Choosing the Right Substrate for Flexible Heaters: A Guide to Copper, Stainless Steel, and FeCrAl

Introduction

Developing a heating element for a small medical device or a rugged outdoor sensor presents a unique thermal engineering challenge. The solution usually does not lie with the heater, but instead with the substrate. Flexible heaters are an effective modern solution to these complicated thermal challenges. However, the performance of the flexible heater is determined by the substrate material on which it is constructed. Many flexible heaters are constructed on polyimide or silicone, but there are a few applications that require the unique properties of a metal substrate.

This guide will provide technical details for three typical metal substrates - Copper (Cu), Stainless Steel (SS), and FeCrAl - to guide the engineer in their substrate choice. Identifying and learning about the specific metal substrate properties are the first steps for an engineer to design an efficient and reliable thermal solution.

What is a Substrate in Flexible Heaters?

Within a flexible heater, the substrate is where the resistive heating element circuit is applied directly as either an etched or bonded layer to the substrate. The substrate provides the structure of the heater while having an impact on the mechanical, thermal, and electrical performance. The substrate selection will influence the flexibility, durability, and heat distribution efficiency of the heater. With that in mind, metal substrates are usually the best option for situations where heat needs to be dissipated quickly or situations with extreme conditions.

Why Your Substrate Choice is Critical for Heater Performance

Choosing the appropriate substrate is an important design decision that affects all aspects of a heater's capability. The material qualities of the substrate are not inert but actively play a role in the heater's performance profile.

● Thermal Management: The substrate's thermal conductivity is extremely important. A substrate with high thermal conductivity (ex, copper) will distribute heat uniformly and rapidly across a surface, which is critical to minimize localized heating and the formation of hot spots and quickly reach uniform temperature. A substrate with lower thermal conductivity will, in turn, help to focus thermal energy only to select areas.  

● Electrical Properties: The electrical resistivity of the substrate will contribute to the final resistance of the heating circuit. Higher resistivity materials like Stainless Steel and FeCrAl are often better candidates for substantial resistance values where less area is occupied.

● Mechanical Durability: The desired durability that the application must endure is dependent on the environment. Applications like industrial machinery or parts in a vehicle will benefit from a substrate like stainless steel (SUS304). It provides numerous positive performance traits like strength and corrosion resistance while benefiting from a long operational life.

● Cost and Manufacturability: The material is a direct contributor to the resulting cost associated with the material and the bill of materials (BOM). Also, complicated shapes and cutouts are achievable with a feasible partner who specializes in cut portions and custom cut-outs.

Conventional, available heaters fall short in real-world applications because they can't handle unique environmental or geometric shapes... Dealing with trade-offs requires a solution that conforms to your design, versus the other way around. JLCPCB Flexible Heater features 100% customizable options, so every engineer doesn't have to worry about being limited to standard options. You define not only the substrate material, but the power density, dimensions, and shape—even for highly irregular geometries and complex cutouts and inner holes. This defined solution guarantees a perfect fit and is designed to optimize efficiency and performance specific to your application.

A Deep Dive into Common Metal Substrates

Copper Substrates: The High-Conductivity Choice

Copper is well-known for its high conductivity, which is why it is commonly the substrate of choice in thermal management applications. When it is used as a heater substrate, it will provide the best possible transfer of heat generated by the resistive element to the surface around the heater.

● Key Properties: Copper features the very highest thermal and electrical conductivity of any base non-precious metal. It is also very malleable to allow it to shape in complex forms without fracture.

● Advantages: The primary advantage of using copper as a heated substrate is its rapid-heating feature and its ability to efficiently redistribute heat, effectively reducing thermal gradients and producing uniform heat performance on the entire heated surface.

● Common Applications: Medical devices, high-performance compute systems, and systems utilized to warm the battery in an electric vehicle would be strong candidates for such a heater substrate due to heater placement and precise temperature control requirements.

Stainless Steel (SUS304) Substrates: The Durable Workhorse

Stainless Steel (specifically grade SUS304) is an excellent material for applications requiring durability and longevity. It provides a compromise between excellent thermal qualities, strength, and cost.

● Key Properties: Stainless steel is an alloy of metal that offers high tensile strength, as well as excellent properties against corrosion and protection against moisture and chemicals. Its thermal conductivity is lower than copper, while its electrical resistivity is quite higher than copper.

● Benefits: Its durability makes it a great material for rugged industrial, automotive, or outdoor environments. In addition, its higher resistivity allows for a better design of heater circuits, and its oxidation resistance allows the heating element to last longer.

● Applications: Commonly used for industrial process heating, food service equipment, automotive components, or electronics enclosures in a harsh environment.

