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Bumpless Package with Backside Metallization

IP.com Disclosure Number: IPCOM000008381D
Publication Date: 2002-Jun-11
Document File: 3 page(s) / 670K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for creating a bumpless buildup layer (BBUL) package in which dielectric layers are built up and patterned on one side, while metallization is deposited on both sides. The metal layers on the front side are patterned to form interconnection layers, while the back side is unpatterned and used for heat spreading. Benefits include better heat extraction and spreading by eliminating the first interface material.

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Bumpless Package with Backside Metallization

Disclosed is a method for creating a bumpless buildup layer (BBUL) package in which dielectric layers are built up and patterned on one side, while metallization is deposited on both sides. The metal layers on the front side are patterned to form interconnection layers, while the back side is unpatterned and used for heat spreading. Benefits include better heat extraction and spreading by eliminating the first interface material.

Background

Currently, heat is extracted from high performance microchips by attaching heat spreaders to them. The heat spreaders are attached using thermal grease, thermally-conductive adhesive, or solder.

General Description

In the disclosed method, the dielectric material is laminated to one side (the front) while copper (Cu) metallization (done in an electrodeposition bath) takes place on both sides (see Figure 1). This causes the backside of the die and substrate to be covered in a blanket film of Cu. After several layers of metallization, the Cu thickness is approximately 50 um. 

Because 50 um is not thick enough for significant heat spreading, more Cu must be added. This is done by additional plating of Cu on the backside only, or by Cu-to-Cu bonding (cold welding) of a Cu slug.

A key issue for the success of the disclosed method is a high-quality bond between the back side Cu metallization and the silicon (Si); this is required to achieve a low thermal resistance. Since an electronless seed layer may not provide such an interface (and in addition would likely be a reliability risk), a sputtered seed is required for the backside. This is done on t...