Lead-Free Solder Bump Bonding Structure Inhibiting Electromigration
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Solution Overview
Problem
Conventional lead-free solder bump bonding structures require a complex manufacturing process and increased costs due to the need for a Ni layer barrier to inhibit electromigration, especially at high current densities, which complicates the miniaturization of electronic components in high-density packaging.
Innovation Solution
A lead-free solder bump bonding structure that forms intermetallic compound layers with scallop shapes at the interface between Cu electrodes and the solder bump, without preforming a Ni layer, to inhibit Cu diffusion and electromigration, using a solder alloy with Sn as the primary component and additives like Ni, Co, and Fe to achieve a flattened IMC interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni layer is formed in advance on the Cu electrode surface to inhibit electromigration, then the reliability against electromigration is improved, but the device complexity and manufacturing burden increase
Solution Approach 1:
The patent applies preliminary action by forming the Ni layer in advance on the Cu electrode surface before mounting the semiconductor device. This pre-formed barrier layer prevents Cu diffusion during subsequent soldering and operation, eliminating the need for additional barrier layer formation steps after device assembly, thus reducing overall manufacturing complexity while maintaining reliability
Solution Approach 2:
The Ni layer serves as an intermediary barrier between the Cu electrode and the lead-free solder bump. This intermediate layer prevents direct contact and diffusion between Cu and solder materials, effectively blocking electromigration pathways without requiring complex multi-layer structures or post-assembly treatments
2Productivity
If the electrode pitch is reduced to 200 μm or less for high-density packaging, then the productivity and packaging density are improved, but the electromigration risk increases due to higher current density
Solution Approach 1:
The patent applies local quality by forming the Ni barrier layer specifically at the Cu electrode-solder bump interface where electromigration occurs most severely. This localized barrier provides targeted protection at the critical high-stress region without requiring overall structural changes, enabling high-density packaging while maintaining local reliability against electromigration
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 reduces manufacturing burdens by eliminating the need for a Ni layer and effectively inhibits electromigration, allowing for high current densities without disconnection failures, thereby enhancing the anti-electromigration characteristics and reducing manufacturing costs.
Implementation Method 1
the intermetallic compound layer has scallop (concavo-convex) shapes with a difference in height that is equal to or greater than 4 [μm] between a bottom portion of a layer thickness portion which is equal to or smaller than 30% of an average thickness of the intermetallic compound layer, and a peak portion adjacent to the bottom portion
Implementation Method 2
when a flowing current per a unit area (current density) increases, an electromigration of Cu at the lead-free solder bonded part (hereinafter, electromigration means the electromigration of Cu) occurs, resulting in a disconnection failure in some cases
Data Source
AI summary
According to a lead-free solder bump bonding structure, by causing the interface (IMC interface) of the intermetallic compound layer at a lead-free-solder-bump side to have scallop shapes of equal to or less than 0.02 [portions/μm] without forming in advance an Ni layer as a barrier layer on the surfaces of respective Cu electrodes of first and second electronic components like conventional technologies, a Cu diffusion can be inhibited, thereby inhibiting an occurrence of an electromigration. Hence, the burden at the time of manufacturing can be reduced by what corresponds to an omission of the formation process of the Ni layer as a barrier layer on the Cu electrode surfaces, and thus a lead-free solder bump bonding structure can be provided which reduces a burden at the time of manufacturing in comparison with conventional technologies and which can inhibit an occurrence of an electromigration.