ltcc thermal gas viscometer heater module - …infoscience.epfl.ch/record/87980/files/2006 maeder...

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LTCC thermal gas viscometer-

Heater module

Thomas Maeder, Caroline Jacq, Giancarlo Corradini, SigfridSträssler, Hansu Birol and Peter Ryser

EPFL-LPM, Lausanne, Switzerland

thomas.maeder@epfl.ch

lpm.epfl.ch

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Determination of gas viscosity

• Purpose: identification of gas mixtures

• Simple sensor principle: time relaxation

Viscous gas

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Determination of gas viscosity

• Purpose: identification of gas mixtures

• Simple sensor principle: time relaxation

Viscous gasThin gas

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Modular LTCC sensor

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Sensor principle

• Pressure differential generated by heating / cooling

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Sensor principle

• Pressure differential generated by heating / cooling

• Pressure measured by membrane sensor

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Sensor principle

• Pressure differential generated by heating / cooling

• Pressure measured by membrane sensor

• Pressure relaxation through meander

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Why LTCC (1) ?

• Ease of structuration

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Why LTCC (2) ?

• Integration of many functions

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Why LTCC (3) ?

• Microreactor & flowsensor

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Why LTCC (3) ?

• Microreactor & flowsensor

• Inclination sensor

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Why LTCC (3) ?

• Microreactor & flowsensor

• Inclination sensor

• Gas sensor (Golonka etal., 1998)

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Why LTCC (3) ?

• Microreactor & flowsensor

• Inclination sensor

• Gas sensor (Golonka etal., 1998)

• Flow sensor (Gongora etal., 2001)

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LTCC for membranes & meanders

• Small spacings

• Intricate layout

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LTCCsintering

Graphiteburnout

Cavities by graphite fugitive phase

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LTCCsintering

Graphiteburnout

Cavities by graphite fugitive phase

• Graphite burnsout shortlybefore LTCCdensifies.

• Spacing can becontrolled byheating rate.

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Heater module (1)

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Heater module (2)

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Heater module (2)

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Heater module (2)

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Results (1/3): thermal resistance

• Good correspondance with model

• Change = increase of air conductivity with temperature

• Some positive temperature drift at low power

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Results (2/3): lid temperature

• Fractional lid temperature rise (rel. to heating resistor)

• Air conductivity rises with increasing temperature.

• Lid (Al2O3) conductivity drops with increasing temp.

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Results (3/3): reference resistor

• Fractional reference resistor temperature rise

• Slight rise with increasing temperature, due toproportionally hotter lid

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Origin of thermal drift

• Thermal resistance vs. weighted reference (block+lid)

• No hysterisis with these boundary conditions

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Transient behaviour

• Very fast resistor response time (!1 s)

• Heating faster than cooling due to TCR

• Additional delayed response due to lid, etc.

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Thermal resistances

• Res. of base & heat sink compound: ca. 3% of total

• Average « parasitic » resistances: ca. 12%

• Lid + module: large resistances, slow equilibration

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Materials (& better alternatives)

0.026AirCavity

0.6Grease + Al2O3Heat sink comp.

0.2

60

Silicone glue

Sn-Ag-Cu solderJoints

24

150

Alumina 96%

Al, Al-SiLid

3

6

LTCC

LTCC+AgModule

Conductivity[W/m/K]

MaterialPart / layer

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Conclusions

• High thermal resistance (! 250"K/W)

• Average cavity !T @ 0.5"W: ca. +60K

• Generated pressure peak: ca. ±0.2"bar

• High speed (! 1s)

• Boundary conditions not yet optimal

• Improvement by using better materials

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Merci / Danke / Grazie / Hvala

THANK

YOU !