Composite structures

A substrate 30, which may be for a MEMS transducer package 300, comprising: at least one die 32a, 32b; and a frame 31 laterally surrounding and in contact with a side surface of the die 32a, 32b. The frame 31 may be formed from a mould material such as an epoxy type material. The substrate 30 may comprise first 32a and second die 32b. The first die 32a may be an ASIC and the second die 32b may be a port-hole die. A microelectromechanical microphone transducer 100 may be provided on the upper surface of the substrate and may overlie a hole 34 provided in the port hole die 32b. The MEMS microphone transducer 100 may comprise a flexible membrane 101, which deflects in response to a pressure differential across the membrane, and a lid portion 200. ASIC die 32a and a port-hole die 32b may be mounted on a carrier tape and the frame 31 may be formed by film assisted moulding. The substrate assembly 30 may then be released from the carrier.