In this paper, we study the influence of the manufacturing conditions of a transverse electromagnetic (TEM) cell for real-time observation of biological cells during their exposure to electromagnetic fields. Microscopic observation is acheived through an aperture in the lower wall of the TEM cell that is sealed with a 700-nm film of the transparent conducting material Indium tin oxide (ITO). The ITO layer is connected to the lower wall with a conductive epoxy adhesive. To ensure a perfect and stable electrical contact, the epoxy must be heated to degas and consolidate. A study on the efficiency of contact provided by the epoxy was carried out according to the heating duration. The results show that a long heating duration more than 12 hours is required to obtain an electrical continuity in the aperture that is insensitive to temperature increase during exposure to electromagnetic fields.