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onding it was compressed down to ~60 µm. As shear mode
a fracture between Ag and the Cu surface was detected (see
figure 17).
III B. HI-LAMBDA TESTER
A first description of the set-up has been given in [6]. The
idea of this test system is to measure the thermal
conductivity of very highly conductive metal-based TIMs
with the help of a steady state technique, using copper bars
as thermal resistors for their large thermal conductivity and
hence good resolution at manageable size. Solders as well as
sintered mono-metal layers could be tested with this method,
that the thermal conductivity is measured under processing
conditions as later in the real application.
7-9 October 2009, Leuven, Belgium
NTC-Resistors as temperature sensors which allow to reach
an accuracy of 0.05 K for the six calibrated temperature
sensors. From that we expect an exceptionally good
resolution of the thermal conductivity in the measurement.
The measurements were done under vacuum to minimize the
convection.
From the comparison between experiments and simulation
it could be find that the accuracy of the results strongly
depends of the dimension of the bonding area. Therefore we
measured the contact area of all tested samples. Figure 19
shows the target-performance comparison of one tested
sample.
Table 1: Correlation Experiment vs Simulation
Sensor # Exp [°C] Sim [°C] ∆T [°C]
T1 97,44 97,41 0,02
T2 93,95 93,85 0,11
T3 90,20 90,26 0,06
T4 32,30 32,25 0,04
T5 28,63 28,67 0,04
T6 25,05 25,10 0,05
λ [W/mK] 403 ± 15
Table 1 shows the compare between experiments and
simulations for one test thermal conductivity of the used Cu
is 390 W/mK, a value measured by the laser flash method.
The heat flow can be measured by knowledge of the
geometry and thermal conductivity of the Cu test sample.
Fig 18: Design of hi-lambda tester.
The Cu bars are 30 mm long
Figure 18 shows the improved design of hi-lambda tester.
Temperatures are measured in six positions. To evaluate the
thermal conductivity of the TIM we compare the measured
temperatures with the equivalent FE-Model.
Fig 19: Microscopy image of contact area. Due to
artefacts during processing of the paste the area is
slightly smaller that the maximum possible value.
Therefore we have to guarantee an exact temperature
measurement. This can be achieved by using calibrated
T [°C]
98
97
96
95
94
93
92
91
90
89
32
31
30
29
28
27
26
25
24
T1
T2
T3
T4
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Position [mm]
T5
Exp
Sim
Fig. 20: Correlation Experiment vs Simulation
Two samples with different BLT of sinter Ag were
measured and simulated. As one can see in table 1 and figure
20, the results of simulation and experiment agree very well
to yield results for the thermal conductivity of sintered silver
between 395 W/mK and 410 W/mK. This value comes very
T6
©EDA Publishing/THERMINIC 2009 230
ISBN: 978-2-35500-010-2