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4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method

Outline
This method is used on multilayer circuit boards or assemblies to disconnect an internal connection at a plated hole. A precision drill press is used with a carbide end mill to make precise cuts at the spokes or internal circuits extending from the hole.

Caution
Extreme care must be taken to prevent damage to adjacent circuits. A microscope must be used during milling when extreme accuracy is required.

Proprietary Information Proprietary
This guide may contain proprietary or copyright-protected information for access by authorized persons only.

Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.

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  Proprietary
IPC-A-600 3.0 Internally Observable Characteristics  Proprietary
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.5 Baking And Preheating
2.7 Epoxy Mixing and Handling
IPC7721 4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method
Tools and Materials
Cleaner
Cleaner
General purpose cleaner for removing contamination.
Coatings
Color Agents
Use to tint the color of epoxy used for solder mask repair or circuit base board repair.
Meter
Continuity Meter
Meter and probes to test for electrical continuity.
End Mills
End Mills
Designed for end cutting and hole boring.
115-3302
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages
235-3050
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Drill
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method
Deleting Inner layer Connection at a Plated Hole, Spoke Cut Method
4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method
Figure 1: Precision Drill System with base plate to pin circuit board in position while cutting inner layers.
4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method
Figure 2: Internal view of plated through hole with inner layer spoke connections.

4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method
Figure 3: Mill adjacent to the plated hole to sever internal spoke connections.
Procedure
  1. Identify the hole that requires rework and clean the area.
  2. Mark the coordinates on the board surface and place the circuit board on the base plate of the precision drill press. (See Figure 1)
  3. Select the appropriate size end mill or drill and insert it into the chuck of the Precision Drill System. The cutting tool should be approximately .010 - .025 mm (.005" - 010") greater than the width of the spoke or circuit to be cut. Set speed to high.

    Caution
    Abrasion operations can generate electrostatic charges.

    Note
    End mills are normally single end, 2 or 4 flute solid carbide.
  4. Mill into the circuit board surface adjacent to the plated hole. The milled holes should be aligned directly above the internal spoke connections. Mill down just deep enough to sever the internal spokes connecting the plated hole to the internal plane. A microscope must be used for accuracy. Up to 4 milled holes may be required. Do not drill deeper than needed. (See Figure 3)
  5. Blow away material with air and clean the area.
  6. Check continuity to be sure that the internal connection has been deleted. Inspect the neighboring circuits to make sure that none of them have been severed or damaged.
  7. Mix the epoxy.
  8. Fill the holes with epoxy flush with the surface. Remove excess.

    Note
    A slight overfill of epoxy may be desired to allow for shrinkage.
  9. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Evaluation
  1. Visual and electrical examination as required.
Procedure for reference only.