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Coefficient of Thermal Expansion Substrate Containing Negative Fillers for Die Package Thermal and Mechanical Stress Reduction

IP.com Disclosure Number: IPCOM000032218D
Publication Date: 2004-Oct-26
Document File: 3 page(s) / 39K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a functionally-graded low Coefficient of Thermal Expansion (CTE) organic substrate that contains inorganic fillers; these fillers have negative thermal expansion in the substrate core, and on the front side alternative build–up films (ABF). Benefits include reducing thermal and mechanical stresses.

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Coefficient of Thermal Expansion Substrate Containing Negative Fillers for Die Package Thermal and Mechanical Stress Reduction

Disclosed is a method that uses a functionally-graded low Coefficient of Thermal Expansion (CTE) organic substrate that contains inorganic fillers; these fillers have negative thermal expansion in the substrate core, and on the front side alternative build–up films (ABF). Benefits include reducing thermal and mechanical stresses.

Background

Thermal mechanical stress is caused by a CTE mismatch between the Si and the package. CTE induced thermal and mechanical stresses in assembly are major issues, and are responsible for many reliability failures. This problem has become much worse when mechanically weak low k CDO is implemented as an interlayer dielectric. Fragile CDO begins to crack during the chip attach process. In addition, Thermal and mechanical stresses become even worse as porous CDO and air gaps are introduced into the dielectric layers of future technologies.

Currently, there are no solutions to this problem. In response, the Pb-free interconnect turns to the more compliant PbSn with stiffer Cu die-side bumps. However, this temporary solution leads to other failures, such as bump limiting metallurgy (BLM) delamination (see Figure 1).

General Description

The disclosed method adds inorganic oxide fillers (with negative thermal expansion) to the substrate core and front side ABF layers, replacing part or all of the SiO2. The substrate with negative CTE fillers has a lower CTE, which reduces the CTE mismatch and the induced thermal mechanical stress in the Si and package. The following outlines the process for the disclosed method (see Figure 2):

1.      Subs...