Foil-to-foil lamination and electrical interconnection of printed components on flexible substrates

• We described and compared two foil-to-foil lamination and interconnection methods.
• Anisotropic conductive adhesive (ACA) method requires less processing steps.
• Through foil vias (TFV) method proved to be more robust to cyclic bending forces.
• ACA and TFV methods shown to have high reliability during environmental ageing.
• The methods are demonstrated for two types of foil-based humidity sensors.

This paper describes and compares two integration methods to structurally laminate and interconnect foil-based components with flexible polymeric substrates. The first method uses isotropic conductive adhesives (ICA) confined in laser-ablated through foil vias (TFV), while the second one uses an anisotropic conductive adhesive (ACA). Both procedures were successfully demonstrated by interconnecting silver-based inkjet printed and gold-sputtered interdigitated capacitive humidity sensors onto flexible PEN carrier substrates, showing functionality, high process yield and low-complexity. The robustness of the assemblies was tested and compared for adhesion, bending, high humidity and temperature cycling. Confined ICA vias show higher mechanical robustness to bending, while both methods remained functional after more than 900 h of environmental ageing. Finally, the interconnections were fully validated at different levels of relative humidity (RH) by comparing the sensor response to that of a commercial sensor.

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