Figure 1: Milling into multilayer
circuit board to expose the
damaged internal circuit.
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| 1. |
Locate and determine the coordinates where the
repair is to be made. Use films or master drawings
of the board as needed.
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Note
Obtain as much information as possible
on the conductive and non-conductive layers
prior to starting the procedure.
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| |
| 2. |
Remove components from the immediate
area if necessary and clean the area. |
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|
| 3. |
Use the microscope and Micro-Drill System and
cut through the base material, one layer at
a time, until the desired inner layer has been
reached. (See Figure 1 and 2).
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Caution
Great care should be taken to prevent
further damage to internal circuits.
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Figure 2: A high quality, Micro-Drill System is recommended
for this delicate operation.
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| 4.
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Each internal circuit should have a flat section
exposed to allow the new circuit to be soldered
in place. (See Figure 3).
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| 5.
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To reduce damage to the internal circuit, complete
the final exposure of the internal circuit using
a knife. (See Figure 3).
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| 6.
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Remove all loose material. Clean
the area. |
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| 7.
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Apply a small amount of liquid flux to the ends
of the internal circuit. Tin the exposed end
of each circuit using solder and a soldering
iron.
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| 8.
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Clean the area. |
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Figure 4: Circuit Track in place
ready to be soldered.
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| 9.
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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 existing circuit a
minimum of 2 times the circuit width.
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| |
| 10.
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Gently abrade the top and bottom of the Circuit
Track with the buffer to remove any protective
coating and clean.
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Note
If needed, the ends of the Circuit
Track may be tinned with solder prior to lap
soldering in place.
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| 11.
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Place the Circuit Track in position.
The Circuit Track should overlap the existing circuit
a minimum of 2 times the circuit width. (See Figure
4). |
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Figure 5: If spacing is critical or the circuit board uses
high frequency circuits, bevel the joint as shown.
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Note
If spacing is critical or the circuit
board uses high frequency circuits, bevel the
joint. (See Figure 5).
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Caution
This bevel joint method may cause
problems with circuit boards exposed to extreme
temperature fluctuations.
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| |
| 12.
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Apply a small amount of liquid flux to the overlap
joint.
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|
| 13. |
Lap solder the Circuit Track to the exposed
internal circuit using solder and a soldering
iron. Make sure the new circuit is properly
aligned.
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|
| 14. |
Clean the area.
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Note
The circuit board may be preheated
prior to filling the area with epoxy. A preheated
PC board will allow the epoxy to easily flow
and level out. Epoxy applied to an unheated
circuit board may settle below the circuit board
surface as the epoxy cures.
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|
| 15. |
Mix epoxy. If desired, add color agent to the
mixed epoxy to match the circuit board color.
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Figure 6: Coat the top and sides of
the new circuit with epoxy. Add
epoxy until flush with top surface.
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| 16.
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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. Continue adding epoxy up to the top
surface of the circuit board or to the height
of the next internal circuit. (See Figure 6).
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Note
A slight overfill of epoxy may be desired to
allow for shrinkage when the epoxy cures.
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|
| 17.
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Cure the epoxy per Procedure 2.7 Epoxy Mixing
and Handling.
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Caution
Some components may be sensitive to high temperature.
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|
| 18. |
Add additional Circuit Tracks if
needed and coat with additional epoxy.
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Figure 7: Completed repair.
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| 19. |
Continue completing all layers
until the top surface of the circuit board is reached.
(See Figure 7).
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|
| 20. |
Clean the board as required.
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|
| 21. |
Apply surface coating to match
prior coating as required.
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Evaluation |
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|
| 1. |
Visual examination for alignment
and overlap of new circuit. |
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|
| 2. |
Visual examination of epoxy coating
for texture and color match. |
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|
| 3. |
Electrical tests as applicable. |
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