Curved Pad Wiring Substrate Stress Relief

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Solution Overview

Problem

Wiring substrates with linear through hole inner walls suffer from stress concentration at the corner of the pad's upper surface, leading to potential breakage of the pad and via wiring, and cracking of the insulation layer during bonding, which compromises connection reliability.

Innovation Solution

A wiring substrate design featuring a pad with a curved connecting surface within a taper-shaped through hole, alleviating stress concentration by dispersing it across the pad's surface, and a manufacturing method that forms the pad with an upper surface curving in a protruding shape to connect with the via wiring, reducing the likelihood of fracturing and improving reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the inner wall surfaces of the through hole are formed in a linear shape, then the manufacturing process is simple, but stress concentrates at the corner of the pad's upper surface leading to potential breakage

Engineering Contradiction:

Improvesimplicity of through hole formationVSAvoidconnection reliability between pad and via wiring

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies curvature by forming the inner wall surface of the through hole in a curved shape rather than a linear shape. This curvature causes the pad's upper surface to have a curved connecting surface that protrudes toward the via wiring, eliminating the corner where stress would concentrate. The curved geometry disperses stress across a broader area, preventing pad and via wiring breakage while maintaining manufacturing feasibility.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Ease of manufacture

If the pad upper surface includes a corner, then the linear through hole formation is easier, but stress concentration causes cracks in the insulation layer

Engineering Contradiction:

Improveease of through hole formationVSAvoidstrength of insulation layer

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The curved inner wall surface of the through hole eliminates the corner formation on the pad's upper surface. This curvature design ensures that the pad's connecting surface is smooth and rounded, preventing stress concentration points that would initiate cracks in the insulation layer. The curved geometry distributes mechanical stress evenly, preserving insulation layer integrity.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Ease of manufacture

If the pad has a planar surface parallel to the bottom of the through hole, then the pad formation is straightforward, but the inclined plane creates stress concentration at the boundary corner

Engineering Contradiction:

Improvestraightforward pad formationVSAvoidstress concentration at pad corner

Core Design Contradiction:

Ease of manufactureVSStress or pressure

Solution Approach 1:

The patent replaces the planar surface with an inclined plane configuration with a curved inner wall surface. This curvature causes the pad's upper surface to form a curved connecting surface that protrudes toward the via wiring, eliminating the sharp corner at the boundary between the planar surface and inclined plane. The curved geometry disperses stress across the connecting surface, preventing stress concentration and potential failure.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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

The curved pad surface design effectively reduces stress concentration, enhancing the connection reliability between the pad and via wiring, while preventing cracks in the insulation layer, thereby improving the overall bonding process and substrate stability.

Implementation Method 1

the curved pad surface design effectively reduces stress concentration, enhancing the connection reliability between the pad and via wiring

Methodology Applied

Scientific EffectStress distribution:

Implementation Method 2

Pads are formed for example by an electroplating method

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS11011457B2Wiring substrate

Publication Date: 2021.05.18 SHINKO ELECTRIC IND CO LTD

AI summary

A wiring substrate includes a first insulation layer containing insulating resin, a first through hole passing through the first insulation layer is the thickness direction, a pad formed within the first through hole, a second insulation layer containing insulating resin and laminated on a first surface of the first insulation layer, and a first wiring layer provided on the second insulation layer and connecting to the pad. A connecting surface of the pad that connects the first wiring layer includes a curved surface that curves in a protruding shape toward the first surface of the first insulation layer.