中龙集团
Dragon Group China Limited
BIRD
®
physical effect is limited, infrared ray has lost some market. When the heat radiation
distribute evenly, objects in different colors absorb and reflect heat radiation unevenly.
The purchase decision of Array Package Rework Station should start from the
reliable technology. It is important to control the process. BIRD AC 4K is easy to operate
and very useful in the soldering of SMD, TH and plastic. It can make the most profit out
of the least investment.
a
. Compatibility of components.
Lead-free soldering is more and more popular. Eutectic solder ball in still the
standard choice in USA. Components manufacturers consider the using of lead-free balls
as the standard.
b
. Setting of temperature difference.
The temperature difference on the surface of components is a must factor to be considered
in quality rework and assembly. Increment of 10 can be accepted.
℃
Temperature
difference of component from top to bottom is another important factor.
c
. Control of temperature curve
To avoid brittle rupture in welding points, the temperature should be better controlled,
especially the heating of PCB bottom. Heating board can't change the temperature in a
short time, so it can't be used in lead-free solder process.
2. Setting and adjustment of temperature curve
Setting of temperature curve is the first and most important step of BGA rework.
Compared with reflow temperature curve, the control of temperature in rework process is
more strict, because in normal reflow oven, the temperature loss id nearly zero. But in the
rework process, the PCB is usually exposed in the air, we heat the components respectively.
In this way, there is much loss of temperature. But we loss can't be made up only by heating.
The reasons are as follows: one is that over heating will damage the components. The other is
that the uneven heating 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.
Summary of Contents for Bird AC-5K
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