This article presents the long-term (1,000 h) behavior of two printed-circuit board materials (Panasonic R1755V, a high-TG glass-epoxy composite and Arlon 85N, a polyimide-based laminate) stored at high temperature (190°C). Tests are performed in air and in nitrogen atmospheres. Electrical and physical measurements are performed regularly (once per week). Almost no degradation is observed for both materials when stored in nitrogen. On the contrary, the board stored in air shows the consequences of ageing. This is especially true for the glass-epoxy material, which becomes unusable after 2 w, because of large swelling.