Reliability of adhesive joints in dual interface smart cards

In dual interface smart cards the adhesive joints between the micro module and card body are critical points for the reliability. There are many issues, which affect the reliability of the joints. The choice of the electrically conductive adhesive is one of the key aspects. In this study three different anisotropically conductive adhesive films and one isotropically conductive adhesive paste has been tested by several methods including e.g. bending, torsion, thermal and humidity tests. The Matlab model has been developed for studying the factors influencing the reliability of adhesive joints in smart cards for thermal cycling and cyclic bending type deformations. Assuming viscoelastic behaviour for the adhesive material and Coffin Manson type failure criterium for the joints the model is able to give information about the effects of different parameters on the durability of the adhesive joints. The experiments carried out show that there are very large differences in reliability between different types of adhesives. For anisotropically conductive adhesives the type of connection pads in the card body is also very important. The connections made with isotropically conductive adhesive are very resistant for bending deformations of the card.