Circuit Technology Center
 
No. 4.3.3
Deleting Inner Layer Connection at a Plated Hole, Drill Through Method

OUTLINE

This method is used on multilayer circuit boards or assemblies to disconnect an internal connection at a plated hole. A 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 redrilled 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.

 

ACCEPTABILITY REFERENCES
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-600 3.0 Internally Observable Characteristics
   
PROCEDURE REFERENCE
CTC 7721 1.0 Foreword
CTC 7721 2.1 Handling Electronic Assemblies
CTC 7721 2.2 Cleaning
CTC 7721 2.5 Baking and Preheating
CTC 7721 2.7 Epoxy Mixing and Handling
IPC 7721 4.3.3 Deleting Inner Layer Connection at a Plated Hole, Drill Through Method

TOOLS & MATERIALS
Cleaner
Color Agent
Continuity Meter
End Mills
Epoxy
Microscope
Oven
Pin Clamps
Precision Drill System
Tape, Kapton
Wipes

PROCEDURE

  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).


  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.

    4. 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.


    7. 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).

    10. 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.

    11. CAUTION
    Some components may be sensitive to high temperature.

     

  11. Clean the area


  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 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).

    13. 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
  
Solutions Across the Board TM

Product Class: R/F
Skill Level: Advanced
Conformance Level: High
Revision: E
Revision Date:  Jul 7, 2000 
Repair Service Charge

  
Deleting Inner Layer Connection at a Plated Hole

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

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

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

  
Figure 4: Completed repair.
Tricks of the Trade
 A routine operation when using a Precision Drill System. This bench top drill has the control needed for accurate hole drilling.
 
 
Home · Services · Guidebook · Products · Training · Top

Circuit Technology Center, Inc.