1 of 23 introduction to ltcc for engineers how to manufacture 3d circuits for microtechnique...

1 of 23Introduction to LTCC for engineers

How to manufacture 3D circuits for microtechnique applications?

With LTCC !

[email protected]

Monday 4 September 2006Thick-film Technology Group, Prof. P. Ryser Laboratoire de Production Microtechnique

http://lpm.epfl.ch/ltcc

Introduction for engineers


The LTCC ?

Low-Temperature, Cofired Ceramic

•Sheets of sintered ceramics (blue, white or black)

•You’re carrying it unaware (mobile phone, car ignition)

•Relatively new material (<20 yrs)

•Developed for highly integrated electronics

raw sheets of LTTC (micro-reactor)

micro-flow sensor assembled

fluidic circuit, management of valves with SMD

electronics


Objectives

•Objectives of my thesisTo integrate in a circuit:- sensors (pressure, temperature, flow)- actuators (electrovalves)- electronics (SMD)by an industrially viable process.

•Objectives of this presentationTo make you discover the LTCC technologyand its multiples possibilities.

Hybrid micro-reactor in LTCC and alumina

Modular gas viscosity sensor


Content

1. The principle of LTCC

2. Properties

3. Realisations at the LPM

4. Concurrent methods

5. State of the art

6. In practice

7. Conclusion


1.1) The principle of LTCC

1. Raw sheets easily cut(laser, punch tool)

2. Layers individually printed(multilayer circuits )

3. Stacking of layers to geta 3D structure

4. Firing-> sintering, monolithic circuit

5. Individualisation and post-firing(assembly by soldering)


1.2) Types of realisations

Circuits:

• fluidic

• electronic

• mechanical

Hybrid micro electrovalve in LTCCM. Gongora-Rubio et al., 2001

M. Gongora-Rubio et al., 1999

www.ltcc.de


1.3) Acronym

The LTCC is dissociated from HTCC:

•Low- LTCC 875°C

•Temperature HTCC 1400-1600°C

•Cofired co-firing of (di)electric pastesLTCC: precious metals (Au, Ag, Pd,

Cu)HTCC: refractory metals (W, Mo,

MoMn)

•Ceramic mix of:- alumina Al2O3

- glasses SiO2 - B2O3 - CaO - MgO- organic binders

- HTTC: essentially Al2O3


1.4) Processing

Raw material comes as:

•sheets or rollsthickness 50-320μm5-6 big manufacturers:DuPont, ESL, Ferro, Heraeus…

•powder: to mix oneself, proprietary LTCC (mass production like automotive, military etc.)

•Simple, yet complex process

•Incompressible times :- lamination 5-15 min- firing 2-8 hrs- post-firings 45 min each www.ltcc.de


2) Physical properties

1. Chemically stable, inert to HCl, NaOH…

2. Thermically stable (>600°C)

3. Low thermal conductivity (3 W/mK)

4. High hardness (8 Mohs)

5. Very good dielectric (low losses at high frequencies, application for GHz antennas)

6. rupture=320 MPa, E=120 GPa, density=3.1

7. High reliability and hermeticity


3) Realisations at the LPM

1. Flow sensor and micro-reactor

2. Gas viscosity sensor Wobbe

3. Force sensor Millinewton

4. Circuit for managing pneumatic valves

5. Hermetic case for sealing tests


3.1) Flow-sensor and micro-reactor

1. Flow sensor- 3 layers of LTCC- principle of the hot-wire anemometer- channel 1 to 2 mm wide

2. Micro-reactor- 2 reactants- 2 flow sensors- 1 calorimeter

Microreactors and micro flowsensor (bottom)Hybrid micro-reactor


3.2) Gas viscosity sensor Wobbe

Modular sensor measuring the Wobbe index:

- 1 base plate- 1 heating module- 1 membrane pressure sensor module

Application: optimisation of combustion in oil-fired boilers

Sensor with its external modules disassembled


3.3) Force sensor Millinewton

Alumina version (200..2000 mN)

• rectangular beam soldered on base plate

• double-side serigraphy (4 R in Wheatstone bridge)

LTCC version (10..100 mN)

• Optimised T-shaped beam

• Young modulus 2.6x smaller

• Better sensitivity

• Half-bridge version(single-sided)

