Abstract Duplex components are one of the proposed concepts for actively cooled plasma-facing structures. This concept introduces a new source of stresses due to the mismatch in the coefficients of thermal expansion between the bounded materials. To ensure equilibrium, singular edge stresses fields are generated at the edge with high values of the involved gradients. Although confined to a very small region, their characterisation is important because debonding starting from this region is one common cause of component failure. Castellated beryllium tiles brazed to a copper alloy (CuCrZr) heat sink has been studied as prototype target plates for the pumped divertor phase of JET. For this system, an eigenvalue analysis is performed for edge stress fields free of singularities and favourable local geometry is deduced. Based on these results, guidelines for component optimisation with respect to those fields are presented. In particular the strong effect of the local geometry is discussed.