{"id":4555,"date":"2026-07-24T06:27:52","date_gmt":"2026-07-24T06:27:52","guid":{"rendered":"https:\/\/blogs.lcsc.com\/blog\/?p=4555"},"modified":"2026-07-24T06:27:52","modified_gmt":"2026-07-24T06:27:52","slug":"heat-transfer-thermal-conductivity-explained","status":"publish","type":"post","link":"https:\/\/blogs.lcsc.com\/blog\/heat-transfer-thermal-conductivity-explained\/","title":{"rendered":"Heat Transfer & Thermal Conductivity Explained"},"content":{"rendered":"

Heat moves through electronics via conduction, convection, and radiation. Thermal conductivity (W\/m\u00b7K) measures how well a material conducts heat by conduction: copper (<\/span>395 W\/m\u00b7K) and aluminum (<\/span>200 W\/m\u00b7K) lead in PCBs and heatsinks, while thermal interface materials fill microscopic gaps to keep junction temperatures under control.<\/span><\/p>\n

Every PCB designer eventually runs into the same wall: a part gets hot, a datasheet lists a mysterious \u03b8JA 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\u2019re selecting components and planning a thermal budget.<\/span><\/p>\n

What Is Heat Transfer? The Three Modes Explained<\/span><\/b><\/h2>\n

Heat transfer describes how thermal energy moves from a hotter region to a cooler one, and it happens through three distinct mechanisms.<\/span><\/p>\n

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  1. Conduction<\/span><\/b> \u2014 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\u2019s leadframe, and across a heatsink base.<\/span><\/li>\n
  2. Convection<\/span><\/b> \u2014 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.<\/span><\/li>\n
  3. Radiation<\/span><\/b> \u2014 heat is emitted as electromagnetic waves and doesn\u2019t require a medium at all. It\u2019s usually a minor contributor in low-power electronics but becomes significant in high-temperature or vacuum applications like satellites.<\/span><\/li>\n<\/ol>\n

    In a typical PCB assembly<\/a>, all three modes act together: conduction pulls heat from a chip\u2019s die to its case and through the board\u2019s copper layers, then convection and radiation carry that heat into the surrounding air or enclosure.<\/span><\/p>\n

    A Practical Heat Transfer Guide for Electronics Design<\/a><\/span><\/b><\/h2>\n

    Turning these three modes into a working thermal design means identifying the dominant heat path and reducing resistance along it:<\/span><\/p>\n

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    1. Find the power dissipation.<\/span><\/b> Calculate or measure worst-case wattage, not just rated power.<\/span><\/li>\n
    2. Identify the heat path.<\/span><\/b> Trace heat from the junction to the case, then to the PCB or heatsink, then to ambient air.<\/span><\/li>\n
    3. Check resistance at each interface.<\/span><\/b> Every solder joint, thermal pad, and air gap adds resistance, in \u00b0C\/W.<\/span><\/li>\n
    4. Add margin for enclosure effects.<\/span><\/b> A part that runs cool on an open bench can run hotter once sealed inside an enclosure.<\/span><\/li>\n
    5. Validate with a thermal resistance calculator or simulation<\/span><\/b> before finalizing a layout, especially for MOSFETs, regulators, and LED drivers.<\/span><\/li>\n<\/ol>\n

      Datasheets publish junction-to-ambient (\u03b8JA) and junction-to-case (\u03b8JC) thermal resistance, both defined under JEDEC\u2019s JESD51 test standards. \u03b8JA covers the full path to open air; \u03b8JC isolates just the path to the case, which matters most once an external heatsink is added.<\/span><\/p>\n

      Thermal Conductivity Explained: What the Numbers Actually Mean<\/span><\/b><\/h2>\n

      Thermal conductivity (k) quantifies how efficiently a material conducts heat, measured in watts per meter-kelvin (W\/m\u00b7K). A higher k means heat moves through the material faster for a given temperature gradient and cross-section.<\/span><\/p>\n

      The relationship is captured in Fourier\u2019s Law of heat conduction:<\/span><\/p>\n

      Q = k \u00d7 A \u00d7 (\u0394T \/ d)<\/span><\/b><\/h3>\n

      Where Q is the heat transfer rate (watts), k is thermal conductivity, A is the cross-sectional area, \u0394T 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 \u2014 more area and less distance both reduce thermal resistance.<\/span><\/p>\n

      Using a Thermal Conductivity Calculator to Estimate Temperature Rise<\/span><\/b><\/h3>\n

      A thermal conductivity calculator applies Fourier\u2019s Law (or the equivalent thermal-resistance form, R = d \/ (k \u00d7 A)) to estimate how much a material or interface will heat up under a given power load. To run a quick manual estimate:<\/span><\/p>\n

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      1. Determine the power (Q) the component dissipates, in watts.<\/span><\/li>\n
      2. Look up or measure the thermal conductivity (k) of the material path.<\/span><\/li>\n
      3. Measure the contact area (A) and material thickness (d).<\/span><\/li>\n
      4. Calculate thermal resistance: <\/span>R = d \/ (k \u00d7 A)<\/span><\/b>.<\/span><\/li>\n
      5. Estimate temperature rise: <\/span>\u0394T = Q \u00d7 R<\/span><\/b>.<\/span><\/li>\n<\/ol>\n

        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.<\/span><\/p>\n

        Thermal Conductivity of Common Electronics Materials<\/span><\/b><\/h2>\n

        Material choice has an outsized effect on thermal performance. The table below compares thermal conductivity values commonly referenced in PCB and enclosure design.<\/span><\/p>\n\n\n\n\n\n\n\n\n\n\n
        Material<\/span><\/b><\/td>\nThermal Conductivity (W\/m\u00b7K)<\/span><\/b><\/td>\nTypical Use in Electronics<\/span><\/b><\/td>\n<\/tr>\n
        Copper<\/span><\/td>\n~395<\/span><\/td>\nPCB planes, heatsinks, vias, busbars<\/span><\/td>\n<\/tr>\n
        Aluminum<\/span><\/td>\n~200\u2013215<\/span><\/td>\nHeatsinks, enclosures, chassis<\/span><\/td>\n<\/tr>\n
        Silicon<\/span><\/td>\n~150<\/span><\/td>\nSemiconductor die substrate<\/span><\/td>\n<\/tr>\n
        Thermal grease\/paste<\/span><\/td>\n~1\u20138<\/span><\/td>\nDie-to-heatsink interface filler<\/span><\/td>\n<\/tr>\n
        FR-4 (PCB substrate)<\/span><\/td>\n~0.3\u20130.4<\/span><\/td>\nStandard PCB base laminate<\/span><\/td>\n<\/tr>\n
        Stainless steel<\/span><\/td>\n~15\u201320<\/span><\/td>\nStructural or corrosion-resistant parts<\/span><\/td>\n<\/tr>\n
        Still air<\/span><\/td>\n~0.026<\/span><\/td>\nNatural insulator; enemy of heat dissipation<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

        Copper\u2019s exceptionally high conductivity is why it dominates PCB heat-spreading planes and thermal vias, while FR-4\u2019s 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 \u2014 filled with insulating air at ~0.026 W\/m\u00b7K \u2014 can dominate the entire thermal path.<\/span><\/p>\n

        Thermal Interface Materials and Component Selection<\/span><\/b><\/h2>\n

        Even a polished heatsink surface has microscopic peaks and valleys that trap air pockets against a component\u2019s case. Thermal interface materials (TIMs) fill these gaps to displace air and create a lower-resistance path to the heatsink.<\/span><\/p>\n