High density electronic device assemblies and techniques for forming high density electronic device assemblies are disclosed. These assemblies and techniques can be used to form compact electronic devices. In one embodiment, substrate arrangements that include a multiple-part substrate can be used to form a high density electronic device assembly. In another embodiment, one or more clips can be used in a high density electronic device assembly to provide mechanical and electrical interconnection between electrical structures that are to be removably coupled together as parts of the high density electronic device assembly. In still another embodiment, a removable cap (and a method for forming the removable cap) can be used for an electronic device housing.