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70 PCB007 MAGAZINE I MARCH 2021 Article by Catherine Shearer ORMET 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 architec- tures are emerging to meet future product re- quirements—particular- ly for mobile electronics and wireless infrastruc- ture to support indus- try megatrends like 5G and autonomous driv- ing. ere are new chal- lenges for forming elec- trical interconnections between different types of package elements while maintaining high volume manufacturabil- ity and reliability across a spectrum of operating environments. In particular, the use of high speed and high frequency dielectric ma- terials complicates the PCB fabrication process. Generally, these low- loss and low-Dk materials are not amenable 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 (such as that manufactured by Ormet) can be used to effect vias to either augment or replace sequentially formed plated micro- via interconnects, which necessitate multiple lamination cycles, as well as plated through- holes (PTH) with their attendant loss of rout- ing density and lossy stubs. TLPS-filled Z-ax- is interconnect layers can be fabricated in par- allel with individual X-Y trace layers or PCB sub- constructions of multiple layers with PTH, inter- leaved, and laminated in a single cycle. e circuit layers, thus electrically joined through the Z-ax- is, can be of the same or different materials, com- plexity and native con- struction. e adhesive surrounding the TLPS interconnects and me- chanically joining the circuit layers can be pre- preg or film adhesive and can be selected for its dielectric and mechanical characteristics. With an appropriate adhesive layer, the TLPS Z-axis interconnect concept is extendable to applications outside of PCB construction including area array assembly and thermal transfer. TLPS Paste-Filled Vias for HF PCBs

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