Experimental Method and Finite-Element Simulation Model for Investigation Into Flip-Chip-on-Film Inner Lead Bonding Parameters

One of the key factors to design reliable eutectic Au-Sn solder joints used in flip-chip-on-film (FCOF) packaging is the bonding temperature distribution at the interface of the gold bump and the copper lead on the inner lead bonding (ILB) process. Furthermore, determining an appropriate bonding force is essential in achieving a suitable compromise between the bonding strength of the ILB process and the gap size in the subsequent resin potting process. Accordingly, this paper proposes a method based on a noncontact laser spot sensor for determining the inner lead interface temperature. The tests are performed using materials from FCOF products at various temperatures in the range of 300 °C-440 °C. The experimental results are used to construct an ANSYS finite-element model of the FCOF system, including the silicon chip, the polyimide film, the copper lead, and the gold bump to simulate a temperature-dependent ILB process. A good agreement is observed between the numerical and experimental results for the deformed profile of the polyimide film/copper lead following the bonding process and the variation of the bump sinking value with the bonding force. Finally, the numerical results are used to construct an FCOF/ILB parameter design chart for selecting the bonding force required to obtain a given gap size and bump sinking value in the FCOF/ILB process.