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4.3.1 Circuit Cut, Surface Circuits

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 and Materials
CircuitMedic Part
Circuit Bond Packs
Clear, superior strength epoxy in two-compartment plastic packages
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Images and Figures
4.3.1  Circuit Cut, Surface Circuits
Circuit Cut, Surface Circuit
4.3.1  Circuit Cut, Surface Circuits
Figure 1: Option A - Make two small cuts with the knife and remove a short section of circuit.
4.3.1  Circuit Cut, Surface Circuits
Figure 2: A high quality, Micro-Drill System is recommended for this delicate operation.

4.3.1  Circuit Cut, Surface Circuits
Figure 3: Make 1 or 2 cuts as needed to cut circuit.
4.3.1  Circuit Cut, Surface Circuits
Figure 4: Completed repair.
Procedure
  1. 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.
  2. Clean the area.
  3. Carefully make two small cuts with the knife and remove the short section of circuit. (See Figure 1) Or use a Micro-Drill as covered in the next step.
  4. 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 dental grade carbide steel for precision cutting and long life.
  5. Carefully make 1 or 2 cuts as needed. (See Figure 3)

    Caution
    Exercise care to avoid damage to adjoining circuits.
  6. Check continuity to be sure that the circuit has been cut.
  7. Clean the area.
  8. Mix epoxy. If desired, add color agent to the mixed epoxy to match the circuit board color.
  9. Coat the area with epoxy if needed. An epoxy dispenser may be used to control the application of epoxy. Remove any excess.
  10. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Evaluation
  1. Visual examination of cuts for spacing, and unintended damage to surrounding circuits.
  2. Electrical tests as applicable.
Procedure for reference only.
 

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