Chemical Displacement Technique for SMT Interconnection and Repair
Original Publication Date: 1988-Nov-01
Included in the Prior Art Database: 2005-Feb-15
A technique for effecting an SMT interconnection that utilizes chemical displacement reaction is described. The principle involves a redox reaction where a noble metal such as silver is precipitated from its solution on reaction with a less noble metal, such as copper, according to the following equation: 2 Ag+ + Cu = Cu2+ + 2 Ag Approximately equal amounts of silver nitrate crystals and N-methyl pyrrolidine liquid were carefully mixed to form a black viscous paste. The paste was loaded into the syringe of a dispensing unit, and requisite amounts were dispensed on to freshly cleaned copper pads of the component foot prints on a carrier. The gullwing, J-leaded, and capacitor components were placed on the respective footprints. The assemblies were baked in an oven at 100oC for 45 minutes to evaporate the solvent.