Laser reflow soldering process with lead-tin solder pads

摘要

An optic module contains a flexible circuit board forming a cable which connects between an optical sub-assembly and a rigid interconnect structure within the optic module. One end of the cable includes lands proximate to through holes for soldered connection to pins which extend from the optical sub-assemblies. At the other end of the cable leads extend across interconnection pads on the surface of the rigid interconnect structure for soldered connection. The top surface of the interconnect pads is 10/90 (Sn/Pb) solder to provide a high temperature soldered joint. Solder flux can not be used because cleaning solvents would contaminate the interconnect structure. An atmosphere of formic acid mixed with nitrogen surrounds the lead and pad and a fluxless solder joint is formed by laser soldering.