Overview
IEC 62047-29:2017 specifies an electromechanical relaxation test method for freestanding conductive thin films under room temperature. The standard defines how to measure time-dependent electromechanical behaviour - electrical resistance and mechanical stress relaxation - of freestanding conductive films used in MEMS, opto‑electronics and flexible/wearable electronics. It is applicable to isotropic, homogeneous, linearly viscoelastic materials and targets materials whose electrical performance can drift over time due to stress relaxation at ambient conditions.
Key topics and technical requirements
- Test principle: apply a prescribed tensile strain, maintain it constant using feedback control, and record electrical resistance and stress as they relax over time. The ratio of electrical to mechanical relaxation characterizes piezoresistive behaviour.
- Specimen design: freestanding test piece with four electrical contacts for four‑wire (Kelvin) measurement; gauge region must be uniform in strain.
- Gauge length l1 ≥ 20 × width l2; width l2 ≥ 10 × thickness h.
- Dimension measurements (l1, l2, h) with ≤ ±5% error.
- Measurement methods:
- Four‑wire resistance measurement to remove contact/lead resistance effects.
- Non‑contact strain measurement (e.g., digital image correlation) recommended so gauge is not disturbed.
- Small measurement current to avoid self‑heating, while preserving resolution.
- Environmental control:
- Temperature stability: fluctuations ≤ ±2 °C (electrical properties are temperature sensitive).
- For humidity‑sensitive polymeric substrates: relative humidity change ≤ ±5% RH.
- Material scope and limits: valid for isotropic, homogeneous, linearly viscoelastic conductive thin films (common in MEMS and flexible electronics).
- Key parameters defined: gauge factor (ΔR/R divided by strain change) and piezoresistive coefficient (relative resistivity change per stress).
Applications and users
Who uses IEC 62047-29:2017:
- MEMS and microfabrication engineers validating long‑term electrical stability of freestanding conductive films.
- R&D teams in flexible/wearable electronics and optoelectronics assessing time‑dependent resistance drift.
- Test labs and materials scientists characterizing piezoresistive properties, gauge factor, and viscoelastic relaxation.
Practical uses:
- Risk assessment for device performance degradation due to stress relaxation at room temperature.
- Qualification of fabrication processes and material selection for freestanding metal films (e.g., Au) and other conductive thin films.
- Supporting design changes to mitigate time‑dependent electrical variation in sensors, interconnects and flexible circuits.
Related standards
Useful cross‑references within the IEC 62047 series:
Keywords: IEC 62047-29:2017, electromechanical relaxation test, freestanding conductive thin films, MEMS testing, four‑wire measurement, gauge factor, piezoresistive coefficient, room temperature testing, viscoelastic materials.