Start at the joining operation
List every heat exposure, including conductor formation, bonding, component attachment, and rework. Record duration and mechanical restraint as well as temperature. A requirement to tolerate a particular soldering process can narrow the candidate constructions before electrical properties matter. Use assembly-profile planning to define the exposure rather than assuming a polymer family guarantees compatibility.
PI and PET comparison worksheet inputs
| Decision | Define | Review |
|---|---|---|
| Assembly | Joining profile and rework expectations | Grade-specific process evidence |
| Dimensional control | Critical tail pitch and outline | Change after manufacturing and assembly |
| Environment | Humidity, fluids and thermal duration | Data for the full insulation system |
| Motion | Installed folds or repeated travel | Representative assembly test |
Compare complete constructions
Toyobo lists biaxially oriented polyester among its industrial films; Qnity publishes separate polyimide film specifications. Neither film overview establishes equivalence between finished circuits. Compare the exact conductor, adhesion system, coating, and terminal design proposed by the fabricator. Review moisture, dimensional change, and handling data in the supplier’s own test context. Keep missing information visible in the selection record.
Design the prototype to settle the choice
Prepare samples that use the intended joining and installation process. Check terminal alignment after assembly, electrical behavior in the intended environment, and the actual movement required in service. The material worksheet can record these unknowns. A lower-cost film is a useful candidate only if the full assembly and acceptance route remains credible; compare that complete route when reviewing quotations.
Before you release the design
- Name the proposed film and conductor system.
- Attach the joining profile.
- Define dimensions measured after assembly.
- Record unresolved supplier-data requests.
Watch points
- Do not apply a single maximum-temperature figure to every PET or polyimide construction.
Practical questions
Can PET be considered for every soldered flex design?
Evaluate the exact laminate and joining process. Do not assume compatibility from the film name or substitute a different assembly method without reviewing the circuit.
Does polyimide eliminate qualification?
No. Adhesives, conductors, finishes, connectors, and installation geometry remain part of the tested assembly.
Technical references
References support the material or design context. Check the exact grade, part number, document revision and project conditions before release.Updated 27 September 2026 · Technical content policy · Engineering guidance supports project review; the agreed drawing defines the build.