Circuit Board Repair Guide > Conductor Repair Procedures > 4.3.3 How to Sever Internal Connections at a Plated Through Hole

How to Sever Internal Connections at a Plated Through Hole

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This repair procedure is used on multilayer circuit boards or circuit board assemblies to disconnect an internal connection at a plated hole. The Precision Drill System is used with a carbide drill, end mill or ball mill to drill out the hole. The hole may then be filled with epoxy and re-drilled to the diameter needed.

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

 
Inner layer connection at plated hole needs to be deleted
Deleting Inner Layer
Connection at a Plated Hole
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 4.3.3 Deleting Inner Layer Connection at a Plated Hole, Drill Through Method

Tools and Materials
Cleaner
Color Agents
Continuity Meter      
End Mills
Epoxy
Microscope      
Oven
Pin Clamps
Precision Drill System      
Tape, Kapton
Wipes

4.3.3 Deleting Inner Layer Connection at a Plated Hole, Drill Through Method

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

Precision Drill System for drilling out plated hole

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


1. 
Identify the hole that requires rework and clean the area.
 
2. 
Mark the coordinates on the board surface and pin the circuit board in place on the base plate of the Precision Drill System. (See Figure 1).
Isolate internal connection(s).

Figure 2: Completely mill through
the hole to isolate the internal connection(s).


3. 
Select the appropriate size end mill, drill or ball mill and insert it into the chuck of the Precision Drill System. The cutting tool should be approximately 0.50 mm (.020") greater than the plated through hole inside diameter. Set speed to high.
   
  Caution
Abrasion operations can generate electrostatic charges.
   
  Note
End mills are normally single end, two or four flute high grade solid carbide.
   
4. 
Completely mill through the hole to isolate the internal connection(s). A microscope should be used for accuracy. (See Figure 2).
   
5.  Blow away material with air and clean the area.
   
6. 
Check continuity to be sure that the internal connection has been deleted. Also check the continuity and inspect the neighboring circuits to make sure that none of them have been severed or damaged.
   
Fill hole with epoxy

Figure 3: Fill the hole with epoxy
up to and flush with the surface.


If desired complete the following steps
   
7. 
Mask the opposite side with Kapton tape or flexible mask to prevent the epoxy from flowing out the opposite side.
   
8.  Mix the epoxy.
   
9. 
Fill the hole with epoxy up to and flush with the surface. Remove excess epoxy. (See Figure 3).
   
 
Note
A slight overfill of epoxy may be desired to allow for shrinkage when epoxy cures.
   
10. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
   
  Caution
Some components may be sensitive to high temperature.
   
11. Clean the area
   
Completed repair drill through method

Figure 4: Completed repair.
12.
Select an end mill or drill as needed. Insert the cutting tool into the Precision Drill System. Mill directly through the center of the cured circuit epoxy. The surface pad remaining may be used as a target location for accuracy. A microscope should be used during milling for accuracy. (See Figure 4).
   
  Caution
Be careful not to re-expose the internal layers of the hole when drilling out the epoxy.
   
13. Clean the area. Inspect the new hole using a microscope.
   
Evaluation
   
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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