OUTLINE

This method is used to change a circuit path at a BGA site for engineering changes or modifications.

NOTE
This procedure requires precision milling equipment and highly trained technicians.

CAUTION
This procedure is not applicable for "via in pad" applications.

   

ACCEPTABILITY REFERENCES
IPC-A-600	2.0	Externally Observable Characteristics
IPC-A-610	11.0	Discrete Wiring
PROCEDURE REFERENCE
CTC 7721	2.1	Handling Electronic Assemblies
CTC 7721	2.2	Cleaning
CTC 7721	2.5	Baking and Preheating
CTC 7721	2.7	Epoxy Mixing and Handling
CTC 7721	4.2.1	Conductor Repair, Foil Jumper, Epoxy Method
CTC 7721	4.4.3	Surface Mount, BGA Pad Repair, Film Adhesive Method.
CTC 7721	6.1	Jumper Wires
CTC 7721	8.5.2	Profile Development, BGA Comp., Hot Gas/Air Method
CTC 7721	8.5.3	Component Replacement, PBGA Comp., Hot Gas/Air Method
CTC 7721	8.5.4	Component Replacement, CBGA Comp., Hot Gas/Air Method
IPC 7721	6.2.1	Jumper Wires, BGA Components, Circuit Track Method

TOOLS & MATERIALS
BGA Pad Repair Kit
Bonding Iron
Bonding Tips
Bonding System
Circuit Frames, BGA Pads
Circuit Tracks
Cleaner
End Mills
Epoxy
Flux, Liquid
Heat Lamp
Knife
Microscope
Milling System
Oven
Precision Drill System
Scraper
Solder
Soldering Iron
Tape, Kapton
Tweezers
Wipes

PROCEDURE

1. Clean the area.



2. Remove the BGA component if installed, remove excess solder from the pads, and clean and inspect the site using standard BGA rework equipment.



3. Cut the short conductor (dog bone) connecting the BGA pad to the connecting via using a Precision Drill System or milling machine and appropriate size end mill. (See Figure 1 and 6).



4. Remove the existing BGA pad. Apply heat from a soldering iron if needed. (See Figure 2)



5. Use a milling machine to mill a shallow groove in the board surface from the BGA pad area to the perimeter of the BGA site. Tight spacing may restrict the width of the channel to 0.25 mm (.010") or less. Use a carbide end mill approximately0.050 mm (.002") wider than the new connecting circuit. (See Figure 3).



6. Bond a replacement BGA pad in place using a bonding system. (See Procedure 4.7.3). The new BGA pad must have a tail that will align with the circuit track to be added next. (See Figure 4).



7. Select a Circuit Track to match the width and thickness of the circuit to be replaced. Cut a length approximately as needed. The Circuit Track should overlap the BGA tail section a minimum of 2 times the circuit width. See Table 1.
Table 1
Common Circuit Track Sizes


Part No.	Thickness	Width
115-5204	.002"	.004"
115-5206	.002"	.006"
115-5208	.002"	.008"
115-5210	.002"	.010"
115-5312	.003"	.120"
115-5315	.003"	.015"
115-5520	.005"	.020"
115-5530	.005"	.030"




8. Gently abrade the top and bottom of the new Circuit Track with the buffer to remove any oxidation and clean.

NOTE
If needed, the ends of the Circuit Track may be tinned with solder prior to lap soldering in place.

 

9. Position this new Circuit Track along the milled groove. The Circuit Track should overlap the existing circuit a minimum of 2 times the circuit width. (See Figure 4).



10. Apply a small amount of liquid flux to the overlap joint.



11. Lap solder the Circuit Track to the BGA tail section using solder and a soldering iron. Make sure the new circuit is properly aligned.



12. Solder one end of a fine gauge wire to the end of the extending circuit. (The opposite end of the wire will be soldered later.) (See Figure 5).



13. Clean the area.



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



15. 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. (See Figure 5).



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


CAUTION
Some components may be sensitive to high temperature.


17. Clean the board as required.



18. Install new BGA per applicable procedures.



19. Route and terminate the other end of the jumper wire.