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
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.
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Additional Items and Supplies
Cleaner
General purpose cleaner for removing contamination.
End Mills
Designed for end cutting and hole boring.
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.
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.
Circuit Bond Epoxy
Circuit Bond is a clear, low viscosity, superior strength epoxy precisely measured out into two-compartment plastic packages, so it's easy to use, and there's no measuring. For over a decade, this high-strength epoxy has been qualified and used by thousands of high-rel electronics manufacturers across the globe.
1.
Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use.
2.
To use Circuit Bond, remove the plastic clip separating the resin and hardener. Squeeze back and forth from one half of the package to the other to mix the contents.
3.
Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed.
4.
Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles.
5.
Color Agent can be mixed in with Circuit Bond to match surface colors if desired.
6.
Apply using a Foam Swab, Micro Probe, or Mixing Stick as required.
7.
Cure Circuit Bond for 24 hours at room temperature or 4 hours at 65°C (150°F).
Specifications
Packaging
2 gram pre-measured packages
Mix ratio
4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)
100/25
Color
Clear, transparent
Pot life
30 minutes
Cure cycle
24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index
1
Specific Gravity
1.20
Percent Solids
100%
Viscosity (after mixing)
2000 cps
Operating temperature range
-55°C to 135°C
Hardness
88 Shore D
Lap Shear, Alum to Alum
1100 psi
Glass Transition Temperature, Ultimate
92°C
Coefficient of Expansion, cm/cm/°C
6 E-05
Dielectric strength
400 volts/mil
Dielectric Constant, 1KHz@25°C
4
Shelf Life
6 months minimum
Circuit Frames
Circuit Frames have a dry-film adhesive backing that is heat-cured in 30 seconds. Use Circuit Frames to repair and replace damaged surface mount pads, lands and conductors without the mess of liquid epoxy, with a bond strength equal to the original, in just a few minutes. The dry-film adhesive backing makes this delicate repair procedure easy, fast, and highly reliable. Circuit Frames are available with a bright tin, tin/lead and nickel/gold plating finishes. This reliable IPC recommended procedure meets the highest conformance level for this type of repair. For over 30 years Circuit Frames have been used by thousands of commercial, medical and military manufacturers around the globe. Below are examples for some Circuit Frame patterns.
Circuit Tracks
Circuit Tracks are rectangular-shaped conductors made of 99.9% pure CDA 11000 copper. These rectangular ribbons closely conform to the original conductor dimensions. The replacement Circuit Track is bonded in place using epoxy.
115-5530 Circuit Track, .005" x .030" (.127 mm x .762 mm)
Images and Figures
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.
Procedure
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)
Note: 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.
Note: 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)
Note: Keep the epoxy height below the BGA pad level.
Caution: Some components may be sensitive to high temperatures.
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.
Evaluation
Visual examination for alignment and overlap of the new circuit.
Visual examination of epoxy coating for texture and color match.
