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Adhesive bonding. Ville Liimatainen 05.03.2013. Contents. Introduction Adhesive bonding Process overview Main features Polymer adhesives Adhesive bonding technology Bond characterization Applications Conclusion. Adhesive bonding.

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adhesive bonding

Adhesive bonding

Ville Liimatainen


  • Introduction
    • Adhesive bonding
    • Process overview
    • Main features
  • Polymer adhesives
  • Adhesive bonding technology
  • Bond characterization
  • Applications
  • Conclusion
adhesive bonding1
Adhesive bonding
  • An intermediate adhesive layer is used to bond two surfaces
  • Successfully used in many industries
    • Cars
    • Airplanes
    • Space shuttles
  • Initially not significant in semiconductor wafer bonding research
    • Small bonding areas (chip-level bonding)
  • An established wafer bonding method nowadays
process overview
Process overview
  • Polymer adhesive applied to one or both surfaces
  • Pressure applied to force the surfaces into close contact
  • Adhesive cured from liquid or viscoelastic state into solid state
    • UV, heat, pressure...
main features
Main features
  • Bonding conditions
    • From RT to ~400°C
    • Low to moderate bonding pressure
  • Pros and cons
    • Low bonding temperature
    • Works with practically any materials
    • Comparably simple, robust, low-cost
    • No hermetic bonds
    • Limited temperature stability
    • Long-term stability in harsh environments?
  • Applications
    • MEMS
    • Sensor packaging
    • 3D IC
    • Temporary bonds
polymer adhesives
Polymer adhesives


UV epoxies (e.g. SU8)

Positive and negative photoresists

Benzocyclobutene (BCB)


Polymethylmethacrylate (PMMA)



Methylsilsesquioxane (MSSQ)

Polyetheretherketone (PEEK)

Thermosetting copolyesters (ATSP)

Thermoplastic copolymers (PVDC)


Liquid-crystal polymers (LCP)


Polymers are large molecules consisting of linked small molecules (monomers)

  • Hardening
    • Solvent evaporation (drying adhesives)
    • Solidification upon cooling (hot melts)
    • Polymerization by chemical reactions (polymer precursors)
      • Mixing of two components, heat, light, moisture...
  • Deposition on wafer surfaces
    • Spin coating, spray coating, electrodeposition, stamping, screen printing, brushing, dispensing
    • CVD (thin films), lamination of films or sheets
  • Selection for wafer bonding
    • Compatibility
    • Physical properties: mechanical and thermal stability, creep strength
    • Chemical resistance, chemical stability
adhesive bonding technology
Adhesive bonding technology
  • Tools
    • Wafer bonders
    • Substrate lamination tools
      • For temporary bonding, CMP, grinding
    • Die bonders
      • For packaging
  • Alignment techniques
    • Back-side alignment, SmartView, IR, transparent wafer, through-wafer holes etc.

Wafer bonder schematic

Substrate lamination tool schematic

Schematic of the ITEC die bonder principle(NXP Semiconductors)

adhesive bonding processes
Adhesive bonding processes
  • SU-8 and BCB widely established adhesives for MEMS and electronic component production
  • Example process: Benzocyclobutene (BCB)
    • Clean the wafers (e.g. H2O2 + H2SO4 or oxygen plasma)
    • Apply adhesion promoter (spin-coat, spray-coat)
    • Deposit BCB by spin or spray coating (usually 1 – 50µm)
    • Softbake, pattern and dry etch the BCB or Expose and develop
    • Soft curing to remove solvents and volatile substances (< 300°C, ambient air)
    • Bonding in a vacuum chamber
      • Establish vacuum
      • Bring the surfaces in contact
      • Apply bonding pressure and heat (180 - 320°C, 30 to 240 minutes)
      • Chamber purge, cool down, release pressure
bond characterization
Bond characterization
  • Wafer bond quality
    • Defect rate
    • Bond strength
    • Stresses
    • Hermeticity
    • Stability
  • Common techniques
    • Bond interface imaging
    • Bond strength measurement
    • Bond hermeticity measurement

acoustic imaging

IR imaging

SEM imaging


3D integrated circuits

  • Fabrication of 3D ICs
  • Integration of ICs with MEMS
  • Fabrication of microcavities for packaging
  • Thin film solar cells
  • RF components
  • BioMEMS

Thin film and device transfer

for MEMS/IC integration

Thin film solar cells

Hydrophobic valves

Microcavities for packaging

  • Adhesive bonding is an established method for MEMS, ICs, their integration and packaging
  • Advantages
    • Low bonding temperature < 200°C
    • Applicable to various wafer materials and structures
    • Wide selection of adhesives adjusted for MEMS and electronic components available
    • Compensation of surface non-uniformities and contamination
    • No electric voltage or current involved
    • Chemical resistance
    • Simple and low-cost process
  • Drawbacks
    • No hermetic sealing (possible with a diffusion barrier)
    • Limited temperature stability
    • Limited long-term stability in harsh environments
    • Variance of the gap between the bonded surfaces
    • (Relatively) low bond strengths