Across high-capacitance multilayer ceramic capacitor (MLCC) manufacturing, carrier films are used as sacrificial substrates for tape-casting barium titanate dielectric slurries and as interleaving covers during blank pressing. The product described as MLCC Release Film is a biaxially oriented polyethylene terephthalate (BOPET) substrate, coated on one side with a crosslinked polysiloxane or acrylic-based release layer. Representative model designations include MLCC-RF-25-R2-AS, which denotes a nominal 25 µm polyester substrate, release class R2, and an antistatic backside. Standard substrate thicknesses are 12 µm, 16 µm, 19 µm, 25 µm, 31 µm, 38 µm, and 50 µm, with slit widths from 300 mm to 1,600 mm and width tolerance ±0.1 mm per ISO 4593. The release layer may be a thermally cured polydimethylsiloxane system or a non-silicone acrylic/carbamate system. The silicone grade is typically selected when release force below 0.15 N/25 mm at 300 mm/min peel speed is required; the non-silicone grade is specified when residual siloxane on the green sheet must be excluded because of subsequent nickel electrode adhesion issues.

In tape casting, the film is unwound under controlled tension between 50 N and 150 N on a slot-die or reverse gravure line. The ceramic slurry, typically 80–90 wt% solids in methyl ethyl ketone/ethanol/toluene mixtures, is applied at wet film thicknesses from 20 µm to 60 µm and dried in multi-zone ovens between 60 °C and 120 °C. The release film supports the unsintered sheet during drying, peeling, and screen printing; it is removed before binder burnout. In lamination, sheets are stacked and pressed at 40–80 °C and 30–70 MPa, with release film interleaving between platen and stack to prevent binder migration onto press surfaces.

The film is used at three points in standard MLCC process flow. First, as a casting carrier: the ceramic slurry is coated directly on the release surface and dried, and the green sheet is peeled from the film before or after printing and sheet stacking. Second, as a printing support: after peeling, the green sheet may be temporarily relaminated to a fresh release film to maintain dimensional stability during screen printing of nickel internal electrodes. Third, as a lamination separator: release film is inserted between the green stack and press platen to prevent resin and binder transfer. The release film is removed before cutting, binder removal, and co-firing; no film residue is permitted in the multilayer body.

On production lines running at 120 m/min, web wander below 0.3 mm per linear metre is required because the release film edge becomes the reference for electrode registration. Polyester substrate modulus and thickness variation affect web wander; a thickness tolerance of ±5% per ISO 4593 is enforced. Incoming inspection also verifies roll hardness, edge cut quality, and cleanliness because splice failures or loose slitting debris are common process interruptions on cast lines operating with tension below 150 N.

Which Surface Characteristics Govern Release Consistency in High-Solids BaTiO₃ Tape Casting?

Release force is measured at 180° peel angle, 300 mm/min peel rate, and 25 mm width in accordance with ISO 29862. On polysiloxane grades, representative release force ranges are 0.03–0.08 N/25 mm for R1, 0.08–0.15 N/25 mm for R2, and 0.15–0.30 N/25 mm for R3. The lower bound is not simply a handling requirement: if release force falls below 0.03 N/25 mm, slurry wetting on the release surface can become insufficient, causing retraction, pinholes, and edge scalloping in cast green sheets. If release force exceeds 0.15 N/25 mm on dielectric layers below 2 µm dry thickness, peel-induced tensile strain can nucleate microcracks that remain after sintering. Surface roughness Ra is controlled to 0.03–0.08 µm on the release side according to ISO 21920-2:2021, with Rz maximum below 0.5 µm. The smooth surface is required because basal plane defects on a 1 µm green sheet are not acceptable in high-layer count stacks; a 0.05 µm increase in Ra can alter local wet coating thickness by more than the dielectric thickness variation allowed by downstream capacitance sorting.

Conditioning before release testing is performed for 24 h at 23 ± 2 °C and 50 ± 5% RH according to ISO 291. Release force is not constant across the roll; compression near the core and blocking at the outer wrap can increase peel force by 10–20% in silicone grades. Therefore, incoming inspection samples are taken at both core and outer wrap positions, and a lot is accepted only if the release force range across those positions is ≤0.05 N/25 mm. Surface roughness measurement is carried out with a contact stylus profilometer, 4 mm evaluation length, 0.8 mm cut-off, according to ISO 21920-2:2021. In addition to Ra, peak count RPc is controlled above 40 peaks/cm to avoid isolated spikes that disrupt thin wet films.

Because the release interface directly contacts an unsintered green sheet before nickel metallisation, residual silicone transfer is treated as a rejection criterion. Silicone migration to the green sheet during drying at 80–120 °C can reduce the surface energy of the dielectric layer, alter screen-printing wetting of the nickel paste, and leave carbon-rich residues after binder burnout. Polar and dispersive surface energy components are tested by contact angle measurement using water and diiodomethane under ASTM D7334. Release-side surface energy on polysiloxane grades is typically 24–30 mN/m, while the non-silicone grades are held above 36 mN/m to ensure Ni paste wetting. Extractable silicone is limited to <0.05 g/m² by solvent extraction followed by X-ray fluorescence or ICP-MS. In comparative failure analysis, general-purpose silicone liners with extractables above 0.15 g/m² have been associated with electrode de-wetting and intermittent capacitance loss in stacks exceeding 400 layers; published multi-plant statistical Cpk data for sub-1 µm green sheets remain limited, so a process-specific qualification is required.

