Circuit Technology Center

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

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.

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
IPC-A-600 3.0 Internally Observable Characteristics
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
Kits and Systems
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.
Tools and Materials
Color Agents
Use to tint the color of epoxy used for solder mask repair or circuit base board repair.
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
Additional Items and Supplies
General purpose cleaner for removing contamination.
Continuity Meter
Meter and probes to test for electrical continuity.
End Mills
End Mills
Designed for end cutting and hole boring.
Precision microscope with stand and lighting for work and inspection.
General purpose oven for drying, baking and curing epoxies.
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
Nonabrasive, low-linting wipes for cleanup.
Circuit Bond Epoxy
Circuit Bond is a clear, low viscosity, superior strength epoxy precisely measured out into two-compartment plastic packages, so it's easy to use, and there's no measuring. For over a decade, this high-strength epoxy has been qualified and used by thousands of high-rel electronics manufacturers across the globe.
1. Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use.
2. To use Circuit Bond, remove the plastic clip separating the resin and hardener. Squeeze back and forth from one half of the package to the other to mix the contents.
3. Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed.
4. Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles.
5. Color Agent can be mixed in with Circuit Bond to match surface colors if desired.
6. Apply using a Foam Swab, Micro Probe, or Mixing Stick as required.
7. Cure Circuit Bond for 24 hours at room temperature or 4 hours at 65°C (150°F).
Packaging2 gram pre-measured packages
Mix ratio4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)100/25
ColorClear, transparent
Pot life30 minutes
Cure cycle24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index1
Specific Gravity1.20
Percent Solids100%
Viscosity (after mixing)2000 cps
Operating temperature range-55°C to 135°C
Hardness88 Shore D
Lap Shear, Alum to Alum1100 psi
Glass Transition Temperature, Ultimate92°C
Coefficient of Expansion, cm/cm/°C6 E-05
Dielectric strength400 volts/mil
Dielectric Constant, 1KHz@25°C4
Shelf Life6 months minimum
Color Agents
Color Agent is a one-part, air-drying, semi-paste ink commonly used to print hard surfaces, including circuit board base materials. Color Agent can be used to tint the color of epoxy used for solder mask repair or circuit baseboard repair. To use, mix a small amount of color agent with 2 part epoxy as the epoxy is initially mixed. Add more color agents to increase the color intensity if needed.
Part No. Description
115-9102 115-9102 Color Agent, Yellow
115-9185 115-9185 Color Agent, Red
115-9293 115-9293 Color Agent, Blue
115-9348 115-9348 Color Agent, Green
115-9358 115-9358 Color Agent, Light Green
115-9376 115-9376 Color Agent, Medium Green
115-9424 115-9424 Color Agent, Dark Gray
115-9457 115-9457 Color Agent, Light Brown
115-9560 115-9560 Color Agent, Dark Green
115-9561 115-9561 Color Agent, Green
115-9995 115-9995 Color Agent, Black
115-9996 115-9996 Color Agent - White
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.
  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 ensure 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.
  1. Visual and electrical examination as required.
Procedure for reference only.