Microsystem Technologies

, Volume 25, Issue 1, pp 121–137 | Cite as

Numerical simulation and experimental validation of heat sinks fabricated using selective laser melting for use in a compact LED recessed downlight

  • Yi-Cheng HuangEmail author
  • Huan-Chu Hsu
Technical Paper


The aim of this study was to design and fabricate heat sinks with high heat dissipation capacity by using selective laser melting (SLM). A low junction temperature was maintained and the lifetime and reliability of the resultant compact LED recessed downlight (CLDL) was increased. A trapezoidal-finned heat sink with horizontal holes (HFSLM) and three-dimensional metal-foam-like heat sink (3DSLM), which both have large surface-area-to-volume ratios, were designed in this study. Each heat sink was mounted to a 10 W CLDL and installed in a test box with the dimensions 105 mm × 105 mm × 100 mm (L × W × H) for evaluating the lifespan of the CLDL in a high-temperature environment with natural convection. The downlights withstood the test, and according to the Arrhenius equation, they had a long lifetime at normal usage temperatures. The results of the stationary simulations agreed with the experimental results. The temperatures at the solder point of the CLDL with the HFSLM and 3DSLM were 88.6 and 91.4 °C, respectively, corresponding to LED junction temperatures of 118.6 and 121.4 °C. These junction temperatures were lower than the specified LED limit temperature of 135 °C. The results of an accelerated life test prediction and in situ temperature measurement testing based on TM-21 extrapolations using LM-80 data indicated that the lumen maintenance of the CLDLs complied with Energy Star® requirements.

List of symbols


Acceleration Factor is the test time multiplier derived from the Arrhenius equation


The volumetric thermal expansion coefficient of the fluid


The specific heat capacity


Natural logarithms (2.71828)


Acceleration energy in electron-volts (eV), thermal activation energy 0.5–0.7 eV for assembly defects


The porosity of the porous material


The volume force (body force) in any point of the fluid


The identity matrix


Temperature Kelvin


The thermal conductivity


The permeability tensor of the porous media


Boltzmann’s constant (Kb = 8.617 × 10−5 eV/k)


Metal core printed circuit board


Dynamic viscosity of air


The pressure


Total power (W) input to LED (If × Vf, If is LED forward current, Vf is forward Voltage)


Density of air


A mass source or mass sink, accounts for mass deposit and mass creation within the domains


Thermal resistance

Rth, b-h

Thermal resistance between MCPCB and aluminum housing

Rth, h-ref

Thermal resistance between aluminum housing and reference point

Rth, hs-box

Thermal resistance between heat sink and test box

Rth, h-hs

Thermal resistance between aluminum housing and heat sink

Rth, j-sp

Thermal resistance between junction and solder point

Rth, sp-b

Thermal resistance between solder point and MCPCB

Rth, sp-ref

Thermal resistance between solder point and reference point




The room atmosphere temperature at 25 °C


MCPCB temperature


Test box temperature


Aluminum housing temperature


Heat sink temperature


Junction temperature


Reference point temperature


Room atmosphere temperature (25 °C)


Solder point temperature


Temperature in normal use, in degrees Kelvin (K =  °C + 273)


Temperature in testing, in degrees Kelvin


The velocity vector



The transpose matrix



The authors would like to acknowledge the support from Laser and Additive Manufacturing Technology Center (LAMC), Industrial Technology Research Institute (ITRI). The authors express their gratitude to Pitotech Co., Ltd., for their technical support. Special thanks is offered to Dr. Forcea Cheng.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Mechatronics EngineeringNational Changhua University of EducationChanghuaTaiwan, ROC

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