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80 DESIGN007 MAGAZINE I JULY 2019 reference pads is 250 µm; from the measure- ment, the actual diameters of the reference pads are well within the tolerance target ±10 µm. Two sizes of microvias were drilled using mechanical drill bits: 150 µm and 250 µm. Fig- ure 6 shows the 150 µm microvias. Figure 7 shows an enlarged view of the microvias and actual measurement. With printed pads as ref- erence, the quality of the drilled microvias can be readily examined. Figure 8 shows the drilled microvias 250 µm in diameter and Figure 9 shows an enlarged view of the microvias and actual measure- ment. With printed pads as a reference, the Figure 6: Drilled microvias in 150- µm diameter. Figure 8: Drilled microvias 250 µm in diameter. Figure 7: Measurements of the drilled microvias (150 µm).