Cracking in Flexible PCB Potting?-Iota

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News > Dynamic industry > Cracking in Flexible PCB Potting?

Cracking in Flexible PCB Potting?

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.

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