Voltage, heater size and material costs all factor into the decision process.

I would like to use a flexible heater in a product I am designing, but I am concerned about cost. Flexible heaters typically seem a lot more expensive than regular (copper) flexible circuits. What is the advantage to using a resistive metal? Why not just use copper for all flexible heaters?

Copper can certainly be used for the heating element material in a flexible heater in many applications. When a design permits copper to be used for the heater, that will usually be the most cost-effective way to go. But how do you know if copper is a good choice for an application?

Cost impacts of copper heating element. The first hurdle to clear to ensure copper is a good cost-effective solution for a heater is the electrical resistance requirement. The biggest problem with using copper as the heating element is that it has very low coefficient of resistance. To get any appreciable resistance in the heating area, very thin copper must be used and element traces made very narrow in order to pack as many lineal inches into the heating area as possible. Both these will work against your goal of reducing costs. Also, base laminates that are clad with less than 0.5oz copper thickness are typically more expensive due to their fragile nature, and industry use of materials this thin is far less than use of 0.5oz or 1oz copper thicknesses. Another drawback of narrow traces is that the manufacturer's yields will be less optimal, which in turn equates to a higher selling price of the end-product. Another downside to incorporating very narrow traces that many designers fail to take into account is the trace width variations from part to part due to etch tolerances.

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.