TECs can be a countermeasure to high current density.

Thermoelectric cooling, or TEC, is seen as a breakthrough in small refrigerators that do not consume a lot of power. Sporting goods stores carry micro-fridges that plug into a car's weird circular power plug. Some of us – not me, of course – can remember when those plugs were used to create a glowing hot element to light cigarettes. Getting cold out of the same socket took a little more technology than creating a short circuit.

Where would you use a TEC device? Aside from keeping a six-pack (or a transplant organ) on ice, electronics can be kept at a reasonable operating temperature with the addition of a component or a cold plate like the one in FIGURE 1. It is 40mm square and 3.2mm thick. The basic function is that it gets cold on one side while getting warm on the other. Put it in the other way to warm up the contents. This can be placed below the board or above the high load component if it has a flat top. More remote placement is possible by incorporating a heat spreader. We'll circle back to that shortly.

Figure 1. A TEC device. (Amazon)

Leave more metal behind.

Being cool used to be easy. Modern times call for a more comprehensive approach to keeping the lights on when it comes to our PCB layouts. The early days of electronics saw through-hole components bearing a single transistor that sat well above the board much like a water tower commands the skyline in a pastoral setting.

The device was free to blow off as much steam as required without scorching the stuff we call FR-4. Fun fact: Did you know that the FR in FR-4 stands for “fire retardant” and that 4 is the number of iterations that lead to the resin/glass combo that undergirds our industry’s history to this day? The material is rated by its ability to withstand high temperatures without breaking down.

One of the most important characteristics of FR-4 is the glass transition temperature, or T_g, where the material simply melts down and fails. It is measured in centigrade, and a working number is between 140° and 170°. That will not be sufficient for extreme environments and hard-working chips. There may be exceptions but you’re nominally looking at exotic dielectric materials that are meant to cater primarily to data centers and broadcast scenarios. The ancient art of ceramics plays a part in withstanding higher temperatures for devices and PCB laminates.