Verification measurements in a “Linn” type high-temperature soldering oven

Abstract

In this paper the technology of the “Linn” type high-temperature soldering oven [1] and the verification measuring methods of the oven are discussed. This oven is mainly used for fixing silicon chips on metal substrates by high temperature soldering process. The solder (manly 96Pb/4Sn) is placed between the Si chip and the metal substrate in a foil form before the soldering process. The soldering foil does not contain any flux, therefore reducing agent has to be applied to avoid the oxidation of the joints during the process. In this case the reducing agent is the Forming gas which is a mixture of 10 vol% H2 and 90 vol% N2. Forming gas is used as an atmosphere for processes that need the properties of hydrogen gas without the explosion hazard. The key factors of this soldering process are the suitable temperature (350–370 °C until 13–15 minutes) and the suitable H2 concentration (8–10 vol%) during this. Therefore we have created accurate methods to measure the H2 concentration and the dynamic heating parameters of the oven (time coefficients of the heating and the heating temperatures). The H2 concentration was measured with an ABB EL3020 H2 analyzer and the dynamic heating parameters was calculated from the temperature changes in the oven which were measured with K-type (NiCr-Ni) thermo-couples.