Micross

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Wirebonded Gold Inductor on Top of ICs
Keywords: Gold inductor, Fine pitch bonding, Power Gold
Fine pitch ball bonding directly over ICs having gold pads plus a permalloy magnetic core, one can now integrate inductors to IC chips. Integrated gold inductor over two microHenry was achieved over IC surface area of 1 x 2 mm. Entire silicon chip plus integrated gold inductor can fit within 1mm thin overmolded package. Ball bonding to gold pads is stronger than wire bonding to conventional aluminum pads. Gold bond pads do not have aluminum oxide. Therefore, bonding onto gold pads requires less ultrasonic scrubbing and achieves superior quality. By simply reusing same bond parameters as used on aluminum pads without optimizing to gold pads, one achieves 10% stronger bonds. Tests show 99.8% confidence level that both ball bond shear and wire pull are stronger on gold pads. Ball bonding at 54um pad pitch will be shown. Bonding to even finer gold pad pitches is envisioned. Consistent gold to gold ball bonding allows smaller starting free air ball diameters (FAB). With smaller FAB, one can achieve smaller bonded ball diameter and thereby approach finer wire pitch. Application of fine pitch gold to gold ball bonding is demonstrated by creating integrated gold inductors directly over BiCMOS circuits. Permalloy magnetic core is 105um thick. Gold wire loop heights are uniformly controlled to less than 250um loop heights over surface of silicon chip. As wire pitch is further reduced, more turns can be wound around magnetic core to create even tinier gold inductors or to form larger value inductor at the same dimension.
James J. Wang,
Power Gold LLC
Phoenix, AZ


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