Bump Electrode Joining With Flattened Solder Bumps for Cu Core Balls

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Solution Overview

Problem

The formation of intermetallic compounds on the surface of Ni layers in Cu core balls leads to non-wetting issues during substrate joining, causing solder to repel and resulting in insufficient adhesion, which is exacerbated by limitations in solder layer thickness and productivity in mass-produced Cu core balls.

Innovation Solution

A method involving the application of a first flux on an electrode, followed by a solder material, deformation to form a flat surface, application of a second flux, and placement of a core material with a Ni layer and solder layer, then heating to join the core material to the electrode using the solder layer, thereby preventing non-wetting and void generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness of the solder layer covering the core portion is increased to prevent non-wetting, then the adhesion of solder to the core portion is improved, but the productivity of Cu core balls decreases and the cost increases

Engineering Contradiction:

Improveadhesion of solder to core portionVSAvoidproductivity of Cu core balls

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies flux to the electrode surface before placing the Cu core ball, and performs a preliminary heating step to melt the solder layer on the core portion. This preliminary action ensures that the solder is already molten and ready to wet the electrode surface when the core ball is placed, eliminating the need for excessive solder layer thickness while ensuring complete coverage and adhesion.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the thermal parameters by controlling the heating temperature and time to melt the solder layer on the core portion before joining. By optimizing these thermal parameters, the solder achieves proper fluidity and wetting characteristics without requiring increased solder layer thickness, thus maintaining productivity while ensuring reliable adhesion.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If solder paste is applied to the electrode before Cu core ball joining to prevent non-wetting, then the adhesion is improved, but void generation and bump height variation occur

Engineering Contradiction:

Improveadhesion of solder to electrodeVSAvoidbump height uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent uses a flux material that is consumed during the joining process to achieve its purpose of promoting wetting and preventing non-wetting. The flux performs its function during the heating and joining stages and then serves no further purpose, similar to disposable materials. This approach achieves reliable adhesion without the defects associated with solder paste application.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If the Cu core ball is joined directly without sufficient solder coverage to maintain productivity, then the production efficiency is maintained, but non-wetting occurs causing poor adhesion

Engineering Contradiction:

Improveproduction efficiency of Cu core ball joiningVSAvoidadhesion of solder to electrode

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces flux as an intermediary substance between the solder layer on the core portion and the electrode. The flux facilitates the wetting process and ensures proper adhesion by promoting the interaction between solder and electrode surfaces. This intermediary enables reliable joining with standard solder layer thicknesses, maintaining both productivity and reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively prevents non-wetting and reduces bump height variations while avoiding the need for thick solder layers, maintaining productivity and ensuring stable substrate joining.

Implementation Method 1

a first flux 16 is applied onto the electrode 14... a second flux 22 is applied to the solder bump 20

Methodology Applied

Scientific EffectOxide film removal by flux: Reduction

Implementation Method 2

heating the substrate to join the core material to the electrode by the solder bump and the solder layer

Methodology Applied

Scientific EffectMelting of solder: Melting

Implementation Method 3

heating the substrate to form a solder bump on the electrode... heating the substrate to join the core material to the electrode by the solder bump and the solder layer

Methodology Applied

Scientific EffectSoldering: Soldering

Data Source

PatentUS11478869B2Method for forming bump electrode substrate

Publication Date: 2022.10.25 SENJU METAL IND CO LTD

AI summary

A method includes applying a first flux onto an electrode provided on a substrate and placing a solder material on the electrode, heating the substrate to form a solder bump on the electrode, deforming the solder bump to provide a flat surface or a depressed portion on the solder bump, applying a second flux to the solder bump; placing a core material on the solder bump, the core material including a core portion and a solder layer that covers a surface of the core portion, and heating the substrate to join the core material to the electrode by the solder bump and the solder layer.