Segmented Package Ring Structure for Molding Crack Reduction
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Solution Overview
Problem
Semiconductor packages, particularly 3DICs, face issues with warpage and cracking due to induced stress from thermal changes and mechanical flexing, primarily caused by rigid molding compounds used in packaging.
Innovation Solution
The package substrate's ring structure is divided into multiple components, with specific materials and dimensions to reduce flexibility and stress, using materials with low thermal expansion coefficients like 36% nickel-iron alloy for some pieces and stainless steel or copper for others, allowing controlled flexibility without warping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid molding compound is used for packaging semiconductor dies, then structural support and protection are improved, but cracking under induced stress increases leading to higher defect rates
Solution Approach 1:
The ring structure is divided into multiple discrete segments positioned around the semiconductor die. These segments are spaced apart to allow controlled movement and stress distribution, preventing crack propagation while maintaining structural support for the rigid molding compound.
Solution Approach 2:
The ring segments are formed with specific material properties including a coefficient of thermal expansion between 3-10 ppm/°C and controlled thickness (5-20 micrometers) to optimize their mechanical response. These parameter adjustments enable the ring structure to flex under stress while supporting the rigid molding compound.
2Stability of the object's composition
If the package substrate is made inflexible to control warpage, then warpage control is improved, but stress on the molding compound increases causing cracking
Solution Approach 1:
The ring structure is segmented into multiple discrete sections that can independently respond to thermal and mechanical stresses. This segmentation allows the substrate to maintain overall dimensional stability while local segments flex to accommodate stress, reducing transmission of stress to the molding compound.
Solution Approach 2:
Different regions of the package structure have different mechanical properties optimized for their specific functions. The ring segments have controlled flexibility and thermal expansion properties that differ from both the rigid molding compound and the substrate, creating a gradient that manages stress distribution while controlling warpage.
3Ease of manufacture
If a single-piece ring structure is used, then manufacturing simplicity is improved, but stress distribution is insufficient leading to molding compound cracking
Solution Approach 1:
The ring structure is divided into multiple segments that can be manufactured separately using standard fabrication processes and then assembled around the semiconductor die. This segmentation improves stress distribution while maintaining manufacturing feasibility through modular construction.
Solution Approach 2:
Multiple separately manufactured ring segments are combined to form a complete circular structure around the die. This merging of discrete components creates the desired stress-distributing geometry while allowing each segment to be optimized for manufacturing.
4Stress or pressure
If the ring structure has high thermal expansion, then thermal stress relief is improved, but warpage control deteriorates
Solution Approach 1:
The ring segments are formed with a specific coefficient of thermal expansion (3-10 ppm/°C) that is higher than the molding compound but controlled to prevent excessive warpage. This parameter optimization allows thermal stress relief while maintaining dimensional stability.
Solution Approach 2:
The ring structure has localized thermal expansion properties that differ from the substrate and molding compound. This creates a thermal expansion gradient that relieves stress at the die interface while the overall ring geometry maintains warpage control through its circular configuration.
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 molding compound stress by 1-10%, lowering defect rates and conserving raw materials, power, and processing resources by minimizing cracking and increasing yield.
Implementation Method 1
The first pieces may be formed of a material having a coefficient of linear thermal expansion (CTE) of no more than approximately 2.5 parts per million (ppm) per degree Celsius (°C.) (ppm/°C.)
Data Source
AI summary
A ring structure on a package substrate is divided into at least four different components, including a plurality of first pieces and a plurality of second pieces. By dividing the ring structure into at least four different components, the ring structure reduces flexibility of the package substrate, which thus reduces stress on a molding compound (e.g., in a range from approximately 1% to approximately 10%). As a result, molding cracking is reduced, which reduces defect rates and increases yield. Accordingly, raw materials, power, and processing resources are conserved that would otherwise be consumed with manufacturing additional packages when defect rates are higher.