Key Takeaways
Electronic-grade polyimide (PI) film is the backbone material for flexible printed circuits (FPC), chip-on-film (COF) packaging, flexible displays (CPI cover windows), and 5G high-frequency substrates. Three parameters drive selection: long-term thermal rating (200/240/260°C), dielectric constant and loss (Dk/Df), and dimensional stability (CTE matching). As of 2026, Chinese domestic PI films have achieved solid substitution in FPC-grade applications, while COF-grade, CPI, and low-loss MPI remain dominated by DuPont, Kaneka, UBE, and Korean suppliers.
1. PI Film Grades and Application Mapping
- Electrical grade: motor slot insulation and wire wrapping, 25–125μm, lowest cost, abundant supply;
- Electronic grade (FPC): base film for flexible copper-clad laminates (FCCL), requiring high surface cleanliness and thickness tolerance within ±3%; mainstream thicknesses are 12.5μm and 25μm;
- COF grade: chips are bonded directly onto the film, demanding CTE matched to copper (16–20 ppm/K) and low moisture absorption — the highest technical barrier;
- MPI (modified PI): targets 5G high-frequency use, with Df as low as 0.002–0.004 at 10GHz, competing directly with LCP;
- CPI (colorless PI): foldable display cover windows, transmittance >88%, haze <1%; supplied mainly by SKC, Kolon, and SK IE Technology.
2. Core Selection Parameters
2.1 Thermal Performance
Check three values, not one: glass transition temperature Tg (typically 360–410°C), long-term service temperature (UL RTI rating, usually 200–240°C), and thermal shrinkage (<0.05% at 200°C/2h). For lead-free reflow processes (260°C peak), always request 260°C/10s shrinkage data from the supplier.
2.2 Dielectric Properties
Standard PI shows Dk ≈3.4 and Df ≈0.004–0.010 at 1MHz, but performance degrades notably after moisture uptake (water absorption 1.3–3.0% is PI’s inherent weakness). For mmWave and 77GHz radar applications, compare measured 10GHz data after humidity conditioning, not datasheet typical values.
2.3 Dimensional Stability
CTE is critical for FCCL lamination and COF packaging. Standard PMDA-type PI runs 30–40 ppm/K, causing warpage against copper (17 ppm/K). BPDA-based films (Kaneka Apical NPI, UBE Upilex-S) achieve 12–20 ppm/K and are the default choice for COF and multilayer FPC.
2.4 Mechanical Properties and Gauge Capability
Tensile strength ≥200MPa and elongation ≥60% are baseline requirements for electronic grade. The ability to reliably supply 7.5μm and 5μm ultra-thin films is a key differentiator between supplier tiers.
3. Supplier Landscape (2026)
- DuPont (Kapton): broadest portfolio — HN (general), EN (low CTE), FPC grades; premium pricing;
- Kaneka (Apical/Pixeo): leading share in FCCL base films; NPI low-CTE grade is the COF mainstream;
- UBE (Upilex-S/VT): benchmark BPDA chemistry with best-in-class dimensional stability; the de facto COF substrate standard;
- SKC and PI Advanced Materials: Korean leaders; PIAM holds the world’s largest capacity with fast expansion into MPI and thermally conductive grades;
- Chinese suppliers: Times New Material, Rayitek, Goofront, ZTT and others. FPC-grade 12.5/25μm films now ship in volume at 20–35% below imported pricing; CPI and COF grades are still in qualification.
4. Procurement Checklist
- Batch-level COA: require per-lot data on thickness tolerance, thermal shrinkage, and surface defects (fish eyes, gel particle density) — not catalog typical values;
- Surface treatment confirmation: cast-type FCCL processes need surface energy ≥50 dyn/cm; specify single-side or double-side corona/plasma treatment in the technical agreement;
- Moisture control: store below 40%RH, use within 24 hours of opening, or bake at 120°C for 2 hours before lamination;
- Qualification path for Chinese alternatives: start with electrical grade and low-layer FPC, accumulate 6+ months of reliability data (85°C/85%RH, thermal shock -55 to 150°C) before migrating to high-end applications;
- Price reference (July 2026): imported electronic-grade 25μm at roughly USD 12–21/m²; comparable Chinese films at USD 8–14/m²; CPI cover films remain above USD 200/m², with the gap driven mainly by yield.
5. Outlook
Three trends to watch: the MPI vs. LCP battle in 5G/6G high-frequency substrates, where MPI currently leads on process compatibility; foldable-driven CPI demand, projected to exceed 4 million m² globally in 2026 despite competitive pressure from UTG; and Chinese high-end capacity ramp-up, with chemical imidization lines coming online that could break through COF-grade qualification within 18 months.
This article is a technical reference for industry buyers. For sample sourcing or supplier evaluation support, contact our team.