V18AUMLA1206_06 Datasheet, PDF (6/9 Pages) Littelfuse – Multilayer Transient Voltage Surge Suppressor

Multilayer Transient Voltage Surge Suppressor
RoHS AUML Varistor Series
Soldering Recommendations
Lead (Pb) Soldering Recommendations
The principal techniques used for the soldering of components in surface
mount technology are IR Re-flow & Wave soldering. Typical profiles are
shown in Figures 8 & 9
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 solderís 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 50˚C before
cleaning.
Lead-Free (Pb-free) Soldering Recommendations
Littelfuse offers the Nickel-Barrier termination finish for the optimum Pb-
free solder performance.
The preferred solder is 96.5/3.0/0.5 (SnAgCu) with an RMA flux, but
there is a wide selection of pastes & fluxes available with which the nick-
el barrier parts should be compatible.
The reflow profile must be constrained by maximums shown in Figure10.
For Pb-free Wave soldering, Figure 9 still applies.
Note: the Pb-free paste, flux & profile were used for evaluation purposes
by Littelfuse, based upon industry standards & 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.
230
FIGURE 8. REFLOW SOLDER PROFILE
300
MAXIMUM WAVE 260 ^oC
250
200
150
SECOND PREHEAT
100
FIRST PREHEAT
50
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
TIME (MINUTES)
FIGURE 9. WAVE SOLDER PROFILE
MAXIMUM TEMPERATURE 260˚C
20 - 40 SECONDS WITHIN 5˚C
RAMP RATE
<3˚C/s
60 - 150 SEC
> 217˚C
PREHEAT ZONE
5.0
6.0 7.0
FIGURE 10. LEAD-FREE RE-FLOW SOLDER PROFILE
192
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