• Easier manufacturing


3.4) Circuit for electrovalves

• Up to 22 layers of LTCC

• 2 levels of interconnections

• Channels 0.3..3 mm wide

• Piloting by SMD electronics

• Brass adapters


3.5) Hermetic case for sealing tests

• Base plate in LTCC, glass lid

• Co-fired electric tracks

• Sn-Pb soldered tungsten wires

• Post-fired sealing cord

• Sn-Bi 138°C solder for the lid

• From drawing board to assembled product: 2 weeks


4.1) Concurrent methods

• SLS (Selective Laser Sintering)- slow- piece by piece prototyping- more for forms than for circuits- porous

• Alumina + classical thick-films- mono-substrate (assembly by sealing)- multilayer, but sequential process- less advantageous for numerous layers- 1400°C (HTCC)


4.2) Concurrent methods

• PCB- Tmax 150°C- difficult machining for fluidics- losses in high frequencies- not hermetic- cheaper for a simple electric circuit

• Alu and epoxy resin- easier processing- only for fluidics

• Silicon- clean room- heavy and complicated processes- partial concurrency because Si ~ m, LTCC ~ 0.1mm-> to use in complement

Stacked fluidic mini-PCB of Fraunhofer IZM Berlin

Pneumotech


5.1) State of the art

M. Gongora-Rubio et al., 1999

J. Kita, Bayreuth, Germany, 2005Peterson, Sandia National Lab, 2005


5.2) State of the art

Fraunhofer IZM Berlin


6.1) Technological problems

In practice one must take into account of:

• Variations of final dimensions due to shrinkage variability (batches + inherent)

• Shrinkage different than announced by manufacturer (10..15% in X-Y, 15-40% in Z)

• Crushing of cavities when following manufacturer’s lamination recommendations

• Delamination of layers at edgeswhen reducing lamination pressureor temperature


6.2) Experimental setup at the LPM

pre-conditioningdrying oven 30min-

120°C

LTCC sheetsthick. 50-320μm6”x6”

laser cutting +air blowing

stackingpin

alignment fixture

lamination uniaxial press 5min - 70°C -

200bar

removal of protection

firingair furnace

8hrs - 875°C

ready for screenprinting and post-

firings

serigraphy of pastes

on raw layers


7) Conclusions

•Robust and reliable technology

•Mature for electronics; under development for fluidics

•Automatisable

•Moderate costs and investments (semi-clean room)

•Infinite possibilities of forms and combinations

•Quasi-unlimited number of layers

•Price for industrial quantities : 1€ / dm2 / layer

•Finesse of structures ~ 50 m


The end

Thank you for your attention!

More information onhttp://lpm.epfl.ch/ltcc

http://personnes.epfl.ch/yannick.fournier

All images without legend are copyrighted from LPM-EPFL.


Appendix – air furnace temperature profile

LTTC Oven Temperature Profile "Yannick 16"

0

100

200

300

400

500

600

700

800

900

1000

000 060 120 180 240 300 360 420

Time [min]

Te

mp

era

ture

[°C

]

burnoutdwell 450°C

100 min(LTCC is at 440°C)

sinteringdwell 895°C

30 min

sinteringramp 895°C

2.5K/min

ramp 200°C-20 K/min

for the LTCC samples to reach a peak temp of 875°C, the oven must be higher ->

ramp 450°C2.4K/min

ramp 230°Cslope 8K/min

ramp 400°C-16 K/min

ramp 660°C10 K/min

Duration [h:min]

Total time

[h:min]

Final temp [°C]

Slope [K/min]

1 Fast ramp 00:25 00:25 230 82 Ramp to 440°C 01:30 01:55 450 2.43 Burnout dwell 100 mins 01:39 03:34 450 04 Fast ramp 00:21 03:55 660 105 Sintering ramp to 875°C 01:35 05:30 895 2.56 Sintering dwell 30 mins 00:30 06:00 895 07 Natural furnace cooling 00:30 06:30 400 -16.58 Fast cooling 00:10 06:40 200 -209 Back to ambiant 00:10 06:50 70 -13

Step


Appendix – comparison of properties


Appendix – specs of two common pastes

1 of 23 introduction to ltcc for engineers how to manufacture 3d circuits for microtechnique...

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