Fine Pitch Wire Bonding with Insulated Cu Wire: Free Air Ball and Ball Bond

As the semiconductor industry pushes for fine pitch and high-density application, there is a growing interest in insulated Cu wire bonding. Insulated Cu wire has flexible wire bond design rules as the insulation layer can prevent wire-to-wire shorts. Previous research works focused mainly on the insulated Au wire stitch bonding. This paper presents the finding of the work performed on 0.8 mil insulated Cu wire bonding on high-density thermally enhanced BGA package with 29 × 29 mm body size. The bonding parameters were optimized and characterized via the existing available wire bonder in the market and compared with the Cu wire bonding. This study investigates the wire bond process in terms of free air ball (FAB) and ball formation. Spherical and residue-free FAB of insulated Cu was achieved with forming gas. This study shows that insulated Cu wire requires less demanding ball bond parameters than Cu wire, indicating softer ball which could be favorable for the sensitive bond structures. Bonding strength in terms of ball shear and wire pull strength for both insulated Cu wire and Cu wire is very similar. Insulated Cu wire has lesser Al splash compared to Cu wire. Other key responses such as Al remnant, pad cratering, and intermetallic compound have been studied and will be discussed in detail in the paper.