Electroless deposition of bumps for TAB technology

Electroless nickel plating was investigated for bumping. Electroless nickel bumps with a height of 265 μm have been selectively formed on aluminium bondpads. The nickel bumps have been inner-lead-bonded by gang bonding to a tape with a thick layer of tin. The adhesion of the bumps was investigated as a function of the pretreatment of the bondpads. It is noted that electroless bumping offers the greatest advantage of reducing the costs of the bumping process because no sputtering equipment or lithography is required. This can be very important if only small quantities of bumped dies are required because the process is independent of substrate size. Electroless bumping may become an alternative to conventional wafer bumping by electrodeposition at least for certain applications