HIT: a standard constructional system for testability and maintainability

A novel equipment practice, known as hierarchical interconnection technology (HIT), is being presented to British and international standards bodies. Its aim is to alleviate some of the problems of surface mounting technology by partitioning printed circuit boards into subunits. The diagnostic testing requirement is thus simplified, since a fault need only be diagnosed to the replaceable subunit (typically one of eight mounted on a double Eurocard). A functional test can deliver this degree of fault localization with only modest demands on design for testability. Because of solderless assembly, defective subunits are readily replaced without the need for skilled labor or specialist rework facilities; and because each subunit has relatively low value, it can be discarded without further diagnosis. The author describes the HIT system and its background, and how it can affect circuit design, manufacture, and field servicing