6.2.1 Jumper Wires, BGA Components, Circuit Track Method

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 References
CTC 2.1 Handling Electronic Assemblies
CTC 2.2.1 Cleaning, Local
CTC 2.2.2 Cleaning, Aqueous Batch Process
CTC 2.5 Baking and Preheating
CTC 2.7 Epoxy Mixing and Handling
CTC 4.2.1 Conductor Repair, Foil Jumper, Epoxy Method
CTC 4.7.3 Surface Mount, BGA Pad Repair, Film Adhesive Method
CTC 6.1 Jumper Wires
CTC 9.2.1 BGA Component Profile Development, Standard
CTC 9.2.2 BGA Component Profile Development, Smart Track
CTC 9.3.1 BGA Rework
IPC7721 6.2.1 Jumper Wires, BGA Components, Circuit Track Method see procedure below

Tools and 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 6.2.1 Jumper Wires, BGA Components, Circuit Track Method

Cut connection to via.

Figure 1: Cut the connection to the via
using a Precision Drill System.
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).
Remove BGA pad.

Figure 2: Remove the BGA pad and mill
a shallow channel into the solder mask
surface.
4.      
Remove the existing BGA pad. Apply heat from a soldering iron if needed. (See Figure 2).

Bond new BGA pad.

Figure 3: Bond a new BGA pad in place.
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).
Solder copper circuit track to tail extending from new BGA pad.

Figure 4: Solder a copper circuit track to
the tail extending from the new BGA pad.
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.
   
Solder wire to circuit track and overcoat with epoxy.

Figure 5: Solder a wire to the Circuit
Track and overcoat with epoxy.
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.
   
Precision drill system.

Figure 6: Precision Drill System
used to cut the connection from the
BGA pad to the via.
17.      
Clean the board as required.
   
18. Install new BGA per applicable procedures.
   
19.
Route and terminate the other end of the jumper wire.
   
Evaluation
   
1.        Visual examination for alignment and overlap of new circuit.
   
2. Visual examination of epoxy coating for texture and color match.
   
3. Electrical tests as applicable.


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6.2.1 Jumper Wires, BGA Components, Circuit Track Method