0-7803-XXXX-X/05/$17.00 ©2005 IEEE 21st IEEE SEMI-THERM Symposium Thermal characterization of a radial micro-channel cooling plate Gy. Bognár 1 , Gy. Horváth 1 , Zs. Kohári 1 , A. J. Pang 2 , M.P.Y. Desmulliez 2 , A. Poppe 1,3 , M. Rencz 1,3 , V. Székely 1 , 1 Deptartment of Electron Devices, Budapest University of Technology & Economics, H-1111 Budapest, Goldmann Gy. tér 3., Hungary e-mail: <bognar | horvath | kohari | szekely | poppe | rencz>@eet.bme.hu 2 MISEC, School of Engineering & Physical Sciences, Heriot Watt University, Edinburgh EH14 4AS, UK, e-mail: a.j.pang@hw.ac.uk 3 MicReD Ltd., Budapest XI, Gulyás u. 27, H-1112 Hungary, e-mail: <poppe | rencz>@micred.com Abstract The thermal behavior of a square nickel plate micro-cooler holding 128 micro-channels in radial arrangement has been investigated. The device is to be used in microelectronic packaging cooling applications. In our study it was attached to a power transistor which was used as a dissipator and a temperature sensor. The thermal transient response to a dissipation step of the transistor was recorded in the measurement. The measured transients (cooling curves) were transformed into structure functions from which the partial thermal resistance corresponding to the cooling assembly was identified. The measurement and the partial thermal resistance identification was carried out at different flow-rates of nitro- gen gas forced through the micro-channels. This way thermal resistance vs. flow-rate and heat-transfer coefficient vs. flow- rate characteristics of the investigated micro-channel cooler were derived. 1. Introduction The rapid advances in transistor density and switching frequency of VLSI circuits as encountered in microprocessors have induced dramatic increases in die heat flux and power consumption at all levels of electronic packaging. Conventional air-cooling systems are reaching their limits [1], thus, new designs are investigated in order to be able to cope with increased heat flux and keeping junction temperatures tolerable [2]. An urgent demand of more efficient cooling has risen, which – among others – resulted in meso and micro- scale thermal management solutions [3]. Prior publications on advanced forced flow cooling solutions (such as [2]) deal with the flow characteristics mainly. In our present paper we describe a thermal characterization method of cooling assemblies through the example of a nickel-based radial micro-channel cooling plate [4]. The very small size device is dedicated for mobile applications. The solutions described in [3] are in the diameter range of 250..1000 µm, while we describe and characterize micro- channel cooling devices with characteristic channel size of 100x45 µm and 100x70 µm. The devices were investigated by thermal transient measurements from which we identified thermal characteristics of the micro-cooler. First a brief overview of the micro-cooler device and its fabrication process is given. The measurement setup and the method of deriving the thermal characteristics are detailed in Section 3. In Section 4 the measurement results are evaluated and a simple experimental model is introduced. The results are presented in Section 4. 2. The structure of the radial micro-channel plate The device (see Figure 1 and Figure 2) was designed to be used in microelectronic packaging cooling applications [4]. The nickel-based micro-channel cooling plate was fabricated on a glass substrate using a two-layer electroforming process borrowed from the UV-LIGA (UV Lithography, Electro- forming, Replication) process. Forced convection of air or liquid is scheduled to be used for cooling in this micro- channel plate. The width of the square plate is 15mm. The Figure 1 Photograph of the micro-channel plate Figure 2 SEM photograph of the inner end of the micro- channels 1 www.fo-son.com Tel: 400-080-1480