Thermal Dimensional Stability, Haze, and Solvent Resistance in Multi-Zone Drying Ovens

A 25 µm MLCC release film specification typically includes thermal shrinkage of not more than 0.5% in machine direction and 0.2% in transverse direction after 30 min at 150 °C per ASTM D1204. The asymmetric MD/TD shrinkage limit is necessary because the film is tensioned through ovens with repeated heating and cooling; differential shrinkage in a 1,200 mm wide web produces transverse curl and print-registration error in subsequent nickel electrode deposition. Haze is specified as <2.5% per ASTM D1003 and clarity at 92% minimum per ASTM D1746; low haze permits optical defect detection with CCD line-scan cameras at 50 µm resolution. Solvent resistance is tested by double-rub or wipe test using methyl ethyl ketone, toluene, and ethanol; the release coating must survive 50 double rubs without coating loss, and the substrate must not swell beyond 0.3% dimensional change after 10 min immersion at 23 °C in methyl ethyl ketone when tested per ASTM D543. In multi-zone ovens, this property prevents solvent-induced surface roughening that would transfer to the cast dielectric. Tensile strength at break under ASTM D882 is 210–240 MPa with elongation at break 120–150%, which allows splicing and winding under 150 N tension without web breaks.

Operationally, antistatic backside treatments are specified for cleanroom tape-casting lines because tribocharge generated during high-speed unwinding can attract airborne particles and interfere with optical inspection. The backside surface resistivity is controlled to 10^8–10^11 Ω/sq per ASTM D257, measured at 23 °C and 50% RH. Particles on the release side are controlled by slitting and packaging in an ISO Class 8 cleanroom; liquid particle count after extraction is limited to <50 particles/cm² for particles ≥0.5 µm using IEST-STD-CC1246E. Ionic contamination is held below 0.5 µg NaCl equivalent/cm² per IPC-TM-650 method 2.3.25. In lamination presses, the release film is placed as a separator between the hydraulic platen and the stacked green sheet assembly at 40–80 °C and 30–70 MPa; the release layer must not stick to the press platen or contaminate the top and bottom cover sheets. Field observations on 60-ton lamination presses with platen parallelism ≤50 µm show that edge flash from the release film is avoided when the film width exceeds the stack width by 10–15 mm.

When Non-Silicone Interleaving Films Can Replace Silicone Release Liners in Ultra-Thin Green Sheet Processes

If the target dielectric layer after sintering is below 1.2 µm, non-silicone acrylic or carbamate release films may be preferred despite their higher release force, typically 0.12–0.25 N/25 mm, because they eliminate polydimethylsiloxane migration risk. However, the higher release force requires adjusting the peeling angle to 90–120° and maintaining a controlled peel speed below 30 mm/min to prevent green sheet cracking. Non-silicone grades have a release-side surface energy of 36–42 mN/m, which improves slurry wetting and nickel paste laydown, but they exhibit higher blocking tendency under lamination pressure above 50 MPa. Therefore, backside texture or antistatic treatment is adjusted to maintain coefficient of friction below 0.4 per ASTM D1894. The product difference from commodity PET liners is material: commodity silicone release liners for pressure-sensitive adhesive applications are produced with coating weights of 0.2–1.5 g/m² and do not specify surface roughness Ra below 0.1 µm, which makes them unsuitable for 1–2 µm green sheet casting. Cellulose-based release paper is excluded because fibre shedding and moisture-induced dimensional change exceed cleanroom particle limits and produce surface defects in dielectric layers. Compared with fluorinated release films, polysiloxane MLCC grades offer lower and more stable release force in the 0.03–0.15 N/25 mm range, but fluorinated films may be used where silicone extractables are entirely prohibited; published data for this specific configuration is limited and must be generated on the target casting line.

Published data for this specific configuration is limited for high-capacitance MLCC builds requiring more than 800 layers with dielectric thickness below 0.8 µm. In such cases, a factorial qualification is executed on a pilot line equipped with a slot-die coater, 30-m three-zone oven, and a synchronized peel station. The response variables are release force after oven passage, green sheet thickness variation measured with a laser micrometer, and surface defect density after nickel screen printing. Qualification lots are rejected if the release force shift exceeds ±15% across the roll length or if thickness variance exceeds ±5% of nominal in the outer 25 mm web edge. The release film is not used above 150 °C in continuous drying zones; prolonged exposure above 150 °C increases MD shrinkage beyond the ASTM D1204 limit and can cause silicone coating embrittlement. It is incompatible with strong alkaline stripping solutions above pH 10 and with prolonged exposure to methylene chloride, which swells the polyester base film and disrupts release coating adhesion.