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will lead to deformation of PCB. Therefore, choosing a right temperature curve is
the key to BGA rework. What's more, different PCB has different material,
thickness and heat dispersion. The corresponding BGA also has different sensitivity
to temperature. To achieve the best rework effect, we should set a special curve for
each component on PCB.
To get a more precise temperature curve, it is necessary to use a sensor.
Generally, we put the sensor on the center of the BGA pad. But it is hard for the
sensor to go through the space between balls and reach the center part. What's more,
nobody can ensure that the data is from the balls or the space. Another method is to
dig a hole at the center of the BGA pad from the back of PCB. Extend the sensor
into the hole and fix it to the back of the PCB, then the sensor can touch the pad
and the thermal conductivity can be ensured. Nowadays most manufacturers adopt
this method.
3. Use of flux paste.
Generally, before mounting a new BGA, the paste should be laid on the pad
with a special micro mesh. But for those common devices such as PBGA or MBGA,
the paste can be laid on the pad directly, and the soldering can be finished by the
melting of soldering balls. Of course, for CBGA, a mesh and soldering paste are
necessary, because the melting point of soldering balls on CBGA is much higher
than common paste, such as Sn63 and pb27.
4. Removal of residual soldering tin and mounting of BGA
Besides the temperature curve, the removal of remained soldering tin and
mounting of BGA are of great importance in BGA rework. Generally, people don't
realize it. But in practice, it often leads to failure in BGA rework.
We usually use copper tin-absorption line to remove the residual tin. In the
rework process, the pad is likely to be destroyed by the wrong operation of the
technician, thus the total process of BGA rework becomes a failure. Therefore, we
should pay more attention. Here are 2 tips: one is to remove the residual tin within
a short time after desoldering BGA. Because at that time PCB has not cooled down
completely and the temperature difference cause less damage to the pad; the other
tip is to use some flux when removing the residual soldering tin, which can improve
the activity of tin. Never move the copper tin-absorption line under the great
pressure of soldering iron. The remounting of BGA calls for the "fine finish" of tin
removal. Thus it ought to be operated by some experienced technicians.
5. Use of IR BEAM
The Full component is entirely covered by the beam, and BGA can be heated
evenly. In the Case of the ZM-DGC 900, You can chose a diameter of the heat you
want to apply according to the size of the IC Component you will work on.
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