Semiconductor Bump Pillar Structure for Solder Reliability
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Solution Overview
Problem
The miniaturization of semiconductor devices has led to increased failure rates of bump solder joints due to their smaller size, which affects the reliability and processing of three-dimensional integrated circuits (3D ICs) using through-Si-vias (TSV) technology, as the smaller diameter and volume of these joints increase the likelihood of failure.
Innovation Solution
The use of a pillar structure made of a metal with lower solderability than copper or a copper alloy, such as nickel-based materials, is implemented, with a height greater than 10 μm to inhibit solder flow and prevent void formation in solder bonds, along with an under bump metallization and a solder layer, to enhance the reliability of semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of bump solder joints is reduced to enable miniaturization of semiconductor devices, then the size of semiconductor devices decreases, but the reliability of bump solder joints deteriorates due to increased failure probability
Solution Approach 1:
A nickel-based pillar structure is introduced as an intermediary between the copper under bump metallization and the solder alloy. This pillar acts as a mediator that prevents direct interaction between copper and solder, thereby preventing copper-solder intermetallic compound formation and improving solder joint reliability in miniaturized devices.
Solution Approach 2:
The copper material is extracted from direct contact with the solder alloy by removing it from the solderable surface. The copper under bump metallization is separated from the solder interface by the nickel-based pillar, eliminating the harmful copper-solder interaction while maintaining electrical connectivity.
2Reliability
If copper or copper alloy is used for the pillar structure, then solderability is improved, but solder overflow and short circuits occur due to excessive solder flow down the pillar
Solution Approach 1:
Different materials with different properties are used at different locations of the bump structure. The nickel-based pillar has low solderability to prevent solder overflow, while the copper under bump metallization provides good solderability at the bonding interface. This local differentiation of material properties solves both problems simultaneously.
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 solution effectively reduces the likelihood of solder overflow and short circuits, improving the reliability and yield of semiconductor devices by inhibiting solder flow down the pillar and maintaining the solder within the joint area, thus addressing the challenges posed by the miniaturization of bump structures.
Implementation Method 1
a metal having a lower solderability (wettability) than copper or a copper alloy to a solder alloy
Data Source
AI summary
A semiconductor device includes a substrate and at least one bump structure disposed over the substrate. The at least one bump structure includes a pillar formed of a metal having a lower solderability than copper or a copper alloy to a solder alloy disposed over the substrate. A solder alloy is formed directly over and in contact with an upper surface of the metal having the lower solderability than copper or a copper alloy. The pillar has a height of greater than 10 μm.