And why not to cut the ground or Vdd plane.

Speculation abounds over what a designer should do when making the stackup and design rules for a four-layer PCB. Much of this speculation or rules-of-thumb came about when those not familiar with the reasons for arranging the layers in a four-layer PCB tried to explain what they saw or heard. This article explains how four-layer PCBs came into existence and guides readers on how to create a set of design rules and stackup that results in a solid, functional design with minimum constraints.

Early logic designs were done with two layers. Power was distributed using traces to connect all the power and ground pins to the power supply rails. Logic devices were packaged in 14- and 16-lead dual inline packages (DIPs). FIGURE 1 is an example of such a two-layer logic design. Logic speeds were slow enough that connecting power with traces instead of planes was “good enough.” Figure 1 is a design the author did using Bishop Graphics tape to create the artwork in the early 1970s.

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