Stacked Solder Bumps with Intermediate Metal Layer for Thermal Reliability
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Solution Overview
Problem
Existing semiconductor devices face challenges in achieving reliable and stable electrical interconnections due to limitations in the fabrication of multi-bump structural electrical interconnections, which affect mechanical and thermal reliability and assembly processes.
Innovation Solution
A method involving the formation of a solder stack with at least two solder layers and an intermediate layer, where the solder layers are reflowed to create stacked solder bumps, with the intermediate layer having a higher melting point than the solder bumps, enhancing electrical connectivity and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single solder layer is used for electrical interconnection, then the fabrication process is simple, but the mechanical and thermal reliability is insufficient
Solution Approach 1:
The solder interconnection is divided into multiple discrete solder bumps stacked vertically, with each bump formed from a separate solder layer. This segmentation allows each layer to contribute to different aspects of reliability while maintaining fabrication simplicity through sequential processing
Solution Approach 2:
Multiple solder bumps are stacked one on top of another in a nested configuration, with each subsequent bump positioned on top of the previous one. This nesting approach achieves complex three-dimensional interconnections while using a systematic, repeatable fabrication process
2Reliability
If solder layers are stacked to form multi-bump structure, then electrical connectivity is improved, but deformation and fracture occur during reflow
Solution Approach 1:
A barrier metal layer with higher melting point is introduced as an intermediary between the solder bumps. This intermediate layer acts as a structural support during reflow processing, preventing deformation and fracture of the solder layers while allowing proper electrical connectivity to be established
Solution Approach 2:
The melting point parameter of the intermediate barrier layer is specifically chosen to be higher than that of the solder layers. This parameter change ensures that the barrier layer remains solid and structurally stable during the reflow process, providing mechanical support to prevent solder deformation
3Reliability
If intermediate layer with higher melting point is added, then thermal reliability is improved, but fabrication complexity increases
Solution Approach 1:
The barrier metal layer is combined with the existing solder bump fabrication process by forming it as part of the same stacked structure. The barrier layer is deposited and patterned together with the solder layers in a unified fabrication sequence, avoiding separate manufacturing steps
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 solution enables improved mechanical and thermal reliability, fine pitch assembly, and high thermal performance by forming a bump stack with a metal layer interposed between solder bumps, reducing deformation and fracture, and allowing for flexible gap control between the semiconductor device and package substrate.
Implementation Method 1
reflowing the solder stack to form a bump stack that is electrically connected to the chip pad
Implementation Method 2
The metal layer may have a melting point greater than the first and second solder bumps
Implementation Method 3
forming a first solder layer, the intermediate layer and a second solder layer which are stacked one atop the other
Data Source
AI summary
An electrical interconnection can be provided using a bump stack including at least two solder bumps which are stacked on one another and at least one intermediate layer interposed between the at least stacked two solder bumps.