A novel research on micro-ball placement machine used for wafer level package

Wafer Level Package (WLP) is a good way to resolve the fine pitch high density IC production. In formal way, it is done by producing bumps on wafers. Several ways to produce bumps are available, such as stencil printing, imprint & photolithography. But the bumps height can not be controlled well in the above methods. Since the micro balls are mass produced in the same size (general less than 3% error on balls diameter), if we can place the micro balls on the wafer in the a proper way, it is a good solution for WLP. A new method and a machine presented here are introduced. The minimum ball size is 60 mum in diameter. Using this kind of machine, the bumps producing process can be shorted and cost down and avoid producing mistakes. In this paper, the basic apparatus introduction and ball placing mechanical pictures are given. The machine has been used in the IC research and fab production since 2008.