Circuit Board Repair Guide > Conductor Repair Procedures > 4.3.4 How to Cut Internal Connections at a Plated Hole

How to Cut Internal Connections at a Plated Hole

Repair Circuit Boards | Repair SMT Pads | Repair BGA Pads | Repair Lands | Repair Edge Contacts
Repair a Conductor | Plated Hole Repair | Base Board Repair | Replace Solder Mask or Coatings

This repair procedure 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.

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

IPC Acceptability References
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-600 3.0 Internally Observable Characteristics

Related Procedure References
CTC 1.0 Foreword - Circuit Board Repair Guide
CTC 2.1 Handling Electronic Assemblies
CTC 2.2.1 How to Clean a Circuit Board
CTC 2.2.2 Cleaning Circuit Boards, Aqueous Batch Process
CTC 2.5 Baking and Preheating of Printed Circuit Boards
CTC 2.7 Epoxy Mixing and Handling
IPC7721 4.3.4 Deleting Inner Layer Connection at a Plated Hole, Spoke Cut Method

Tools and Materials
Color Agents
Continuity Meter      
End Mills
Pin Clamps
Precision Drill System      
Tape, Kapton
Inner layer connection at plated hole nees to be deleted
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

Printed Board Type: R/F  |  Skill Level: Expert  |  Conformance Level: High  |  Rev.: E  |  Rev. Date: Jul 7, 2000

Precision Drill System to drill out plated hole

Figure 1: Precision Drill System
with base plate to pin circuit
board in position while drilling
out plated hole.

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).
Plated through hole with inner layer spoke connections

Figure 2: Internal view of plated
through hole with inner layer
spoke connections.

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.
Abrasion operations can generate electrostatic charges.
End mills are normally single end, two or four flute high grade solid carbide.
Mill to sever internal spoke connections

Figure 3: Mill adjacent to the
plated hole to sever internal
spoke connections.
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
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 liquid circuit board epoxy flush with the surface. Remove excess.
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.

Links to Related Products

Circuit board epoxy for ciruit repair  
Circuit Bond Kit 115-1322: Liquid circuit board epoxy
Circuit Bond Kit contains 10 packages of clear, low viscosity, superior strength epoxy ideal for circuit board use. The epoxy is precisely measured out into two-compartment plastic packages. This adhesive is easy to use and there's no measuring.

Color Agents for Circuit Boards
Matching epoxy to the color of the circuit board being repaired is easy when you use a color agent. Color agents may also be applied directly to the circuit board surface for color matching.

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