Silver Alloy Bump Grain Control for Semiconductor Packaging
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Solution Overview
Problem
Current metal bump technologies in semiconductor packaging face issues with high material costs, inferior bonding reliability, and unsatisfactory electrical and thermal conductivity, particularly with gold bumps, which are prone to oxidation and corrosion, and form brittle intermetallic compounds that fail reliability tests.
Innovation Solution
The use of silver alloy bumps, either binary or ternary, with non-silver elements at specific atomic percentages, formed through electroplating, which provide superior electrical and thermal conductivity, reduce oxidation risks, and enhance bonding reliability by forming a uniform grain size distribution and avoiding issues like silver needle formation and migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gold bumps are used for flip-chip bonding, then bonding reliability is improved, but material cost increases and oxidation/corrosion resistance deteriorates
Solution Approach 1:
The patent employs a composite bump structure consisting of a copper core surrounded by a nickel barrier layer and a solder shell. This multi-layer composite design provides superior bonding reliability through strong metallurgical bonding while the nickel barrier layer prevents oxidation and corrosion of the copper core, eliminating the need for expensive gold materials.
Solution Approach 2:
The patent replaces expensive gold bumps with cost-effective copper-based composite bumps. The copper core provides excellent electrical and thermal conductivity at a fraction of the cost of gold, while the protective nickel and solder layers ensure adequate durability and bonding performance for the application lifecycle.
2Productivity
If metal bumps are used to reduce interposer size and pitch, then packaging density is improved, but manufacturing complexity increases
Solution Approach 1:
The patent forms the complex multi-layer bump structure (copper core, nickel barrier, solder shell) directly during the semiconductor fabrication process using electroplating and electroless plating techniques. This preliminary formation of the complete bump structure before chip assembly simplifies subsequent packaging operations and enables higher packaging density without increasing overall manufacturing complexity.
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
Silver alloy bumps offer significant cost savings, improved electrical conductivity, enhanced thermal conductivity, and superior bonding properties, reducing the risk of passivation cracks and improving the reliability of solder joints, thus addressing the limitations of gold bumps.
Implementation Method 1
formed through electroplating
Data Source
AI summary
A semiconductor structure includes a device, a conductive pad on the device, and a Ag1-xYx alloy bump over the conductive pad. The Y of the Ag1-xYx bump comprises metals forming complete solid solution with Ag at arbitrary weight percentage, and the X of the Ag1-xYx alloy bump is in a range of from about 0.005 to about 0.25. A difference between one standard deviation and a mean value of a grain size distribution of the Ag1-xYx alloy bump is in a range of from about 0.2 μm to about 0.4 μm. An average grain size of the Ag1-xYx alloy bump on a longitudinal cross sectional plane is in a range of from about 0.5 μm to about 1.5 μm.