Citizen CBM-202PC-04 User Manual page 40

1) Temperature gradient 1
If a temperature rises abruptly, each joint of the surface mounting device to the package
will have different temperature. As a result, the package may warp due to a difference in
the thermal expansion factor of the material, thus damaging the chip.
necessary to heed the upper limit of an ascending rate.
activity rate of the reflow unit.
2) Preheating
The temperature of the parts and PCB is adjusted under the melting temperature of the
solder to stabilize soldering and ease a thermal shock.
temperature of the surface mounting device.
3) Temperature gradient 2
The upper limit of the ascending temperature is the same as in 1).
determined by necessity to contain the peak temperature and time mentioned in 4) within
the specified ranges.
4) Peak temperature and time
In order to minimize damages on the package, the peak temperature and time must be most
heeded. Since the peak time has a direct effect on a drop of package strength and a steam
pressure in the package, it is desired to be kept as low as possible.
required to be minimized because the steam pressure increases along with a lapse of time.
The conditions mentioned here are provided at a coincident point of the above-mentioned
allowable range and a solderable range.
not average values, care should be taken not to exceed the upper-limit values when setting
the conditions.
mounting methods.
Fig. 9.2 Infrared Reflow and Air Reflow Recommended Conditions
Fig. 6.2 and Fig. 6.3 shows the recommended conditions for the different
The lower limit depends on the
Generally, set to near the rated
As they are represented by upper-limit values,
40
CBM-202PC-04 User's Manual
Therefore, it is
The lower limit is
The peak time is
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