Chapter 8: Hybrid Technology and Multichip Modules

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Chapter 8 Hybrid Technology and Multichip Modules

• Hybrid mixture, i. e. Components and wiring
  integrated on the substrate. Picture shows a thin
  film hybrid for seismic electronics.

The course material was developed in INSIGTH II,
a project sponsored by the Leonardo da Vinci
program of the European Union
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Types of Hybrids and Multichip Modules

• Thick film technology
• High temperature thick film hybrid technology
• Polymer thick film hybrid technology
• Thin film technology
• Conventional thin film technology (one conductor
  layer)
• Multilayer thin film technology
• Multichip modules
• Multilayer ceramic (MCM-C) (C for ceramic)
• Multilayer thin film (MCM-D) (D for deposited)
• Multilayer fineline circuit boards (MCM-L) (L for
  laminated)
• Please also confer to Chapters 3 and 5 for basic
  processes

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High Temperature Thick Film Technology

• Important substrate properties
• Dimensional stability
• Good adhesion
• High thermal conductivity
• Thermal compatibility with components
• High electrical resistivity
• Low dielectric constant (not satisfied in
  alumina)
• Low dielectric loss tangent
• Good machinability (not satisfied in ceramics)
• Low price

4
Screen Printing and Stencil Printing

• Fig. 3.11 Screen printing a) and b) Printing
  process, c) and d) Details of the screen

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High Temp Thick Film, continued

• Practical materials
• Alumina
• Aluminium nitride
• (Beryllia)
• (Silicon carbide)
• Table 8.1Properties of substrate materialsfor
  hybrid technology.P Plastic In Insulator

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Conductor Materials

• Composition
• Functional element (metal particles)
• Binder (glass particles)
• Solvents
• Desired properties
• High electrical conductivity
• Good adhesion to substrate
• Good solderability
• Good bondability
• Low price

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Conductor Materials, continued

• Practical functional element
• Gold
• Ag/Pd
• Ag/Pt
• Copper

Table 8.2 Properties of thick film conductor
systems
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Thick Film Resistors

• Important properties
• Large range of resistor values
• High stability
• Low thermal coefficient of resistivity
• Low voltage coefficient of resistivity
• Low noise
• Materials
• Oxides of ruthenium
• Oxides of iridium, rhodium, osmium
• Sheet resistance 1 - 109 ohms/sq

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Properties of Thick Film Resistors

• Table 8.3 Typical properties of thick film
  resistors.

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Termination of Thick Film Resistors

• Fig. 8.2 Thick film resistor with termination

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Insulators / Dielectrics

• Desired properties
• High insulation resistance
• High breakdown field
• Low dielectric constant (insulation)
• Suitable/high dielectric constant (dielectric)
• Low temperature coefficient (dielectric)
• Low voltage coefficient (dielectric)
• Low loss tangent
• Little porosity

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Insulators / Dielectrics, continued

• Materials
• Aluminium oxide/glass (insulator)
• Ceramics/glasses as for capacitors (dielectric)
• Please also see Chapter 4

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Insulators / Dielectrics, continued

• Table 8.4 Typical properties of printed and
  discrete capacitors.

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Production Process for High Temperature Thick
Film Technology

• Layout and photolithographics
• CAD work
• Photo or laser plotting of master films
• Printing screens made with master films

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Production process, continued

• Printing process
• Printing
• Drying at 100 - 150 C
• Firing at 700 - 1000 C
• Fig 8.1 Typicaltemperature profilefor thick
  filmfiring.

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Production process, continued

• Testing and laser trimming
• Initial value targeted 20 - 30 below specified
  value
• Laser trimming to increase resistance within
  0.5 or 1.0

Fig. 8.4 Probe card for testing of thick- and
thin film hybrid circuits. Coaxial probes are
used for high frequency signals.
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Laser trimming
a)
b)
c)

• Fig. 8.5 Laser trim cut forms a) L-cut, the
  most common b) Top hat plunge cut c) Digital
  trimming, which is most used for high precision
  thin film resistors

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Laser trimming, continued

• Fig. 8.6 Laser trimmer for thick film hybrid
  circuits, ESI Model 44.

