Paddle-less Stacked Die Assemblies with Offset Bond Pads
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Solution Overview
Problem
Conventional stacked die MCM configurations face challenges in accessing bond pads below the top die for wire bonding and suffer from thermal stress due to the significant difference in thermal expansion coefficients between the metal die paddle and semiconductor dice, leading to potential device failure and increased package height.
Innovation Solution
A semiconductor die assembly using a redistribution element with a substrate of semiconductor material or similar thermal expansion coefficient, eliminating the need for a die paddle, allows for lateral offsetting of dice to expose bond pads and reduces package height by using a paddle-less lead frame with tie bars for structural support and encapsulation symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a die paddle is used to provide alignment and support of the semiconductor die stack, then structural support is improved, but package height increases significantly and thermal stress problems occur
Solution Approach 1:
The patent removes the die paddle component entirely from the assembly. Instead of using a separate die paddle for support, the redistribution layer serves multiple functions including mechanical support and electrical redistribution, thereby eliminating the height contribution of the die paddle while maintaining structural integrity
Solution Approach 2:
The redistribution layer is designed to perform multiple functions: electrical signal redistribution between dice, mechanical support for the die stack, and thermal management. This multi-functionality eliminates the need for a separate die paddle, reducing overall package height while maintaining structural support
2Strength
If a die paddle is used to provide alignment and support, then structural support is improved, but thermal stress increases due to CTE mismatch
Solution Approach 1:
By removing the die paddle from the assembly, the source of thermal stress caused by CTE mismatch between metal paddle and silicon dice is eliminated. The redistribution layer provides necessary support without introducing thermal expansion compatibility issues
Solution Approach 2:
The patent changes the material parameters of the support structure by replacing metal die paddle materials with organic or ceramic materials that have CTE values matched to silicon, thereby reducing thermal stress while maintaining structural support functionality
3Device complexity
If dice are stacked directly on a die paddle, then assembly is simplified, but access to bond pads of lower dice becomes difficult
Solution Approach 1:
The patent implements lateral offsetting of dice in the stack, where each die is positioned at a different lateral position rather than directly on top of the previous die. This creates staggered access to bond pads while maintaining a compact vertical footprint, enabling wire bonding without requiring lateral displacement of the entire stack
4Ease of operation
If laterally smaller spacers are used between dice to allow access to bond pads, then bond pad accessibility is improved, but manufacturing precision requirements increase
Solution Approach 1:
The redistribution layer is formed with pre-defined opening patterns that anticipate and accommodate the lateral offsetting of dice. These openings are created during the redistribution layer formation process, allowing bond pads to be accessed without requiring high-precision alignment during subsequent die stacking operations
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 solution enables efficient wire bonding, reduces package height, increases die thickness for improved yield and handling, and minimizes thermal stress, allowing for more dice to be stacked without compromising mechanical or electrical integrity.
Implementation Method 1
temperature change can create significant thermal stress between the die paddle and the adjacent semiconductor die due to the significantly greater coefficient of thermal expansion (CTE) of the metal die paddle relative to the silicon material of the semiconductor dice
Data Source
AI summary
A stacked semiconductor die assembly includes at least two partially offset semiconductor dice with bond pads located adjacent at least one peripheral side thereof supported on a redistribution element formed of a material of substantially similar CTE to that of the dice, and a paddle-less lead frame secured to the redistribution element during fabrication, including encapsulation. The assembly is configured to be substantially vertically symmetrical with respect to inner ends of lead fingers of the lead frame to facilitate uniform encapsulant flow. The semiconductor die assembly may be configured in a package with leads extending from two sides thereof, such as a thin small outline package (TSOP), or four sides thereof, such as a quad flat pack (QFP).