Lead-Free Tin Solder Bonding with Titanium-Nickel Interlayer

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The use of lead-tin alloy solder in semiconductor devices poses environmental concerns, and the existing tin-based solder manufacturing processes are complex and costly due to issues with passive film formation on titanium layers and the need for thick nickel layers and precise soldering conditions.

Innovation Solution

A semiconductor device with a tin-based solder layer is manufactured using a minimum number of metal layers, where a first metal layer (e.g., titanium, aluminum, or iron-nickel-chromium alloy) and a second metal layer are used to form an alloy layer with the solder, simplifying the process and reducing costs by controlling the soldering conditions and using a tin-based solder layer with a lead-free composition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a titanium layer is used as the first metal layer to provide adhesiveness and ohmic contact, then the bonding property is improved, but a passive oxide film is easily formed on the Ti layer which is difficult to remove, making it difficult to directly bond the Ti layer to the solder

Engineering Contradiction:

Improveadhesiveness and ohmic contactVSAvoiddifficulty to bond to solder

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

A nickel layer is introduced as an intermediary between the titanium layer and the tin-based solder layer. The nickel layer serves as a mediator that prevents direct contact between the solder and the oxidized titanium surface, enabling successful bonding while preserving the adhesive properties of the titanium layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bonding structure is segmented into multiple functional layers: a titanium layer for adhesiveness, a nickel layer for solder bonding, and a tin-based solder layer. This segmentation allows each layer to perform its specific function without interference from the limitations of other materials.

Inventive Principle:

Principle #1Segmentation

2Strength

If a thick nickel layer is formed on the titanium layer to enable solder bonding, then the bonding property is improved, but the manufacturing cost becomes higher

Engineering Contradiction:

Improvebonding propertyVSAvoidmanufacturing cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The thickness of the nickel layer is optimized to a specific range (50-500 nm) to achieve the minimum necessary thickness for effective solder bonding. This parameter optimization reduces material consumption and manufacturing cost while maintaining adequate bonding properties.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If precise soldering conditions are controlled to achieve proper bonding, then the bonding quality is improved, but the manufacturing cost becomes higher

Engineering Contradiction:

Improvesoldering condition controlVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The nickel layer acts as a sacrificial or consumable intermediate layer that facilitates the soldering process. By providing a solder-friendly surface, it enables less stringent soldering conditions and reduces the need for highly precise and costly process control.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Strength

If lead-tin alloy solder is used for bonding, then the bonding property is improved, but environmental protection requirements are violated due to safety and harmfulness concerns

Engineering Contradiction:

Improvebonding propertyVSAvoidenvironmental harm

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The solder composition is changed from lead-tin alloy to lead-free tin-based alloy, modifying the material parameters to eliminate toxic lead content while maintaining bonding functionality through the optimized multi-layer metal structure.

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 approach simplifies the manufacturing process, reduces costs, and achieves strong bonding between the semiconductor substrate and the base member while ensuring environmental safety through the use of lead-free solder.

Implementation Method 1

heating the substrate with the base member so that the second metal layer is diffused into the solder layer

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

the first metal layer and the solder layer are reacted to form a first alloy layer

Methodology Applied

Scientific EffectAlloying reaction: Chemical Bonding

Implementation Method 3

the tin-based solder is heated up to a solidus temperature of the solder. Thus, the solder is reflowed so that the substrate is soldered on the heat radiation member

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS7579212B2Semiconductor device having tin-based solder layer and method for manufacturing the same

Publication Date: 2009.08.25 DENSO CORP

AI summary

A semiconductor device includes: a semiconductor substrate; a base member; a tin-based solder layer; a first metal layer; and a first alloy layer. The semiconductor substrate is bonded to the base member through the first metal layer, the first alloy layer and the tin-based solder layer in this order. The first alloy layer is made of a first metal in the first metal layer and tin in the tin-based solder layer. The first metal layer is made of at least one of material selected from the group consisting of titanium, aluminum, iron, molybdenum, chromium, vanadium and iron-nickel-chromium alloy.