The number of pads which interconnect microprocessor to both RAM and secondary cash increases rapidly for the microprocessor after 64 bits. This increase requires a material revolution for high density interconnection such as bumps which are microconnectors. The bumps show sharp humps at the upper flow side for the Reynolds numbers of 40.57 and 81.14. The lower flow side also has humps and their height decreases with the increase of Reynolds number. The hump becomes flat at the upper flow side for a Reynolds numbers of 405.7 and the lower flow side no lorge shows the hump. In this report, the bump formation mechanism is discussed with microscopic flow and mass transfer which were calculated by numerical flow computation. The bump shapes, mentioned above are caused by following two microscopic flow patterns. One is the separated vortices both at the upper and lower flow side cathode corners, and the other is penetration flow which starts from the upstream bulk solution to the cathode center and to the lower side bulk solution. The two-dimensional calculated flux profiles coincide well with the above mentioned observed bump shapes.