The Properties of Electrical Substrate
When you hold a circuit board, a transformer component, or a high-voltage insulator in your hand, it looks like a single, solid piece of material. But to the engineers who design with it, every laminate tells a story – one written in numbers like Tg, Dk, Df, and Td.
Those numbers don’t just live in data sheets (like those offered in our laminate resource center). They shape whether a device performs reliably in a jet engine, a satellite, or the electronics inside your car. Understanding what those terms mean – and why they matter – can turn a good design into a great one.
The Hidden Language of Laminates
Every thermoset composite – from fiberglass-reinforced epoxy to advanced polyimide – has a set of performance characteristics that define how it behaves when things get hot, fast, or electrically intense. Think of these as the “vitals” of a material, the same way horsepower and torque describe an engine.
Here’s a closer look at the properties that separate everyday materials from those that push performance forward.
Glass Transition Temperature (Tg): Where Things Start to Move
If you heat a thermoset composite slowly, there’s a point where it stops acting like a rock and starts behaving more like rubber. That’s the glass transition temperature, or Tg – the threshold where molecular chains loosen up and begin to move.
Below Tg, the resin is rigid and strong. Above it, it expands and flexes. For most epoxy-based laminates, that point sits between 130°C and 180°C. Step up to high-performance polyimide systems, and you’re looking at 200°C to 250°C or more – a necessity for applications like aerospace, where sustained heat is part of the job description.
In short: a higher Tg means your part keeps its shape when the heat is on.
UL-94 Flammability: The Burn Test
Of all the material properties sought out by engineers, flammability is one of the most critical.
UL-94 is less about chemistry and more about survival. In this standardized test, a flame is literally applied to the material – and how quickly it stops burning determines its classification.
- V-0 means it extinguishes itself in under 10 seconds.
- V-1 takes a little longer but still puts itself out.
- HB burns slowly along the surface.
It’s a quick, visual way to separate materials that can handle a spark from those that shouldn’t be near one. Electrical manufacturers and aerospace engineers rely on V-0 materials to meet safety codes and peace of mind alike.
Dielectric Constant (Dk): The Speed of a Signal
Electric signals move through materials the way sound moves through air – and the dielectric constant tells you how fast that happens. The vacuum of space is a perfect 1.0. Most epoxy laminates hover around 4.0 to 4.8, while PTFE-based materials can dip below 3.0.
The lower the Dk, the faster the signal. That’s why high-frequency circuit designers chase materials with low dielectric constants – they keep signal delay, distortion, and impedance in check. In microwave and antenna applications, a few tenths of a point can mean the difference between clear reception and noise.
Dissipation Factor (Df): The Signal Saver
Even the best materials lose a little bit of electrical energy as heat. The dissipation factor measures how much. Engineers call it “loss tangent,” but you can think of it as a material’s tendency to waste signal strength.
A PTFE laminate with a Df of 0.0009 is almost frictionless for electrons, while standard epoxy materials might be around 0.02. The lower the number, the cleaner the signal. That’s why telecommunications and radar systems live and die by this metric.
Thermal Decomposition (Td): The Breaking Point
Every polymer has its limits. Push it too far, and it starts to decompose – chemically breaking down and releasing gases. The thermal decomposition temperature, or Td, marks that red line.
Measured by thermogravimetric analysis (TGA), it’s usually defined as the point where the material loses 5% of its weight. It’s not a temperature you want to reach in service – by then, blistering or charring has already begun – but it’s a good measure of long-term heat resistance.
For context, most high-reliability laminates don’t even blink until well past 350°C.
CTE and Thermal Expansion: The Silent Stress Test
When materials heat up, they expand. In the vertical (Z) direction, that expansion can wreak havoc on plated-through holes in multilayer PCBs.
That’s where the coefficient of thermal expansion (CTE) comes in – usually expressed as a total percentage change from 50°C to 260°C. A standard polyimide might expand about 1.2%, while a filled epoxy composite can cut that in half.
Less expansion means less stress – and a longer-lasting board.
Thermal Conductivity: The Heat Highway
Every engineer knows heat is the enemy of longevity. The hotter a component runs, the faster it fails.
That’s why thermal conductivity – measured in watts per meter-Kelvin – is a big deal. It determines how quickly a material can carry heat away from a hotspot. Even a modest improvement can double service life for every 10°C drop in temperature.
In practical terms, materials with higher thermal conductivity help keep components cool, circuits stable, and designs running for years instead of months.
Copper Peel Strength: Holding It Together
Copper peel strength might not sound glamorous, but it’s a measure of reliability at the microscopic level. It defines how tightly copper foil sticks to a laminate under heat and stress.
Good adhesion depends on chemistry, resin formulation, and processing – and it’s what prevents delamination during soldering, machining, or use. In high-performance laminates, peel strength becomes the glue that keeps everything together, both literally and figuratively.
Water Absorption: The Unseen Threat
Water and electricity don’t mix – especially in precision composites.
A material that absorbs too much moisture (anything over about 0.2%) can swell, blister, or change its dielectric properties. PTFE-based laminates, by contrast, practically shrug off moisture, keeping electrical performance stable even in humid environments.
Putting It All Together
Each of these properties interacts with the others in a delicate balance. Lowering Df might mean higher cost. Boosting Tg might slightly reduce adhesion. The art of engineering lies in finding the right combination for the job.
That’s why Atlas Fibre engineers work closely with designers and sourcing teams to align material properties with real-world demands – from temperature cycles and vibration to electrical precision and mechanical load.
Because in the end, numbers don’t just describe performance. They define it.