6.2.2 Jumper Wires, BGA Components, Through Board Method
This method is used to add a jumper at a BGA site by running the jumper through a hole in the board. This method is normally used for engineering changes or modifications.
This procedure requires precision milling equipment and highly trained technicians. This method is used when there is a buried via, and other methods of terminating to the opposite side are not an option.
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.
Figure 1: Mill a hole through the board and insert a Teflon sleeve.
Figure 2: Insert a copper Circuit Track into the plated hole and Teflon sleeve.
Figure 3: Solder the Circuit Track to the plated hole connected to the BGA pad.
Figure 4: Overcoat the new connection with epoxy.
Clean the area.
Remove the BGA component if installed, remove excess solder from the pads, and clean and inspect the site.
Remove solder mask from the via pad terminating to the subject BGA pad. Do not remove any solder mask from the "dog bone" area.
Mill a hole through the board at the precise coordinates using a Precision Drill System and End Mill of the appropriate size. (See Figure 1 and 5)
Although both power and ground planes may be cut, inner layer signal traces must be avoided.
Carefully inspect the milled hole and clean the area.
Insert an appropriately sized Teflon sleeve into the milled hole. This sleeve will insulate the new conductor and prevent shorting to the inner layers. (See Figure 1)
Select a Circuit Track to match the width of the circuit to be installed. Cut a length approximately as needed. The overlap solder connection should be a minimum of 2 times the circuit width.
Gently abrade the top and bottom of the new Circuit Track with the buffer to remove any oxidation and clean.
If needed, the ends of the Circuit Track may be tinned with solder prior to lap soldering in place.
Insert one end of the Circuit Track into the plated hole connected to the BGA pad. Insert the opposite end through the Teflon sleeve. (See Figure 2)
Apply a small amount of liquid flux and lap solder the Circuit Track to the plated hole connected to the BGA pad using solder and a soldering iron. Make sure the new circuit is properly aligned. (See Figure 3)
Clean the area.
Mix epoxy per procedure 2.7.
Coat the top and sides of the new circuit with epoxy. The epoxy bonds the new circuit to the base board material and insulates the circuit. (See Figure 4)
Keep the epoxy height below the BGA pad level.
Some components may be sensitive to high temperature.
Clean the board as required.
Install new BGA per applicable procedures.
Solder a jumper wire to the exposed Circuit Track on the opposite side of the circuit board. Route and terminate the jumper wire as needed.
Visual examination for alignment and overlap of new circuit.
Visual examination of epoxy coating for texture and color match.