create the structure in Figure 1 is to fabricate a PCB using the ordi- nary lamination, drilling, and plating pro- cesses employed for any multilayer PCB. Once this is done, a laser drill is used to create the Figure 1: An example of stacked microvias.

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