Laser Welding Semiconductor Metallization with Cup-Shaped Copper Attachment

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Solution Overview

Problem

Conventional laser welding techniques for attaching copper pieces to semiconductor metallizations pose a high risk of thermal destruction due to varying reflectivity and absorption of copper at different temperatures, leading to excessive heat exposure and potential damage to thin metallization layers and insulation layers.

Innovation Solution

The use of an attachment piece with a flat side and a thin point, where the thin point is formed with a cup shape open away from the semiconductor metallization, and laser light with wavelengths of 800 nanometers or less, allows for precise control of welding depth and minimizes thermal exposure by maintaining a stable absorption of laser energy and avoiding sudden reflectivity changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional laser welding is used to weld copper attachment pieces to semiconductor metallizations, then welding speed and productivity are improved, but the semiconductor components are subjected to high thermal loading which can irreversibly destroy the semiconductor components

Engineering Contradiction:

Improvewelding speedVSAvoidthermal loading on semiconductor

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the laser wavelength parameter from conventional infrared wavelengths (e.g., 1064 nm) to blue or green wavelengths (450-532 nm). This parameter change exploits the fact that copper has higher absorption coefficient at these shorter wavelengths, enabling welding at lower power densities and thus reducing thermal loading on the semiconductor while maintaining productivity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a copper interlayer or copper coating on the attachment piece as an intermediary that preferentially absorbs the blue/green laser energy. This intermediary layer acts as a heat sink that protects the semiconductor from direct thermal exposure while still enabling the welding process to proceed at high speed

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If high laser power output is used to couple the laser beam into copper at the start of welding, then welding initiation is improved, but the sudden transformation of power output when copper melts exceeds the scope for processing and increases the risk of heat exposure

Engineering Contradiction:

Improvewelding initiationVSAvoidheat exposure during melting

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the laser wavelength to blue or green ranges where copper exhibits more stable absorption characteristics across the temperature range. This eliminates the abrupt reflectivity change that occurs with conventional infrared lasers, allowing for stable power output throughout the welding process without sudden transformations when melting occurs

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements feedback control of the laser power output based on monitoring of the welding process parameters. This feedback mechanism detects the melting stage and adjusts the power output accordingly to maintain stable processing within the safe operating window, preventing excessive heat exposure while ensuring reliable welding initiation

Inventive Principle:

Principle #23Feedback

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 reduces the risk of semiconductor component damage by maintaining a low welding depth and ensuring mechanical stability, while achieving high manufacturing accuracy and reliability in the laser welding process.

Implementation Method 1

it is known, for instance, to weld copper attachment pieces to semiconductor metallizations by means of disk lasers, fiber lasers, or CO2 lasers

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

the absorption of copper increases... the power output of the laser as a whole is suddenly transformed in the melt pool

Methodology Applied

Scientific EffectAbsorption of laser energy: Absorption (EM radiation)

Implementation Method 3

an attachment piece (30, 30') having a flat side with a thin point (40)... the thin point (40) is formed with a cup shape of the attachment piece (30, 30')... allows for precise control of welding depth

Methodology Applied

Scientific EffectGeometric confinement of energy:

Data Source

PatentUS20230207516A1Method for Welding an Attachment Piece to a Semiconductor Metallisation by Laser Welding

Publication Date: 2023.06.29 SIEMENS AG

AI summary

Various teachings of the present disclosure include a method for welding an attachment piece to a semiconductor metallization using laser welding. The method may include: arranging an attachment piece having a flat side with a thin point so the flat side faces the semiconductor metallization; and welding the flat side to the semiconductor metallization. The flat side rests against a flat side of the semiconductor metallization over an entire surface area of the flat side. The thin point is formed with a cup shape of the attachment piece. The cup shape is open in the direction away from the semiconductor metallization.