Figure 1: Remove the defective pad
and prepare connecting via.
|
| 1. |
Clean the area.
|
| |
| 2. |
Carefully remove the defective
pad to avoid damaging the integral via. |
| |
|
| 3. |
Use a knife and scrape off any epoxy residue,
contamination or burned material from the board
surface.
|
| |
| 4. |
Scrape off any residue from the
exposed via. (See Figure 1). |
|
Figure 2: Trough or gully recessed
into board to permit circuit routing to
be level with board surface.
|
| 5. |
Clean the area. |
| |
|
| 6. |
Apply a small amount of liquid flux to the via
connection on the board surface. Using the appropriate
size solder braid remove solder from the via.
Clean the area.
|
| |
|
| 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.
In this procedure a trough or gully must be
recessed into the board from the via location
to the outside edge of the affected pad. This
permits the via to pad connecting circuit adequate
space for routing without interfering with the
pressing of the new BGA pad. (See Figure 2).
|
|
Figure 3: 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 3).
|
| |
|
| |
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.
|
|
Figure 4: 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 new
pad. In order to ensure that the final pressed
pad lays flat, it may be necessary to remove
the film from the whole length of the connecting
circuit up to the pad itself. (See Figure 4).
|
| |
|
| |
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.
|
| |
|
| 10. |
Cut out and trim the new pad. Cut
out from the plated side. |
|
Figure 5: Connecting circuit is fit
into via. |
| 11.
|
Turning the pad upside down, place the pad on
the board so that the connecting circuit can
be fit into the via. Ensure the connecting circuit
is running over the previously cut trough. (See
Figure 5). The connecting circuit of the new
BGA pad will be inserted into the integral via
hole of the original BGA pad.
|
| |
|
| 12. |
Insert the connecting circuit into
the via and carefully flux the connection area. |
| |
|
| 13. |
Solder the connecting circuit into
the via. |
| |
|
| 14. |
Lay the connecting circuit into the bottom of
the trough. If required, apply a securing film
of high strength thermosetting epoxy over the
connecting circuit to secure in place and provide
a flat surface on which to press the new BGA
pad.
|
| |
|
| 15. |
Fold over the new BGA pad 180° and place the
new pad into position on the circuit board surface
using high temperature tape to help in alignment.
|
| |
|
|
Figure 6: Bond the new pad using a Bonding System.
|
| 16.
|
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 6).
|
| |
|
| |
Note
The tip used for bonding
should be as small as possible but should completely
cover the entire surface of the new pad.
|
| |
|
| 17. |
Position the circuit board so that it is flat
and stable. Gently place the hot bonding tip
onto the Kapton tape covering the new pad. Apply
pressure as recommended in the manual of the
repair system or repair kit for 5 seconds to
tack the new pad in place. Carefully peel off
the tape.
|
| |
|
| |
Caution
Excessive bonding
pressure may cause measling in the circuit board
surface or may cause the new pad to slide out of
position. |
|
Figure 7: Completed repair. |
| 18. |
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
an additional 30 seconds to fully bond the pad.
After the bonding cycle remove the tape used
for alignment. The new pad is fully cured. Carefully
clean the area and inspect the new pad for proper
alignment. (See Figure 7).
|
| |
|
| 19. |
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.
|
| |
|
| |
Caution
Some components may be sensitive
to high temperature. |
| |
|
| 20. |
Apply surface coating to match
prior coating as required. |
| |
|
|
Evaluation |
| |
|
| 1.
|
Visual examination. |
| |
|
| 2. |
Measurement of new pad width and
spacing. |
| |
|
| 3. |
Electrical continuity measurement. |
|
