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  • Method for determining quantity and composition of gases released during stirring liquid indium-tin eutectic solders [Elektronski vir]
    Erjavec, Bojan, 1950-2023 ; Šetina, Janez ; Jenko, Monika, metalurginja
    Reduced outgassing of liquid In eutectic alloys during the vacuum soldering of small-volume vacuum devices such as compact photomultipliers and image intensifiers is important for the prolonged ... operational lifetime. Increased dark current and ion spots are the consequence of photocathode ion bombardment due to limited gas sorption properties of integrated getters, especially in the case of methane and argon. In order to reduce the solder outgassing, an additional mechanical stirring of liquid In-alloy solders, before transferring tube subassemblies in vacuum and performing the final sealing, has been introduced in production. In this work, a new method and its measurement capabilities to determine quantity and composition of gases, released during the mechanical stirring of liquid, previously vacuum-baked In-Sn eutectic solders of different quality, is presented. The new analytic method consists of a static gas accumulation phase and a dynamic gas expansion phase. Determination of gas quantity is based on the measurement of total pressure of gases released during the stirring in a test chamber, being attached to an accumulation chamber with a known volume, using an inert reference spinning rotor gauge (SRG). Determination of gas composition is based on the observation of ʹpressure-burstsʹ belonging to the accumulated gases after their admission into an analytic chamber equipped with an in situ calibrated quadrupole mass spectrometer (QMS) and pumped by a dry turbomolecular pump unit. Results of the outgassing test of two InSn preforms (washers) weighing somewhat less than 0.5 g are selected to show the measurement performance of the new method. The solder samples produced from rods of 4N purity are cast in N[sub]2 and vacuum. The released gas quantity equals 1.2x10[sup]{-6} mbarL and 5x10[sup]{-7} mbarL, respectively. Integration of ʹpressure-burstsʹ over time and multiplication by the corresponding calibration factors (consisted of effective pumping speed/relative gas sensitivity) show that in both cases H[sub]2, CH[sub]4 and CO are the main gas species released during the stirring phase. In addition, higher CH[sub]4 and CO relative content is present in the case of the N[sub]2 cast sample. The measurement uncertainty of released gas quantity measurements is estimated to be less than 3 %. It includes the measurement uncertainty of a precise and long-term stable SRG, if calibrated by N[sub]2 only, and the measurement uncertainty of the accumulation chamber volume determined by the static gas expansion method. The lowering of a total gas content detection limit below 1x10[sup]{-7} mbarL is dependent on the time stability of a SRG zero signal due to changes in ambient temperature and rotor frequency, volume of the accumulation chamber and increase of the background pressure in the same chamber during the stirring phase. The determination of the absolute gas composition with an appropriate measurement uncertainty is dependent on the time stability of QMS relative gas sensitivities, therefore frequent in situ calibrations of QMS are needed to be performed. New calibration factors are obtained by the dynamic gas expansion method using known quantities of gases from the mass range 1 to 50 amu, being introduced and prepared in the accumulation chamber.
    Source: 18th International Vacuum Congress (IVC-18) [also] International Conference on Nanoscience and Technology (ICN+T 2010) [also] 14th International Conference on Solid Surfaces (ICSS-14) [also] Vacuum and Surface Sciences Conference of Asia and Australia (VASSCAA-5), August 23-27, 2010, Beijing, China [Elektronski vir] : abstract CD (1 str.)
    Type of material - conference contribution
    Publish date - 2010
    Language - english
    COBISS.SI-ID - 853674

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