Sacrificial Pillar Layout for Flip-Chip Coplanarity Control

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Solution Overview

Problem

In semiconductor packages, variations in the height of conductive pillars due to different areal densities can lead to non-joints or smashed joints during flip-chip bonding, resulting in reliability issues and electrical shorts.

Innovation Solution

The use of sacrificial pillars with a defined areal density is introduced to create a buffer zone, ensuring a uniform plating pattern and maintaining coplanarity of live conductive pillars within a tolerable range, which are then removed after forming the live conductive pillars.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If direct chip attach methods are used to reduce footprint, then package size is reduced, but variations in conductive pillar heights cause non-joints or smashed joints

Engineering Contradiction:

Improvepackage footprintVSAvoidconductive pillar height uniformity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

Sacrificial pillars are formed in advance during the plating process to control the height of live conductive pillars. The sacrificial pillars are removed after bonding, having served their purpose of ensuring uniform height during manufacturing.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Sacrificial pillars act as intermediary structures that influence the plating process to achieve uniform live conductive pillar heights. They mediate between the plating process and the final pillar height, ensuring consistency without being part of the final product.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If conductive pillars have different heights, then manufacturing flexibility is increased, but bonding reliability deteriorates due to opens and smashed joints

Engineering Contradiction:

Improvepillar height variationVSAvoidbonding joint reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

Different regions of the semiconductor die are assigned different areal densities of sacrificial pillars tailored to local requirements. This local customization ensures that each region achieves the desired live conductive pillar height uniformity while maintaining overall design flexibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The areal density of sacrificial pillars is adjusted as a controllable parameter to achieve target live conductive pillar heights. By changing the density parameter in different regions, uniform bonding reliability is achieved across the entire device.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If sacrificial pillars are used to control coplanarity, then manufacturing precision is improved, but device complexity increases

Engineering Contradiction:

Improvecoplanarity of conductive pillarsVSAvoidstructure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Sacrificial pillars are temporary structures formed during manufacturing, used to control coplanarity, and then discarded after serving their purpose. This approach achieves high manufacturing precision without permanent structural complexity.

Inventive Principle:

Principle #34Discarding and recovering

Solution Approach 2:

Sacrificial pillars are inexpensive, temporary structures that are formed, used for a brief period during manufacturing, and then removed. Their temporary nature allows them to solve the coplanarity problem without adding permanent complexity to the device.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 improves the coplanarity of conductive pillars, reducing the incidence of non-joints and smashed joints, thereby enhancing the yield and reliability of semiconductor device assemblies by maintaining consistent areal densities and preventing abrupt changes in pillar heights.

Implementation Method 1

it has been discovered that the heights of conductive pillars formed by plating processes may be correlated to areal densities

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS11894329B2Semiconductor device assembly with sacrificial pillars and methods of manufacturing sacrificial pillars

Publication Date: 2024.02.06 MICRON TECHNOLOGY INC

AI summary

Sacrificial pillars for a semiconductor device assembly, and associated methods and systems are disclosed. In one embodiment, a region of a semiconductor die may be identified to include sacrificial pillars that are not connected to bond pads of the semiconductor die, in addition to live conductive pillars connected to the bond pads. The region with the sacrificial pillars, when disposed in proximity to the live conductive pillars, may prevent an areal density of the live conductive pillars from experiencing an abrupt change that may result in intolerable variations in heights of the live conductive pillars. As such, the sacrificial pillars may improve a coplanarity of the live conductive pillars by reducing variations in the heights of the live conductive pillars. Thereafter, the sacrificial pillars may be removed from the semiconductor die.