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Dot-to-Dot Maskless Bulk Interconnect Process
Keyword(s): 3-D packaging; electroless plating; memory packaging; interconnect; roll-to-roll
Abstract: Dot-to-dot (D2D) is a bulk, maskless process for creating electrical interconnections between adjacent features. It does not require the features to be aligned to a mask or other tool and is thus applicable even to complex curved and folded surfaces. The principle can be illustrated by a set of dimensionless points scattered on a plane. Each point is a circuit node electrically connected to a surrounding circular region of radius b. Where the separation between points is greater than 2b, no connection is made. Where the distance is less than 2b, adjacent circles join and establish a connection. Long wires linking multiple nodes are formed wherever a series of points are separated by less than 2b. While physically realizable D2D connections are built-up from finite- sized regions rather than points, the principles are the same. Since all connections on a large number of workpieces may be formed simultaneously, manufacturing costs should be extremely low. This paper is a comprehensive examination of D2D technology. It begins with an overview of stacked packaging and suggests a one-dimensional approach to attaining precise inter- layer alignment. Models for stacked module geometry and plating process capability are used to predict minimum attainable wiring pitch. Initial experiments using electroless nickel plating and a planar substrate support the fundamental viability of the D2D approach. Test patterns demonstrate wiring on pitches as low as 50 µm, with increasingly robust results at larger pitches. Future work should focus on better understanding joint formation and controlling spurious plating nucleation on actual substrate stacks.
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