Figure 1: Remove the damaged pad with integral via.
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| |
Note
Prior to proceeding determine whether
this procedure or 4-7-4 Surface Mount, BGA Pad
with Integral Via Repair, is the appropriate
method. This method is best used when a connecting
circuit or plane clearly runs from the integral
via and is close to the board's affected surface
to permit exposure of the circuit for the repair
connection.
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|
| 1. |
Clean the area.
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| 2. |
Carefully remove the defective
pad to avoid damaging the integral via (See Figure
1). |
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| 3. |
Use knife and scrape off any epoxy residue,
contamination or burned material from the board
surface.
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Figure 2: Micro-Drill System and ball mills.
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| 4.
|
Using a Micro-Drill system (See Figure 2) and
the appropriate ball mill down to the connecting
circuit, exposing the copper surface of the
etch (See Figure 3). Be careful not to cut through
the circuit.
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Figure 3: Using a Micro-Drill
expose the copper circuit by recessing a trough or gully.
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Figure 4: Tin the circuit with solder.
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| 6.
|
Apply a small amount of liquid flux to the circuit
connection now exposed beneath the surface of
the board. Tin the circuit with solder (See
Figure 4 ). Clean the area.
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|
| 7. |
In general, the area for the new pad on the
board surface must be smooth and flat. If internal
fibers of the board are exposed, or if there
are deep scratches in the surface, they should
be repaired. Refer to appropriate procedure.
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|
Figure 5: Select a replacement pad
that matches the missing pad.
|
| 8.
|
Select a replacement BGA pad that most closely
matches the surface mount pad to be replaced.
If a special size or shape is needed they can
be custom fabricated. (See Figure 5). Ensure
the selected pads attached circuit matches the
width and thickness of the circuit to be replaced.
Trim the width approximately as needed. The
circuit should overlap the existing circuit
a minimum of 2 times the circuit width.
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|
|
| |
Note
New BGA pads are fabricated from copper foil.
The foil is plated on the top side with solder,
and an adhesive bonding film is applied to the
bottom side.
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Figure 6: Scrape off the adhesive bonding film from the
solder joint connection area on the back of
new pad.
|
| 9.
|
Before trimming out the new pad, carefully scrape
off the adhesive bonding film from the solder
joint connection area on the back of the replacement
circuit portion of the new pad. In order to
ensure that the final pressed pad lays flat
(and the new circuit is properly connected to
the exposed board circuit), it may be necessary
to remove the film from the whole length of
the connecting circuit up to the pad itself.
(See Figure 6).
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|
| |
Caution
When handling the replacement pad, avoid touching
the epoxy backing with your fingers or other
materials that may contaminate the surface and
reduce the bond strength.
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|
| 10. |
Cut out and trim the new pad. Cut
out from the plated side. |
|
Figure 7: Connecting circuit
connected to the exposed and
tinned circuit.
|
| 11.
|
Place the pad on the board so that the connecting
circuit can be fit into the trough containing
the board's tinned circuit (See Figure 7).
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|
Figure 8: Bond the new pad using
a Bonding System.
|
| 12.
|
Select a bonding tip with a shape to match the
shape of the new pad. See bonding tip chart
in the replacement parts section of the manual
provided with the repair system or repair kit.
(See Figure 8).
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| |
|
| |
Note
The tip used for bonding should be as small
as possible but should completely cover the
entire surface of the new pad.
|
| |
|
| 13. |
Position the circuit board so that
it is flat and stable. Gently place the bonding
tip directly onto the new pad. Apply pressure as
recommended in the manual of the repair system or
repair kit for 30 seconds to fully bond the pad.
The new pad is fully cured. Carefully clean the
area and inspect the new pad for proper alignment.
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| |
|
| |
Caution
Excessive bonding pressure may cause measling
in the circuit board surface or may cause the
new pad to slide out of position.
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|
| 14. |
Apply flux to the overlapping connecting circuit
in the bottom of the trough. Solder in place.
Clean the area.
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| |
|
| |
Note
The circuit board may be preheated prior to
filling the area with epoxy. A preheated circuit
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. |
| |
|
| 16. |
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.
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| |
|
| |
Note
A very slight overfill of epoxy may be desired
to allow for shrinkage when the epoxy cures.
Additionally, in order to allow the circuits
appearance to match the board, it may be necessary
to mask the circuit prior to filling the excavated
area.
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| |
|
| 17. |
Cure the epoxy per Procedure 2.7
Epoxy Mixing and Handling. |
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|
| |
Caution
Some components may be sensitive to high temperature.
|
| |
|
| 18. |
Additional epoxy can be applied around the perimeter
of the new pad to provide additional bond strength.
Mix epoxy. Cure the epoxy per Procedure 2.7
Epoxy Mixing and Handling. Use the maximum recommended
heat cycle to ensure the highest strength bond.
BGA pads are routinely subjected to one or more
reflow cycles.
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| |
|
| |
Caution
Some components may be sensitive to high temperature.
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| |
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|
Figure 9: Completed repair.
|
| 19. |
Apply surface coating to match
prior coating as required. (See Figure 9) |
| |
|
Evaluation |
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|
| 1.
|
Visual examination |
| |
|
| 2. |
Measurement of new pad width and
spacing. |
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|
| 3. |
Electrical continuity measurement. |
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