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Damaged Mounting Hole Repair
Damaged Mounting Hole Repair
Figure 1: Damaged ejector handle mounting hole.
For this repair we're looking at the process to correct base board damage, or to correct a design error at an ejector handle location, see Image 1. The ejector handle is often held in place by a roll pin that is pressed into a non plated hole on the circuit board.

When the ejector handle is retracted, the lever action will be used to press in, or eject the circuit board into, or out of a connector, or card cage. With this action, the ejector handle roll pin will put considerable stress inside the ejector handle mounting hole. Standard circuit board construction will easily withstand this stress, but what about a modified, or repaired mounting hole location?

Damaged Mounting Hole Repair
Image 2: Over sized hole drilled to remove damage.
There are a few repair processes that we have used to repair, or modify, a non-plated hole location on circuit boards. Using a standard epoxy fill process is often employed for mounting holes, or alignment holes where the "extra strength" is not a requirement. See: 3.3.1 Hole Repair, Epoxy Method

A second procedure uses replacement board material, instead of epoxy alone to provide added strength for those applications where "extra strength" is a critical requirement. See: 3.3.2 Hole Repair, Transplant Method

The following is a refinement of the the transplant procedure to optimize the results and achieve the highest strength.

Damaged Mounting Hole Repair
Image 3: Dowel plug used for for hole transplant.
1. Drill out holes using a milling machine. Ensure holes are drilled on center by using data points. Pin the circuit board on the table of a milling. See Image 2.

2. Inspect the holes carefully. Hole walls must be smooth and perfectly clear of debris.

3. Seal the bottom surface of the board with high temperature tape. This will prevent epoxy leakage and avoid air entrapment when the epoxy coated dowel is placed in the hole from the top side of the board.

Damaged Mounting Hole Repair
Image 4: Dowel plug installed and epoxied in place.
4. Apply epoxy to the dowel plug and the wall of the hole. See Image 3.

5. Insert the dowel into the hole. Ensure the dowel plug is inserted evenly, and the epoxy is present around the entire hole circumference.

6. Bake the board as required to fully cure the epoxy.

7. Remove the high temperature tape and inspect for voids in the epoxy. If present, grind out the defects, re-epoxy and re-bake boards.

Damaged Mounting Hole Repair
Image 5: Completed repair of ejector handle hole location.
8. Ensure top and bottom surfaces of dowel are level with board surface, machine if needed. See Image 4.

9. Drill the finished hole at the specified location. See Image 5.

The result of this repair process is an extra strength repair capable of withstanding the typical forces applied to a normal circuit board.

Several members of the Circuit Technology Center team contributed to this feature story.