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40 PCB007 MAGAZINE I AUGUST 2019 High-density interconnect (HDI) demands that vias that do not contain component leads be plugged with either a polymeric paste or electroplated copper. In this column, the tech- nology drivers for via filling/plugging in the context of HDI are presented. Performance-driven electronic systems con- tinue to challenge companies in seeking a more innovative semiconductor package methodol- ogy. The key market driver for semiconductor package technology is to provide greater func- tionality and improved performance without increasing package size. As semiconductor die elements shrink in size, companies are seek- ing to further increase package density and en- hance functional performance. This, in turn, drives designers to expand the current role of the interposer to interconnect both heteroge- neous logic functions and homogeneous mem- ory within a single package outline. The package interposer is the key enabler; this is especially true as glass-reinforced, ep- oxy-based materials, and high-density copper interconnect capability will continue to carry a primary role for array configured packag- ing. From a PCB fabrication standpoint, engi- neers must adopt the manufacturing processes to include via fill and via plugging technolo- gy. I will dive into details of these processes over the next few editions of "Trouble in Your Tank." However, this particular column will fo- cus on the need for via filling and some of the methods used to carry out the process. Why Fill Vias? Microvias, buried vias, and plated through- holes are filled with conductive or non-con- ductive materials for a number of reasons: • Improved reliability (avoidance of trapped air or liquids) • Improved planarity of multilayer structures (for more reliable surface mount or improved photolithography) • Higher interconnect density (e.g., via-in- pad vs. dog bone designs, Figure 1) Via Hole Filling and Plugging, Part 1 Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY Figure 1: Via-in-pad versus dog bone design.

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