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Production process, continued

• Fig. 8.7 Process flow for mounting of thick film
  hybrid circuits based on a) Naked ICs and
  gluing of discrete components.

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Production process, continued

• Fig. 8.7 Process flow for mounting of thick film
  hybrid circuits based on b) Soldering of
  packaged ICs and discrete components.

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Polymer Thick Film Technology

• In polymer thick film hybrid technology (PTF)
  conductors, resistors and insulating layers use a
  polymer matrix instead of glass matrix, and these
  are made in several layers on ordinary printed
  wiring board laminates, flexible substrates and
  injection moulded plastic materials that can
  serve as combined printed circuits and chassis.

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Polymer Thick Film, continued

• Advantages
• Low price
• Simple processes
• Fast production throughput
• Well suited for repair/modification
• Printed resistors possible
• Additive technology
• Printed wiring boards for substrates
• Specialities
• Membrane switch panels
• Contacts

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Polymer Thick Film, continued

• Limitations
• Satisfies only moderate environmental
  requirements
• Low/moderate complexity
• High sheet resistivity in conductors
• Special design rules
• Limited solderability
• Limited shelf life for pastes
• Limited availability

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Polymer Thick Film, continued

• Fig. 8.8 Polymer Thick film (PTF) carbon
  technology, for
• a) Keyboard contacts.
• b) Contacts of LCD- displays.
• c) Sliding potentiometer.
• CPTF means carbon type PTF.

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Polymer Thick Film, continued

• Materials
• Matrix Thermosetting /thermoplastic polymer
• Conductor Ag, Cu, C
• Solvents
• Additives to adjust consistency
• Ceramic or other additives

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Polymer Thick Film, continued

• A typical process
• The starting material is a laminate with a single
  sided etched conductor pattern in Cu foil
• 1. Cleaning of the board
• 2. Printing of PTF insulation layer, 2 prints,
  drying in between
• 3. Drying
• 4. UV curing
• 5. Printing of PTF conductor
• 6. Drying
• 7. Curing in IR in-line furnace
• 8. Chemical plating of metal (Optional)
• 9. Printing of top layer
• 10. Drying
• 11. Curing in IR furnace.

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Polymer Thick Film, continued

• Fig. 8.9 Membrane switch panel, principle.

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PTF, continued

• Fig. 8.10 PTF based printed wiring boards a)
  Single sided board with PTF for one complete
  conductor layer on top of one Cu foil conductor
  plate. b) Double sided, through hole plated
  board with one extra PTF conductor layer on each
  side. c) Double sided board through hole
  printed PTF conductor, instead of through hole
  plating.d) PTF resistor

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Thin Film Technology

• Substrate materials
• Alumina, glass, silicon
• Conductor materials
• Gold, aluminium
• Resistor materials
• NiCr (Chrom nickel), Ta2N (Tantal nitride)
• Insulation/dielectrics/passivation materials
• SiO2 (Silicon dioxide), SiN3 (Silicon nitride),
  Al2O3 (Aluminium oxide), Ta2O5 (Tantal oxide)

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Thin Film Technology, continued

• Table 8.5 Properties of thin film resistors.
  (d skin depth. Evap Vacuum evaporation. Sp
  Sputtering)

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Thin FilmProcessing

• Photolithography and etching
• Vacuum evaporation
• Sputtering
• Plating
• Oxidation
• Fig. 8.11 Process flow for production of thin
  film hybrid circuits.

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Vacuum Deposition and Sputtering

• Vacuum evaporation
• Chamber evacuated toless than 10-6 Torr
• Resistance heating
• Metal evaporation

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Other Methods for Deposition of Conducting or
Insulating Films

• DC Sputtering (Fig. 3.13.a)

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Deposition, continued

• Radio Frequency AC Sputtering (Fig.3.13.b)

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Thin Film Processing, continued

• Fig. 8.12 Structure of thin film resistor with
  gold termination.

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Thin Film Processing, continued

• Fig. 8.13 Thin film microwave circuit,
  schematically.

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Thin Film Processing, continued

• Fig. 8.14 Thin film transistors, structure.

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Thin Film Processing, continued

• Circuit production
• Glueing
• Wire bonding
• Testing
• Packaging in hermetic (metal) box

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Wire Bonding

• Ultrasonic
• Thermo-compression
• Thermosonic
• Geometry Types
• Ball - wedgeShown in illustration
• Wedge - wedge

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What are Multichip Modules?

