Geometry and Bond Improvements for Wire Ball Bonding and Ball Bumping

Mobile electronic products continually require finer I/O pitches for packaged integrated circuits. Wireless phones, PDA, and digital cameras continue to merge into a common device which will benefit from finer pitch and lower profile wire bonding or ball bumping using flip chip and stacked chip technologies. Inherent variations in materials, tools, and process can cause variations in ball shape and size, stitch shape, bond quality, and thus yield. The importance of geometry will depend on the application. For example, flip chip applications will typically have ball bump height as a primary concern and bump diameter as a secondary concern. Other applications such as ball-in-corner are not concerned with bump height and only care about diameter and shape. Ball and stitch bonding also requires control of the stitch geometry for visual inspection and optimum pull strength.

The industry currently has many techniques to maintain a consistent stitch impression at varied ball-stitch angles in the XY plane. This paper will present Adaptive Bond Deformation(tm), a method recently developed to control the geometry of both ball and stitch according to process parameter inputs supplied by the user. This technique adapts to normal variations in bond surface, bond tool coupling, part fixture, and other difficult to measure influences to produce bonded ball bumps and stitches with up to 8X improvement in geometry consistently, with similar or better results for ball shear and pull strength when compared to non-adaptive bonding.

This paper will first establish definitions for ball bump and ball-stitch geometric dimensions. Example shapes will be shown for application case studies and the affect of Adaptive Bond Deformation(tm) on geometry and bond integrity for each will be presented. The paper will also show case study signatures of non-adaptive and adaptive geometry control as captured by traceability tools available for measuring bond deformation of every bond in real-time. Comparison of the case studies is provided to show analysis capabilities, and process control limiting features which will automatically alert the operator if outside of limits.