Process Makes Electroless Nickel/Gold Wafer Bumping Economical for Flip-Chip Packaging

Flip-chip technology is a driving force in achieving increased speed and performance along with higher I/O count for a variety of applications. This article discusses a low-cost wafer-level bumping process based on electroless nickel/gold (Ni/Au) under-bump metallization (UBM) that is suitable for all current flip-chip interconnection technologies. Today, all commercially viable flip-chip methods require that a bump formation be placed on the chip I/O to act as the interconnection. Established techniques, however, like the C4 process(1,2) do not answer the cost requirements for the consumer market. Alternatively, a selective chemical plating method can significantly reduce costs associated with bumping, since this method does not require masking or metal sputtering. Additionally, this technology enables the parallel processing of multiple wafers, resulting in high throughput