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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