Browse Prior Art Database

Fabricating Balling Masks

IP.com Disclosure Number: IPCOM000093899D
Original Publication Date: 1966-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Vogt, RT: AUTHOR [+2]

Abstract

This method forms terminal ball centering apertures in masks. Each aperture in a mask has a countersunk portion to receive a solder pad. Conventional ball centering masks are fabricated by laminating two sheets together. The top sheet is provided with apertures only slightly larger than the terminal balls to be centered. The lower sheet is provided with larger apertures to receive the solder pads provided to secure the balls by solder reflow to the substrate, typically a transistor chip. The fabrication of such a laminated mask is difficult, tedious, and consuming of time.

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Fabricating Balling Masks

This method forms terminal ball centering apertures in masks. Each aperture in a mask has a countersunk portion to receive a solder pad. Conventional ball centering masks are fabricated by laminating two sheets together. The top sheet is provided with apertures only slightly larger than the terminal balls to be centered. The lower sheet is provided with larger apertures to receive the solder pads provided to secure the balls by solder reflow to the substrate, typically a transistor chip. The fabrication of such a laminated mask is difficult, tedious, and consuming of time.

Fabrication of one-piece balling masks having countersunk apertures by etching a metal mask blank from opposite sides through aligned, dissimilar sized apertures has been done. However, when the opposite etched apertures meet, an annular, radially inwardly directed projection is formed at the junction which is objectionable. This projection, in use, forms an undercut portion which frequently is disposed under overhanging portions of the ball terminal. When the masks are subsequently removed from the substrates, the ball terminals may be dislodged or loosened.

This method fabricates one-piece balling masks free of the mentioned projection. The method consists of forming on mask blank 8, by conventional photolithographic techniques, resist masking layers 10 and 12. The latter have a relatively small aperture 14 on the top side, slightly larger than the ball terminal to b...