Frequency Agile Microwave Oven
Bonding System (FAMOBS)
From feasibility study to production prototype
Prof. Marc Desmulliez
Heriot-Watt University
Edinburgh, UK
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Contents
• Microwave heating – principles and applicators
• Funding schemes and partners
• Project overview
• Open end oven prototypes
• Results - Curing
• Conclusions and future work
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FAMOBS funding schemes
FAMOBS (UK)
•
•
•
18 month research project (feasibility
and project deepening)
Funded by the IeMRC
3 research partners + 4 industrial
partners
FAMOBS (EU)
•
•
•
Project funded by the European
Commission within FP7
3 year project starting in November
2008
5 industrial collaborators, 4 RTD
performers and 4 SME associations
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Microwave heating
•
Generates heat at the molecular level by forced oscillation of
polar bonds
•
Materials ability to absorb microwaves depends on:
•
Complex permittivity, conductivity, frequency & temperature
•
Heating is volumetric as compared to thermal transfer from
convection heating
Convection – heat penetrates from surface
Microwave – uniform heat generation
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Microwave Applicators
Semiconductor manufacturing
GERLING APPLIED ENGINEERING, INC
.
http://www.2450mhz.com/PDF/Doc/900065.pdf
Lambda Technologies
(http://www.microcure.com/)
TM
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 polymer
dielectrics in semiconductor manufacturing and packaging
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Challenges – Multiphysics modelling
8/28
Open ended oven integration
FAMOBS oven
prototype system
Microwave oven on
die placement arm
Die, Adhesives,
Encapsulants, Underfills, etc
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FAMOBS System Stakeholder Map
GE Aviation
IDM
Fabless
PCB
FAMOBS
System
Research
Test
Q&R
Services
Foundry
Packaging
10/28
Other applications
• Petroleum compounds extraction
• Ceramic composites sintering and annealing
• Sintering of carbon composites
• Bonding applications for micro-fluidic, microelectronics and
MEMS
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Manufacturing capability
readiness levels
Phase of Development
Phase 4
Production
Improvement
Phase 3
Production
Implementation
Phase 2
MCRL
10
9
State of Development
Continuous improvement to fully capable production process
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
8 run lengths
7 Capability and rate confirmed via economic run lengths on production
6
Process optimised for capability and rate using production equipment
5
Basic capability demonstrated using production equipment
Phase 1
4
Process validated in laboratory using representative equipment
Manufacturing
technology
proven and
assessment in
laboratory
environmental
3
Experimental proof of concept completed.
2
Applicability and validity of concept described and examined or demonstrated
1
Process concept proposed with scientific foundation
Pre-Production
in relevant
environmental
Process concept proposed. Process unreported in literature, potential for generating
IP.
(source : Nabil Gindy, University of Nottingham)
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1st generation prototype – PT1
MCRL1
PT1
MCRL2
MCRL3
PT2
•
PT3
PT4
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)
•
PT5
•
•
•
•
MCRL5
MCRL6
Evanescent field used for heating
The electrical length of the cavity can be controlled
through adjustment of additional conducting rods.
Disadvantages:
PT6
MCRL4
Mechanical design for control of length of conducting
rods
Substantial heat generated within dielectric
MCRL7
MCRL8
MCRL9
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2nd generation prototype – PT2
MCRL1
PT1
MCRL2
MCRL3
PT2
Single Feed, Multiple Heating Spots @ ≈ 10.19GHz
PT3
PT4
•
•
The fringing field depth of the evanescent field can be
controlled through proper choice of bulk dielectric
permittivity
Disadvantages:
• Excessive loss tangent (tanδ) of dielectric insert
PT5
• Substantial heat generated within dielectric
- curing occurred through thermal conduction
PT6
MCRL4
MCRL5
MCRL6
MCRL7
MCRL8
• Decrease in cavity Q Factor
- quasi degeneracy disturbs modal field pattern within cavity
McRL9
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3rd generation prototype – PT3
MCRL1
PT1
PT2
•
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 ‘XBand’ connectors (SMA, SMB)
MCRL4
•
Purchase of MMCX connectors suitable up to
5GHz
McRL5
•
Very poor coupling from feed line into cavity.
McRL6
•
Drilling of connector hole (dia. 0.8mm) caused
a failure within the ceramic.
McRL7
•
Results suggest lower permittivity (er < 10)
cavity would be more suitable.
