Substrates Used for Polyimide Deposition 

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Polyimide (PI) Films & Spin-On Coatings

UniversityWafer, Inc. supplies polyimide (PI) films and spin-on coatings used for passivation, stress-buffering, and redistribution-layer (RDL) dielectrics in advanced packaging and MEMS. Pair PI with the right wafer substrate and thickness to control bow, protect interconnects, and enable flexible structures.

Request Polyimide (PI) Coated Wafers

Spin-on and photosensitive polyimide (PSPI) for passivation, RDL, and stress-buffering applications. Available from 2 – 50 µm.

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When to Choose Polyimide

  • Stress buffer: Relieves CTE mismatch between metals and oxides to reduce cracking/warpage.
  • Passivation: Protects BEOL from moisture/contaminants while keeping flexibility.
  • RDL dielectric: Insulation for fan-out / wafer-level packaging with UV-patternable PSPI.
  • Flexible interconnects: Bending-tolerant films for sensors and packaging on thin wafers.

Quick Spec Template (Copy/Paste)

  • Substrate: Si(100) or Si(111) DSP, dia ____ mm, thickness ____ µm, TTV ≤ ____ µm
  • PI Type: Spin-on / Photosensitive (PSPI)
  • Target Film: ____ µm (single-coat) or ____ µm total (multi-coat)
  • Soft Bake: ____ °C / ____ min | Cure/Imidize: ____ °C / ____ min (N₂)
  • Patterning: Via diameter ____ µm; etch or UV-develop window
  • Electrical: k = ____ ; Dielectric strength ≥ ____ MV/cm
  • Surface: RMS ≤ ____ nm; Adhesion promoter (yes/no)

Process Tips

  • Use edge-bead removal to keep PI off the wafer edge for better chucking and litho alignment.
  • Multi-coat for thicknesses > ~15 µm; bake between coats to prevent voids.
  • For PSPI, calibrate exposure/PEB to achieve vertical via sidewalls and clean metal pads.
  • Verify bow/warp after cure—adjust bake ramps and substrate thickness as needed.

What Is Polyimide (PI)?

Polyimide (PI) is a high-temperature, chemically resistant polymer widely used as a dielectric, stress buffer, passivation, and flexible interconnect layer in microelectronics. Its unique combination of mechanical strength, flexibility, and thermal stability makes it essential in MEMS, wafer-level packaging, and flexible electronics.

Polyimide-coated semiconductor microchip structure showing interconnect layers and passivation, representing UniversityWafer polyimide wafer materials

Why Polyimide Matters in Semiconductor Processing

Unlike inorganic films such as silicon nitride or thermal oxide, polyimide provides an organic dielectric that relieves stress, reduces wafer bow, and enables conformal coverage over topography. It is also a key material for fan-out packaging and redistribution layer (RDL) integration.

Common Polyimide Types

  • Spin-On Polyimide (non-photosensitive): Applied via spin coating and patterned with dry-etch or O₂ plasma after curing.
  • Photosensitive Polyimide (PSPI): UV-patternable formulations simplify lithography for vias and RDL patterning.
  • Thermoplastic vs Thermosetting: Thermosetting PIs form irreversible crosslinks for high reliability; thermoplastic PIs offer easier rework.

Process Overview

Typical process flow:

  1. Spin-coat polyimide onto wafer (thickness 2–25 µm typical).
  2. Soft bake (80–150 °C) to remove solvent.
  3. Pattern (expose & develop for PSPI or dry-etch for standard PI).
  4. Cure/imidize in N₂ or vacuum oven at 300–400 °C for final film properties.

Cured PI films exhibit excellent chemical resistance, adhesion, dielectric strength (2–4 MV/cm), and dimensional stability under temperature cycling.

Applications & Functions

  • Stress-Buffer Layer: Mitigates thermal stress between metals and silicon or oxide layers.
  • Passivation: Protects underlying interconnects and devices from humidity, contamination, and mechanical damage.
  • Dielectric in RDL: Electrical insulation between routing layers in fan-out wafer-level packaging (FOWLP).
  • Flexible Interconnects: Used in flex substrates and sensor arrays requiring bending and thermal cycling endurance.
  • Adhesion Promotion: Serves as an interlayer between metals (Cu, Al) and oxide/nitride dielectrics.

Advantages Over Other Dielectrics

  • High thermal stability up to 400 °C (suitable for Cu/Al backend processing).
  • Low dielectric constant (k ≈ 3.2–3.5) → reduces capacitance and crosstalk.
  • High tensile strength with low modulus for mechanical flexibility.
  • Excellent adhesion to Si, SiO₂, Si₃N₄, and various metals.
  • Compatible with spin coating, spray coating, or lamination on silicon, sapphire, and GaAs wafers.

Thickness & Property Range

Property Typical Range
Film Thickness2 – 50 µm (spin-coated)
Glass Transition Temp (Tg)250 – 360 °C
Dielectric Constant (k)3.1 – 3.5
Dielectric Strength2 – 4 MV/cm
Tensile Strength100 – 200 MPa

PI vs PBO (Polybenzoxazole)

While both materials are used as polymer dielectrics, polyimide offers higher thermal resistance and chemical durability, whereas PBO provides lower dielectric constant and moisture absorption. PI is preferred for high-temperature backend-of-line (BEOL) and power MEMS applications.

Substrates for Polyimide Coating