4.2.3 Conductor Repair, Welding Method

This procedure is used to repair short breaks or opens in circuits on circuit boards. A parallel gap welder is used to weld a jumper ribbon across the damaged conductor.

Caution: Welding current and voltages may affect component reliability on assembled circuit boards. The repaired section must not reduce the circuit width, spacings, or current carrying capacity below the allowable tolerances.

Caution: Subminiature parallel gap welding is extremely sensitive to the proper placement of the electrode tip. Inconsistent welds can occur due to poor electrode tip placement, incorrect tip size, or improper weld settings.

Preparation: Prior to using any welding equipment, certain precautions should be taken. The equipment should have electrodes cleaned, aligned, and set for the proper board thickness.

Test samples that have similar circuit widths, spacing, thickness, surface finish, contour, etc. Observe and test the weld quality, alignment, discoloration, fusion, and the appearance of the base material in the area of the weld. Readjust the weld equipment settings and repeat until acceptable results have been achieved.

The alignment of the welded ribbon to the circuit pattern should be within 0.050 mm (.002"). The weld bond strength should exceed the circuit/base material bond strength.

Minimum Skill Level - Advanced Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience. Conformance Level - High This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.

Acceptability References IPC-A-600 2.0 Externally Observable Characteristics IPC-A-610 10.0 Laminate Conditions

Procedure References 1.0 Foreword 2.1 Handling Electronic Assemblies 2.2 Cleaning 2.7 Epoxy Mixing and Handling IPC7721 4.2.3 Conductor Repair, Welding Method

Tools, Materials and Supplies Abrader Mild abrasive for removing oxides and contaminants. Circuit Bond Epoxy Clear, superior strength epoxy in two-compartment plastic packages. Flex-Rack PCB Holder Sturdy rack for PCBs used for rework and positioning. Cleaning Brushes Disposable brushes for solvent cleaning and application of coatings. Cleaner General purpose cleaner for removing contamination. Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming. Precision Tool Set Nine precision-crafted tools for detailed circuit board work. Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips. Tweezers Multiple sizes and tip configurations of tweezers for various small parts handling needs. Wipes Nonabrasive, low-linting wipes for cleanup.