Circuit Board Repair Guide > Basic Circuit Board Repair Procedures > 2.4.3 Replace Solder Mask or Coatings on Printed Circuit Boards at BGA Locations

Replace Solder Mask or Coatings on Printed Circuit Boards at BGA Locations

Repair Circuit Boards | Repair SMT Pads | Repair BGA Pads | Repair Lands | Repair Edge Contacts
Repair a Conductor | Plated Hole Repair | Base Board Repair | Replace Solder Mask or Coatings

This coating replacement procedure is used to replace solder mask or coatings on printed circuit boards at BGA locations. BGA locations provide unique challenges due to their inaccessibility after reflow, exposure to high temperatures, and requirement that the BGA pads only are surrounded by mask. Vias and circuits that are exposed may cause shorting or BGA solder joint starvation.

IPC Acceptability References
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-610 10.0 Laminate Conditions
 
Soldermask required at BGA site
Soldermask Required at BGA Site

Related Procedure References
CTC 1.0 Foreword - Circuit Board Repair Guide
CTC 2.1 Handling Electronic Assemblies
CTC 2.2.1 How to Clean a Circuit Board
CTC 2.2.2 Cleaning Circuit Boards, Aqueous Batch Process
CTC 2.5 Baking and Preheating of Printed Circuit Boards
CTC 2.7 Epoxy Mixing and Handling

Tools and Materials
Brush
Cleaner
Epoxy
Foam Swabs
Heat Lamp
Microscope
Oven
Wipes  

2.4.3 Coating Replacement, Solder Mask, BGA Locations

Printed Board Type: R/F/W/C  |  Skill Level: Intermediate  |  Conformance Level: High  |  Rev.: A  |  Rev. Date: May 9, 2001

Scrape down to copper surface

Fig. 1: Scrape down to the copper surface to create a barrier to solder flow between pad and via.


1.  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.
 
2. Remove all excess solder from 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.
 
 
3. 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.
 
Apply replacement coating

Fig. 2: Apply the replacement coating. A wood stick or small dispenser may be used.


Dog Bone area coated with soldermask

Fig. 3: "Dog Bone" area coated with solder mask.
4.  Mix the epoxy or replacement coating.
 
5. Apply the replacement coating to the board surface as required. (See Figure 2).  Apply a thin coating of liquid circuit board 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.
 
6. 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
 
1.  Visual examination for texture, color match, adhesion and coverage.
   
2. Electrical tests to conductors around the repaired area as applicable.




Links to Related Products


Circuit board epoxy for ciruit repair   Circuit Bond Kit 115-1322: Liquid circuit board epoxy
Circuit Bond Kit contains 10 packages of clear, low viscosity, superior strength epoxy ideal for circuit board use. The epoxy is precisely measured out into two-compartment plastic packages. This adhesive is easy to use and there's no measuring.

Color Agents for Circuit Boards
Matching epoxy to the color of the circuit board being repaired is easy when you use a color agent. Color agents may also be applied directly to the circuit board surface for color matching.



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