Outline
This procedure is used to repair minor damage to circuit base board material. Scrapes and scratches in the base board material may be caused by accidents during handling. Burns in the base material may be caused by improper use of soldering and desoldering tools.
Caution
This method may be used when the damage extends deep into the base material, but not completely through. If the base board material is damaged completely through, see Procedure No. 3.5.2 or 3.5.3.
Caution
Surface circuits may need to be replaced in the damaged area. Be sure that the appropriate circuit diagrams, or photographs reflecting the original circuits are available so that they may be replaced after repairing the base board material. Damage to internal circuits or planes may have to be restored using surface wires.
Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.
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.
Microscope
Precision microscope with stand and lighting for work and inspection.
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Mixing Picks
Unique mixing sticks have a paddle shape on one and sharp pick on the opposite end.
Oven
General purpose oven for drying, baking and curing epoxies.
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
Damaged Base Material
Figure 1: Scrape away damaged base board material with a knife.
Figure 2: Micro-Drill System.
Figure 3: An undercut, to enhance mechanical strength, may be desired for class 3 product.
Figure 4: Apply the epoxy with a mixing stick sharpened at the end.
Figure 5: For large areas, apply the epoxy with a foam swab to create a texture.
Figure 6. Completed repair.
Procedure
Clean the damaged area.
Scrape away the damaged base board material using a knife. All damaged base board material and solder mask must be removed at the surface. (See Figure 1) or mill away the damaged base board material using the Micro-Drill System and ball mill. All damaged base board material and solder mask must be removed. (See Figure 2)
Note
To clearly see that all damaged material has been removed, flood the area with alcohol or solvent. Damaged internal fibers of the base material will show up clearly.
Caution
Abrasion operations can generate electrostatic charges.
Note
An undercut to enhance mechanical strength may be desired for class 3 product. (See figure 3)
Remove all loose material and clean the area.
Where needed, apply High Temperature tape to protect exposed parts of circuit board.
Note
The circuit Board may be preheated prior to filling the area with epoxy. A preheated PC board will allow the epoxy to easily flow and level out. Epoxy applied to an unheated circuit board may settle below the circuit board surface as the epoxy cures.
Mix the epoxy. If desired, add color agent to the mixed epoxy to match the PC board color.
Fill the area with epoxy up to and flush with the circuit board surface. No fibers of laminate material should be exposed. A mixing stick sharpened at the end may be used to apply and spread the epoxy. For large areas, apply the epoxy with a foam swab to create a texture in the surface. (See Figures 4 and 5)
Note
A slight overfill of epoxy may be desired to allow for shrinkage when epoxy cures.
Note
Epoxy may be applied using a foam swab to restore the surface appearance.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution
Some components may be sensitive to high temperature.
After the epoxy has cured remove the tape.
If needed, use a knife or scraper and scrape off any excess epoxy. Scrape until the new epoxy surface is level with the surrounding circuit board surface.
Remove all loose material. Clean the area. (See Figure 6)
Note
If needed, apply an additional thin coating to seal any scraped areas.
Evaluation
Visual examination for texture and color match.
Electrical tests to conductors around the repaired area as applicable.
No excess epoxy covering circuits or sensitive areas.
