Datasheet

1.2 Leadless NTC thermistors
In case of NTC thermistors without leads, soldering is restricted to devices which are provided
with a solderable metallization. The temperature shock caused by the application of hot solder
may produce fine cracks in the ceramic, resulting in changes in resistance.
To prevent leaching of the metallization, solder with silver additives or with a low tin content
should be used. In addition, soldering methods should be employed which permit short soldering
times.
1.3 SMD NTC thermistors
SMD NTC thermistors can be provided with a nickel barrier termination or on special request with
silver-palladium termination. The use of no-clean solder products is recommended. In any case
mild, non-activated fluxes should be used. Flux residues after soldering should be minimized.
SMD NTCs with AgPd termination are not approved for lead-free soldering.
Nickel barrier termination
Figure 1
SMD NTC thermistors, structure of nickel
barrier termination
The nickel barrier layer of the silver/nickel/tin termination (see figure 1) prevents leaching of the
silver base metallization layer. This allows great flexibility in the selection of soldering parameters.
The tin prevents the nickel layer from oxidizing and thus ensures better wetting by the solder. The
nickel barrier termination is tested for all commonly-used soldering methods according to IEC
60068-2-58. Insufficient preheating may cause ceramic cracks. Rapid cooling by dipping in sol-
vent is not recommended.
The following test and process conditions apply for nickel barrier termination.
Temperature measurement B57861S
Miniature sensors with bendable wires S861
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Important notes at the end of this document.