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TAB technolgy is quite an old contact method for semiconductors. It has become an established technique for high volume applications like watches und calculators. This technolgy requires bumped wafers. The conventional wafer bumping process requires a sputtered plating base for the electrodeposition of the bumps. This plating base is coated with a resist which is structured by lithography. The bumps are deposited in the openings of the resist by electrodeposition. This process can be substantially simplified by the use of electroless metal deposition. Electroless bumping offers the advantage of a maskless process independent of substrate size: single item or complete wafer. Electroless nickel plating was investigated for bumping. Electroless nickel bumps with a height of 25 pm have been selectively formed on the aluminum bondpads. The adhesion of the bumps was investigated as a function of the pretreatment of the bondpads. The nickel bumps have been inner lead bonded by gang bonding to a tape with a thick layer of tin.

An electroless bumping method was developed both for fiip chip and TAB applications. Electroless NdCu plating is a maskless low-cost approach to bumping directly on aluminum bondpads. An immersion tin layer for coating and soldering is plated on the copper. Due to the high alkalinity (pH > 12) of electroless Cu baths, a thick Ni layer of about 7 Lt m is required on the aluminum for sealing. A shear strength of 180 cN and a contact resistance of less than 2 ma for the bumps were obtained. Because of the high hardness of nickel, conventional gang bonding techniques are not applicable. The hardness of electroless copper is about 200 -26, and after annealing in the range of 1-150 -26.Thermwompression gang bonding of Au plated tape to the NilCdSn metallization was carried out. The average pull strength was 50 cN. The influences of the size and electroless solder plating of the deposited copper are also investigated.

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