Stability of electrical resistance of isotropic conductive adhesives within mechanical stress

This work is focused on investigation of influence of dynamic mechanical load (bending of testing boards) on resistance of the adhesive joints. The load has been induced by a definite deflection of testing boards (fiberglass laminated PCB assembled with 1206 SMD resistors). There were used four different types of isotropic electrically conductive adhesives (two types of one-component, one type of two-component adhesive and one type of conductive lacquer). The frequency of one cycle per second (1 Hz) has been used for generation of the dynamic load (2000 cycles of bend have been applied). For the analysis of adhesive joint resistance has been used precision LCR meter HP 4284A with continual measuring software (WEE Pro v6.0). The dynamic load has caused changes of basic electrical parameters of the bonds The more of deflections has been applied the more changes of parameters have been found. Nevertheless increasing of joint resistance is not linear and it is not same, for all tested adhesives - initial rising of resistance is in most cases higher than changes after few cycles. From our experiment it is evident that for low deflection of testing board there are both of permanent and also elastic deformations in adhesive joints (graphs of joint resistance have not continual rising trend).