Solder Via for Optical Waveguide Electrical Contact

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Solution Overview

Problem

The existing methods for forming electrical contact in optical waveguides result in a long distance between the chip and mirror after bonding, insufficient mechanical strength of gold bonds, and chemical damage to the optical waveguide due to the use of electroless plating and copper wiring.

Innovation Solution

A resist pattern is formed over the electrode pad on the electrical substrate, with solder plating applied and the optical waveguide layers removed to expose the solder, creating a conformal via that reduces the distance between the chip and mirror and enhances mechanical bonding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a filled via with copper wiring and electroless plating is used, then electrical contact is established, but the distance between chip and mirror becomes lengthy

Engineering Contradiction:

Improveelectrical contactVSAvoiddistance between chip and mirror

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The invention extracts and removes the electroless plating step from the conventional via formation process. By eliminating this chemical processing step, the via structure is simplified, allowing the chip to be bonded directly to the via opening without requiring additional spacing for plating layers, thus reducing the distance between chip and mirror while maintaining electrical contact functionality

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of filling the via hole with copper wiring and applying electroless plating as in conventional methods, the invention inverts the approach by leaving the via opening exposed and using a solder bump directly on the via pad. This inverted structure eliminates the need for chemical plating processes and reduces the overall height, bringing the chip closer to the mirror

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If gold plating is used for electrode pad, then corrosion resistance and electrical contact are improved, but mechanical strength of bonding is insufficient

Engineering Contradiction:

Improvecorrosion resistance and electrical contactVSAvoidmechanical strength of bonding

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The invention uses a composite material approach by combining solder material with the via pad structure. The solder bump provides both excellent electrical conductivity and strong mechanical bonding properties, while the underlying via pad (without electroless plating) maintains corrosion resistance. This composite structure simultaneously achieves reliable electrical contact, corrosion resistance, and enhanced mechanical strength

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention changes the material parameter from gold plating to solder material for the electrode contact. Solder offers superior mechanical bonding strength compared to gold while maintaining good electrical conductivity and corrosion resistance through proper material selection and processing, thus improving the mechanical strength parameter without sacrificing electrical or chemical performance

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If electroless plating solution is used, then seed layer is formed for copper plating, but chemical damage occurs to optical waveguide

Engineering Contradiction:

Improveseed layer formationVSAvoidchemical damage to optical waveguide

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The invention extracts and completely removes the electroless plating solution processing step from the manufacturing process. By eliminating this chemical process, the source of chemical damage to the optical waveguide is removed entirely. The seed layer formation is replaced with a direct solder deposition process on the via pad, achieving the same functional result without harmful chemical exposure to the optical waveguide layers

Inventive Principle:

Principle #2Taking out (Extraction)

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 distance between the chip and mirror, provides a strong metal bond using solder, and minimizes chemical damage to the optical waveguide, improving mechanical strength and reducing insertion loss.

Implementation Method 1

solder plating is formed on a surface of the electrode pad

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS9772462B2Via for electrical contact passing through layers of optical waveguide in multilayer structure including electrical substrate and laminated layers of optical waveguide

Publication Date: 2017.09.26 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A structure is formed which is prepared as a via for electrical contact passing through layers of an optical waveguide, in a multilayer structure including an electrical substrate and the laminated layers of the optical waveguide. The surface of an electrode pad is plated with solder. The layers of the optical waveguide are formed above the portion plated with solder are removed to expose the portion plated with solder. A device is prepared having both a light-emitter or photoreceptor in optical contact with the optical waveguide, and a stud (pillar). The stud (pillar) is inserted into the portion in which layers of the optical waveguide have been removed, and the plated solder is melted to bond the electrode pad on top of the electrical substrate to the tip of the inserted stud (pillar).