Circuit Technology Center

Damaged Mounting Hole Repair

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

When the ejector handle is retracted, the lever-action ejects the circuit board from the 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 used to repair or modify a non-plated hole location on circuit boards. A standard epoxy fill process is often employed for mounting holes or alignment holes where the "extra strength" is not required. 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 transplant procedure to optimize the results and achieve the highest strength.
  1. Damaged Mounting Hole Repair
    Image 3: Dowel plug used for for hole transplant.
    Drill out holes using a milling machine. Ensure holes are drilled in the center by using data points. Pin the circuit board on the table of a milling machine. See Image 2.
  2. Inspect the holes carefully. Hole walls must be smooth and 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.
  4. Apply epoxy to the dowel plug and the hole wall. 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. Damaged Mounting Hole Repair
    Image 4: Dowel plug installed and epoxied in place.
    Bake the board as required to cure the epoxy fully.
  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.
  8. Ensure top and bottom surfaces of the dowel are level with the board surface, machine if needed. See Image 4.
  9. Drill the finished hole at the specified location. See Image 5.

Damaged Mounting Hole Repair
Image 5: Completed repair of ejector handle hole location.
This repair process is an extra-strength repair capable of withstanding the typical forces applied to a standard circuit board.

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