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40 PCB007 MAGAZINE I JUNE 2021 Article by Catherine Shearer and Gary Legerton EMD ELECTRONICS, SAN DIEGO, CALIFORNIA Abstract e electronic packaging industry is un- dergoing a revolutionary convergence be- tween the printed circuit board segment and the semiconductor packaging segment. New, streamlined and hybrid package architectures are emerging to meet future product require- ments—particularly for mobile electronics and infrastructure to support industry mega- trends like 5G. ere are new challenges for forming electrical interconnections between different types of package elements while maintaining high volume manufacturability and reliability. In particular, the use of high speed and high frequency dielectric materials complicates the PCB fabrication process. Generally, these low-loss and low Dk materials are not amena- ble to multiple lamination cycles due to the na- ture of their chemistry; however, convention- al PCB fabrication techniques that circumvent this problem by using plated through-holes in- troduce undesirable resonance structures and consume precious real estate that could other- wise be used for routing. Transient liquid phase sintering (TLPS) paste vias can be used to either augment or re- place sequentially formed plated microvia in- terconnects, which necessitate multiple lami- nation cycles, as well as plated through-holes (PTHs) with their attendant loss of routing density and lossy stubs. TLPS-filled Z-axis in- terconnect layers can be fabricated in parallel with individual X-Y trace layers or PCB sub- constructions of multiple layers with PTH, in- terleaved, and laminated in a single cycle. e circuit layers thus electrically joined through the Z-axis can be of the same or different mate- rials, complexity, and native construction. e adhesive surrounding the TLPS interconnects and mechanically joining the circuit layers can be prepreg or film adhesive and be selected for its adhesive, dielectric, and mechanical char- acteristics. With an appropriate adhesive lay- er, the TLPS Z-axis interconnect concept is extendable to applications outside of PCB TLPS Z-Axis Interconnect Solutions for Thermal Transfer and Electrical Connection in PCBs

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