Effects of morphology and surface characteristics of poly(imide siloxane)sand deep UV/O-3 surface treatment on the interfacial adhesion of poly(imide siloxane)/alloy-42 leadframe joints

The effect of surface characteristics and morphology of poly(imide siloxane ) (PIS) on the true interfacial adhesion between PIS films and alloy-42 sub strates was studied. The effect of the viscosity of PIS films and the surfa ce treatment of deep UV/O-3 (d-UV/O-3) on alloy-42 plates on the peel stren gth of PIS films/alloy-42 joints has also investigated. 3,3',4,4'-benzophen one tetracarboxylic dianhydride/2,2'-bis[4-(3-aminophenoxy)phenyl]sulfone ( BTDA/m-BAPS) based PIS films with alpha,omega-bis(3-aminopropyl)polydimethy l siloxane (APPS) molecular weight M-n = 996 g/mole (PIS9Siy) show two phas es in all compositions and the linear dependence of the critical surface te nsion on the surface concentration of the silicon, [Si-surf], on the PIS fi lms. The PIS films with the APPS M-n = 507 g/mole (PIS5Siy) or M-n = 715 g/ mole (PIS7Siy) exhibit a morphology change from a homogeneous phase to an i nhomogeneous phase starting at the mole ratio (y) of APPS/PIS = 2.7% and 1. 1%, respectively. The curves of critical surface tension dependence on the [Si-surf] discontinue or deflect at these two compositions, respectively. T he treatment of d-UV/O-3 on alloy-42 plates improves the wetting on the all oy surface and promotes the peel strength between the PIS films and alloy-4 2 plates by a magnitude of greater than or equal to 20%. These results show that the flowability of the same PIS films bonding at different temperatur es significantly affects the bonding strength of the joints, but the flowab ility of different PIS films bonding at the same temperature, e.g. 400 degr ees C, is not the key factor governing the bonding strength of the joints. The true interfacial adhesion of the PIS5Si0.6/alloy-42 joint is 80% higher than that of the unmodified BTDA/m-BAPS based polyimide film/alloy-42 join t. However, zero true interfacial adhesion is obtained between the PIS9Siy films and alloy-42 plates. The wetting kinetics experiment shows that the h igher the siloxane content in the PIS, the higher the activation energy for the adhesive bonding process. Moreover, the phase sepration significantly increases the activation energy. The scanning electron micrographs of the p eeled-off PIS film surfaces from the PIS/alloy-42 joints reveal the rougher surface morphology from the sample with the higher interfacial adhesion.