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48 The PCB Magazine • October 2017 crovias now provides an advantage. Looking at the simple lumped models of PCB vias in Fig- ure 6 shows that the smaller microvia has near- ly 1/10 th the inductance and capacitance of a through-hole via. Via-in-Pad and Short Via Lengths Bogatin's article provides the partial self-in- ductance of a microvia 2 mils deep and 1 mil in diameter as less than 10 pH (where pH = pico- HDI'S BENEFICIAL INFLUENCE ON HIGH-FREQUENCY SIGNAL INTEGRITY Henrys), while a drilled via, 10 mils in diameter and 32 mils deep has a partial self-inductance of almost 200 pH [2] . This is significant for high- er frequency designs. Bogatin goes on to point out that at 300 MHz, the impedance of an HDI microvia is only 18 milliohms compared to the through-hole via which is 400 milliohms. The via-in-pad reduction of inductance is even more dramatic. One of the largest sourc- es of inductance to devices and decoupling ca- Figure 6: Via comparison. Figure 7: Loop difference.