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Surface Mount Varistors > CH Series
Lead (Pb) Soldering Recommendations
The principal techniques used for the soldering of
components in surface mount technology are IR Re-?ow
and Wave soldering. Typical pro?les are shown on the right.
Re?ow Solder Pro?le
CH series devices have silver - platinum terminals (Ag/Pt),
and the recommended solder is 62/36/2 (Sn/Pb/Ag), 60/40
(Sn/Pb) or 63/37 (Sn/Pb). Littelfuse also recommends an
RMA solder ?ux.
Wave soldering is the most strenuous of the processes.
To avoid the possibility of generating stresses due to
thermal shock, a preheat stage in the soldering process
is recommended, and the peak temperature of the solder
process should be rigidly controlled.
250
200
150
100
50
MAXIMUM TEMPERATURE
230°C
40-80
SECONDS
ABOVE 183°C
RAMP RATE
<2°C/s
PREHEAT DWELL
PREHEAT ZON E
When using a re?ow process, care should be taken to
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
ensure that the CH chip is not subjected to a thermal
gradient steeper than 4 degrees per second; the ideal
gradient being 2 degrees per second. During the soldering
process, preheating to within 100 degrees of the solder's
peak temperature is essential to minimize thermal shock.
Once the soldering process has been completed, it is
still necessary to ensure that any further thermal shocks
are avoided. One possible cause of thermal shock is hot
printed circuit boards being removed from the solder
process and subjected to cleaning solvents at room
temperature. The boards must be allowed to cool gradually
to less than 50oC before cleaning.
Figure 7
Wave Solder Pro?le
300
250
200
150
100
TIME (MINUTES)
MAXIMUM WAVE 260°C
SECOND PREHEAT
50
FIRST PREHEAT
0
0.0
0.5
1.0
1.5
2.0 2.5 3.0
3.5
4.0
4.5
Lead–free (Pb-free) Soldering Recommendations
Figure 8
TIME (MINUTES)
CH series devices have silver - platinum terminals (Ag/Pt),
and the recommended Lead-free solder is 96.5/3.0/0.5
(SnAgCu) with an RMA ?ux, though there is a wide
Lead–free Re-?ow Solder Pro?le
selection of pastes and ?uxes available that should be
compatible.
300
250
MAXIMUM TEMPERATURE 260?C,
TIME WITHIN 5?C OF PEAK
20 SECONDS MAXIMUM
The re?ow pro?le must be constrained by the maximums
in the Lead–free Re?ow Pro?le. For Lead–free Wave
soldering, the Wave Solder Pro?le still applies.
Note: the Lead–free paste, ?ux and pro?le were used for
evaluation purposes by Littelfuse, based upon industry
standards and practices. There are multiple choices of all
200
150
100
50
RAMP RATE
<3?C/s
PREHEAT ZONE
60 - 150 SEC
> 217?C
three available, it is advised that the customer explores the
optimum combination for their process as processes vary
considerably from site to site.
Figure 9
0
0
1.0
2.0
3.0 4.0
TIME (MINUTES)
5.0
6.0
7.0
CH Varistor Series
Revision: August 30, 2010
?2010 Littelfuse, Inc.
Speci?cations are subject to change without notice.
Please refer to www.littelfuse.com/series/CH.html for current information.
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