Outline
This method is used to repair severe damage to a hole or to modify the size, shape, or location of an unsupported tooling or mounting hole. The hole may have component leads, wires, fasteners, pins, terminals, or other hardware run through it. This repair method uses a dowel of matching board material and high-strength epoxy to secure the dowel in place. After the new material is bonded in place, a new hole can be drilled. This method can be used on single-sided, double-sided, or multilayer circuit boards and assemblies.
Caution: Damaged inner-layer connections may require surface wire adds.
Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Additional Items and Supplies
Cleaner
General purpose cleaner for removing contamination.
End Mills
Designed for end cutting and hole boring.
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
General purpose oven for drying, baking and curing epoxies.
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
Wipes
Nonabrasive, low-linting wipes for cleanup.
Circuit Bond Epoxy
Circuit Bond is a clear, low viscosity, superior strength epoxy precisely measured out into two-compartment plastic packages, so it's easy to use, and there's no measuring. For over a decade, this high-strength epoxy has been qualified and used by thousands of high-rel electronics manufacturers across the globe.
1.
Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use.
2.
To use Circuit Bond, remove the plastic clip separating the resin and hardener. Squeeze back and forth from one half of the package to the other to mix the contents.
3.
Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed.
4.
Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles.
5.
Color Agent can be mixed in with Circuit Bond to match surface colors if desired.
6.
Apply using a Foam Swab, Micro Probe, or Mixing Stick as required.
7.
Cure Circuit Bond for 24 hours at room temperature or 4 hours at 65°C (150°F).
Specifications
Packaging
2 gram pre-measured packages
Mix ratio
4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)
100/25
Color
Clear, transparent
Pot life
30 minutes
Cure cycle
24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index
1
Specific Gravity
1.20
Percent Solids
100%
Viscosity (after mixing)
2000 cps
Operating temperature range
-55°C to 135°C
Hardness
88 Shore D
Lap Shear, Alum to Alum
1100 psi
Glass Transition Temperature, Ultimate
92°C
Coefficient of Expansion, cm/cm/°C
6 E-05
Dielectric strength
400 volts/mil
Dielectric Constant, 1KHz@25°C
4
Shelf Life
6 months minimum
Images and Figures
Damaged Hole, Non Plated
Figure 1: New hole is milled to encompass entire damaged area.
Figure 2: Place replacement dowel in position and bond with epoxy.
Figure 3: Cut off excess material and re-drill holes as required.
Figure 4: Micro-Drill System.
Procedure
Clean the area.
Drill out the damaged or improperly sized hole using a carbide end mill or drill. Mill the hole using a precision drill press or milling machine for accuracy. The diameter of the cutting tool should be as small as possible yet still encompass the entire damaged area. (See Figure 1)
Note: Abrasion operations can generate electrostatic charges.
Cut a piece of replacement base material rod. The base material rod is made from FR-4 dowel stock. Cut the length approximately 12.0 mm (0.50") longer than needed.
Clean the reworked area.
Use High-Temperature Tape to protect exposed parts of the circuit board bordering the rework area.
Mix the epoxy.
Coat both the dowel and the hole with epoxy and fit together. Apply additional epoxy around the perimeter of the new material. (See Figure 2) Remove excess epoxy.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution: Some components may be sensitive to high temperatures.
Remove the tape and cut off the excess material using the razor saw. Mill or file the dowel flush with the board surface. (See Figure 3)
Complete the procedure by redrilling holes and adding circuitry as required. (See Figure 3)
Note: Apply surface coating to match prior coating as required.
Clean the reworked area.
Evaluation
Visual and dimensional examination of the reworked area for conformance to drawings and specifications.
