Browse Prior Art Database

Improved Via Design for Bumped Chips

IP.com Disclosure Number: IPCOM000038008D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Moskowitz, PA: AUTHOR [+2]

Abstract

The TAB (tape automated bonding) process calls for the fabrication of metal bonding platforms or bumps on the I/O contact pads of the chip to be TAB bonded. It is desirable that the chip top surface metal, usually aluminum with a small percentage of another metal, be completely sealed by the bump. This will protect the aluminum from exposure to corrosion. The conventional technique that does this calls for overlapping the edges of the bump on the edges of the chip top passivation layer. As a result of the thickness of the passivation, a dimple remains in the top of the bump. This is undesirable, as the dimple may lead to incomplete contact and poor bonding of the TAB lead to the bump.

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Improved Via Design for Bumped Chips

The TAB (tape automated bonding) process calls for the fabrication of metal bonding platforms or bumps on the I/O contact pads of the chip to be TAB bonded. It is desirable that the chip top surface metal, usually aluminum with a small percentage of another metal, be completely sealed by the bump. This will protect the aluminum from exposure to corrosion. The conventional technique that does this calls for overlapping the edges of the bump on the edges of the chip top passivation layer. As a result of the thickness of the passivation, a dimple remains in the top of the bump. This is undesirable, as the dimple may lead to incomplete contact and poor bonding of the TAB lead to the bump.

The solution to the problem, shown in the figure for the chip, 25, allows the sealing of the top level metal pad, 10, without producing a dimple in the top of the bump, 15. The metal pad, 10, is made smaller than the bump, 15, while the top level passivation, 20, is made larger than the bump. The bump completely seals the metal, 10, while its edges rest on a lower level of passivation, 30. All lines connected to the metal pad are below the passivation, 30, on the lower metal layer, 40. The top surface of the bump, 15, will tend to show the underlying topography, with relief on the order of one micron. Thus is contrasted to the conventional approach where the relief is on the order of several microns, the thickness of the top passivation, 20, whos...