This paper reports on the influence of the copper concentration on the mechanical behaviour during thermal cycling and during isothermal holds of Al-Cu thin films on Si substrates. The Cu concentration has been varied in the range between 0 to 1 at.%
Upon heating, the films with the larger amount of Cu showed a clear maximum in compressive stress. Moreover, during cooling these samples show a tensile stress increase at the onset precipitation temperature. Further cooling below 200 °C leads to the characteristic tensile stress increase often observed for Al-Cu thin films. An isothermal hold during cooling at 250 °C leads to temporary strengthening of all Al-Cu. The extent of the strengthening is dependent on the Cu concentration and is clearly dependent on the duration of the isothermal hold. Upon further cooling the strengthening disappears and the stress develops according to the original stress temperature dependence. The observations are discussed in terms of solid solution hardening and precipitation hardening.