Flip-Chip Bonding with Gallium-Indium Solid Solution

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Solution Overview

Problem

Semiconductor devices mounted using flip-chip connections experience thermal stress and warping due to differences in thermal expansion coefficients between semiconductor elements and organic substrates, leading to reduced bonding strength and potential electrical failures.

Innovation Solution

The use of gallium or indium in a solid solution as a bonding material between the semiconductor element and the substrate, with copper diffusion under vacuum to create a solid solution, allowing for bonding at lower temperatures and reducing thermal stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If lead-free solder is used for bonding at high temperature, then environmental compatibility is improved, but thermal stress and warping increase due to coefficient of thermal expansion difference

Engineering Contradiction:

Improveenvironmental compatibilityVSAvoidthermal stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The invention changes the bonding temperature parameter from high temperature (250°C for lead-free solder) to low temperature (room temperature or slightly elevated), thereby eliminating thermal stress while maintaining environmental compatibility through the use of gallium or indium bonding materials

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces expensive gold bumps with cheaper copper bumps, and uses gallium or indium bonding materials that enable low-temperature bonding, thereby reducing overall device cost while maintaining bonding reliability

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Strength

If underfill resin is applied before temperature drop, then bonding strength is improved, but void formation occurs when applied at high temperature

Engineering Contradiction:

Improvebonding strengthVSAvoidvoid formation

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention performs the bonding action at low temperature before underfill resin application, thereby enabling strong bonding without void formation. The sequence is reversed from conventional methods: bonding first, then underfill application

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the bonding temperature parameter to low temperature, which eliminates void formation in underfill resin while maintaining strong bonding strength through the use of gallium or indium bonding materials

Inventive Principle:

Principle #35Parameter changes

3Productivity

If connecting pad width is reduced to achieve smaller pitch, then integration density is improved, but bonding area and bonding strength are reduced

Engineering Contradiction:

Improveintegration densityVSAvoidbonding strength

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The invention changes the bonding temperature parameter to low temperature and uses gallium or indium bonding materials, thereby achieving strong bonding on small connecting pads without requiring large bonding areas, enabling smaller pitch and higher integration density

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method enhances bonding reliability by reducing thermal stress and preventing void formation in underfill resin, while maintaining strong electrical connections and preventing peeling or breaking of the bonded portion.

Implementation Method 1

copper diffusion under vacuum to create a solid solution

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

copper diffusion under vacuum to create a solid solution

Methodology Applied

Scientific EffectVacuum: Vacuum

Implementation Method 3

enhances bonding reliability by reducing thermal stress and preventing void formation in underfill resin

Methodology Applied

Scientific EffectThermal stress reduction: Thermal Expansion

Data Source

PatentUS7750484B2Semiconductor device with flip-chip connection that uses gallium or indium as bonding material

Publication Date: 2010.07.06 SHINKO ELECTRIC IND CO LTD

AI summary

A method of manufacturing a semiconductor device in which a semiconductor element 10 is mounted on a substrate 20 through a flip-chip connection, includes the steps of cladding gallium as a bonding material 30 to a connecting pad 22 formed on a surface of the substrate 20, diffusing copper from the connecting pad 22 formed of the copper into the bonding material 30 through heating under vacuum, thereby bringing a state of a solid solution of the gallium and the copper, and aligning a connecting bump 12 formed on the semiconductor element 10 with the connecting pad 22 and bonding the connecting bump 12 to the connecting pad 22 through the bonding material 30 in a state of a solid solution under heating.