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12 The PCB Magazine • April 2015 A. Evolution of microvia laser technology In the mid 1990s, component grid pitch dropped and difficulty encountered connecting high I/O components with multilayer PTH PCB technology. Industry responded to this chal- lenge by developing microvia technology such as photo dielectric, plasma etched and laser drilling methods as well as reducing mechani- cally drilled through vias below 150 µm. How- ever, as photovia technology needs special pho- tosensitive material and plasma does not work with FR-4, laser drilling now predominates pro- duction due to its flexibility. Initially, the lasers available, TEA CO2 and UV Nd:YAG had several drawbacks limiting use- fulness and accuracy. With TEA CO2 lasers of 10600 nm wave length, an inability to drill copper and unreli- able galvanometers with slow rep rates and a tendency to miss pulses made it a difficult pro- cess. Copper apertures had to be etched as con- formal masks or windows slightly larger than the final microvias and the long wavelength of the lasers left a thin carbonized layer that had to be removed with strong desmear. mm pitch technology development work has been started several years ago for mobile termi- nals [4] . Simultaneously microvia size and pad diameter have been reduced being typically 75 µm and 200 µm, respectively. The industry is targeting to go down to 50 µm microvias and 150 µm pad size within the next few years [2] . This miniaturization is driving the line/ space and the SMT pad size reduction in any- layer HDI PCBs. As the use of the anylayer technology is enabling the miniaturization by giving more freedom for designers allowing the connections between all layers. A capability im- provement of fine line manufacturing processes is obvious and new manufacturing and process- ing solutions are necessary for the PCB industry to fulfill the requirement of these new designs. II. ALV HDI PCB Key Manufacturing Challenges The key manufacturing steps in ALV PCB miniaturization point of view are the multilayer pressing, laser drilling, imaging, etching and plating processes, and how to optimize the pro- cess for high volume, robust, reliable, and cost effective manufacturing. NExT-GENERATION ULTRA-THIN HDI PCB MANUFACTURING CHALLENGES continues FeAture Figure 2: Illustration of 0.3 mm pitch design guidelines.