> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—It is well-known that different parameters of firing and post-firing processes have impact on electrical properties of low temperature co-fired ceramic (LTCC) materials. Here we show another temperature-related factor that can influence these properties. We show how much spatial non-uniformity of temperature distribution inside a box furnace can influence the dielectric constant of different LTCC substrates. We have tested two popular LTCC materials, namely DP 951 and DP 9K7, over the frequency range from DC to 7 GHz. Our results show that transverse spatial difference in temperature of only 6 C can result in 3-4 %-difference of dielectric constant, depending on the position of a material sample inside the box furnace. We have also found that dielectric constant of the two materials show disparate behavior under the same temperature distribution. The obtained results should be useful for designers and developers of LTCC microwave components and antennas. Index Terms—LTCC substrates characterization, dielectric constant, LTCC firing process. I. INTRODUCTION ICROWAVE characterization of LTCC materials has been the subject of research for more tha a decade. Among various factors, which influence electrical parameters of LTCC substrates, the firing process plays an important role and hence it has been under investigation by many researchers [1]-[7]. Although suppliers of LTCC materials provide information about the firing process, there are still some factors, which can have significant influence on electrical parameters of these materials. For example, a deviation of the peak firing temperature and the dwell time from the recommended values may lead to significant change of electrical parameters of the ceramic substrates and packaging. This problem was investigated in the case of various custom- made and commercial LTCC materials (A6, CT700, DP 943, and 951) in [1]-[4]. In turn, the impact of thermal post- processing on RF/microwave characteristics and geometric properties of LTCC materials (DP 943 and 9K7) was investigated in [5]. Another characteristic under investigation was influence of ambient temperature on electrical properties of custom-made and commercial LTCC materials [6]-[7]. This work was supported by the Polish National Science Centre, Grant No. N N515 496940. The authors are with Wrocław University of Technology, Wrocław, 50 – 370, Poland (e-mail: beata.barteczka@pwr.wroc.pl ) Yet another important practical factor, which may influence electrical properties of LTCC materials, is the quality of a furnace used in the sintering process. It is evident that non- uniform spatial distribution of temperature inside the furnace should have noticeable impact on these properties. Nevertheless, to our best knowledge, the quantitative description of this impact has never been published in the open literature. In order to investigate this issue the dielectric constant of two LTCC materials, i.e. DP 951 (ε r =7.8) and DP 9K7 (ε r =7.1), has been determined for various positions of a material sample inside a box furnace. The dielectric constant has been measured by means of the method of two microstrip lines [8]-[9]. Our experiment has been organized into several stages. First, we have designed two simple microstrip line structures taking into account: characteristics of both the LTCC materials, space inside our furnace and requirements of the method used to measure the dielectric constant (sec. II.A). In the next step, we have prepared several dozen of samples (microstrip lines) for each ceramic material, using standard LTCC technology (sec. II.B). Then, we have determined spatial distribution of temperature inside our box furnace (sec. II.C). Afterwards, we have tested all samples and determined their dielectric constant (sec. II.D). Finally, we have analyzed the obtained data and determined the relationship between the value of dielectric constant and the spatial distribution of temperature inside the box furnace (sec. III). II. DESCRIPTION OF THE EXPERIMENT A. Microstrip line structure and parameters In the first step of our experiment we have determined the allowable size and parameters of the microstrip line structure, which was used for testing the selected LTCC materials. To this end, we have taken into account the inner dimensions of our box furnace (Nabertherm HTC 03/16), the necessary size of tooling strips on the LTCC panel, and the minimal width of a single microstrip line substrate (according to [10]). As a result, we have discovered that only 4 microstrip line structures (4 samples) with dimensions of 20 mm  100 mm can be placed on a single LTCC panel inside our box furnace. The thickness of the microstrip line substrate has been chosen so that the structure is not too brittle. Therefore, in the case of DP 951, the substrate has been composed of 4 layers of Influence of Temperature Distribution Inside a Furnace on Electrical Properties of LTCC Materials B. Barteczka, A. Dąbrowski, P. Słobodzian, Member, IEEE, L. Golonka, Member, IEEE M