• A multichip module (MCM) is a single unit
  (package) containing two or more chips and an
  interconnection substrate which function together
  as a system building block.

MCM-L MCM-C MCM-D From http//www.aws.cit.ie/re
search/wirelessnodes/index.htm
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Types of Multichip Module Substrates

• 3 basic multichip modules
• MCM-D deposited thin-film multilayers (D for
  deposited)
• MCM-C thickfilm or cofired ceramic technology (C
  for ceramic)
• MCM-L based on organic laminate technology(L for
  laminated) derived from conventional PWB
  technology(also known as chip-on-board, COB)

Pictures from http//www.aws.cit.ie/research/wire
lessnodes/index.htm
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Multilayer Thin Film MCM-D

• Process
• 1. Spinning polyimide insulation
• 2. Deposition Al metallization
• 3. Photolithography, wet etch
• 4. Spinning polyimide
• 5. Etching vias
• 6. Repetition steps 1 - 5
• 7. Metallization and etching of metal

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MCM-D, continued

• Fig. 8.15 a) ATTs structure for multilayer
  thin film. Please also see also Figure 2.13.

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MCM-D, continued

• Fig. 8.15 b) Cross section of Raychems High
  Density Interconnect (HDI) schematically and
  observed through microscope.

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MCM-D, continued

• Fig. 8.16 Elements of the design rules for
  Raychems HDI technology

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MCM-D, continued

• Fig. 8.17 Characteristic impedance for Raychems
  HDI as function of the ratio between conductors
  width and dielectric thickness.

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MCM-D, continued

• Fig. 8.18a) Dissipation factor for Raychems
  HDI

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MCM-D, continued

• Fig. 8.18. b)Typical attenuation, as function
  of frequency, for Raychems HDI. Even at 10 GHz
  attenuation in the conductor metal dominates.

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MCM-D, continued

• Advantages
• Optimal thermal match when Si substrate
• High thermal conductivity in Si 150 W/C x m
• Termination resistors and decoupling capacitors
  integrated in substrate
• Compatibility with
• Wire bonding
• TAB
• Flip chip
• Very high conductor density/package density
• Very good high frequency properties
• Good mechanical properties of Si substrate
• High reliability

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MCM-D, continued

• Disadvantages
• Low availability and high cost
• Polyimide is hygroscopic
• Important properties change
• Reliability problems
• Hermetic encapsulation necessary
• Immature technology

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Multilayer Ceramic Modules - MCM-C

• Materials
• Alumina
• Aluminium nitride
• Pioneer IBM
• Fabrication Green Tape process

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MCM-C, continued

• Fig. 8.19 Production process for multilayer
  ceramic, schematically.

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MCM-C, continued

• Advantages
• High thermal conductivity
• Low TCE, match to Si, GaAs, SMDs
• Compatible to flip chip, wire bonding, TAB, SMD
  soldering
• Control over characteristic impedance
• Hermetic encapsulation possible, high reliability
• Many conductor layers, high yield
• Edge contacts, etc. brazed on

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MCM-C, continued

• Disadvantages
• Low electrical conductivity in inner layers (Rsq
  15 mOhm/sq)
• High dielectric constant, ?r 9 - 10
• High startup cost for custom specific circuits

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MCM-C, continued

• Fig. 8.20 Combination of naked chips in cavities
  and soldered, packaged SMD components on
  multilayer ceramic module

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MCM-C, continued

• Fig. 8.21.a Characteristic impedance for
  typical geometries and dimensions, Al2O3-based
  multilayer ceramic a) Open microstrip.

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MCM-C, continued

• Fig. 8.21.b Characteristic impedance for
  typical geometries and dimensions, Al2O3-based
  multilayer ceramic b) Buried microstrip.

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MCM-C, continued

• Fig. 8.21.c Characteristic impedance for
  typical geometries and dimensions, Al2O3-based
  multilayer ceramic c) Stripline.

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MCM-C, continued

• Table 8.6 Properties of alumina-based high
  temperature multilayer ceramic.

