external thermal resistance - substrates: led fundamentals

LED Fundamentals

External Thermal Resistance –Substrates

01-03-2012

T

External Thermal Resistance Rth SBPCB OPTIONS FOR SMT

TJunction

RthJS LEDFR4 PCB

LEDS

TSolder Point

thJS

Metal Core PCB

RthSB Substrate Technology

TBoard

RthBAHeat Sink Flexible Circuit PCB

Ambient

thBA

LED Fundamentals | External Thermal Resistance - Substrates|

Enlarged Solder Pads

Influence of Increasing Solder Pad AreaInfluence of Increasing Solder Pad Area

▲Simplest method to distribute heat▲No additional costs▲No additional costs▼Low component density


Thermal Vias

Design Parameters for Thermal ViasDiameterPitchCu wall thickness

▲Simple way to increase heat ytransfer in the vertical direction

▲Low cost▼Effect of soldering wicking for g g

open plated vias

Thermal vias filled ith ld t

Plated through hole th l i


with solder pastethermal vias

Thermal Vias effective vertical thermal conductivity

(0,8mm FR4 board, 25µm Cu plating in vias)120.0

80.0

100.0

W/m

K] 100.0E-6

200.0E-6300 0E-6

via diameter

60.0

cond

uctiv

ity [W 300.0E 6

400.0E-6500.0E-6700.0E-61.0E-3

20 0

40.0

ther

mal

-

20.0

000.0E+0 200.0E-6 400.0E-6 600.0E-6 800.0E-6 1.0E-3


000 0 0 00 0 6 00 0 6 600 0 6 800 0 6 0 3

via pitch [m]

Metal Core Printed Circuit Board

Circuit Layer Copper ~ 400W/mK

Di l t i P l 0 9 W/ K 3 W/ KDielectric Polymer 0.9 W/mK – 3 W/mK

Base Plate Aluminum or Copper 150 W/mK – 400 W/mK

▲Good in plane and through plane conduction

▼Costs higher than FR4▼Costs higher than FR4▼Mostly single sided designs


PCB heat conduction

FR4 ith i i d 2-sided FR4MCPCB Single sided FR4 FR4 with maximized

solder pads2 sided FR4with thermal vias

Aluminium Plate t = 1.5 mm FR4 PCB t = 0.8 mm

Dielectric t = 75 µm = 2.2 Wm-1K-1Maximized Solder Pads Solder Pads t = 70 µmSolder Pads t = 35 µm Solder Pads t = 70 µm

OSLON SSL typ. VF = 3.2 V, IF = 350 mA

PD = 1 W Tamb = 25°C

Free convection and radiation Steady State Solution


yp F F amb y

PCB Heat Conduction

FR4 ith i i d FR4 ith th l

Rth

Single sided FR4

45K/W

MCPCB

3K/W

FR4 with maximized solder pads

28K/W

FR4 with thermal vias

8K/WRthSB

Junction Temperature

Rise

45K/W

53°C

3K/W

10°C

28K/W

35°C

8K/W

15°C


Rise

PCB on Heat sink MCPCBSingle sided FR4 PCBOSLON SSL MCPCBSingle sided FR4 PCBOSLON SSL

Rth 7 KW 1 P 1 W

PCB Technology Junction Temperature at Tamb = 25°C

RthJS = 7 KW-1; PD = 1 W Recommended Solder Pads Copper t = 35 µm

Free Convection and RadiationSteady State Solution

IF = 350 mA, VF = 3.2 VTamb = 25°C

PCB Technology Junction Temperature at Tamb 25 C

Metal Core PCB 63.3°C

Single Sided FR4 PCBwith recommended solder pads

105.2°C


Thank you for your attention.Thank you for your attention.


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

i i ti f f OSRAM O t S i d t G bH' t i i foriginating from one of OSRAM Opto Semiconductor GmbH's partners, or in view of products being a combination of an OSRAM Opto Semiconductor GmbH's product and a product of one of OSRAM Opto Semiconductor GmbH's partners. Furthermore, OSRAM Opto Semiconductors GmbH cannot be made liable for any damage that occurs in p y gconnection with the use of a product of one of OSRAM Opto Semiconductor GmbH's partners, or with the use of a combination of an OSRAM Opto Semiconductor GmbH's product and a product of one of OSRAM Opto Semiconductor GmbH's partners.
