Literature Abstracts

LOVASCO.F. and OIEN.M.A., IPC Technical Review, Vol. 31, No. 1, p. 18, December (1989)/January (1990) A new area‐distributed surface‐mount technology has been developed at AT&T Bell Laboratories that is suitable for the solder assembly of VLSI packages onto printed circuit boards. This new ‘double‐bump’ technology entails the controlled overlapping of two molten solder‐bumps on both package and substrate to form a nearly cylindrical joint. A mechanical stand‐off is used to control the final separation between the 1C package and the printed circuit board, and hence the solder joint height and shape. A simple analytical model has been developed which provides a good understanding of the solder joint geometries which are achievable and how the joint geometry is influenced by the principal design and process parameters. This new assembly technology offers several advantages. It is an evolutionary development of the well established solder‐bump technology but it provides a column‐like joint geometry and thus offers a potential for better reliability and higher density. It provides a large process window because it allows for the inspection of wettability of package and substrate before assembly, and the assembly process itself involves the melting together of two molten solder surfaces. Finally, it offers the potential for the electrical inspection of hidden solder joints.