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Method of Evaluating Laminate Design and Other Package Design Variables Using A Sensing Underfill

IP.com Disclosure Number: IPCOM000211828D
Publication Date: 2011-Oct-19
Document File: 7 page(s) / 509K

Publishing Venue

The IP.com Prior Art Database

Abstract

The disclosed invention is a rapid method of evaluating package design variables using a sensing underfill. The method provides a cost-effective, rapid screening method for assessing stress in the first-level interconnect region for various package designs and bond and assembly procedures.

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Method of Evaluating Laminate Design and Other Package Design Variables Using A Sensing Underfill

Stress management is a critical concern for microelectronic packages built with organic laminates. The stress mainly originates from the large Coefficient of (linear) Thermal Expansion (CTE)-mismatch between the laminate and the chip. The impact of several package design variables on stress is an important consideration in package reliability evaluation. How the laminate design impacts the stress distribution in the first-level interconnect region (region between the chip and laminate) is of particular interest. Further, fatigue failures of various interconnect designs and the impact of local stress gradients on underfill failure are additional areas of significance in package reliability.

Currently, the packaging community overwhelmingly relies on Finite Element Method models for stress characterization in packages and for design evaluation. While more cost-effective than hardware proto-typing, there is often still discrepancy between model predictions and observed failures which begs for improved methods of evaluating stress in packages with subsequent model improvement.

Direct stress measurement techniques are therefore necessary. There are currently no suitable, cost-effective methods of rapidly analyzing the impact of laminate design on stresses in the first-level interconnect region. Strain gauges may be incorporated into test dies [1], however fabrication of such test dies is expensive and the dies cannot be reused after the package is underfilled which further magnifies qualification costs.

A cost-effective rapid screening method of assessing stress in the first-level interconnect region for various package designs and bond and assembly procedures is necessary and is the subject of this invention. The disclosed invention is a rapid method of evaluating package design variables using a sensing underfill.

The components of the invention are:

1. The sensing underfill. This consists of carbon nanotube strain sensors in a polymeric encapsulant. The sensing underfill is applied in the gap between the die and laminate (i.e., in the first-level interconnect region).

2. The Raman spectral shift of carbon nanotubes. This is used to track the strain state of the carbon nanotubes and, in turn, the stress distribution of their environment.

3. A model first-level package. In this, the die is a transparent die, such as glass that is joined to a laminate of interest. The glass die is a cost-effective alternative to silicon and facilitates the Raman measurement of the interconnect region due to the transparency of glass.

The stress state in the sensing underfill can then be measured for model first-level packages with different laminates, different interconnect structures, and for different bond and assembly conditions.

Sensing Method

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Page 02 of 7

The use of carbon nanotubes for stress measurement in composites leveraging the shift in their...