Varistor Products

©2010 Littelfuse, Inc.

Revision: January 10, 2011

SM7 Series Varistor

Surface Mount Varistors > SM7 Series

Specifications are subject to change without notice.

Please refer to www.littelfuse.com/series/sm7.html for current information.

Lead (Pb) Soldering Recommendations

Wave soldering is the most strenuous of the processes.

To avoid the possibility of generating stresses due to

process should be rigidly controlled.

ensure that the SM7 chip is not subjected to a thermal

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

Lead–free (Pb-free) Soldering Recommendations

compatible.

standards and practices. There are multiple choices of all

optimum combination for their process as processes vary

considerably from site to site.

PREHEAT ZONE

PREHEAT DWELL

RAMP RATE

<2°C/s

MAXIMUM TEMPERATURE

230°C

TIME (MINUTES)

250

200

150

100

50

0

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

40-80

SECONDS

ABOVE 183°C

TIME (MINUTES)

300

250

200

150

100

50

0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

MAXIMUM WAVE 260°C

SECOND PREHEAT

FIRST PREHEAT

MAXIMUM TEMPERATURE 250˚C,

TIME WITHIN 5˚C OF PEAK

20 SECONDS MAXIMUM

PREHEAT ZONE

RAMP RATE

<3˚C/s

60 - 150 SEC

> 217˚C

TIME (MINUTES)

300

250

200

150

100

50

0

0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Reflow Solder Profile

Wave Solder Profile

Lead–free Re-flow Solder Profile