Recovery Process for Wafers That Missed the BLM Operation
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
A process is described in this article for removing Pb-Sn solder-balls and associated debris inadvertently deposited on wafers lacking the required underlay metallurgy (BLM operation). This metallurgy is necessary to electrically and mechanically connect terminal solder pads to chips, its omission resulting in defective connections. Wafers exhibiting this problem can be recovered successfully for return to normal terminal metal processing starting with the BLM operation, if removed prior to reflow and reworked by the process here disclosed. The Pb-Sn pads are first removed from the wafer by etching with 1:1 acetic acid/hydrogen-peroxide solution for approximately five minutes. Any remaining residues (lead oxides, etc.) on the quartz can be cleaned by etching with 5:1 BHF = 1.2% glycerine for one-half minute at 30ŒC.