Rigid-flex can meet the speed you need – with the right design and materials.

I am designing G a rigid-flex and was just told it will be higher frequency. What do we have to do differently?

Answer: As the phrase goes, "I feel the need...the need for speed!" We are seeing more and more applications with signal speeds in the GHz ranges. As clock speeds on chips increase, it is important for the circuit boards to keep up the pace.

When it comes to high speed, rigid-flex is very capable of meeting the challenge. It all comes down to good design and material selections.

For the high-speed signals, think in all three dimensions. Map out which layers carry these signals. Rigid and flex layers will have different dielectrics and copper types. If all the high-speed signals reside within the rigid layers only and do not span the flex region, concentrate just on those rigid layers and associated materials. For this discussion, however, let's assume that one or more of the flex layers will be involved.

Three methods for incorporating non-heating leads into a heater pattern.

A flexible heater is needed where Constantan or Inconel is used for the heating area. Is there a way to incorporate a resistive layer into a standard flex circuit to have non-heating (copper) leads going to the heater pattern?

Answer: Yes, this is a common request and can certainly be done. Several methods are used to accomplish this, with limitations. A couple of these methods require selective plating of copper onto the resistive alloy element traces to lower the resistance, or using plated vias on other layers to make the non-heating connections. This works well on copper/nickel alloys like CuNi 715 or Constantan, but not so much so on Inconel 600 (these are the three most common resistive alloys used in flexible heater construction). The Inconel restriction is covered in more depth later in this column.