The scope of electroless copper plating technology is evolving to applications with smaller structures and smoother substrates, where adhesion of the copper film can be hard to achieve. The extent to which different factors, such as film stress and hydrogen evolution, contribute to delamination and blister formation on smooth organic substrates is a topic of active discussion. Stress and strain evolution is reported here for a nickel- and formaldehyde-free formulation for a range of plating bath temperatures. X-ray diffraction, with the sin(2) psi method, was used to monitor the strain within the copper crystallites during and after their growth. Substrate bending measurements were used to detect the average stress of the film. This technique indicates a 60 nm wide zone of tensile stress at the interface between substrate and film. During and immediately following deposition, the average substrate stress is more compressive than implied by the strain of the Cu crystallites. After deposition, the additional compressive stress seen by substrate bending relaxes until it matches the Cu crystallite strain. Furthermore, the thermal substrate contraction effect upon termination of plating is considered, since it may influence the film adhesion. (C) 2013 The Electrochemical Society. All rights reserved.