3.5.2 Base Material Repair, Area Transplant Method
Outline
This procedure is used to repair mechanical or thermal damage to circuit board base material. This method is used when extended areas of base material must be completely replaced. This method may be used on single sided, double sided or multilayer circuit boards or assemblies.
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 - 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.
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.
Oven
General purpose oven for drying, baking and curing epoxies.
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
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: Mill away the damaged base material using the Micro-Drill System and ball mill.
Figure 2: Bevel edge using the Micro-Drill System or file.
Figure 3: Mill a step into the edge of the circuit board.
Figure 4: Mill a step onto the edge of the replacement base material.
Figure 5: Bond replacement piece in place.
Figure 6: Completed repair.
Figure 7: Micro-Drill System.
Procedure
Clean the area.
Mill away the damaged board material using the Micro-Drill System and ball mill. Remove all evidence of the damaged material. No fibers of laminate material should be exposed. At the surface file the edges to ensure that the opening is rectangular or uniform in shape. (See Figure 1)
Caution
Abrasion operations can generate electrostatic charges.
Clean the area.
Bevel the edge using the Micro-Drill System and ball mill or using a file. (See Figure 2)
Install an end mill into the chuck of a Precision Drill System. Set the speed to maximum and machine a step or lap joint in the edge of the circuit board where the new base material will be installed. The depth and width of the step should be approximately 1/2 of the circuit board thickness. (See Figure 3)
Caution
Exercise care to avoid damage to any internal conductors. If any internal conductors are damaged, surface wires may be required.
Cut or machine a piece of replacement base board material that is the same thickness and type as the piece removed. The replacement piece must be precisely the same size and shape of the opening including the step joint.
Install an end mill into the chuck of a Precision Drill Press. Machine a step onto the entire mating edge of the replacement base material. The dimensions of the step should match the size of the step in the circuit board milled groove. (See Figure 4)
Where required apply High Temperature Tape to protect exposed parts of circuit board bordering the prepared area.
Check the fit to be sure the new base material properly mates with the step in the circuit board.
Mix the epoxy.
Coat both the tongue and groove surfaces with epoxy and fit together. (See Figure 5) Remove excess epoxy.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
After the epoxy has cured remove the High Temperature Tape.
If needed scrape off any excess epoxy using a knife or scraper.
Note If needed, apply additional thin coating to seal any scraped areas.
Clean the area.
Complete by drilling holes, slots, etc. or adding circuitry as required.
Evaluation
1. Dimensions of area replaced should be checked to conform to specifications require.
