Frequency Agile Microwave Oven

Bonding System (FAMOBS)

From feasibility study to production prototype

Prof. Marc DesmulliezHeriot-Watt University

Edinburgh, UK

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• Microwave heating – principles and applicators

• Funding schemes and partners

• Project overview

• Open end oven prototypes

• Results - Curing

• Conclusions and future work

Contents

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FAMOBS funding schemes

FAMOBS (EU)

• Project funded by the European Commission within FP7

• 3 year project starting in November 2008

• 5 industrial collaborators, 4 RTDperformers and 4 SME associations

FAMOBS (UK)

• 18 month research project (feasibility and project deepening)

• Funded by the IeMRC• 3 research partners + 4 industrial

partners

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Microwave heating

• Generates heat at the molecular level by forced oscillation ofpolar bonds

• Materials ability to absorb microwaves depends on:

• Complex permittivity, conductivity, frequency & temperature

• Heating is volumetric as compared to thermal transfer fromconvection heating

Convection – heat penetrates from surface Microwave – uniform heat generation

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http://www.2450mhz.com/PDF/Doc/900065.pdf

Microwave Applicators Semiconductor manufacturing

GERLING APPLIED ENGINEERING, INC.

Lambda TechnologiesTM

(http://www.microcure.com/) 5/28

Project overview - FAMOBS

• To develop an open-ended ‘microwave oven’ for in-situ curing and bonding within microelectronics processing applications.

• Research has been on several fronts and consists of

• Design of open ended oven

• Pulsing and VFM implementation

• RF modelling

• Multiphysics modelling

• System integration

• Characterisation of cured specimens

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Open ended oven - A gain in productivity

Traditional Assembly Process

FAMOBS Manufacturing Process

(Source: Prof. Chris Bailey, University of Greenwich)

• In addition, microwave processing is more efficient than a convection oven(increase in heating ‘rate’ by a factor of 10 depending on the material)

• For the rapid curing of both conductive and non conductive based polymerdielectrics in semiconductor manufacturing and packaging

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Challenges – Multiphysics modelling

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Open ended oven integration

Microwave oven on die placement arm

Die, Adhesives, Encapsulants, Underfills, etc

FAMOBS oven prototype system

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FAMOBS System Stakeholder Map

FAMOBS

System

Research

Foundry

Test Q&R

Services

FablessIDM

PCB

Packaging

GE Aviation

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Other applications

• Petroleum compounds extraction

• Ceramic composites sintering and annealing

• Sintering of carbon composites

• Bonding applications for micro-fluidic, microelectronics andMEMS

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Manufacturing capability

readiness levels

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9

10

7

6

5

4

3

2

1

8

Fully production capable process qualified on full range of parts over extended period

Fully production capable process qualified on full range of parts over significant run lengths

Capability and rate confirmed via economic run lengths on production

Process optimised for capability and rate using production equipment

Basic capability demonstrated using production equipment

Process validated in laboratory using representative equipment

Experimental proof of concept completed.

Applicability and validity of concept described and examined or demonstrated

Process concept proposed with scientific foundation

Process concept proposed. Process unreported in literature, potential for generating IP.

Manufacturing technology proven and assessment in laboratory environmental

Pre-Production in relevant environmental

Production Implementation

Phase 3

Phase 2

Phase 1

Ph

ase

of

Dev

elo

pm

ent

MCRL State of Development

Continuous improvement to fully capable production processProduction Improvement

Phase 4

(source : Nabil Gindy, University of Nottingham)

MCRL1

MCRL2

MCRL3

MCRL4

MCRL5

MCRL6

MCRL7

MCRL8

MCRL9

• The electrical length of the cavity can be controlledthrough adjustment of additional conducting rods.

• Disadvantages:• Mechanical design for control of length of conducting

rods• Substantial heat generated within dielectric

• Waveguide Cavity Resonator• Open end – access to cavity volume • 2 waveguide sections

• Dielectric filled propagating section• ‘Air’ filled cut-off section• fc

(dielectric) < fc(air)

• Evanescent field used for heating

1st generation prototype – PT1

PT1

PT2

PT6

PT5

PT4

PT3

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MCRL1

MCRL3

MCRL5

MCRL6

MCRL7

MCRL8

McRL9

• Excessive loss tangent (tanδ) of dielectric insert

• Substantial heat generated within dielectric

- curing occurred through thermal conduction

• Decrease in cavity Q Factor

- quasi degeneracy disturbs modal field pattern within cavity

Single Feed, Multiple Heating Spots @ ≈ 10.19GHz

• The fringing field depth of the evanescent field can becontrolled through proper choice of bulk dielectricpermittivity

• Disadvantages:

2nd generation prototype – PT2

MCRL4

MCRL2

PT1

PT2

PT6

PT5

PT4

PT3

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MCRL1

MCRL3

McRL5

McRL6

McRL7

McRL8

McRL9

• Higher dielectric constant, er = 30; Q = 10,000

• 11mm2 x 110mm ceramic dielectric

• Testing did not produce measurable results

• Cross-section was overly small compared to ‘X-Band’ connectors (SMA, SMB)

• Purchase of MMCX connectors suitable up to5GHz

• Very poor coupling from feed line into cavity.

• Drilling of connector hole (dia. 0.8mm) causeda failure within the ceramic.

• Results suggest lower permittivity (er < 10)cavity would be more suitable.