FeCrAl Substrates: The High-Temperature Specialist

FeCrAl alloys (Iron-chromium-aluminum alloy) are a type of material devised for high-temperature applications. When the conditions become too extreme for copper or stainless steel, FeCrAl becomes the substrate material of choice.

● Characteristics: The defining characteristics of FeCrAl are its very high electrical resistivity and the ability to develop a stable protective aluminum oxide layer at elevated temperatures. The protective layer will keep the base alloy from oxidizing and allow for reliable operation at temperatures that would destroy the other metals.

● Benefits: It will operate at higher temperatures and allow for very high-power densities. This means it can be used in applications requiring extreme or concentrated heat.

● Uses: FeCrAl alloys are also commonly used in laboratory equipment, analytical usage, and industrial heaters that require a strong, high-temperature performance.

Substrate Comparison: Copper vs. Stainless Steel vs. FeCrAl

To simplify the selection process, it's helpful to see a direct comparison of these materials. The material you choose will always be a trade-off between thermal performance, durability, and cost. Below is the material properties chart for substrates available from JLCPCB Flexible Heater, followed by a summary comparison.

Comparison table of copper vs. stainless steel vs. FeCrAl substrate material properties for flexible heater design.

How Substrates Are Integrated into Flexible Heaters

In most cases, a metal substrate heater will have a chemically etched resistive circuit pattern onto the substrate material surface. This will enable consumers to have intricate and exact heating paths for their application.

To simplify this, JLCPCB Flexible Heater has a user-focused engineer platform. Designers may upload their plans readily in a simple file format, such as Gerber, DXF, or DWG, reducing the technical barriers from design to manufacturing. The intended performance of any design depends on the precision of the manufacturing process, and JLCPCB Flexible Heater maintains exact tolerances in an effort to provide precision manufacturing, such as maintaining 0.5-1.0mm on dimensions and resistance values of ±5%. The result is a product that will have the same intended behavior as the original design. If aesthetics are important to the application, there is also a 100% visual inspection service available as an optional add-on to ensure critical quality control.

Conclusion: Making the Right Choice for Your Project

The ideal flexible heater substrate depends on the requirements of your application, including temperature, speed, environment, and cost. There is no "right" material, just the most appropriate for your design. The most important thing is to weigh the trade-offs: choose Copper for speed and uniformity, Stainless Steel for durability in a tough environment, and FeCrAl when high heat is essential.

Transitioning from theory to prototype doesn't have to be complex or costly. JLCPCB Flexible Heater provides a one-stop shop for all your thermal integration needs, all organized to improve R&D efficiency. The full customization experience is offered through a simple online closed-loop: Quote → Pay → Track → Receive. Our online pricing structure allows for complete transparency and removes any back-and-forth. We also do not enforce a minimum order quantity (MOQ). We provide rapid iterations of single prototypes for customers to re-iterate their designs, and can ship small batches in as quickly as 72 hours, so you can test your designs faster than you ever thought possible.

FAQs

Q: How does the substrate thickness influence the heater performance and flexibility?

A: The thickness of the substrate will influence the thermal Mass of the heater, and its mechanical flexibility. A thicker substrate will be stiffer and can support more power and likely provide better heat distribution. A thinner substrate will allow better flexibility and will enable the heater to conform to tighter curved surfaces. It will also heat up more quickly with its smaller thermal mass. This means deciding between flexibility and durability with your application.

Q: Can I ask for a different substrate material that is not specified like pure copper for my custom heater?

A: Yes. You can request that option. We standardize on materials that are commonly used, like Copper, Stainless Steel (SUS304), and FeCrAl, because each has been used successfully for heaters. However, if you needed to explore the possibilities of other option requests, we can look at that option. If you needed a requirement such as pure Copper for thermally conductive purposes, simply leave a note in the remark field when you place the order. Our Engineers will review it because they will be able to accommodate your design requirement.

Q: Besides the substrate, what other custom options does JLCPCB Flexible Heater offer?

A: JLCPCB Flexible Heater supports full customization to meet your exact needs. This includes specifying power density, overall dimensions, and preassembled wiring to install easily with optimized layouts. Our one-stop services also include free circuit design support and consultations with our experts to help you qualify prototypes faster. Upon request only, we perform 100% resistance testing, and we will perform thorough visual inspections to confirm that every piece of your order will be manufactured to the highest quality.

Q: How can I provide my design for a complex custom-shaped heater?

A: For high-quality production, we recommend turning in the design as a Gerber file (packaged as a ZIP or RAR) or as a CAD drawing in DXF or DWG. We've designed our platform to be engineer-friendly, accepting all standard file types (up to a file size of 100MB), so that you can express highly irregular geometries, cutouts, or inner holes.