Constantan Flexible Printed Circuit (FPC), Constantan Flexible PCB

Constantan Flexible Printed Circuit Board (PCB, FPC)

MADPCB can work with a wide variety of flex circuit materials to give you the electrical and mechanical performance you require. However, to get the lowest possible cost for your flexible circuit, it’s advisable to design your circuit using standard materials whenever possible. Using uncommon conductor materials, like constantan, Cupro-Nickel; uncommon polyimide thickness, like 4mil, 5mil PI core; uncommon conductor thickness, like 2oz, 3oz, …, 5oz; in your design can add significantly to both the cost and the lead time of your circuit. While, our emphasis on quality and design for manufacture has led us into every application across a huge range of markets in all areas. Constantan FPC (flexible printed circuit) is not commonly used because of its difficulty to be manufactured with. Our experience has led to further constantan-related capacities including adhesive constantan laminates and controlled resistance via copper micro plating.

What’s Constantan Flexible Circuit?

The conductive materials of flexible circuit (FPC) can be copper, constantan, cupro-nickel, inconel, silver filled epoxy, carbon and Aluminum. What’s Constantan Flexible Circuit (FPC)? Constantan FPC (also variously referred to around the world as constantan flexible circuit, constantan flex circuit and constantan flex PCB), is a flexible circuit, in which the conductive circuit patterns are etched and built by constantan, which is a copper-nickel alloy that consists of 55% copper and 45% nickel. The electrical and thermal conductivity of copper make it an obvious choice as a conductor in printed circuit board (PCB) construction, but in many applications that require flexible circuit boards, constantan can be far more suitable. Those applications include conditions or extreme heat or cold, where copper’s low resistance becomes a liability. Constantan is one of several metals that has proven effective for its higher resistance and lower thermal conductivity. Constantan in flexible PCBs is an ideal choice for many applications.

 Why Constantan Flexible PCB?

Some flexible PCBs need to work in extreme cold circumstances, like in 0 Kelvin (-273.15oC). How can you solve the leakage of coldness? Or your flexible circuit is designed for hot circumstances, like 373.15 Kelvin (100oC), how can you solve the leakage of warm? Maybe you have some experience with flex circuits in that range of temperatures, but you must be aware that using copper conductors (/traces) you can not get rid of the leakage of warm and coldness. Now, you may consider using constantan in your flexible PCB, because the main feature of constantan is the very low Temperature Coefficient of Resistance (TCR), which is constant over a wide range of temperatures. That’s the point of why you need to choose constantan flex PCB. Constantan is typically used in flex PCB applications such as strain gauges, thermo couples and infrared imaging.



Electrical Resistivity at Room Temperature

4.9×10-7 Ω·m

Temperature Coefficient at 20 °C

8 ppmK-1

Temperature Coefficient -55 to 105 °C

±40 ppmK-1

Thermal Conductivity at 23 °C

19.5 W/(m·K)

Surface Finish of Constantan Flexible PCB

All of our flexible circuits can be built with a combination of stiffener areas in rigid or polyimide, plated or unplated with various surface finishes, such as immersion gold, immersion silver and immersion tin, onto the RA or ED copper surface. But constantan FPC is special, which is built with constantan but not copper. Constantan is a copper-nickel alloy (55% copper and 45% nickel), which features with high resistance and lower thermal conductivity. If apply any surface finish onto the large constantan-pouring areas, the constantan flex PCB will lost its characteristics; If apply onto a few constantan pads on terminals, the affects will not much. But do you know what the surface finish of constantan flexible PCB? It's dependable on different areas.

  • Constantan Fingers: The exposed constantan areas are a few fingers, which need to plug into a connector on another device. In such designs, the surface finish can be immersion gold and hard gold.

  • Constantan PADs: Constantan PCB has such design is very few, and we can only apply immersion gold on the PADs, or leave the constantan pads empty with no surface finish.

We can apply immersion gold or hard gold -gold on nickel. But for hybrid multilayer constantan PCB, there is only one constantan layer, which is always in between other copper layers. Then the exposed surface are copper pads, copper annular rings, testing points and other elements need to explosure. In this structure, the surface finish can also be immersion gold and hard gold. Through many experiments, MADPCB knows how to achieve the best surface finish on constantan FPC.

Constantan flexible PCBs are mostly used as flex cable or antenna, in which the constantan exposed area is few, and may only annular rings. For this kind constantan flex PCB, we need to make it as a three layers constantan flexible circuit. Why? because can not apply any kind surface finish directly onto the surface of the constantan to break the unique characteristics of constantan. Adding two outer copper layers, then only keep the annular rings and etch off all other copper. In next steps, we need to do electroless copper plating, copper plating and make it a plated through holes (PTHs). Then it becomes a common flexible circuit, we can do any kind surface finish on it.

Layer Count of Constantan Flex PCB

Constantan flex circuits can be printed single- or double-sided, multi-layer, or in combinations of rigid and flexible PCBs. But the constantan trace widths and spacings are big enough. Different types or layers require unique processing in their fabrication. The choice for many designs includes thin, durable, material like constantan in flexible PCBs. Constantan’s resistance remains stable across an extreme range of temperatures as well as in high pressure and other stressful situations. These qualities have made constantan foil a desirable conductive material for flex circuits designed for hostile operating environments and rugged electronics.

In addition to solving the problem of thermal conductivity due to extreme external temperatures, constantan flexible PCB can help maintain long-term reliability in situations when internal temperatures remain high. As electronics become faster and smaller, they require innovative designs and materials to deal with heat buildup. Along with the effective design of heat sinks and air flows, the use of constantan as a conductor can lower thermal conductivity in flexible PCBs.

MADPCB uses state-of-art automated equipment to maintain in the highest quality standards and ensure that the products we manufacture exceed all specified IPC Class 2 and Class 3 requirements. We support prototype and low-to-high volume constantan flexible PCB manufacturing. We pride ourselves in being a true constantan flex PCB cost provider if highly reliable and competitive products. Contact us for more information about constantan flexible circuit (FPC) design, manufacturing and assembly, or request a quick quote.