Sacrificial Pillar Layout for Conductive Pillar Coplanarity
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Solution Overview
Problem
In semiconductor packages, variations in the height of conductive pillars due to differing areal densities can lead to non-joints and 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, thereby reducing the risk of non-joints and smashed joints by acting as a buffer zone during the plating process and subsequently being removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If direct chip attach methods are used to reduce footprint, then package size is reduced, but manufacturing precision deteriorates due to height variations in conductive pillars causing non-joints and smashed joints
Solution Approach 1:
Sacrificial pillars are formed in advance during the plating process to control the height of live conductive pillars. The sacrificial pillars act as placeholders that define the plating depth, ensuring that live conductive pillars achieve uniform heights before the sacrificial pillars are removed. This preliminary action prevents height variations that would cause non-joints or smashed joints during bonding.
Solution Approach 2:
Sacrificial pillars serve as intermediary structures during manufacturing. They are temporarily present to control the plating process and ensure uniform height of live conductive pillars, then removed after serving their purpose. These intermediary structures mediate between the plating process and the final bonding operation, enabling precise height control without affecting the final package design.
2Reliability
If conductive pillars are made taller to ensure connection, then connection reliability is improved, but device complexity increases due to risk of smashed joints and electrical shorts
Solution Approach 1:
The sacrificial pillars are formed beforehand to pre-establish the correct plating depth. This preliminary structure guides the plating process to create live conductive pillars of precise, uniform heights that are optimal for bonding, eliminating the need for excessive height that would cause smashed joints or shorts while ensuring sufficient height for reliable connections.
Solution Approach 2:
The invention changes the parameter control approach from post-formation selection to in-process control. By using sacrificial pillars as physical references during plating, the height parameter of live conductive pillars is precisely controlled at the source, ensuring uniformity without requiring complex post-processing or selection procedures.
3Strength
If conductive pillars are made shorter to avoid smashing, then joint integrity is improved, but manufacturing precision deteriorates due to non-joints from insufficient height
Solution Approach 1:
Sacrificial pillars act as intermediary reference structures during the plating process. They provide a physical template that ensures live conductive pillars are formed to the exact required height for optimal joint integrity. This intermediary approach enables precise height control, ensuring pillars are tall enough for reliable connections but not so tall as to cause smashing during bonding.
4Manufacturing precision
If sacrificial pillars are used to control height uniformity, then manufacturing precision is improved, but device complexity increases due to additional manufacturing steps
Solution Approach 1:
The formation of sacrificial pillars and live conductive pillars is merged into a single plating operation. Both types of pillars are formed simultaneously in the same plating bath, using the same plating process parameters. This merging eliminates the need for separate fabrication steps while achieving precise height control through the sacrificial pillar template approach.
Solution Approach 2:
The sacrificial pillars serve multiple functions: they act as height references during plating, define the plating depth for live conductive pillars, and can be removed in a single subsequent step. This multi-functionality reduces the overall process complexity despite adding the sacrificial pillar formation step, as one structure performs multiple critical roles in ensuring height uniformity.
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 enhances the coplanarity of conductive pillars, improving the yield and reliability of direct chip attach methods by maintaining the heights of live conductive pillars within a predetermined range, thus mitigating the risks of non-joints and smashed joints.
Implementation Method 1
a plating process may be performed to form sacrificial pillars and conductive pillars
Data Source
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.