LED Cooling Solutions - Bergquist Company - #2

Bergquist Thermal Solutions Insure Color Consistency

laximum Lifecycles For Your LEDs.

Light EmittingDiodes [LED si have been around for yeas, prrnarSy concentrated in ach motets as cell phones PDAs and other consumer electrorics 9nce most of these poductshave relatively ■j. short lifecydes, protecting LEDs jjr/ wasi't a prmary concern because the product world fail or become obsolete long before the LED

adiermrenisin led o=sgnand proceseesarecontnelty boosting ight output to rival ino3rKteaBrt, tumescent, and even haogen tght sources, trie need to protect the LEDsagafoS heat build-up is greater than ever before. Three and iw-watt LEDsare now commonptce, and industry eicperts aeptedcttigiO-wal LED aaSabitty h the inext few yeas Fbwer LEDs of greater than ore-watt are attest akvays surface mounted cevioesThis is because the axis* leadsto the die in a tested parage do not conduct enough heat away from tre LED. Chp-on-boad (COB. flip chips and thermaly effidert packages are errergngasthe standard thermal iTHixprnent paiaging solution for Fbwer LEDs

IMSLTI

vs more forward curert to be appied to the LED, which means more light and possibly reducing the number of LEDs reqUed for the desired id* output. Maintanng a cooler assembly at an ecjjvafent power equates to more light per die. Circuit Board Comparison Models

Insulated Metal arbitrates (IMS) and standard FR-4 are commorty usad droit board materials in conjunction with Fbwer LEDs EergquJd'sTrerrra Ctad IMSis a thin, thermally conductive layer bonded to an aluminum or copper substrate for heat dissipation (see illustration below)The ley to Thermal Ctetfs superior memni Rvmnn

performance lies in Ss dielectric

isolation with hkjh Hiermal con- |^_l5

dudivftyandbondsthebas |§_[0

metal and droit foil together. |^v ₅

Other manutadurers us star- I .

layer, but prepreg doesn't provide tire high thermal conductivity and resulting thermal performance required to heto assure the to

brightest ight output for high-intensty LEDsTherirei Clad or materialsare available from The Efercqiist Company in three effferert thermal corvJuctivttic^HighTm'rjwatij-e(HT). MtfthFtrpose (MR and Low Thermal Impedance (LTI). F&ckacjng Conclusion

There ae several options available for thermal management of Power LEE The most critical thermal path h the stack is the one with the highest thermal resistance. Good practice attests that you reduce the thermal resistance of that layer with Thermal Clad hstead of FR-4.

The Effect of Temperature

The LEOscotor, or wavelength, wil! change with temperature. As the de temperane increases the wavelength of the color increasesThis is particularly rnportart with write idt.The human eye can dfferertiate ara color chances in white light.W hen Power LEDsare populated in an array consistent thermal resistance from one de to the next assures consistent color. Eecause of the comparatively tow thermal resistance Thermal Clad otters versus FR-4. de temperane is less affected by slight variances in the junction-to-case thermal resistance that occurs with tin eclectic or epoxy-de mounting techniques It is also possible to pack the die more dosely in an assembly that utilizes good thermal rraxicternert techniques, thereby reducing the effects of temperature.

Generally, a 50 percent crop in tight output for a conaant-forward current indicates end-of-life for Power LEDsWrth proper thermal rrenagemert, Power LED lifetimes can exceed 100,000 hours