External Thermal Resistance - Substrates: LED Fundamentals

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In this presentation on External Thermal Resistance we will look at the thermal resistance of various substrate types, thermal management with printed circuit boards, and examples that compare the thermal resistance of various substrate technologies.

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External Thermal Resistance - Substrates: LED Fundamentals

  1. 1. LED FundamentalsExternal ThermalResistance –Substrates01-03-2012
  2. 2. External Thermal Resistance Rth SB PCB OPTIONS FOR SMT TJunction LEDS FR4 PCB RthJS LED TSolder Point Metal Core PCB RthSB Substrate Technology TBoard Heat Sink Flexible Circuit PCB RthBA AmbientLED Fundamentals | External Thermal Resistance - Substrates| Page 2
  3. 3. Enlarged Solder Pads Influence of Increasing Solder Pad Area ▲Simplest method to distribute heat ▲No additional costs ▼Low component densityLED Fundamentals | External Thermal Resistance - Substrates| Page 3
  4. 4. Thermal Vias Design Parameters for Thermal Vias Diameter Pitch Cu wall thickness ▲Simple way to increase heat y transfer in the vertical direction ▲Low cost ▼Effect of soldering wicking for g g open plated vias Plated through hole Thermal vias filled thermal vias th l i with solder paste ith ld tLED Fundamentals | External Thermal Resistance - Substrates| Page 4
  5. 5. Thermal Vias effective vertical thermal conductivity (0,8mm FR4 board, 25µm Cu plating in vias) 120.0 100.0 via diameter 100.0E-6 W/mK] 80.0 200.0E-6 thermal conductivity [W 300.0E 6 300 0E-6 400.0E-6 500.0E-6 60.0 700.0E-6 1.0E-3 40.0 20.0 20 0 - 000 0 0 000.0E+0 200.0E-6 00 0 6 400.0E-6 00 0 6 600 0 6 600.0E-6 800 0 6 800.0E-6 1.0E-3 0 3 via pitch [m]LED Fundamentals | External Thermal Resistance - Substrates| Page 5
  6. 6. Metal Core Printed Circuit Board Circuit Layer Copper ~ 400W/mK Dielectric Di l t i Polymer P l 0.9 W/mK 0 9 W/ K – 3 W/ K W/mK Base Plate Aluminum or Copper 150 W/mK – 400 W/mK ▲Good in plane and through plane conduction ▼Costs higher than FR4 ▼Mostly single sided designsLED Fundamentals | External Thermal Resistance - Substrates| Page 6
  7. 7. PCB heat conduction FR4 with maximized ith i i d 2 sided 2-sided FR4 MCPCB Single sided FR4 with thermal vias solder pads Aluminium Plate t = 1.5 mm FR4 PCB t = 0.8 mm Maximized Solder Pads Solder Pads t = 70 µmDielectric t = 75 µm  = 2.2 Wm-1K-1 Solder Pads t = 35 µm Solder Pads t = 70 µm  OSLON SSL  PD = 1 W  Free convection and radiation  typ. VF = 3.2 V, IF = 350 mA yp  Tamb = 25°C  Steady State Solution y LED Fundamentals | External Thermal Resistance - Substrates| Page 7
  8. 8. PCB Heat Conduction MCPCB FR4 with maximized ith i i d FR4 with th ith thermal l Single sided FR4 solder pads vias RthSB 3K/W 45K/W 28K/W 8K/W Junction Temperature 10°C 53°C 35°C 15°C RiseLED Fundamentals | External Thermal Resistance - Substrates| Page 8
  9. 9. PCB on Heat sink OSLON SSL Single sided FR4 PCB MCPCB RthJS = 7 KW-1; PD = 1 W 1 IF = 350 mA, VF = 3.2 V Free Convection and Radiation Recommended Solder Pads Copper t = 35 µm Tamb = 25°C Steady State Solution PCB Technology Junction Temperature at Tamb = 25°C 25 C Metal Core PCB 63.3°C Single Sided FR4 PCB 105.2°C with recommended solder padsLED Fundamentals | External Thermal Resistance - Substrates| Page 9
  10. 10. Thank you for your attention.LED Fundamentals | External Thermal Resistance - Substrates| Page 10
  11. 11. Disclaimer All information contained in this document has been checked with the greatest care. OSRAM Opto Semiconductors GmbH can however, not be made liable for any damage that occurs in connection with the use of these contents. OSRAM Opto Semiconductor GmbH makes no representations and warranties as to a possible interference with third parties intellectual property rights in view of products originating f i i ti from one of OSRAM Opto Semiconductor GmbHs partners, or in view of f O t S i d t G bH t i i f products being a combination of an OSRAM Opto Semiconductor GmbHs product and a product of one of OSRAM Opto Semiconductor GmbHs partners. Furthermore, OSRAM Opto Semiconductors GmbH cannot be made liable for any damage that occurs in p y g connection with the use of a product of one of OSRAM Opto Semiconductor GmbHs partners, or with the use of a combination of an OSRAM Opto Semiconductor GmbHs product and a product of one of OSRAM Opto Semiconductor GmbHs partners.LED Fundamentals | External Thermal Resistance - Substrates| Page 11

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