Conductive Pillar With Hollow Core for Solder Confinement
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Solution Overview
Problem
Conventional solder bumps in flip chip technology face limitations in thermal and electrical performance, especially in smaller geometries and tighter pitches, and require significant solder for mechanical and electrical connections, which can lead to reliability issues and electrical shorts.
Innovation Solution
The development of conductive pillars with a hollow core and a recessed top surface, formed through a process involving a seed layer, sacrificial plugs, and multiple conductive layers, which are then capped with solder bodies to create stable, non-reflowable pillars that provide improved thermal and electrical performance while reducing solder usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder bumps are used to provide mechanical and electrical connections, then connections can be established between bond pads and package, but thermal and electrical performance is limited especially in smaller geometries and tighter pitches
Solution Approach 1:
The patent changes the material parameters by replacing solder material with conductive pillar material (such as copper, tungsten, or cobalt), and changes the structural parameters by forming pillars with hollow cores and recessed top surfaces. These parameter changes enable improved thermal and electrical performance while maintaining compatibility with smaller geometries and tighter pitches.
Solution Approach 2:
The patent employs composite structures by combining conductive pillar material with solder material (capping the pillar), creating a hybrid interconnect structure that leverages the advantages of both materials: the high conductivity of the pillar material and the reflowability of the solder cap.
2Reliability
If conventional solder bumps are used for mechanical and electrical connections, then connections are established, but significant solder is required which can lead to reliability issues and electrical shorts
Solution Approach 1:
The patent extracts the bulk solder material from the interconnect structure, replacing it with a minimal solder cap on top of the conductive pillar. This extraction eliminates the harmful effects of excessive solder (such as electrical shorts and reliability issues) while retaining the necessary solder function for bonding.
Solution Approach 2:
The patent applies solder material locally only where needed (as a cap on the pillar top surface) rather than using it throughout the entire interconnect volume. This local application of solder provides the necessary bonding interface while minimizing the total solder quantity and associated reliability risks.
3Reliability
If conductive pillars with hollow core and recessed top surface are formed, then solder usage is reduced and thermal/electrical performance is improved, but manufacturing process complexity increases
Solution Approach 1:
The patent performs preliminary actions by forming sacrificial plugs before depositing the conductive pillar material. These sacrificial plugs define the hollow core geometry, and their removal after pillar formation creates the desired hollow structure with recessed top surface, simplifying the overall manufacturing sequence.
Solution Approach 2:
The patent uses sacrificial plugs as intermediary elements during manufacturing. These temporary structures guide the formation of the hollow core and recessed top surface, and are removed after serving their purpose, enabling complex geometry creation without requiring complex direct fabrication processes.
Data Source
AI summary
A pillar-type connection includes a first conductive layer that includes a hollow core. A second conductive layer is connected to the first conductive layer defining a conductive pillar that includes a top surface defining a recess aligned with the hollow core.