InFO Package Recess Structure for Flat RDL Photolithography
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Solution Overview
Problem
As semiconductor dies become smaller and more functional, conventional packaging technologies face challenges in increasing I/O pad density, leading to difficulties in packaging yield due to limited pad pitch and solder bridge issues in fan-in packages, and the need for redistributing I/O pads in fan-out packages.
Innovation Solution
The development of an Integrated Fan-Out (InFO) package structure with recesses in molding compound, where redistribution lines are formed over molded device dies, allowing for increased I/O pad density by redistributing pads to a larger area, and recessing the molding compound between closely located dies to eliminate humps that interfere with subsequent photolithography processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fan-in package technology is used to package smaller dies, then throughput is improved and cost is reduced, but the number of I/O pads is limited due to limited die area and pad pitch
Solution Approach 1:
The patent transitions from fan-in to fan-out packaging, effectively changing the spatial dimension of I/O pad arrangement. Instead of confining pads to the die surface area, the redistribution layer extends the pad layout to a larger planar area, increasing the number of pads that can be accommodated without reducing pad pitch.
Solution Approach 2:
The patent introduces a redistribution layer that segments the I/O pad function from the die substrate. The pads are separated into two functional groups: bonding pads on the die surface for electrical connection, and I/O pads on the redistribution layer for external connection, allowing independent optimization of each.
2Quantity of substance
If pad pitch is decreased to increase I/O pad density, then more pads can be packed, but solder bridges may occur
Solution Approach 1:
By moving the I/O pads to the redistribution layer plane rather than the die surface, the patent creates additional spatial separation between adjacent pads. This dimensional transition allows maintaining larger pad pitch while increasing overall pad count through expanded layout area.
3Quantity of substance
If fan-out packages are used to increase I/O pad density, then pads can be redistributed to greater area, but humps in molding compound interfere with subsequent photolithography processes
Solution Approach 1:
The patent performs preliminary planarization by recessing the molding compound between dies before applying the redistribution layer. This advance action eliminates the hump formation that would otherwise interfere with subsequent photolithography processes, ensuring a flat surface for precise pattern alignment.
Solution Approach 2:
The patent removes the problematic hump structures by recessing the molding compound in the inter-die regions. This extraction of the harmful geometric feature eliminates the interference with photolithography while preserving the fan-out packaging benefits.
4Adaptability or versatility
If more functions are integrated into smaller semiconductor dies, then device functionality is improved, but packaging becomes more difficult and yield decreases
Solution Approach 1:
The patent segments the packaging structure into distinct functional layers: the die substrate containing integrated circuits, the molding compound for protection, and the redistribution layer for I/O connections. This segmentation allows each layer to be optimized independently, accommodating higher device functionality without compromising packaging yield.
Solution Approach 2:
By transitioning to fan-out packaging with redistribution layers, the patent expands the connection interface area beyond the die boundaries. This dimensional expansion provides sufficient space for high-density I/O connections required by multi-functional dies, maintaining packaging yield despite increased device complexity.
Data Source
AI summary
A package includes a first die and a second die. The first die includes a first substrate and a first metal pad overlying the first substrate. The second die includes a second substrate and a second metal pad overlying the second substrate. A molding compound molds the first die and the second die therein. The molding compound has a first portion between the first die and the second die, and a second portion, which may form a ring encircles the first portion. The first portion and the second portion are on opposite sides of the first die. The first portion has a first top surface. The second portion has a second top surface higher than the first top surface.