Methods of Printing Copper for PCB Repair

Abstract

Damage and defects that occur in printed circuit board assembly (PCBA) often lead to the disposal of expensive components. In cases where laminate and circuitry have been removed, traditional repairs in the manufacturing process have not been able to return devices into service. This study examines the use of aerosol jet printing (AJP) and traditional engineering fluid dispensing (EFD) as methods to service repairs of damaged PCBAs.Surface mount component failures on PCBAs may occur as a result of a bad solder joint or problems with the component. In order to salvage such a PCBA, the component must be physically removed from the board and a new be attached. During the removal of PCBA components, pad cratering may occur, where the pad and laminate are damaged/removed along with the component. This leaves behind a crater in place of the pad, rendering the board unrepairable and thus, unusable. Trace damage is another common failure in PCBs. A repair to either sort of damage often requires reconnections of intricate circuitry to be made. Trace repair has traditionally been serviced by soldering a wire between the undamaged regions, rerouting the connection. In the case of fine conductive traces, as seen in devices which are becoming smaller as heterogeneous packaging innovations continue to progress, traditional methods will not be able to service this sort of damage.Aerosol jet printing, a direct-write additive manufacturing process commonly used in flexible hybrid electronics, could save expensive PCBs by repairing cratered pads and damaged traces. The use of AJP has been successful in repairing damaged modules, however the process has not been optimized for general repairs on FR4. The use of AJP and EFD to repair damaged circuitry on FR4 laminate and to fill pad craters with copper nanoparticle ink is demonstrated. Copper ink structures are uniformly sintered to achieve a solderable surface and good adhesion to the exposed laminate and remaining copper on the PCB. Processing conditions and methods to minimize voiding, cracking, and oxidation are discussed. The confined dimensions of the craters bring additional challenges to printing and curing as large structures are desired, but require tailored drying and sintering schedules to ensure good adhesion and minimize voids.