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due to a large thermal resistance in the part of parallel
connection and a small resistance value in the part of serial
connection, respectively. Thus, the materials of air and SiOB
could be reasonably removed both in the model calculation
and the CoventorWare simulation [7] so that more than 80%
reduction of required mesh was achieved as well as the
requirements of CPU and DRAM operation in this case. Fig.
5 (a) shows the probable paths of thermal flow predicted by
the equivalent ETCM after removing the air and SiOB in the
thermal conducting system. Since VCSEL and thermal via
have comparable thermal conductivity (see Table. 1) and the
thickness of the operating VCSEL and the adjacent one can
have two-order magnitude larger than that of thermal via, the
thermal via would become the main path of the thermal flow
as the expectation in this work.
Furthermore, the paths of the thermal flow depicted in Fig.
5 (b) extracted from the simplified thermal conducting system
constructed in the simulation verify the validation of the
equivalent ETCM by showing the possible paths of thermal
flows on the principal components. The simulation results
can not only obviously present the main paths of thermal flow
as the prediction of the equivalent ETCM, but also indicate
the hottest point that in the outermost corner of the operating
VCSEL where the most far from the possible paths of the
thermal flow. It is important to find out the hottest point in a
thermal conducting system due to possible unexpected
functionality degradation or even device failure due to a great
quantity of thermal accumulation will easily happen at the
point. In fact, according to the indications of derived
equivalent ETCM, the value of the hottest point could always
easily happen at the joints of the heating source and source of
thermal flow and the hottest temperature should relate with
the characteristics of material and geometry of Z 1 and
7-9 October 2009, Leuven, Belgium
the conditions of boundary A. For the purpose of furthermore
validation of mentioned characteristics of the hottest point,
Fig. 6 shows the scheme of the simplified thermal conducting
system with single operating VCSEL established by the
equivalent ETCM. The model calculation of the temperatures
of node points A, B, and C depicted in Fig. 6 are 80.2, 79.2,
and 75°C, respectively. The results reveal that the hottest
temperature is at node A and the main path of thermal flow is
from node B to C as the prediction of the equivalent ETCM
and having excellent match with simulation demonstration in
Fig.5 (b). Therefore, it is worthy for system-IC designers and
engineers to analyze the worsen cases at those joints and
study the thermal behaviors of Z 1 and boundary A seriously by
means of the network model or equivalent ETCM.
Fig. 7 shows the IR microscope detected temperature
distribution of SiOB heated by the operated VCSEL. The
bottom of SiOB is constrained with a bias temperature
A
B
Fig. 6. The scheme of the simplified thermal conducting system with single
operating VCSEL established by the equivalent ETCM. The model
calculation of the temperatures of node points A, B, and C are 80.2, 79.2,
and 75°C.
C
(a)
(b)
Hottest point
Fig. 5. (a) The simplified thermal conducting system established by the
indication of the equivalent ETCM. The material of air and SiOB were
removed in the system to reduce the required meshes as well as the CPU
time. (b) The thermal flow on principal components extracted from
CoventorWare simulation provides a verification of the equivalent ETCM.
Hottest point was also labeled in the simulation result and indicated the point
of possible unexpected functionality degradation or even device failure due
to a great quantity of thermal accumulation.
Fig. 7. The measured temperature distribution of SiOB heated by the
operating VCSEL using IR microscope. Only a laser diode is operated by
probe B with 8mA input current and 2V bias voltage.
©EDA Publishing/THERMINIC 2009 11
ISBN: 978-2-35500-010-2