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66 SMT007 MAGAZINE I DECEMBER 2020 Article by Maarten Cauwe, et al. IMEC-CMST, ET AL. Abstract High-density interconnect (HDI) printed cir- cuit boards (PCBs) and associated assemblies are essential to allow space projects to benefit from the ever-increasing complexity and func- tionality of modern integrated circuits such as field-programmable gate arrays (FPGAs), dig- ital signal processors (DSPs), and application processors. Increasing demands for function- ality translate into higher signal speeds com- bined with an increasing number of I/Os. To limit the overall package size, the contact pad pitch of the components is reduced. The combination of a high number of I/Os with a reduced pitch places additional demands on the PCB, requiring the use of laser-drilled microvias, high aspect ratio core vias, and small track width and spacing. While the asso- ciated advanced manufacturing processes have been widely used in commercial, automotive, medical, and military applications, reconcil- ing these advancements in capability with the reliability requirements for space remains a challenge. This article provides an overview of the ongo- ing European Space Agency (ESA) project on high-density PCB assemblies, led by imec with the aid of ACB and Thales Alenia Space in Bel- gium. The goal of the project is to design, eval- uate, and qualify HDI PCBs that are capable of providing a platform for assembly and the routing of small pitch AAD for space projects. Two categories of HDI technology are consid- ered: two levels of staggered microvias (basic HDI) and (up to) three levels of stacked micro- vias (complex HDI). In this article, the quali- fication of the basic HDI technology in accor- dance with ECSS-Q-ST-70-60C is described. The results of the thermal cycling, intercon- nection stress testing (IST), and conductive anodic filament (CAF) testing are provided. The test vehicle design and test parameters for each test method are discussed in detail. Introduction Two main drivers are commonly identified for HDI PCBs: (1) the small pitch and high number of I/Os of key components and (2) the increas- ing performance of these components resulting in high-speed signal lines on the boards. The use of microvias allows reducing the length of High-Density PCB Technology Assessment for Space Applications

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