Abstract
This master’s thesis studies thermal management and thermomechanical
reliability of radar sensor demonstrator package for the 24 GHz band. The
package consists of a RFIC flip chip bonded on a LTCC module attached to a
printed circuit board. The work includes fabricating test structures and
performing measurements and tests on them. Flotherm simulation software is
used to assist in improving thermal management and thermomechanical
reliability. The usability of the software in this kind of study is also
evaluated.
Temperature measurements on test structures revealed that vias right under the
flip chip bumps cool the chip most efficiently. The version in which signals
and grounds were first distributed to the edge areas of the module and then
connected through the LTCC layers with vias had higher chip temperature in
both simulations and measurements. Underfill applied under the RFIC chip was
also found to enhance the thermal management of the package.
Thermomechanical reliability tests revealed that to ensure reliability of
demonstrator package the LTCC module should be as small as possible. The
fatigue life predictions made with Flostress software were substantially
longer than real test results because fatigue damage was not due to crack in a
solder joint as the simulator assumed. Instead the damage was located on
printed circuit board. The discovery demonstrated that joints are not the most
susceptible to thermally induced stresses and strains after all, an
assumption which was taken for granted in whole study.
Flotherm was concluded to be a useful tool for thermal management since it
gave reasonable results and managed to imitate the thermal behaviour of the
structure. In contrast thermomechanic simulations made with Flostress module
gave over optimistic results. However when attributes were changed to
investigate the effect of package dimensions and simulation circumstances,
simulations followed real situation quite well. Thus it was concluded that
even though Flostress was unable to predict fatigue life accurately it can be
used for comparing different designs from thermomechanical reliability point
of view.
Original language | English |
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Qualification | Master Degree |
Awarding Institution |
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Place of Publication | Oulu |
Publisher | |
Publication status | Published - 2004 |
MoE publication type | G2 Master's thesis, polytechnic Master's thesis |
Keywords
- Thermomechanical failures
- thermal vias
- thermal cycling
- thermal simulation
- Flotherm