Development of 3-dimensional memory module using anisotropic conductive adhesive films

The memory modules used in most modern electronic equipment, ranging from portable electronic information devices to computers to ATM electronic switching systems, are facing not only greater demands for smaller size and lower cost, but also new demands for larger memory capacity. To satisfy such needs, NEC has developed a small-size, low-cost, large-capacity memory module, which consists of three-dimensionally stacked memories by use of anisotropic conductive adhesive films. The memory module comprises stack memories consisting of 3D mounted multiple memory ICs and a single glass epoxy substrate on which multiple stack memories are mounted. A stack memory consists of two single memories, a spacer substrate, and external connection terminals. A single memory consists of a memory IC mounted on a glass epoxy substrate. The two single memories are electrically connected to each other by use of a spacer substrate and anisotropic conductive film (ACF). The external connection terminals, which consist of copper core-filled solder balls, are then mounted on the single memory in the lower stage of the stack memory. The method used for radiation of the heat generated by stacking was verified by simulation. It became clear from the simulation results that the method did not present any problem for the memory ICs used at this time. It also became clear that the method of mounting a heat sink for high heat generating ICs in the future could be a promising solution. The method, subjected to all types of reliability tests, revealed no problem at all.