4.3.1 Circuit Cut, Surface Circuits

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Outline

This method is used to sever a circuit or short. A small section of the circuit is removed, forming a break. The width of the break should be at least as wide as the minimum conductor spacing. The Surgical Knife or high-speed Micro-Drill System is used. This method is recommended for surface circuit cuts only. After cutting, the area is sealed with epoxy.

Note: This method is recommended for surface circuit cuts only.

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 4.3.1	Conductor Cut, Surface Conductors

Tools, Materials and Supplies

Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.

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.

Color Agents
One part, semi-paste ink used to tint the color of epoxy and for direct printing on circuit board surfaces.

Cleaner
General purpose cleaner for removing contamination.

Continuity Meter
Meter and probes to test for electrical continuity.

Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.

Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding.

Microscope
Precision microscope with stand and lighting for work and inspection.

Oven
General purpose oven for drying, baking and curing epoxies.

Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.

Wipes
Nonabrasive, low-linting wipes for cleanup.

Procedure

Procedure

Identify the circuit or short to be cut. Determine from the artwork or drawings where the best location is to make the break. The width of the break should at least match the minimum required electrical spacing.
Clean the area.
Carefully make two small cuts with the knife and remove the short section of the circuit. (See Figure 1) Or use a Micro-Drill as covered in the next step.
Select the appropriate size ball mill and insert it into the Micro-Drill System. Set the speed to high. (See Figure 2) The ball mill should be approximately the same width as the circuit to be cut.
Note: Ball mills should be made of dental-grade carbide steel for precision cutting and long life.
Carefully make 1 or 2 cuts as needed.
Caution: Exercise care to avoid damage to adjoining circuits.
Check continuity to ensure the circuit has been cut.
Clean the area.
Mix epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
Coat the area with epoxy if needed. An epoxy dispenser may be used to control the application of epoxy. Remove any excess.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

Evaluation

Visual examination of cuts for spacing and unintended damage to surrounding circuits.
Electrical tests as applicable.

Images and Figures

Circuit Cut, Surface Circuit

Figure 1. Option A - Make two small cuts with the knife and remove a short section of circuit.

Figure 2. Make 1 or 2 cuts as needed to cut circuit.

Figure 3. Completed repair.

4.3.1 Circuit Cut, Surface Circuits

Perform controlled surface circuit cuts to isolate or modify PCB traces. Covers precision cutting techniques and inspection methods to prevent unintended damage. Minimum Skill Level: Advanced Conformance Level: High

Perform controlled surface circuit cuts to isolate or modify PCB traces. Covers precision cutting techniques and inspection methods to prevent unintended damage.

Minimum Skill Level: Advanced
Conformance Level: High