Interconnect Structure Mitigating Electromigration via Conductive Projections
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Solution Overview
Problem
Electromigration in interconnect structures of microelectronic assemblies leads to void formation and reliability issues due to differing diffusion rates of materials, especially in high-performance devices, and existing solutions like barrier metals or dopants present reliability and cost challenges.
Innovation Solution
The use of conductive projections and dielectric layers in interconnect structures reduces the distance between metallic elements, promotes inter-metallic compound formation, and minimizes current concentration gradients, thereby reducing electromigration by extending the surface area of copper within the solder mass and preventing direct contact between solder and pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder mass is used to bond contact pads between substrates, then mechanical securing and electrical connection are achieved, but void formation occurs due to different diffusion rates between solder and copper
Solution Approach 1:
A conductive projection extending into the solder mass acts as an intermediary between the contact pad and solder, reducing direct contact between dissimilar metals (copper and solder). This intermediate structure promotes inter-metallic compound formation and extends the copper surface area within the solder, thereby reducing diffusion rate differences and preventing void formation while maintaining mechanical and electrical connection functions
Solution Approach 2:
The conductive projection creates a localized region of extended copper surface area within the solder mass, concentrating inter-metallic compound formation in specific areas. This local modification of material distribution reduces the overall diffusion rate difference between solder and copper, preventing void formation while preserving the bulk mechanical and electrical connection properties
2Reliability
If voids form in interconnect structures, then current density increases in surrounding areas, but this accelerates diffusion rate differences and leads to faster void formation and failure
Solution Approach 1:
The conductive projection serving as an intermediary distributes current more evenly through the interconnect structure by extending copper into the solder mass. This reduces current concentration gradients in the surrounding solder areas, preventing the acceleration of diffusion rate differences that would otherwise lead to faster void formation and interconnect failure
3Reliability
If barrier metals or dopants are used to decrease electromigration, then electromigration is reduced, but reliability issues and cost increases occur
Solution Approach 1:
The invention extracts the barrier function from separate barrier metal layers or dopant additions and integrates it into the conductive projection structure itself. By extending the copper contact pad into the solder mass, the structure inherently promotes controlled inter-metallic compound formation and reduces diffusion rate differences without requiring additional barrier materials, thereby reducing device complexity while maintaining electromigration resistance
Solution Approach 2:
The conductive projection serves multiple functions simultaneously: it provides mechanical support, establishes electrical connection, reduces diffusion rate differences between solder and copper, and prevents void formation. This multi-functionality eliminates the need for separate barrier metal layers or dopant treatments, reducing overall device complexity while achieving electromigration resistance
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 decreases the likelihood of void formation and enhances the reliability of microelectronic assemblies by slowing down electromigration and reducing current concentration gradients, leading to improved mechanical and electrical stability.
Implementation Method 1
electromigration is caused by the different diffusion rates of materials used in interconnect assemblies
Implementation Method 2
promotes inter-metallic compound formation
Implementation Method 3
Electromigration is a main cause of interconnect failure
Implementation Method 4
preventing direct contact between solder and pads
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A microelectronic assembly 10 includes a first surface 22 and a first thin conductive element 52 exposed at the first surface 22 and having a face 54 comprising first and second regions. A first conductive projection 56 having a base 58 connected to and covering the first region of the face 54 extends to an end 62 remote from the base. A first dielectric material layer 40 covers the second region of the first thin element 52 and contacts at least the base 58 of the first conductive projection 56. The assembly 10 further includes a second substrate 18 having a second face 24 and a second conductive projection 76 extending away from the second face 24. A first fusible metal mass 70 connects the first projection 56 to the second projection 76 and extends along an edge of the first projection 56 towards the first dielectric material layer 40.