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56 PCB007 MAGAZINE I SEPTEMBER 2022 Summit Interconnect's Gerry Partida recently spoke with the I-Connect007 Editorial Team about his research into root causes of weak microvias. Rather than a single manufacturing process cause, Gerry suggests that microvia reliability is the culmination of several mate- rial interactions and that contrary to popular belief, microvias can still be stacked in small, tight packaging densities. He highlights the need for simulation, as well as some of his find- ings that he plans to publish in a paper at IPC APEX EXPO 2023. Nolan Johnson: Gerry, I understand your team has been doing some research into microvia stacking and will have a paper at the upcoming IPC APEX EXPO on this topic. What have you been learning? Microvias Can Be Stacked in Certain Packages Gerry Partida: Remember back in the early days of HDI, we would stack microvias as deep and plentiful as we wanted to? en people started experiencing intermittent failures. Boards got hot, the components would fail, and it went back and forth. Manufacturing did something wrong, the assembler overbaked the boards, and it would go back and forth again. A lot of designs started to suffer, especially certain mil- itary products that would stack microvias. We would ask, "Why isn't it working? Why does it work when it does work?" Most of the micro- vias that were stacked originally were small BGA packages. ey were 0.4 mm or 0.5 mm, and those densities drove you to stack. ese designs oen were for the commercial OEMs, but if something failed, the commercial guys didn't come back to discuss the issues. Interview by the I-Connect007 Editorial Team

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