Segmented Capture Pad for Lead-Free Solder Stress Relief

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Solution Overview

Problem

The transition to lead-free solder bumps in integrated circuits leads to increased stress and defects due to thermal expansion mismatch between chips and substrates, resulting in cracks and delamination issues, particularly during the cooling phase of the reflow process.

Innovation Solution

A segmented capture pad structure is formed over an insulative material with openings that direct shear stresses away from metal pads and interconnects, terminating fatigue crack initiation and preventing delamination by dissipating stress into the underlying insulative layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If lead-free solder bumps are used to meet lead-free requirements, then environmental compliance is improved, but thermal expansion mismatch increases causing stress and cracks

Engineering Contradiction:

Improveenvironmental complianceVSAvoidthermal expansion mismatch stress

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The capture pad is segmented into multiple sections with openings between them, allowing the structure to flex and accommodate thermal expansion differences. This segmentation enables the pad to absorb stress through controlled deformation rather than cracking, directly addressing the thermal expansion mismatch problem while maintaining lead-free solder compatibility

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the physical parameters of the capture pad by introducing openings and segments, altering its mechanical properties to be more compliant and stress-resistant. This parameter change allows the pad to adapt to thermal expansion variations without failing, resolving the contradiction between using lead-free solder and managing thermal stress

Inventive Principle:

Principle #35Parameter changes

2Reliability

If high stress Pb-free C4 bumps are used to achieve lead-free soldering, then soldering compliance is improved, but adhesion between C4 bump and Cu wire deteriorates

Engineering Contradiction:

Improvelead-free soldering complianceVSAvoidC4 bump to Cu wire adhesion

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The segmented capture pad structure creates multiple smaller contact zones rather than one large continuous pad. This segmentation reduces the stress concentration at any single point, preventing delamination and adhesion failure between the C4 bump and underlying Cu wire while maintaining lead-free soldering integrity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The segmented pad structure acts as an intermediary element between the C4 bump and the Cu wire interconnect. It provides a compliant interface that absorbs stress and protects the critical adhesion interface, allowing lead-free soldering to proceed without compromising bond strength

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If continuous capture pad structure is used for simple manufacturing, then manufacturing complexity is reduced, but stress concentration increases causing fatigue cracks

Engineering Contradiction:

Improvecapture pad fabrication simplicityVSAvoidresistance to fatigue cracks

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The capture pad is divided into segments with openings, which can be fabricated using standard photolithography and etching processes. While slightly more complex than a continuous pad, the segmentation is achieved through conventional manufacturing steps and provides significant benefits in stress distribution and fatigue resistance

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The openings in the segmented pad, which might seem to complicate manufacturing, actually convert the potential harm of stress concentration into a benefit by creating stress-relief zones. The manufacturing process includes these openings as part of the standard pattern formation, transforming a potential defect into a functional stress-management feature

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 effectively eliminates fatigue cracks and delamination in BEOL vias and metal interconnects, reducing manufacturing costs and enhancing the reliability of lead-free C4 connections by absorbing and dissipating shear stresses, thereby preventing white bumps and interfacial failures.

Implementation Method 1

The solder bump is deposited on the capture pad and the openings over the dielectric layer... absorbing and dissipating shear stresses

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Implementation Method 2

dissipating stress into the underlying insulative layer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS9087754B2Structures and methods for improving solder bump connections in semiconductor devices

Publication Date: 2015.07.21 MARVELL ASIA PTE LTD

AI summary

Structures with improved solder bump connections and methods of fabricating such structures are provided herein. The structure includes a via formed in a dielectric layer to expose a contact pad and a capture pad formed in the via and over the dielectric layer. The capture pad has openings over the dielectric layer to form segmented features. The solder bump is deposited on the capture pad and the openings over the dielectric layer.