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4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Outline
This method is used to replace damaged BGA pads with new dry film adhesive backed pads. The new pads are bonded to the circuit board surface using a specially designed bonding press or bonding iron. Electrical connection is made to a via circuit which is originally manufactured integral to the pads.

Note
This method uses replacement BGA pads. The new pads are fabricated from copper foil. They are available in a variety of sizes and shapes and are generally supplied solder plated. If a special size or shape is needed they can be custom fabricated.

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.

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
IPC7721 4.7.5 Surface Mount, BGA Land with Integral Via Repair Circuit Extension Film Adhesive Method
Tools and Materials
CircuitMedic Part
Bonding Iron, 120 VAC
Delivers the optimal heat for curing adhesive bonding film.
CircuitMedic Part
Bonding System
System designed to repair lifted and damaged conductors, pads, BGA pads, SMT pads.
Soldering Iron
Bonding Tips
Used to cure adhesive backed circuit frames for pad, land and contact repair.
Soldering Iron
Circuit Frames
Replacement circuits with a dry-film adhesive backing for conductor repair.
Cleaner
Cleaner
General purpose cleaner for removing contamination.
CircuitMedic Part
Circuit Bond Packs
Clear, superior strength epoxy in two-compartment plastic packages
CircuitMedic Part
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
Microscope
Microscope
It is a challenge to undertake precision repair without a good microscope.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
CircuitMedic Part
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Soldering Iron
Soldering Iron, Solder and Flux
A well maintained soldering iron is a must at every tech bench.
CircuitMedic Part
Tweezer, Point Tip
Fine point tweezers for precision work.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 1: Remove the damaged pad with integral via.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 2: Micro-Drill System and ball mills.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 3: Using a Micro-Drill expose the copper circuit by recessing a trough or gully.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 4: Tin the circuit with solder.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 5: Select a replacement pad that matches the missing pad.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 6: Scrape off the adhesive bonding film from the solder joint connection area on the back of new pad.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 7: Connecting circuit connected to the exposed and tinned circuit.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 8: Bond the new pad using a Bonding System.
4.7.5 Surface Mount, BGA Pad, Integral Via, Circuit Extension Method
Figure 9: Completed repair.

Procedure

Note
Prior to proceeding determine whether this procedure or C4-7-4 Surface Mount, BGA Pad with Integral Via Repair, is the appropriate method. This method is best used when a connecting circuit or plane clearly runs from the integral via and is close to the board's affected surface to permit exposure of the circuit for the repair connection.
  1. Clean the area. 

  2. Carefully remove the defective pad to avoid damaging the integral via (See Figure 1)

  3. Use a knife and scrape off any epoxy residue, contamination or burned material from the board surface.

  4. Using a Micro-Drill system (See Figure 2) and the appropriate ball mill down to the connecting circuit, exposing the copper surface of the etch (See Figure 3) Be careful not to cut through the circuit.

  5. Clean the area

  6. Apply a small amount of liquid flux to the circuit connection now exposed beneath the surface of the board. Tin the circuit with solder (See Figure 4) Clean the area.

  7. In general, the area for the new pad on the board surface must be smooth and flat. If internal fibers of the board are exposed, or if there are deep scratches in the surface, they should be repaired. Refer to appropriate procedure.

  8. Select a replacement BGA pad that most closely matches the surface mount pad to be replaced. If a special size or shape is needed they can be custom fabricated. (See Figure 5) Ensure the selected pads attached circuit matches the width and thickness of the circuit to be replaced. Trim the width approximately as needed. The circuit should overlap the existing circuit a minimum of 2 times the circuit width.

    Note
    New BGA pads are fabricated from copper foil. The foil is plated on the top side with solder, and an adhesive bonding film is applied to the bottom side.

  9. Before trimming out the new pad, carefully scrape off the adhesive bonding film from the solder joint connection area on the back of the replacement circuit portion of the new pad. In order to ensure that the final pressed pad lays flat (and the new circuit is properly connected to the exposed board circuit), it may be necessary to remove the film from the whole length of the connecting circuit up to the pad itself. (See Figure 6)

    Caution
    When handling the replacement pad, avoid touching the epoxy backing with your fingers or other materials that may contaminate the surface and reduce the bond strength.

  10. Cut out and trim the new pad. Cut out from the plated side.

  11. Place the pad on the board so that the connecting circuit can be fit into the trough containing the board's tinned circuit (See Figure 7)

  12. Select a bonding tip with a shape to match the shape of the new pad. See bonding tip chart in the replacement parts section of the manual provided with the repair system or repair kit. (See Figure 8)

    Note  
    The tip used for bonding should be as small as possible but should completely cover the entire surface of the new pad.

  13. Position the circuit board so that it is flat and stable. Gently place the bonding tip directly onto the new pad. Apply pressure as recommended in the manual of the repair system or repair kit for 30 seconds to fully bond the pad. The new pad is fully cured. Carefully clean the area and inspect the new pad for proper alignment

    Caution 
    Excessive bonding pressure may cause measling in the circuit board surface or may cause the new pad to slide out of position.

  14. Apply flux to the overlapping connecting circuit in the bottom of the trough. Solder in place. Clean the area

    Note
    The circuit board may be preheated prior to filling the area with epoxy. A preheated circuit 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.

  15. Mix epoxy. If desired, add color agent to the mixed epoxy to match the circuit board color.

  16. Coat the top and sides of the replaced circuit with epoxy. The epoxy bonds the new circuit to the base board material and insulates the circuit. Continue adding epoxy up to the top surface of the circuit board.

    Note
    A very slight overfill of epoxy may be desired to allow for shrinkage when the epoxy cures. Additionally, in order to allow the circuits appearance to match the board, it may be necessary to mask the circuit prior to filling the excavated area.

  17. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling

    Caution
    Some components may be sensitive to high temperature.

  18. Additional epoxy can be applied around the perimeter of the new pad to provide additional bond strength. Mix epoxy. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling. Use the maximum recommended heat cycle to ensure the highest strength bond. BGA pads are routinely subjected to one or more reflow cycles.

    Caution
    Some components may be sensitive to high temperature.

  19. Apply surface coating to match prior coating as required. (See Figure 9)
Evaluation
  1. Visual examination.

  2. Measurement of new pad width and spacing.

  3. Electrical continuity measurement.

Procedure for reference only.