Component manufacturers continue to seek breakthroughs, adding functions and reducing size, while fan-out is left to the designer.

While the printed circuit board is composed of sheets of dielectric and conductor layers, it’s the vias that really bring a circuit to life and keep it going. Permitting signals to pass from one layer to another makes this a 3-D puzzle that can scale to a staggering number of layers.

You don’t have to go back many decades to find a time when we called them printed wiring boards. (Officially, the standards still do.) Components were mounted to what looked like a pegboard: rows of evenly spaced holes where the leads of the part extended through two or more of the holes. You just added wire. As far as routing consistency, every board was a one-off, built up one wire at a time.

Give credit to government agencies for driving PCB technology toward higher reliability. Along the way, the “industrial complex” responded with the following electronics innovations:

• Individual transistors advanced to integrated circuits using dual-inline package technology.
• Axial- and radial-leaded passive through-hole components gave way to surface mount types with and without leads.
• Quad flat packages (QFP) and similar devices came along with a full perimeter of signal pins, plus a ground slug taking the central area inside the single ring of pins.
• Ball grid array (BGA) packages now featured a partial or full field of pins.

Shortening and folding traces takes creativity and persistence, as long as the timing budget is met.

Printed circuit boards are becoming more complex, with high-speed interfaces more common. Whether it is a PCIe, Ethernet, USB or memory of some kind, clock nets proliferate across the board. Those clocks have kindred spirits in nets that want to hit the receiver in conjunction with the ticking clock.

Crucial parameters of a group of traces include the target length or maximum. Less is more. Most other signals on the board will switch periodically. Meanwhile, the clock switches all the time. The clock uses the same voltage, but the constant stream of “10101010101…” creates more energy fields than a seemingly random sequence of ones and zeros. These constantly shifting reactive clock net fields are the reason we shield the clock, giving it space to do its thing.

Shorter traces equal lower electromagnetic emissions. Shorter clocks have comparatively lower emissions and are less lossy. This gives rise to the use of available length matching tolerance to minimize the length of the clock, starting with finding the longest member of the group. Look at that net; locate any extra bends or places where it can be shortened.