McRL8
PT5
PT6
MCRL3
•
PT3
PT4
MCRL2
McRL9
15/28
4th generation prototype – PT4
•
PT1
Optimised design with dielectric insert for improved heating
rate
MCRL1
MCRL2
MCRL3
PT2
MCRL4
PT3
MCRL5
PT4
PT5
PT6
• Bulk Dielectric
 er = 2.1
 Length = 90mm
• Dielectric Insert
 er = 6
 Optimised length = 3.5mm Temperatures recorded with PT4,
PT2 and a convection oven
MCRL6
MCRL7
MCRL8
MCRL9
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4th generation prototype – PT4
MCRL1
PT1
MCRL2
MCRL3
PT2
MCRL4
PT3
MCRL5
Temperatures recorded with the optimised, normal open end oven and a convection oven
PT4
PT5
PT6
Electric field distribution comparing shift
in maxima due to inclusion of an
optimised dielectric insert: a) TM11, 1st
mode b) TM11, 2nd mode
•
Measurement temperature results for a
150oC curing cycle by pulsing the
source.
Disadvantages:
• Temperature measurement
• Couldn’t be integrated with the placement machine
MCRL6
MCRL7
MCRL8
MCRL9
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5th generation prototype – PT5
Open end /
load section
PT1
MCRL1
MCRL2
MCRL3
PT2
Pyrometer
MCRL4
PT3
MCRL5
PT4
PT5
PT6
McRL6
• New design for integration with the pick and
placement machine
• Integrated IR pyrometer for temperature
sensing
MCRL7
MCRL8
MCRL9
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5th generation prototype – PT5
MCRL1
PT1
MCRL2
MCRL3
PT2
MCRL4
PT3
•
PT4
Results of the IR pyrometer measured temperature
curves for a 150oC curing cycle by pulsing the source.
The pulsing method has resulted in a better control
of programmed temperature with a temperature
accquisition rate of 1 Hz.
•
PT5
• Disadvantages:
PT6
•
•
Dielectric losses in the bulk dielectrics and insert
Difficulty in the integration of pyrometer
MCRL5
MCRL6
MCRL7
MCRL8
McRL9
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6th generation prototype – PT6
MCRL1
PT1
PT2
•
Different air cross-sections
MCRL2
•
Designed and modelled
MCRL3
MCRL4
Advantages
Advantages
PT3 •
Easier integration
of pyrometer
•
Easier integration
of pyrometer
MCRL5
No losses
duelosses
to dielectric
filling and no need of replacing dielectrics
•
No
due to dielectric
Could
be easier
for and
tuning
(impedance
matching) with extra tuners (screws)
filling
no need
of replacing
PT4
MCRL6
No need of precise control
of the robotic arm as material can be moved inside
the cavity
dielectrics
•
Could be easier for tuning
MCRL7
(impedance matching) with
PT5
extra tuners (screws)
MCRL8
•
No need of precise control of
the robotic arm as material can
PT6
MCRL9
be moved inside the cavity
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FAMOBS oven prototypes
Different air cross-sections – reduced dielectric
losses and easier pyrometer integration
PT5
PT1
P1
PT2
P2
PT3
PT6
PT4
P5
Higher dielectric constant dielectric
Very poor coupling from feed line into cavity.
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Curing investigation with PT2, PT4 and PT5 ovens
Open chip
(a)
•
Chip after
curing
(c)
Outcome
•
•
•
•
(b)
Chip after
cavity-fill
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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Infrared temperature profiles
With PT2
With PT4
00:00:10.00
With out control loop, ~ 15 W full power
With PT5
00:00:10.00
00:2:30.00
Optimised open ended oven with control loop feedback
1 Hz temperature acquisition rate
•
Peak temperature recorded by the thermal imaging camera versus heating
time
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Curing investigation - Results
Comparison of different curing cycles
Temperature (oC)
Measurement
150
150
Fibre optic
thermometer
(PT4)
Fibre optic
thermometer
(PT4)
Pyrometer(PT5)
Two step: 115 and 150
Pyrometer(PT5)
180
•
•
Temperature
sampling rate
(Hz)
12.5 and 5.5
Degree of cure
Time
(s)
98%
270
12.5 and 5.5
81%
180
1
100%
Tg is 115 oC
Closer to 100%
Tg is 100 oC
270
1
270
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
RF source, Pulsed Power FAMOBS oven integrated
amplifier, Isolator
with a pyrometer
(Dimensions 11.25×20×1
cm)
Control
(Lab view)
•
Possibility for compact power delivery modules for integration with the
pick and placement machine
25/28
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
Contact Details
Prof. Marc Desmulliez,
Tel: +44 (0)131 451 3340
Fax: +44 (0)131 451 4155
Email: [email protected]
Heriot-Watt University
Riccarton,
Edinburgh,
EH14 4AS, UK.
http://www.hw.ac.uk
Website: www.famobs.eu
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