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.
Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.
Conformance Level - Medium
This procedure may have some variance with the physical character of the original and most likely varies with some of the functional, environmental and serviceability factors.
Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips.
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Tweezers Multiple sizes and tip configurations of tweezers for various small parts handling needs.
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Wipes Nonabrasive, low-linting wipes for cleanup.
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Bonding Iron Tips
Bonding Iron Tips fit into the handheld Bonding Iron. The bottom surface of each Bonding Tip is used to apply heat and pressure to bond adhesive-backed replacement lands, pads, and edge contacts to a circuit board surface. The pressure/force listed is the recommended load in pounds to apply to the top surface of the replacement adhesive-backed pads, lands, and conductors. The load is based on the Bonding Tip surface area to meet the recommended load for Circuit Frames at 200 - 400 psi.
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: Cut the connection to the via using a Precision Drill System.
Figure 2: Remove the BGA pad and mill a shallow channel into the solder mask surface.
Figure 3: Bond a new BGA pad in place.
Figure 4: Solder a copper circuit track to the tail extending from the new BGA pad
Figure 5: Solder a wire to the Circuit Track and overcoat with epoxy.
Procedure
Clean the area.
Remove the BGA component if installed, remove excess solder from the pads, and clean and inspect the site using standard BGA rework equipment.
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 Figures 1 and 6)
Remove the existing BGA pad. Apply heat from a soldering iron if needed. (See Figure 2)
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)
Bond a replacement BGA pad in place using a bonding iron. (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)
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.
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.
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)
Apply a small amount of liquid flux to the overlap joint.
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 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)
Clean the area.
Mix epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
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)
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution: Some components may be sensitive to high temperatures.
Clean the board as required.
Install new BGA per applicable procedures.
Route and terminate the other end of the jumper wire.
Evaluation
Visual examination for alignment and overlap of the new circuit.
Visual examination of epoxy coating for texture and color match.
