Protruding Electrode Solder Joint Anti-Electromigration
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Solution Overview
Problem
Existing micro solder joints in electronic packaging have limited anti-electromigration capabilities due to rapid formation of intermetallic compounds under increased temperature or temperature cycling, leading to reduced flexibility and increased rigidity, which compromises reliability and performance.
Innovation Solution
A bump structure and electronic packaging solder joint structure are developed, featuring a substrate, pad, electrode, and protruding electrode with a conductive material layer, where the protruding electrode forms an intermetallic compound layer that is continuous and directly connected to the electrodes, enhancing both mechanical stress resistance and anti-electromigration properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of intermetallic compound in micro solder joint is increased to improve anti-electromigration capability, then the solder joint becomes harder and more rigid, but the flexibility and toughness are reduced, making it liable to be damaged in temperature cycling reliability testing
Solution Approach 1:
The solder joint is segmented into distinct functional layers: a first solder layer containing intermetallic compounds for anti-electromigration protection, and a second solder layer with lower intermetallic content for flexibility and toughness. This segmentation allows each layer to optimize its properties independently, resolving the contradiction between hardness and flexibility.
Solution Approach 2:
Different regions of the solder joint are given different compositions and properties. The first solder layer (near the electrode) has high intermetallic compound content for electromigration resistance, while the second solder layer (outer region) has low intermetallic content for mechanical flexibility. This local differentiation of quality allows simultaneous optimization of both anti-electromigration capability and mechanical properties.
2Reliability
If temperature cycling reliability testing is performed to test the solder joint, then the intermetallic compound forms rapidly and transforms the solder completely, but the solder joint becomes too rigid and is liable to be damaged
Solution Approach 1:
The solder joint is divided into layers with different intermetallic compound contents. During temperature cycling, the first layer with high intermetallic content provides stability and resistance to electromigration, while the second layer with low intermetallic content maintains flexibility and absorbs thermal stress, preventing damage during temperature cycling reliability testing.
Solution Approach 2:
The second solder layer with low intermetallic compound content acts as a cushioning layer that absorbs and mitigates the harmful effects of rapid intermetallic formation and thermal expansion/contraction during temperature cycling. This pre-designed flexible layer prevents the rigid first layer from cracking or failing under thermal stress.
3Reliability
If a continuous intermetallic compound layer is formed to enhance anti-electromigration properties, then the electromigration resistance is improved, but the manufacturing complexity increases
Solution Approach 1:
The electrode structure is preliminarily designed with a protruding portion before soldering. This pre-formed protrusion serves as a template that guides the formation of the first solder layer, ensuring that the intermetallic compound-rich layer forms continuously and uniformly during the bonding process. This preliminary action simplifies the manufacturing by eliminating the need for complex post-processing to create the continuous intermetallic layer.
Solution Approach 2:
The bonding process itself is utilized to form the continuous intermetallic compound layer. During the reflow or eutectic bonding process, the intermetallic compounds naturally form and continue through the first solder layer due to the controlled composition and the presence of the electrode protrusion. This self-organizing behavior during bonding reduces manufacturing complexity by eliminating separate steps to create the continuous intermetallic structure.
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 achieves improved reliability and performance by maintaining flexibility while enhancing anti-electromigration capabilities through the formation of a continuous intermetallic compound layer within the solder joint, which can be integrated with existing processes.
Implementation Method 1
Intermetallic compound (IMC) is formed by an interreaction between a part of the metal and the solder in the solder joint after eutectic bonding
Implementation Method 2
The bonding method of the micro solder joints mainly uses an eutectic bonding and is an irreversible chemical reaction
Data Source
AI summary
A bump structure includes a substrate, a pad, an electrode and a protruding electrode. The pad is disposed on the substrate. The electrode is formed by a first metal material and disposed on the pad. The protruding electrode is formed by a second metal material and disposed on the electrode, wherein a cross-sectional area of the protruding electrode is less than a cross-sectional area of the electrode.