2.4.3 Coating Replacement, Solder Mask, BGA Locations

Outline

This method replaces 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 to surround the BGA pads with masks. The exposed Vias and circuits 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.

Acceptability References
IPC-A-600 2.0	Externally Observable Characteristics
IPC-A-610 10.0	Laminate Conditions


Procedure References
1.0	Foreword
2.1	Handling Electronic Assemblies
2.2	Cleaning
2.5	Baking And Preheating
2.7	Epoxy Mixing and Handling

Kits and Systems ▼

Tools and Materials ▼

Additional Items and Supplies ▼

Images and Figures

2.4.3 Coating Replacement, Solder Mask, BGA Locations

Soldermask Required at BGA Site

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 before 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 sides) using solder braid or desoldering tools. The BGA pads should be flat, and the vias should be clear of solder.
Note: Vias with solder trapped inside may "volcano" underneath the reflowed component. If possible, it is important to remove the solder.
Scrape solder off the "Dog Bone" section between the BGA pad and the connecting via. (See Figure 1)
Note: This prevents 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's 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 temperatures.

Evaluation

Visual examination for texture, color match, adhesion, and coverage.
Electrical tests to conductors around the repaired area as applicable.