Gold Stud Bumping

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Gold stud bumping is a process of the flip chip application method. The gold stud bump flip chip assembly process creates conductive gold bumps on the die bond pads, and connects the die to the substrate with adhesive or ultrasonic assembly. Since stud bumping can be done on a wire bonder, it does not require wafers or under-bump metallization. Stud bumping with flip chip is fast, efficient, and flexible for product development.

Microcircuits today also consist of one or more microchips/ICs (also called die) for its control. These die need to be connected to all other components of the circuit in order to make the device work as a whole. One commonly used interconnection method is ball bonding process technology. Automatic ball bonders today can use Au wires from .7 – 2 Mil (18 - 50µm).

However, in order to be able to precisely hit the small bond pads of a die (≤100µm), device packaging requires a highly controlled, highly accurate wire bonding process. One basic requirement is the generation of a repeatable size of a “Free-Air Ball” (FAB): the start of any ball bonding sequence.

ball bumps with gold wire gold wire free air balls


Mobile electronic products continually require finer geometries for packaged integrated circuits. Wireless phones, PDA and digital cameras continue to merge into a common device that will benefit from finer pitch and lower profile wire bonding or ball bumping for flip chipstacked chip and other advanced packaging technologies. Inherent variations in materials, tools and process can cause variations in ball shape and size, stitch shape, bond quality, and thus, yield.

Palomar Technologies Solution

The 8000i Wire Bonder is the only available system that can produce co-planarized gold bumps in one step. A unique feature of this system is the ball bumper and stud bumper configuration.

The 8000i Wire Bonder uses a unique bond-head motion to form precise gold ball bumps by repeatable, smooth shearing of the wire off the top of the bump without leaving a tail. This provides a consistent formation of flat <20 micron high bumps, thus eliminating the need for a secondary coining process. It also allows formations of bumps with a height consistency of +/-2 microns, 3 sigma.

The 8000i Wire Bonder is equipped with a unique patented Deep Access Dual Axis Bond Head™. In addition to the linear Z-movement (Zl) for deep access applications, its tilting transducer (Zr) guarantees the precise tail length generation which is necessary to form consistent, repeatable ball bumps.

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