Circuit Board Repair Guide > Plated Hole Repair > 5.3 Plated Hole Repair, Inner Layer Connection

Plated Hole Repair, Inner Layer Connection

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This plated hole repair 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.

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.
Damaged plated hole with inner layer connecton needs repair
Damaged Plated Hole with
Inner Layer Connection
This method 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.

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
IPC7721 5.3 Plated Hole Repair, Inner Layer Connection

Tools and Materials
Ball Mills
End Mills
Eyelet Press      
Eyelets, Various Sizes      
Flux, Liquid
Micro Drill System
Pin Gauges
Precision Drill System
Setting Form Tool, Various Sizes      
Setting Anvil, Various Sizes
Soldering Station


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.

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.  

5.3 Plated Hole Repair, Inner Layer Connection

Printed Board Type: R  |  Skill Level: Expert  |  Conformance Level: Medium  |  Rev.: E  |  Rev. Date: Mar 28, 2001

Precision Drill System with circuit board pinned

Figure 1: Precision Drill System
shown with circuit board pinned
in place.

Clean the area.
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).
Expose inner layer signal or plane

Figure 2: Mill down to and expose
inner layer signal or plane.

4.  Insert the appropriate ball mill, end mill or drill into the chuck of the drill press.
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.
Select the side of the assembly that will have a counterbored hole milled into it. This side preferably would have no surface connection.
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).
Great care must be taken to control the depth of the milled hole to prevent damage to the inner layer signal or plane.

Solder eyelet barrel to exposed inner layer signal

Figure 3: Solder the eyelet barrel
to the exposed 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.
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.
Use a microscope and inspect the solder fillet from the eyelet to the inner connection and perform electrical tests as required.
Fill milled hole with epoxy

Figure 4: Fill the milled hole with
the epoxy up to, and level with,
the surface of the board.

15. Mix the epoxy as required.
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.
Circuit board eyelet press

Figure 5: Set the eyelet using an
Eyelet Press.

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.
Eyelet barrel formed flat to circuit board surface

Figure 6: Eyelet barrel formed
flat to circuit board surface.

20. Apply firm even pressure to form the eyelet barrel. (See Figure 6).
Install the component lead and solder, if required.
22. Clean the area.
Visual examination, dimensional requirement of land diameter and inside diameter.
2.  Electrical continuity as required.

Links to Related Products

Circuit board eyelet press 110-5202  
Circuit Board Eyelet Press 110-5202
Rugged, heavy duty circuit board eyelet press precisely forms eyelets in circuit boards for repair or assembly. Eyelet press has 6.5" throat depth to accommodate 12" wide circuit boards. This eyelet press will deliver years of maintenance-free reliable production.

Plated Hole Repair Kit used to repair damaged plated through holes  
Plated Hole Repair Kit 201-3140
Plated Hole Repair Kit includes all the tools and materials you'll need to repair damaged plated through holes in circuit boards. This circuit board repair kit includes a variety of eyelet sizes, carbide ball mills for drilling, and setting tools to form the eyelets conforming to IPC guidelines.

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