Development of Interconnects by Electroless Nickel Plating
Date Issued
2015
Date
2015
Author(s)
Chen, Yan-Bin
Abstract
As the progress of the electronic packaging, the critical dimension continues to reduce in size. At the scale of micro bump, solder joints would encounter some issues affecting its reliability. A low temperature process of interconnection technology of chips without using solder was researched in this paper. Because of selective plating and uniformity in thickness, electroless nickel plating was applied to pillar interconnection in flip chip bonding. Copper pillars were interconnected by electroless nickel plating at 74 ℃ and the plating time was decided by the distance between two pillars. The samples were inspected and analyzed by optical microscope (OM) and scanning electron microscope (SEM). Different methods were tested to optimize the electroless nickel bonding, including Triton X-100 addition, sample rotation and dome-shaped pillar. The results of electroless nickel plating of aligned chips without any additive showed that nickel only plated on the surface near the entrances of the gap. By adding Triton X-100 to the plating bath, the pillar array located at the central of chip could be plated by nickel, however, the cross-sectional images showed some irregular voids trapped and seams in the nickel plating layer. To increase the mass transfer of reactants in the gap, rotation was applied to the sample while electroless nickel plating. A void with disk-like shape could be observed in the plated nickel layer of the sample been rotated. Not only flat-topped pillar but also dome-shaped pillar were tested in this experiment. According to the results of electroless nickel plating using dome-shaped pillars with sample rotation, the plated nickel layer showed three different cases of bonding, first, a seam across the whole pillar existed in the nickel layer, second, some discontinuous seams remained in the nickel layer, third, a seam-less bonding.
Subjects
electroless nickel plating
dome-shaped copper pillar
flip chip bonding
copper pillar array
Type
thesis
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