In our daily work we learned Shelf-Life isn’t always a specification, which engineers require. This is clear to understand, as specifications like Resistance value, Resistance tolerance and the stability due to temperature changes (TCR) are the most basic specifications for all electronic engineers. The next selection is mostly made on Power, size or assembling restrictions, but who’s taking care of the Shelf-Life of a Resistor?
Le Grand K
In November 2018 the General Conference on Weights and Measures (CGPM) decided to change the definitions of the Kilogram “Le Grand K”. This was needed because “Le Grand K” changed during the year about 50µg.
Realising that international specialists (57 countries) decided to change “Le Grand K” due to Shelf-Life changes, made us realise that Self-Live become more and more important, also for precision resistors. Of course you will not directly recognise the influence of Self-Live at the weight system in your local supermarket. But what about calibration equipment, which they use occasionally to check the uncertainty of their measurement equipment?
Shelf-life is mainly the result of external influence, same as “Le Grand K”. In most resistor technologies the ingress of oxygen and moisture cause big influence on the Shelf-Life. Due to the high process temperature and mechanical stress a glass package isn’t the right solution for resistors. To improve the Shelf-Life of high precision Foil resistors they will be packed in a metal package with glass seal and Kovar eyelets. Often Hermetically-Sealed package are oil filled because oil also acts as a thermal conductor. High precision SMD Foil resistors are mainly use ceramic package to create hermetically sealing.
Basic number of the Shelf-life for different technologies are given in below overview:
- Reference Resistors: 1ppm/6year
- High Precision Hermetically-Sealed Foil Resistors: 2 ppm/6year
- High Precision Molded-package Foil Resistors: 25 ppm/year
- Thin-Film Resistors: 300 ppm/year
- Thick-Film Resistors: 2000 ppm/year
Above overview indicates whenever you a precision resistor, engineers should consider which technology meets the requested Shelf-life. Check this button for our complete product range precision resistors.Precision resistors
Batenburg Mechatronica can help by selecting the best Shelf-Life performance for your application. Also for customised reference resistors, Batenburg can support for the best solution.