6.2.2 Jumper Wires, BGA Components, Through Board Method

Outline

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.

Note: 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

Conformance Level - High

Tools and Materials

Circuit Bond Epoxy Clear, superior strength epoxy in two-compartment plastic packages.

Circuit Frames Circuit Frames for surface mount pad, BGA pad and conductor repair.

Circuit Tracks Copper conductors to repair circuit board damage including traces and conductors.

Cleaner General purpose cleaner for removing contamination.

End Mills Designed for end cutting and hole boring.

Flex-Rack PCB Holder Sturdy rack for PCBs used for rework and positioning.

High Temp Tape Discs High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming.

Microscope Precision microscope with stand and lighting for work and inspection.

Milling Machine Use for precision milling of circuit board materials.

Oven General purpose oven for drying, baking and curing epoxies.

Precision Drill Precision drill press for accuracy and controlled depth drilling.

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

Scraper, Curved Tip Hardened stainless steel tip for scraping solder mask and removing defects.

Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips.

Tweezers Multiple sizes and tip configurations of tweezers for various small parts handling needs.

Wipes Nonabrasive, low-linting wipes for cleanup.

Procedure

Procedure

1. Clean the area.
2. Remove the BGA component if installed, remove excess solder from the pads, and clean and inspect the site.
3. Remove solder mask from the via pad terminating to the subject BGA pad. Do not remove any solder mask from the "dog bone" area.
4. 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) 
   Note: Although both power and ground planes may be cut, inner-layer signal traces must be avoided.
5. Carefully inspect the milled hole and clean the area.
6. Insert an appropriately sized Teflon sleeve into the milled hole. This sleeve will insulate the new conductor and prevent shorting to the inner layers. 
7. 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.
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 before lap soldering in place.
9. 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)
10. 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 aligned correctly. (See Figure 3)
11. Clean the area. Mix epoxy per procedure 2.7.
12. 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)
    Note: Keep the epoxy height below the BGA pad level.
    Caution: Some components may be sensitive to high temperatures.
13. Clean the board as required.
14. Install new BGA per applicable procedures.
15. 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.

Evaluation

1. Visual examination for alignment and overlap of the new circuit.
2. Visual examination of the epoxy coating for texture and color match.
3. Electrical tests as applicable.

Images

Jumper Wires, BGA Components, Through Board Method

Mill a hole through the board and insert a Teflon sleeve

Insert a copper Circuit Track into the plated hole and Teflon sleeve.

Solder the Circuit Track to the plated hole connected to the BGA pad.

Overcoat the new connection with epoxy.