Heat moves through electronics via conduction, convection, and radiation. Thermal conductivity (W/m·K) measures how well a material conducts heat by conduction: copper (395 W/m·K) and aluminum (200 W/m·K) lead in PCBs and heatsinks, while thermal interface materials fill microscopic gaps to keep junction temperatures under control.
Every PCB designer eventually runs into the same wall: a part gets hot, a datasheet lists a mysterious θJA number, and a board that worked fine on the bench starts throttling in an enclosure. This guide breaks down heat transfer and thermal conductivity from first principles, then shows how to apply the numbers when you’re selecting components and planning a thermal budget.
What Is Heat Transfer? The Three Modes Explained
Heat transfer describes how thermal energy moves from a hotter region to a cooler one, and it happens through three distinct mechanisms.
- Conduction — heat moves through direct contact between materials, driven by vibrating atoms and, in metals, free electrons passing energy along. This is the dominant mode inside a PCB, through a component’s leadframe, and across a heatsink base.
- Convection — heat is carried away by a moving fluid, typically air. Natural convection relies on buoyancy from warm air rising; forced convection uses a fan or blower to move more air across a surface and remove heat faster.
- Radiation — heat is emitted as electromagnetic waves and doesn’t require a medium at all. It’s usually a minor contributor in low-power electronics but becomes significant in high-temperature or vacuum applications like satellites.
In a typical PCB assembly, all three modes act together: conduction pulls heat from a chip’s die to its case and through the board’s copper layers, then convection and radiation carry that heat into the surrounding air or enclosure.
A Practical Heat Transfer Guide for Electronics Design
Turning these three modes into a working thermal design means identifying the dominant heat path and reducing resistance along it:
- Find the power dissipation. Calculate or measure worst-case wattage, not just rated power.
- Identify the heat path. Trace heat from the junction to the case, then to the PCB or heatsink, then to ambient air.
- Check resistance at each interface. Every solder joint, thermal pad, and air gap adds resistance, in °C/W.
- Add margin for enclosure effects. A part that runs cool on an open bench can run hotter once sealed inside an enclosure.
- Validate with a thermal resistance calculator or simulation before finalizing a layout, especially for MOSFETs, regulators, and LED drivers.
Datasheets publish junction-to-ambient (θJA) and junction-to-case (θJC) thermal resistance, both defined under JEDEC’s JESD51 test standards. θJA covers the full path to open air; θJC isolates just the path to the case, which matters most once an external heatsink is added.
Thermal Conductivity Explained: What the Numbers Actually Mean
Thermal conductivity (k) quantifies how efficiently a material conducts heat, measured in watts per meter-kelvin (W/m·K). A higher k means heat moves through the material faster for a given temperature gradient and cross-section.
The relationship is captured in Fourier’s Law of heat conduction:
Q = k × A × (ΔT / d)
Where Q is the heat transfer rate (watts), k is thermal conductivity, A is the cross-sectional area, ΔT is the temperature difference, and d is the material thickness. This equation explains why a thin, wide copper plane moves heat more effectively than a thick, narrow one — more area and less distance both reduce thermal resistance.
Using a Thermal Conductivity Calculator to Estimate Temperature Rise
A thermal conductivity calculator applies Fourier’s Law (or the equivalent thermal-resistance form, R = d / (k × A)) to estimate how much a material or interface will heat up under a given power load. To run a quick manual estimate:
- Determine the power (Q) the component dissipates, in watts.
- Look up or measure the thermal conductivity (k) of the material path.
- Measure the contact area (A) and material thickness (d).
- Calculate thermal resistance: R = d / (k × A).
- Estimate temperature rise: ΔT = Q × R.
Online thermal conductivity calculators and simulation tools (from heatsink manufacturers, silicon vendors, and thermal software providers) automate this math and let you compare material or geometry options quickly before committing to a physical prototype.
