Folded Flexible PCB Die Package With Exposed Signal Test Pads
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Solution Overview
Problem
Existing die packaging methods face challenges with large package sizes, high costs, and the inability to provide signal test points for high-speed signals due to limited interconnection space and the need for additional metal layers or dummy die layers.
Innovation Solution
A die package structure and method using a flexible printed circuit board that can be folded to align and solder pads on multiple dies, allowing for signal test points and reducing package volume and cost by eliminating the need for additional metal layers or dummy die layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple dies are placed horizontally in a package structure with metal wires for interconnection, then electrical signals can be interconnected between dies, but the package size becomes large and wire crossing increases the risk of errors
Solution Approach 1:
The patent transitions from horizontal placement to vertical stacking of dies, utilizing the third dimension (height) to arrange multiple dies. This stacking approach reduces the planar area occupied by the package while maintaining interconnection capabilities through vertically arranged test pads and bonding wires.
Solution Approach 2:
The patent introduces an intermediary structure (the test pad arrangement on die surfaces) that enables signal extraction and testing without requiring additional metal wiring layers. This intermediary approach allows high-speed signal testing while avoiding the complexity of metal layer routing and wire crossing.
2Ease of manufacture
If a metal layer is added on one of the dies to avoid wire crossing, then wire layouts can be arranged to change pad positions and sequences, but the package size increases and cost increases
Solution Approach 1:
The patent extracts the signaling and testing functions from the metal wiring layer and relocates them to dedicated test pads on the die surfaces. This extraction eliminates the need for additional metal layers while maintaining the ability to access and test signals, thereby reducing package area and manufacturing complexity.
3Area of stationary object
If dies are stacked with each other, then package size is reduced, but additional dummy die layers are needed to fill vacant spaces
Solution Approach 1:
The patent makes the test pads serve multiple functions: they act as both interconnection points for signal transmission between stacked dies and as accessible test points for signal measurement. This multi-functionality eliminates the need for separate dummy die layers while maintaining structural integrity and reducing overall package complexity.
4Adaptability or versatility
If additional metal layers are added on dies for interconnection, then pad position and sequence changes are enabled, but the cost increases
Solution Approach 1:
The patent replaces expensive additional metal layers with simpler, lower-cost test pad structures directly formed on the die surfaces. This substitution achieves the same pad layout adaptability function at reduced material cost and 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
The solution provides signal test points on electrical paths between dies, reduces package volume, and lowers costs by utilizing a flexible printed circuit board that can be folded to align pads, enabling efficient interconnection without the need for additional metal layers or dummy die layers.
Implementation Method 1
soldering the plurality of first hollow pads to the plurality of first pads, respectively; soldering the plurality of second hollow pads to the plurality of second pads, respectively
Data Source
AI summary
A die package structure and a method for fabricating the same are provided. The method includes: fixing a first die on a package base; aligning first hollow pads of a flexible printed circuit board with first pads of the first die, and fixing the flexible printed circuit board; soldering the first hollow pads to the first pads; fixing a second die on the flexible printed circuit board to overlap with the first die; folding the flexible printed circuit board, such that second hollow pads of the flexible printed circuit board are aligned with second pads of the second die, and signal test pads of the flexible printed circuit board are exposed; fixing the flexible printed circuit board on the second die; soldering the second hollow pads to the second pads; soldering metal wires to the signal test soldering pads; and soldering package pins to the metal wires.