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50 DESIGN007 MAGAZINE I NOVEMBER 2018 proper control over solder printing processes for outer surface component attachment. When the thickness of component parts is greater than 0.2 mm, it can result in a slightly raised surface area at each component loca- tion. The raised areas will continue to impact the planar condition of each additional circuit layer resulting in irregular outer surface topog- raphy. For components with a thickness greater than the prepreg material, it will be necessary to provide a cavity in the dielectric, which was also detailed in Part 4. The cavity feature is generally prepared within the dielectric lay- ers before lamination. The opening can be mechanically punched, laser ablated, or milled while the material remains in the sheet form. Embedding discrete component elements within the PCB structure is not a trivial pro- cess. Embedded components will increase the cost of the raw board, so a thorough technical evaluation must be made to justify implemen- tation based on fabrication, product volume, and projected life cycle. Next month, Part 6 of this series will con- sider alternative techniques for embedding active semiconductor elements, die prepara- tion, and mounting and termination method- ologies. DESIGN007 Vern Solberg is an independent technical consultant specializing in surface mount technology, microelectronics design, and manufacturing technology. To read past columns or contact Solberg, click here. conductive polymer to terminated embedded components, a plated copper microvia can be a less complex method for providing the electri- cal interface. However, to prepare for this termination alternative, the passive devices selected for direct microvia interface must be furnished with copper alloy-plated terminals. Although copper-plated terminals are not generally stocked in the commercial component distri- bution channels, they are an available option by ordering the components directly from the manufacturer or through the manufacturer's representative. The basic component attachment process begins with the deposition or printing of a small amount of non-conductive adhesive material at the designated attachment sites followed by the precise placement of the devices and thermal curing to lock the com- ponents in position. A layer of resin-coated copper or glass-reinforced prepreg material is then laminated over the passive components, fully encasing them with the polymer material. The process employs both heat and pressure to complete the lamination. Next, laser abla- tion of the microvia holes over the terminals of the components is performed, followed by copper plating, imaging, and an etching pro- cess to complete the mechanical and electrical interface between the passive device terminals and upper layer circuit pattern. When micro- via plate termination and etch processes are complete, the substrate is made ready for addi- tional build-up circuit layering (Figure 2). A primary concern is the post-lamination surface condition. The outer surfaces of the finished circuit board must remain flat to have Figure 2: A 01005 microvia termination. (Source: IPC-7092)