QFN Mold Cavity Segmentation to Reduce Micro Voiding
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Solution Overview
Problem
MAP molded QFN semiconductor packages exhibit degraded solder joint and board level reliability due to higher levels of micro voiding in the mold compound during polymerization, leading to a wider variation in the coefficient of thermal expansion.
Innovation Solution
Implementing a mold compound injection port over the center point of the mold cavity and using a mold compound middle mold chase with ridges to minimize micro voiding, resulting in improved mechanical properties and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MAP molded QFN packaging applies mold compound to multiple microelectronic components simultaneously in one large common mold cavity, then productivity is improved, but manufacturing precision deteriorates due to higher levels of micro voiding and wider variation in coefficient of thermal expansion
Solution Approach 1:
The patent divides the single large common mold cavity into multiple separate individual mold cavities, each dedicated to one microelectronic component. This segmentation allows each component to be molded independently with its own injection port, eliminating the micro voiding issues that occur when multiple components share a single cavity. The segmentation maintains high productivity by still allowing simultaneous molding of multiple components while achieving the manufacturing precision needed for consistent coefficient of thermal expansion.
2Device complexity
If a single large common mold cavity is used for multiple components, then device complexity is reduced, but reliability deteriorates due to degraded solder joint and board level reliability
Solution Approach 1:
The mold assembly is segmented into multiple individual cavities, each providing dedicated molding for one component. This segmentation eliminates the harmful interactions between adjacent components during molding, preventing micro voiding that compromises solder joint reliability. While the structure becomes slightly more complex than a single cavity, the segmentation is achieved through a systematic array layout that maintains manufacturing efficiency.
3Ease of manufacture
If mold compound is injected into a large common cavity, then ease of manufacture is improved, but manufacturing precision deteriorates due to micro voiding during polymerization
Solution Approach 1:
The injection molding process is segmented into multiple independent injection ports, each serving one mold cavity. This allows the mold compound to be injected directly into each small cavity rather than filling a large common cavity, which prevents micro voiding during polymerization. Each injection port enables precise control of filling parameters for its dedicated cavity, achieving high manufacturing precision while maintaining ease of manufacture through automated molding.
4Manufacturing precision
If individual mold cavities with separate injection ports are used for each component, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Multiple individual mold cavities are merged into a single integrated mold assembly that functions as one cohesive unit. The separate injection ports and cavities are combined in an array configuration, allowing simultaneous molding of multiple components in one operation. This merging approach achieves the manufacturing precision of individual cavities while avoiding the complexity of multiple separate molds, as the entire array is molded in a single cycle.
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
The solution reduces micro voiding, leading to a lower coefficient of thermal expansion and enhanced solder joint and board level reliability.
Implementation Method 1
higher levels of micro voiding in the mold compound during polymerization of the mold compound during a mold compound curing process
Data Source
AI summary
A semiconductor package may have a microelectronic component electrically coupled to a plurality of leads which extend to a perimeter of the semiconductor package. A mold compound, which is electrically insulating, contacts the plurality of leads and the microelectronic component. Mold Array Process (MAP) molded Quad Flat No-Lead (QFN) packaging may apply mold compound to multiple microelectronic components simultaneously. After molding, the packages are cured and singulated. A mold compound middle mold chase with a mold cavity for each package and a mold compound injection port associated with each semiconductor package to distribute the mold compound may decreases micro voiding of the mold compound, raise the coefficient of thermal expansion, and improve board level reliability. Semiconductor packages formed with a mold compound injection port corresponding to each package may have a gate cull on the exterior of the semiconductor package where the mold compound enters the mold cavity.