As foldable phones, smart bands, and AR glasses enter the peak prototyping season for spring 2026, multiple FPC (flexible printed circuit) module manufacturers report micro-cracks or even copper foil fractures in potting compounds during low-temperature bending tests. Investigation reveals the issue stems not from the filler or curing process, but from the silicone oil itself—specifically, certain phenyl-containing or highly crosslinked silicone oils whose glass transition temperature (Tg) has risen above –60°C, becoming brittle under cold flexing at –40°C.
This exposes a critical blind spot: not all silicones are inherently “soft.”
-
Pure linear polydimethylsiloxane (PDMS) features a flexible backbone with a typical Tg ≤ –125°C, maintaining high elasticity even in extreme cold;
-
Phenyl-modified silicones, while offering better thermal stability and refractive index, introduce rigid aromatic rings that significantly raise Tg—when phenyl content exceeds 10%, Tg can climb to –70°C or even –50°C, leading to stress concentration and cracking under repeated flexing.
“A customer demands both ‘high-temperature resistance and bendability,’ but we can’t sacrifice low-temperature elasticity for thermal performance,” shared a supplier of electronic adhesives. “Now, premium foldable display projects explicitly require potting compounds with Tg < –50°C and validation through 50,000 dynamic bend cycles.”
To address this, we recommend formulators prioritize three key criteria when selecting base fluids:
-
Use high-purity linear PDMS without phenyl, vinyl, or other rigid functional groups;
-
Require suppliers to provide DSC-measured Tg values (not theoretical estimates), ideally ≤ –80°C for safety margin;
-
Control crosslink density—excessive Si-H/Si-Vi ratios create rigid networks that reduce flexibility.
We have already supplied an ultra-low-Tg silicone solution (DSC-tested Tg = –128°C) to multiple foldable display supply chain customers. Combined with optimized filler surface treatment, this enables potting compounds to withstand repeated bending at R=1mm radius at –55°C with no cracking or electrical performance degradation.
In the era of flexible electronics, “soft” is no longer a descriptive word—it’s a technical specification.
Don’t let a single bottle of silicone become the final barrier to your new product ramp-up.
Request our Low-Tg Silicone Selection Guide for Flexible Electronics and real Tg test reports. We support rapid sample delivery to help you secure your spring launch window.
