Outline
This method is used to replace solder masks or coatings on circuit boards at BGA locations. BGA locations provide unique challenges due to their inaccessibility after reflow, exposure to high temperatures, and the requirement that the BGA pads only are surrounded by masks. Vias and circuits that are exposed may cause shorting or BGA solder joint starvation.
Minimum Skill Level - Intermediate
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general 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.
Professional Repair Kit
Kit to repair circuit board damage including pads, lands, conductors, base material and plated holes.
Master Repair Kit
Kit to repair circuit board damage including pads, lands, conductors and base material.
Base Board Repair Kit
Kit to repair base board and laminate damage on circuit boards.
Circuit Bond Kit
Includes packages of clear, low viscosity, superior strength epoxy for circuit board damage repair.
Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.
Tools and Materials
Cleaning Brushes
Disposable brushes for solvent cleaning and application of coatings.
Color Agents
Use to tint the color of epoxy used for solder mask repair or circuit base board repair.
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.
Foam Swab, Small
Swabs for use with solvents and application of color agents and epoxies.
Micro Probes
Sharp probes for dispensing adhesive and positioning small objects.
Additional Items and Supplies
Cleaner
General purpose cleaner for removing contamination.
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
General purpose oven for drying, baking and curing epoxies.
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
Color Agents
Color Agent is a one-part, air-drying, semi-paste ink commonly used to print hard surfaces, including circuit board base materials. Color Agent can be used to tint the color of epoxy used for solder mask repair or circuit baseboard repair. To use, mix a small amount of color agent with 2 part epoxy as the epoxy is initially mixed. Add more color agents to increase the color intensity if needed.
Figure 1: Scrape down to the copper surface to create a barrier to solder flow between pad and via.
Figure 2: Apply the replacement coating. A wood stick or small dispenser may be used.
Figure 3: "Dog Bone" area coated with soldermask
Procedure
Clean the area.
Caution: Surfaces to be coated must be thoroughly cleaned prior to coating to ensure adequate adhesion, minimized corrosion, and optimized electrical properties.
Remove all excess solder from the BGA pad and the via (top and bottom side) using solder braid or desoldering tools. BGA pads should be flat and the vias clear of solder.
Note: Vias with solder trapped inside may "volcano" underneath the reflowed component. It is important to remove the solder if possible.
Scrape solder off the "Dog Bone" section between the BGA pad and connecting via. (See Figure 1)
Note: This is to prevent solder from flowing down the "Dog Bone" path to the via location.
Mix the epoxy or replacement coating.
Apply the replacement coating to the board surface as required.(See Figure 2) Apply a thin coating of epoxy to prevent interference with component placement. Adding a color agent to the epoxy is not recommended since it may slightly reduce the epoxy strength or adhesion.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling. Provide a full cure time to ensure maximum epoxy strength.
Caution: Some components may be sensitive to high temperature.
Evaluation
Visual examination for texture, color match, adhesion, and coverage.
Electrical tests to conductors around the repaired area as applicable.
