Memory device packaging - from leadframe packages to wafer level packages

摘要

The digital revolution has taken the consumer electronics by a storm in just two-short years. Portable and handheld electronics devices now have insatiable appetite for digital storage. Hence, memory cards in the form of USB Drive (U-drive), compact flash (CF), secured digital (SD), memory stick, and multimedia card (MMC) are now proliferating in the market. Moreover, the volatile memory dynamic random access memory (DRAM) for PC and notebook computing and gaming are also increasing in density and speed. With all these improvement, the memory device packaging technology is also evolving rapidly, from the traditional leadframe packages to smaller chip scale packages (CSP) and wafer level packages (WLP). This paper will cover the four major topics: (1) Review of the DRAM packages and their applications -DRAM packages are used primarily in the fabrication of DIMM modules that are inserted to the motherboards in PC and notebook computers. With newer DRAM technology in double date rate (DDR) and its second generation, DDR2, to be deployed this year, the clock rate is much higher and the number of I/Os increasing. Packages therefore are changing from the leadframe TSOP type 2 to faster CSPs such as fine pitch BGA (FBGA). (2) Review of the flash memory card packages - non-volatile memory flash and SRAM packages are generally smaller and have had lower density of 256Mb and below. But more recently high density (512Mb) and hence larger flash devices are more common. The conventional package TSOP type 1 may become inadequate to meet new performance demands and the form factor for miniaturization. Alternative new packages such as VFBGA CSP are described. (3) Stacking - 3D stacking have now been widely utilized to increase the memory density and saving weight and space. The two main options for stacking - die stack and package stack, each has its own advantages and concerns. The selection criteria and suitable applications for both the DRAM DIMM modules and various flash memory card formats are discussed in detail. (4) Future trends and conclusion - the convergence of packaging technology for the computing and consumer electronics is apparent under the same market and technology drivers - form factor miniaturization, lightweight, low profile, high speed, and high performance. Packaging for high-density memory devices is moving toward faster and smaller CSP packages, with the technology and processes for wafer level CSP and wafer level 3D stacking emerging in the horizon.