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Research Papers

# Design of a Static TIM Tester

[+] Author and Article Information
V. Székely

Department of Electron Devices, Budapest University of Technology and Economics, Budapest H-1111, Hungaryszekely@eet.bme.hu

E. Kollár

Department of Electron Devices, Budapest University of Technology and Economics, Budapest H-1111, Hungarykollar@eet.bme.hu

G. Somlay

Department of Electron Devices, Budapest University of Technology and Economics, Budapest H-1111, Hungarysomlay@eet.bme.hu

P. G. Szabó

Department of Electron Devices, Budapest University of Technology and Economics, Budapest H-1111, Hungaryszabop@eet.bme.hu

M. Rencz

Department of Electron Devices, Budapest University of Technology and Economics, Budapest H-1111, Hungaryrencz@eet.bme.hu

The paper uses both the notions of the thermal resistance ($Rth$, in K/W units) and the thermal resistance of unit area ($θ$, in $K cm2/W$ units). If the cross-sectional area of the heat flow is $1 cm2$, their numerical value is equal. $Rth (K/W)=θ (K cm2/W)/area (cm2)$.

Also the TIM material is homogeneous.

If the temperature dependence of the sample's behavior is measured, it has to be calculate with the temperature dependence of this additional thermal resistance.

For the sake of visuality, we permitted here larger offset values than the usually appearing ones.

In all the examples, the $Rth$ values relate to the $1 cm2$ active area of the sample holder.

A commercial thermal grease was applied, with unknown parameters.

J. Electron. Packag 132(1), 011001 (Feb 25, 2010) (9 pages) doi:10.1115/1.4000715 History: Received January 19, 2009; Revised May 20, 2009; Published February 25, 2010; Online February 25, 2010

## Abstract

Testing the thermal properties of thermal interface material (TIM) has been a big challenge for decades. Recent development trends made this challenge even bigger, as now the values that have to be measured are extremely small. In this paper, we present a newly developed TIM tester equipment that is targeting to overcome all the problems that present industrial TIM testing methods face. The main idea behind our design is to use the capabilities of microelectronics in order to make small sized sensors both for temperature and heat-flux sensings. This way it is possible to place these sensors in the closest proximity of the measured sample. This paper presents details of all the technical solutions of the newly developed static TIM tester that is capable to measure $Rth$ of unit area values in the order of $0.01 K cm2/W$ with good accuracy. Special attention is made to analyze and eliminate the possible sources of measurement inaccuracy. A number of measurement examples prove the usability of the developed measuring instrument.

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## Figures

Figure 1

The basic parts of the measurement arrangement

Figure 2

The mechanical arrangement

Figure 3

Photograph of the mechanical design (the sensor chips have not yet been built in)

Figure 4

Image of the microscope observing the two grips of the sample holder with the sensor chips. The thickness of the sample (TIM foil) is 250 μm.

Figure 5

Block diagram of the electronics (PCU=Peltier control unit, MU=measurement unit)

Figure 6

Preamplifier unit

Figure 7

Layout of the sensor chip

Figure 8

The sensor chip

Figure 9

Temperature dependence of the heat-flow sensor sensitivity. The sensor area is 0.5 cm2 (dots: measured values, straight line: approximation).

Figure 10

Parallelism control

Figure 11

To the calculation of additional thermal resistance

Figure 12

Nonparallel grips: (a) the calculation model and (b) partitioned heat-flow sensor

Figure 13

Thermal conductance versus extent of nonparallelism

Figure 14

Schematic of the sample and its surroundings

Figure 15

Drop out of the temperature offset error (marks: measured data, solid lines: approximating functions)

Figure 16

Thermal simulation of the sample holder. The figure depicts the heat-flow density in W/m2 units.

Figure 17

The inhomogeneity of the heat flux in the sample region (simulation result: heat pumping 80 W)

Figure 18

Thermal resistance of an Al2O3 plate versus temperature (raw data, not corrected by Rth add).

Figure 19

Thermal resistance versus pressure function of a commercial TIM material (solid line: vendor data, marks: measured, corrected values)

Figure 20

Figure 21

Thermal conductance versus extent of nonparallelism (2D case)

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