Integrated circuits continue to shrink in size, and the associated decrease in size of the wire bond pad on both the die and substrate presents substantial challenges in the manufacturing process.
To ensure high device reliability and minimize manufacturing costs, it is important to optimize the wire bonding process to ensure good bond strengths and yields. Poor bond strengths and low yields are often due to upstream contamination sources or the selection of materials in advanced packaging. Gas plasma technology can be used to clean pads prior to wire bonding to improve bond strengths and yields.
Typical results of pull strength improvement for a quad flat no-lead (QFN) package with bond pads contaminated with epoxy bleed out is displayed in the figure below. The die was attached with conductive epoxy; oven cured; direct plasma treated; and wire bonded with 25-micron wire. A statistically valid set of samples yielded a mean pull strength of 10.00 grams with a CpK of 2.07 with plasma, compared to a mean pull strength of 3.89 and CpK of 0.03 without plasma. Furthermore, the mean shear strength increased from 25.62 grams without plasma to 28.17 grams with plasma.
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