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Method for using ultrasound to cure and strengthen the underfill epoxy for flip-chip packages

IP.com Disclosure Number: IPCOM000144759D
Publication Date: 2007-Jan-06
Document File: 5 page(s) / 232K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for using ultrasound to cure and strengthen the underfill epoxy for flip-chip packages. Benefits include improved functionality, improved performance, improved reliability, and improved cost effectiveness.

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Method for using ultrasound to cure and strengthen the underfill epoxy for flip-chip packages

Disclosed is a method for using ultrasound to cure and strengthen the underfill epoxy for flip-chip packages. Benefits include improved functionality, improved performance, improved reliability, and improved cost effectiveness.

Background

      The conventional epoxy underfill and curing process is conducted in an oven. Hot air flows around trays holding polymer substrates to cure the epoxy (see Figure 1).

       However, this process results in a coarse grain structure and can cause reliability problems for flip-chip packages, such as severe delamination of underfill between the die and substrate. Additionally, fatigue of bump material and bump metallization/die passivation degradation can occur. These failures are due to the epoxy material not being strong enough to withstand the stresses (see Figure 2).

      One conventional solution is to cure the epoxy material in the flip-chip package. However, this approach requires a longer curing time, which has a high energy cost.

      Another solution is to reduce the epoxy curing time in the oven. However, the epoxy viscosity cannot be controlled consistently with heat.

      Increasing the curing temperature can shorten the curing time. However, energy costs are increased. As a result, no 100% solution exists to resolve this issue.

General description

      The disclosed method uses ultrasound to cure and strengthen the underfill epoxy for flip-chip packages. The method reduces the epoxy curing time in the oven by increasing the polymerization rate of the epoxy materials.

      The key elements of the disclosed method include:

•     Ultrasound to change the epoxy polymer structure to a finer grain

•     Ultrasound to increase the polymerization rate of epoxy materials

•     Ultrasound to control the epoxy material viscosity

•     Reduced epoxy curing time at a high temperature in an oven

Advantages

      The disclosed method provides advantages, including:
•     Improved functionality due to providing ultrasound curing to strengthen the underfill epoxy for flip-chip packages
•     Improved performance due to enabling the epoxy to flow evenly

•     Improved reliability due to increasing the epoxy mechanical strength

•     Improved reliability due to preventing void formation between the die and substrate

•     Improved reliability due to controlling the warpage of the polymer substrate

•     Improved cost effectiveness due to reducing the cost of ene...