Thermosonic Copper Pillar Flip Chip Bonding

Solution Overview

Problem

Conventional flip chip die bonding processes, such as copper-tin bonding, are costly and complex due to multi-step assembly processes involving flux placement, reflowing, and cleaning, which erodes the cost savings of using copper-tin bonds over gold bonds.

Innovation Solution

A one-step, flux-free thermosonic die bonding process using copper pillar bumps with a bonding cap, where thermal and mechanical energy is applied to bond the die to a substrate, potentially melting the solder cap to form a connection, and ultrasonic energy is used to press the die onto the substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional copper-tin flip chip die bonding process is used, then cost savings compared to gold bonding is achieved, but manufacturing complexity increases due to multi-step assembly processes

Engineering Contradiction:

Improvebond strengthVSAvoidassembly process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines multiple separate assembly steps (flux placement, die attachment, reflow soldering, flux cleaning) into a single integrated thermosonic bonding process. The thermosonic bonder simultaneously applies heat, ultrasonic energy, and pressure to achieve bonding without requiring separate flux application and cleaning steps, thereby simplifying the manufacturing process while maintaining reliable copper-tin bonds.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent extracts and eliminates the flux step from the conventional copper-tin bonding process. By using thermosonic bonding, the process achieves clean bonding without requiring flux materials, thereby removing the need for flux placement and cleaning steps, reducing process complexity and contamination risks.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If conventional copper-tin flip chip die bonding process is used, then cost savings compared to gold bonding is achieved, but manufacturing cost increases due to additional process steps

Engineering Contradiction:

Improvebond strengthVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent combines multiple separate assembly steps (flux placement, die attachment, reflow soldering, flux cleaning) into a single integrated thermosonic bonding process. The thermosonic bonder simultaneously applies heat, ultrasonic energy, and pressure to achieve bonding without requiring separate flux application and cleaning steps, thereby simplifying the manufacturing process while maintaining reliable copper-tin bonds.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent extracts and eliminates the flux step from the conventional copper-tin bonding process. By using thermosonic bonding, the process achieves clean bonding without requiring flux materials, thereby removing the need for flux placement and cleaning steps, reducing process complexity and contamination risks.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If conventional copper-tin flip chip die bonding process is used, then cost savings compared to gold bonding is achieved, but contamination risks increase due to flux materials

Engineering Contradiction:

Improvemanufacturing costVSAvoidcontamination

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and eliminates the flux step from the conventional copper-tin bonding process. By using thermosonic bonding, the process achieves clean bonding without requiring flux materials, thereby removing the need for flux placement and cleaning steps, reducing process complexity and contamination risks.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent converts the potential harm of flux materials (contamination) into a benefit by eliminating them entirely. The thermosonic bonding process uses ultrasonic energy and heat to achieve clean bonding directly, transforming the process from one that requires harmful chemical fluxes to one that achieves bonding through physical energy fields, thereby eliminating contamination risks.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

4Reliability

If gold-to-gold thermosonic interconnect process is used, then bond strength and electrical performance are improved, but material cost increases due to use of expensive gold

Engineering Contradiction:

Improvebond strengthVSAvoidmaterial cost

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent replaces expensive gold bumping materials with cheaper copper-tin bumping materials. The copper-tin bumps provide sufficient bond strength and electrical performance for the application, eliminating the need for expensive gold while maintaining acceptable reliability. This substitution of materials directly addresses the cost issue while preserving the essential bonding function.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent changes the material composition parameter from gold to copper-tin, and相应地 changes the bonding process parameters to thermosonic conditions (temperature, pressure, ultrasonic power) optimized for copper-tin bonding. This parameter change enables cost-effective bonding while maintaining reliable electrical and mechanical connections.

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 simplifies the assembly process, reduces contamination risks, and achieves strong, reliable bonds between copper pillar bumps and substrate pads in a single step, lowering manufacturing costs while maintaining high performance.

Implementation Method 1

applying ultrasonic energy to the at least one copper pillar bump while applying mechanical pressure to press the die to the substrate

Methodology Applied

Scientific EffectUltrasonic vibration: Ultrasonic Vibration

Implementation Method 2

applying thermal and mechanical energy to the at least one copper pillar bump to bond the die to the substrate

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 3

applying mechanical pressure to press the die to the substrate

Methodology Applied

Scientific EffectMechanical pressure: Compression

Implementation Method 4

applying sufficient thermal and mechanical energy to at least partially melt the solder cap to bond the die to the substrate

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS7642135B2Thermal mechanical flip chip die bonding

Publication Date: 2010.01.05 SKYWORKS SOLUTIONS INC

AI summary

A thermal mechanical process for bonding a flip chip die to a substrate. The flip chip die includes a plurality of copper pillar bumps, each copper pillar bump of the plurality of copper pillar bumps having a copper portion attached to the die and a bonding cap attached to the copper portion. The process includes positioning the die on the substrate such that the bonding cap of each copper pillar bump of the plurality of copper pillar bumps contacts a corresponding respective one of a plurality of bonding pads on the substrate, and thermosonically bonding the die to the substrate.