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60 DESIGN007 MAGAZINE I JANUARY 2019 • Procuring semiconductors in a wafer format • Outsourcing metallization and thinning • Testing embedded mixed function assemblies The PCB fabricator will need to perform a full, functional electrical test at the substrate level. One question is, "How do we test, what do we test, and what features are needed to enable test?" Ideally, the originating companies will bring together the two primary suppliers: the circuit board fabrication specialist and assembly service provider. These partnerships must be willing to adjust their portion of the generated revenue against the overall process yield, which includes the sharing of losses from fabrication process defects and losses due to damaged components. DESIGN007 Vern Solberg is an independent technical consultant specializing in surface mount technology, micro- electronics design, and manufacturing technology. To read past columns or contact Solberg, click here. Using the fiducial target features on the copper surface as a guide, the components are placed into the partially cured adhesive pattern with the copper-plated terminal features of the die facing down. A thermal curing process follows to complete the bonding of the semiconductor element to the copper foil base. Resin-coated copper (RCC) foil is next laminated over the backside of die encapsulating the element. The embedded structure then follows a microvia ablation and plating procedure similar to that previously outlined. Additional circuit layers are sequentially added to complete interconnects to components mounted on the outer surface(s) of the substrate or PCB. Summary The decision to embed components within the PCB or substrate structure must be reinforced with a compelling need to improve product performance, minimize product size, or meet stringent operating environment concerns. Embedding components is not a trivial endeavor and should include a strong and reliable support group of suppliers. Key issues to be addressed include: Figure 4: Die-first (facedown) coreless assembly process sequence.