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5.3 Plated Hole Repair, Inner Layer Connection
Outline
This procedure describes the use of flat set eyelets for the repair of a through connection that has an inner layer connect. No surface wire is used. The inner layer reconnect is established by soldering the barrel of an eyelet to the exposed inner layer and the connection is encapsulated in high strength epoxy.

Caution
This is a complex repair procedure that demands the proper tools and materials. To expect reliable results, repair technicians must have a high level of expertise. Use this method only when alternative methods are unacceptable.

Caution
This procedure requires very accurate control over the location and depth of a milled hole. It is recommended that a precision drill system be used in combination with a high power stereo microscope.

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

Conformance Level - Medium
This procedure may have some variance with the physical character of the original and most likely varies with some of 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
IPC7721 5.3 Plated Hole Repair, Inner Layer Connection
Tools and Materials
Cleaner
Cleaner
General purpose cleaner for removing contamination.
End Mills
End Mills
Designed for end cutting and hole boring.
Eyelets
Eyelets
Copper or brass eyelets electroplated with tin used for plated hole repair.
CircuitMedic Part
Eyelet Press
Heavy duty eyelet press designed to set and form eyelets in circuit boards.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
Microscope
Microscope
It is a challenge to undertake precision repair without a good microscope.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Pin Gauges
Pin Gauges
Use to provide accurate measurements for thickness and hole diameters.
Precision Drill
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
Soldering Iron
Soldering Iron, Solder and Flux
A well maintained soldering iron is a must at every tech bench.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
5.3 Plated Hole Repair, Inner Layer Connection
Damaged Plated Hole with Inner Layer Connection.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 1: Precision Drill System shown with circuit board pinned in place.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 2: Mill down to and expose inner layer signal or plane.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 3: Solder the eyelet barrel to the exposed inner layer signal or plane.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 4: Fill the milled hole with the epoxy up to, and level with, the surface of the board.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 5: Set the eyelet using an Eyelet Press.
5.3 Plated Hole Repair, Inner Layer Connection
Figure 6: Eyelet barrel formed flat to circuit board surface.

Eyelet Selection Criteria

ID - Inside Diameter
The eyelet inside diameter should be a .075 - .500 mm (.003"-.020") greater than the component lead diameter.

LUF - Length Under Flange
The length of the eyelet barrel under the flange should be .630 - .890 mm (.025" - 035") greater than the thickness of the circuit board. This added length allows for proper protrusion when setting the eyelet.

FD - Flange Diameter
The eyelet flange diameter should be small enough to prevent interference with adjacent lands or circuits.

OD - Outside Diameter
The clearance hole drilled through the circuit board should allow the eyelet to be inserted without force but should not exceed .125 mm (.005") greater than the eyelet outside diameter.

Note

Be sure to select an eyelet meeting the proper criteria. An eyelet with an oversize flange may interfere with adjacent circuits. An eyelet that is too short will not protrude through the circuit board for proper setting.

Procedure

  1. Clean the area.

  2. Select an eyelet using the Eyelet Selection Criteria. Use a pin gauge and caliper to measure the existing plated hole dimensions.

  3. Pin the circuit board to the base of the Precision Drill System. (See Figure 1)

  4. Insert the appropriate ball mill, end mill or drill into the chuck of the drill press.

  5. Mill or drill out the hole. The drilled hole should be approximately .030 mm (0.001") larger than the eyelet O.D. Inspect to ensure no metallic particles or burrs remain.

  6. Select the side of the assembly that will have a counterbored hole milled into it. This side preferably would have no surface connection.

  7. Select an end mill approximately .050 - .075 mm (.020" - .030") larger than the eyelet diameter. Insert into the Precision Drill System and mill down to and expose the inner layer signal or plane. (See Figure 2)

    Caution
    Great care must be taken to control the depth of the milled hole to prevent damage to the inner layer signal or plane.

  8. Clean the area.

  9. Apply a small amount of flux to the exposed signal or plane and tin with solder.

  10. Clean the area.

  11. Insert the eyelet into the hole from the side opposite the milled hole, then apply a small amount of flux into the milled hole.

  12. Solder the eyelet to the exposed inner layer signal or plane by applying heat from a soldering iron to the barrel of the eyelet. (See Figure 3)

  13. Completely remove any solder flux residue by spray rinsing with cleaner.

  14. Use a microscope and inspect the solder fillet from the eyelet to the inner connection and perform electrical tests as required.

  15. Mix epoxy as required.

  16. Fill the milled hole with the epoxy up to, and level with, the surface of the board. (See Figure 4) The epoxy filler material should be free of voids and air bubbles.

  17. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

  18. Select the proper setting tools and insert them into the eyelet press. (See Figure 5)

  19. Turn the circuit board over and rest the eyelet flange on the lower setting tool.

  20. Apply firm even pressure to form the eyelet barrel. (See Figure 6)

  21. Install the component lead and solder, if required.

  22. Clean the area.

Evaluation

  1. Visual examination, dimensional requirement of land diameter and inside diameter.

  2. Electrical continuity as required.

Procedure for reference only.