3rd generation prototype – PT3

MCRL2

MCRL4

PT1

PT2

PT6

PT5

PT4

PT3

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MCRL1

MCRL3

MCRL4

MCRL5

MCRL6

MCRL7

MCRL8

MCRL9

• Optimised design with dielectric insert for improved heating rate

• Bulk Dielectric er = 2.1 Length = 90mm

• Dielectric Insert er = 6 Optimised length = 3.5mm

4th generation prototype – PT4

MCRL2

Temperatures recorded with PT4, PT2 and a convection oven

PT1

PT2

PT6

PT5

PT4

PT3

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Temperatures recorded with the optimised, normal open end oven and a convection oven

4th generation prototype – PT4

MCRL1

MCRL3

MCRL4

MCRL5

MCRL6

MCRL7

MCRL8

MCRL9

MCRL2

Measurement temperature results for a 150oC curing cycle by pulsing the

source.

Electric field distribution comparing shift in maxima due to inclusion of an optimised dielectric insert: a) TM11, 1st mode b) TM11, 2nd mode

• Disadvantages:• Temperature measurement• Couldn’t be integrated with the placement machine

PT1

PT2

PT6

PT5

PT4

PT3

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MCRL1

MCRL3

MCRL4

MCRL5

McRL6

MCRL7

MCRL8

MCRL9

Pyrometer

Open end /

load section

• New design for integration with the pick and placement machine

• Integrated IR pyrometer for temperature sensing

5th generation prototype – PT5

MCRL2

PT1

PT2

PT6

PT5

PT4

PT3

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5th generation prototype – PT5

MCRL1

MCRL3

MCRL4

MCRL5

MCRL6

MCRL7

MCRL8

McRL9

MCRL2

• Results of the IR pyrometer measured temperaturecurves for a 150oC curing cycle by pulsing the source.

• The pulsing method has resulted in a better controlof programmed temperature with a temperatureaccquisition rate of 1 Hz.

• Disadvantages:• Dielectric losses in the bulk dielectrics and insert• Difficulty in the integration of pyrometer

PT1

PT2

PT6

PT5

PT4

PT3

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Advantages

Easier integration of pyrometer

No losses due to dielectric filling and no need of replacing dielectrics

Could be easier for tuning (impedance matching) with extra tuners (screws)

No need of precise control of the robotic arm as material can be moved inside the cavity

PT1

PT2

PT6

PT5

PT4

PT3

MCRL1

MCRL2

MCRL3

MCRL4

MCRL5

MCRL6

MCRL7

MCRL8

MCRL9

• Different air cross-sections

• Designed and modelled

• Advantages• Easier integration of pyrometer• No losses due to dielectric

filling and no need of replacing dielectrics

• Could be easier for tuning (impedance matching) with extra tuners (screws)

• No need of precise control of the robotic arm as material can be moved inside the cavity

6th generation prototype – PT6

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P1 P2 P5

PT1 PT2 PT3PT4

PT5 PT6

FAMOBS oven prototypes

Different air cross-sections – reduced dielectric losses and easier pyrometer integration

Higher dielectric constant dielectric Very poor coupling from feed line into cavity.

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Curing investigation with PT2, PT4 and PT5 ovens

(a) (b)

Open chip Chip after

cavity-fill

Chip after

curing

(c)

• Outcome• An LM2940C-12 voltage regulator chip in a QFN package successfully tested for

functionality after curing• Observations suggested that ‘hardening’ of the encapsulant paste occurred with no

apparent damage to the chip package• EO1080 encapsulant samples cured at different temperature profiles to evaluate the

degree of cure

• High power continuous wave source not suitable for sensitive packages• SFM – Single Frequency Microwave (pulsed) with feedback control• VFM – Variable Frequency Microwave with feedback control

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00:00:10.00 00:2:30.00

00:00:10.00

With out control loop, ~ 15 W full power

Optimised open ended oven with control loop feedback

1 Hz temperature acquisition rate

• Peak temperature recorded by the thermal imaging camera versus heating

time

Infrared temperature profiles

With PT2 With PT4

With PT5

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Temperature (oC) Measurement Temperature sampling rate

(Hz)

Degree of cure Time

(s)

150 Fibre optic thermometer

(PT4)

12.5 and 5.5 98% 270

180 Fibre optic thermometer

(PT4)

12.5 and 5.5 81% 180

150 Pyrometer(PT5) 1 100%

Tg is 115 oC

270

Two step: 115 and 150 Pyrometer(PT5) 1 Closer to 100%

Tg is 100 oC

270

Comparison of different curing cycles

Curing investigation - Results

• Measurement methods and the cure cycles are compared by degree of cure.• Complete curing is achieved with lower pulse rate but without any reduction

of overall cure time of 270 seconds.

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System integration - solid state components

• Possibility for compact power delivery modules for integration with the pick and placement machine

Control

(Lab view)

RF source, Pulsed Power

amplifier, Isolator

(Dimensions 11.25×20×1

cm)

FAMOBS oven integrated

with a pyrometer

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Conclusions

• A multidisciplinary project requiring different classes of experts

• Design for system integration

• Research not necessarily follow a linear pattern

• A new generation oven with a pyrometer attached has been designed, fabricated and RF tested

• Successful curing has been achieved with the new integrated oven

• Pulsing technique used tends to control the temperature of the curing material quite accurately

• Hotspots and thermal runaway problems avoided with controlled curing

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Future work

• Multi-physics model needed to ling data to the degree of cure

• Further evaluation of cure should be under taken with commercial packages

• System design• Further tests in integration of device into precision

placement machine• Efficient coupling of power from source to cavity

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Contact Details

Heriot-Watt University

Riccarton,

Edinburgh,

EH14 4AS, UK.

http://www.hw.ac.uk

Prof. Marc Desmulliez,

Tel: +44 (0)131 451 3340

Fax: +44 (0)131 451 4155

Email: m.desmulliez@hw.ac.uk

Contact

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Website: www.famobs.eu