42

Varistor Products

©2009 Littelfuse, Inc.

Revision: January 15, 2010

ML Varistor Series

Surface Mount Multilayer Varistors (MLVs) > ML Series

Specifications are subject to change without notice.

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

Lead (Pb) Soldering Recommendations

The principal techniques used for the soldering of

components in surface mount technology are IR Re-flow

and Wave soldering. Typical profiles are shown on the right.

The recommended solder for the ML suppressor is

a 62/36/2 (Sn/Pb/Ag), 60/40 (Sn/Pb) or 63/37 (Sn/Pb).

Littelfuse also recommends an RMA solder flux.

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.

When using a reflow process, care should be taken to

ensure that the ML 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 50º C before cleaning.

Lead–free (Pb-free) Soldering Recommendations

Littelfuse offers the Nickel Barrier Termination option (see

"N" suffix in Part Numbering System for ordering) for the

optimum Lead–free solder performance, consisting of a

Matte Tin outer surface plated on Nickel underlayer, plated

on Silver base metal.

The preferred solder is 96.5/3.0/0.5 (SnAgCu) with an RMA

flux, but there is a wide selection of pastes and fluxes

available with which the Nickel Barrier parts should be

compatible.

The reflow profile must be constrained by the maximums

in the Lead–free Reflow Profile. For Lead–free wave

soldering, the Wave Solder Profile still applies.

Note: the Lead–free paste, flux and profile were used for

evaluation purposes by Littelfuse, based upon industry

standards and practices. There are multiple choices of all

three available, it is advised that the customer explores the

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 260˚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

Figure 14

Figure 15

Figure 16