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Improvement in Stencil Printing for the Higher Quality of Bumps
Keywords: stencil printing, bump, solder paste
Stencil printing offers a high-production method of solder bump deposition but has several problems in delivering precise solder bump shape at small pitches less than 150 m. In this paper two previously unexamined factors of bump formation are studied. First of them is stencil vibration after stencil separation from printed circuit board. Second factor is variation of snap-off distance after initial stage of bump formation (stencil aperture filling). Novel add-on device was developed and fabricated for control of these factors. This device is simple, compact and easy for installation in the commercial stencil printing machine. Several design modifications of this add-on device have been verified for operation at the existing production equipment. Suggested mechanism demonstrated robust repeatability and workability in manufacturing line. There was no need to change main machine operation mode parameters. Evaluation of measured standard deviations of bump heights and volume as well as the quality demands are shown.
Yong-Kwan Lee, Senior Research Engineer
Samsung Electro-Mechanics Co.
Suwon, Gyungi-Do 443-743,
Republic of Korea (South)

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