Thermal Conductivity of Common Electronics Materials
Material choice has an outsized effect on thermal performance. The table below compares thermal conductivity values commonly referenced in PCB and enclosure design.
| Material | Thermal Conductivity (W/m·K) | Typical Use in Electronics |
| Copper | ~395 | PCB planes, heatsinks, vias, busbars |
| Aluminum | ~200–215 | Heatsinks, enclosures, chassis |
| Silicon | ~150 | Semiconductor die substrate |
| Thermal grease/paste | ~1–8 | Die-to-heatsink interface filler |
| FR-4 (PCB substrate) | ~0.3–0.4 | Standard PCB base laminate |
| Stainless steel | ~15–20 | Structural or corrosion-resistant parts |
| Still air | ~0.026 | Natural insulator; enemy of heat dissipation |
Copper’s exceptionally high conductivity is why it dominates PCB heat-spreading planes and thermal vias, while FR-4’s low conductivity means heat mostly has to travel through copper layers rather than straight down through the board itself. This gap is also why thermal interface materials matter so much: without them, microscopic air gaps between a chip and a heatsink — filled with insulating air at ~0.026 W/m·K — can dominate the entire thermal path.
Thermal Interface Materials and Component Selection
Even a polished heatsink surface has microscopic peaks and valleys that trap air pockets against a component’s case. Thermal interface materials (TIMs) fill these gaps to displace air and create a lower-resistance path to the heatsink.
- Thermal pads — pre-cut, compressible silicone sheets, good for uneven surfaces and repeatable assembly.
- Thermal paste/grease — high-conductivity compound in a thin layer between chip and heatsink, common for CPUs, MOSFETs, and power modules.
- Phase-change materials — solid at room temperature, softening at operating temperature to fill gaps more completely than static pads.
- Thermally conductive adhesives — bond a heatsink permanently while conducting heat, useful where mechanical clips aren’t practical.
For thermally demanding designs, check package type (TO-220, D2PAK, QFN with exposed pad), published θJA/θJC values, and the manufacturer’s recommended TIM thickness. LCSC stocks heatsinks, thermal pads, thermal paste, and power packages in matching case sizes, so a thermal solution can be sourced alongside the active components in one order.
Frequently Asked Questions
Q: What’s the difference between heat transfer and thermal conductivity?
Heat transfer is the broader phenomenon of thermal energy moving between objects or regions, and it happens through three mechanisms: conduction (direct contact), convection (moving fluid, usually air), and radiation (electromagnetic waves, no medium needed). Thermal conductivity is a narrower, measurable material property — expressed in W/m·K — that quantifies how efficiently a specific material conducts heat by conduction alone. In practice, a designer uses the concept of heat transfer to map the overall path heat takes out of a device, and uses thermal conductivity values to calculate how much resistance each material along that path adds, using Fourier’s Law (Q = k × A × ΔT / d).
Q: Which material has the highest thermal conductivity used in electronics?
Among materials commonly used in electronics manufacturing, copper leads at roughly 395 W/m·K, making it the standard choice for PCB heat-spreading planes, thermal vias, and heatsink bases. Aluminum follows at around 200–215 W/m·K and is favored where weight and cost matter more than absolute performance, such as extruded heatsinks and enclosures. Silicon, the semiconductor die material itself, conducts at roughly 150 W/m·K. Diamond and certain synthetic composites exceed all of these, sometimes reaching 1,000+ W/m·K, but their cost limits use to niche high-power or aerospace applications rather than routine PCB design.
Q: How do I calculate thermal resistance from thermal conductivity?
Thermal resistance is calculated as R = d / (k × A), where d is the material’s thickness, k is its thermal conductivity in W/m·K, and A is the cross-sectional area the heat flows through. A larger area or thinner material lowers resistance and improves heat dissipation, while a thicker or lower-conductivity material raises it. Once you have R, multiply it by the power dissipated (Q) to estimate the temperature rise across that material: ΔT = Q × R. This is the same math thermal conductivity calculators use, just automated with a lookup table of common material values.
Q: Does a thicker heatsink always dissipate heat better?
Not necessarily. Adding thickness increases the heatsink’s thermal mass and conduction path, but beyond a certain point the gains taper off because conduction resistance through the base metal is rarely the bottleneck — convection at the fin surfaces usually is. Surface area, fin spacing, fin count, and airflow (natural or forced) typically have a much bigger impact on total heat dissipation than adding raw material volume. In practice, optimizing fin geometry and airflow path delivers better cooling per gram than simply making the heatsink thicker.
Conclusion
Understanding heat transfer and thermal conductivity turns thermal design from guesswork into a calculation you can verify before a board is ever fabricated. Start from the power a component dissipates, trace the full heat path, and choose materials and thermal interface products with conductivity values that match the job.
Ready to build your thermal solution? Browse LCSC’s selection of heatsinks, thermal pads, thermal paste, and power semiconductor packages to find parts that match your design’s thermal budget.
