Variable Width Solder Bumps for Stress Distribution
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Solution Overview
Problem
The semiconductor packaging industry faces challenges with stress generation and cracking in solder bumps due to thermal cycling, particularly at corner regions of semiconductor dies, which reduces yield and is exacerbated by the need for wider bumps that occupy more space.
Innovation Solution
The solution involves forming wider solder bumps only over high-stress regions and using a combination of under bump metallurgy (UBM) structures with varying widths and heights to distribute stress, along with adjusting solder paste thickness to ensure proper bonding and alignment, thereby reducing stress and cracking risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If wider solder bumps are used to reduce stress, then stress distribution improves, but the area occupied by solder bumps increases
Solution Approach 1:
The patent applies different bump widths at different locations on the semiconductor die. Specifically, corner regions (high-stress areas) have wider solder bumps to reduce stress concentration, while center regions have narrower bumps. This local differentiation optimizes stress distribution without unnecessarily increasing the total area occupied by all bumps.
Solution Approach 2:
The solder bump array is segmented into different regions with different characteristics. The die is divided into corner regions and center regions, each with appropriately sized bumps. This segmentation allows the system to address stress issues locally without affecting the entire bump array uniformly.
2Strength
If solder bump size is increased to improve bonding strength, then bonding reliability improves, but the number of bumps that can be placed in a given area decreases
Solution Approach 1:
The patent implements local quality by making corner bumps wider than center bumps. The corner bumps, being in high-stress regions, require greater width for adequate bonding strength and stress distribution. The center bumps can be narrower since they experience less stress, thereby maximizing the number of bumps that can be placed in the available area.
3Ease of manufacture
If uniform bump widths are used across the die, then manufacturing simplicity is maintained, but stress concentration at corners increases
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through non-uniform bump widths. Corner bumps are made wider to specifically address the high-stress conditions at corner regions, while center bumps maintain smaller widths. This approach prioritizes reliability in critical areas while accepting increased 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
This approach effectively reduces stress and cracking in solder bumps, improving the yield of package structures by maintaining desired shapes and configurations while maintaining the same distance between the substrate and semiconductor die, thus enhancing the reliability of the package.
Implementation Method 1
reflowing the first bump structure and the second bump structure with the first solder paste structure and the second solder paste structure, respectively, to bond the semiconductor die to the substrate
Data Source
AI summary
Structures and formation methods of a package structure are provided. The package structure includes a semiconductor die and a substrate bonded to the semiconductor die through a first bonding structure and a second bonding structure therebetween. The first bonding structure and the second bonding structure are next to each other and the second bonding structure is wider than the first bonding structure. The first bonding structure has a first under bump metallurgy (UBM) structure and a first solder bump thereon, and the second bonding structure has a second UBM structure and a second solder bump thereon. The second UBM structure has a maximum width larger than that of the first UBM structure, and the second solder bump has a maximum width larger than that of the first solder bump.