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Low Temperature Multilayer Ceramic Modules -
LTMCM-C

• Substrate materials
• Glasses, glass ceramics
• Mullite, corderite, lead borosilicate glass...
• Conductors
• Gold, silver, AgPd
• Resistors
• Similar to thick film
• Properties Table 8.7.

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LTMCM-C, continued

• Table 8.7 Electrical and physical properties of
  low temperature multilayer ceramic. a)
  Electrical properties.

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LTMCM-C, continued

• Table 8.7 Electrical and physical properties of
  low temperature multilayer ceramic. b) Resistor
  Performance - Resistance and TCR.

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LTMCM-C, continued

• Table 8.7 Electrical and physical properties of
  low temperature multilayer ceramic. c) Physical
  properties.

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LTMCM-C, continued

• Advantages
• Low process temperature
• Most process steps can be done in high
  temperature thick film production line
• Flexibility in conductor materials, low sheet
  resistivity
• Plating not necessary for bonding
• Screen printed resistors
• Low er dielectric materials

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LTMCM-C, continued

• Disadvantages
• High costs
• Low thermal conductivity
• Brittle materials
• Low availability

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Power Electronic Modules

• Challenges
• Spread the heat, reduce thermal resistance
• Reduce thermal stress
• Provide electrical insulation for 2.5 kV
• Design for EMC, reduce L
• Higher integration "smart power

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Power Electronic Modules, continued

• Technologies
• Polymer on metal
• Thick film
• Plated ceramic substrate
• Direct Copper Bonding (DCB)
• Plasma sprayed dielectric on metal base

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Power Electronic ModulesDirect Copper Bonding

• Fig. 8.22 a) The coefficient of thermal
  expansion for direct copper bonding (DCB)
  substrates with a layer of 0,6 mm alumina
  sandwiched between Cu layers of various
  thicknesses as given in the figure.b) The
  number of thermal cycles to fracture for DCB
  substrates with varies Cu thickness. The cycles
  were in the temperature interval -40 - 110C.

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Direct Copper Bonding, continued

• Fig. 8.23 Power electronic module Toshiba data
  sheet. The substrate (top) is DCB with AlN
  insulation. It is soldered to a heavy Cu plate,
  environmentally protected with silicone gel and
  mounted in a plastic package with heavy screw
  terminals. Each of the transistor chips and diode
  chips conducts up to 50 A current.

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Combination Technologies

• Multilayer thin film - on - multilayer ceramic
• Fig. 8.24 High performance modules made in a
  combination of multilayer thin film and multi
  layer ceramic technology a) NEC Corporation
  computer SX-3 using flop TAB carrier on thin film
  and alumina based substrate. b) IBM Enterprise
  System/9000 packaging hierarchy using flip chip,
  polyimide/copper thin film on 63 layers glass
  ceramic substrate.

a)
b)
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Combination Technologies, continued

• Thin film - on - thick film (ame, Horten).
  Fig.8.25

1. Alumina substrate. 2.a,b,c,d Printed
conductor on first layer. 3. Printed dielectric
film. 4. Optional compensation printed in
vias. 5.a,b,c Printed conductor on second
layer. 6. Glass based dielectric. 7. a,b,c,d
Tantalum nitride resistive layer.
8.a,b,c,d Molybdenum diffusion barrier. 9.a,b,c
Thin film gold lines. 10. Via hole between thin
film and thick film conductive layer. 11.
Contact area in thick film. Gold- platinum
or gold-palladium. 12.a,b Resistor in thin film
made by selective etching in thin film
structure
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End of Chapter 8 Hybrid Technology and
Multichip Modules

• Important issues
• Thick film technology
• Understand the basic material considerations
• Substrate materials
• Thick film pastes
• Understand the basic manufacturing steps
• Process flow diagrams from printing to final test
• Chip-and-wire or SMD component assembly
• Distinguish between High Temperature and Polymer
  Thick Film Technologies
• Thin Film Technology
• Understand the basic material considerations
• Substrates Ceramic, glass or silicon
• Thin film conductors, resistors and dielectrics
• Understand the basic manufacturing steps
• Process flow diagrams from deposition to final
  test
• Hybrid Multichip Modules
• MCM-D and MCM-C Basic process steps
• Combination technologies
• Applications with special requirements