Various interconnection techniques for use in conjunction with thin film planar devices are described. The special character of the substrate imposed a number of limitations on processing and assembly, the most restrictive being that all interconnections should be made at the lowest possible temperature, at the same time being capable of repair. The method of mounting integrated circuit chips directly on the 2 μm thick copper circuitry uses soldering techniques for both chip mounting and the connections from chip to copper circuitry. The connection system used to make ground and signal connections between adjacent planes and the special handling and soldering equipment produced for this work, and the processes used to manufacture connection straps and overlays are described. The metallurgical aspects of soldered interconnections are discussed, particularly with regard to the effects of short range diffusion which greatly influences both the metallurgical structure and the resultant mechanical integrity of joints in the size range covered. © 1968, The Institution of Electronic and Radio Engineers. All rights reserved.