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|Substrate Printing for Micro BGA|
|Keywords: Substrate bumping, MicroGBA , Ultra fine pitch printing|
|As the demand for faster, smaller, cheaper and smarter electronic products such as cell phones, pagers and PDAs increase, the demand on packaging footprint also increases. Flip chip and micro BGA are ideal response to the more functionality and compact packaging demand. But, assembly of flip chip and micro BGA comes with its own challenges. The primary challenge is to provide reliable mechanical and electrical interconnection. The most cost effective way to provide both mechanical and electrical interconnection is application of solder paste via stencil printing process. Stencil printing is a common process in the surface mount and other packaging process. The guideline for stencil design, paste formulation and printing equipment is well developed for mainstream SMT process. When it comes to ultra fine pitch application, some of the previously developed guideline may no longer hold. New guidelines may need to be developed to address the requirements of ultra fine pitch printing. It is believed by most assembler that 50-70% of the end of the line defect is contributed to the stencil printing process. Controlling the amount of solder paste deposit to meet the ultra fine pitch application is critical to the process. This paper will describe work done in the area of micro BGA assembly using various stencil design, materials and process factors through a series of design of experiment. Bump size of 65 microns to 150 microns will be the focus of this discussion.|
|Rita Mohanty, Director Advanced Development