Transfer-Molded Solder Bumps for Accessible Flip-Chip Qubit Packaging
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Solution Overview
Problem
The integration of qubits into semiconductor packages other than wire-bonded packaging is hindered by the inability to access the Josephson junction after package fabrication, preventing adjustments to the design frequency and thermal or chemical processes.
Innovation Solution
A method involving a transfer mold with a solder pillar is used to form metallic bonds between the solder pillar and a wettable pad on a substrate, allowing for thermal isolation and access to the Josephson junction through holes in the substrate, enabling adjustments to the qubit design frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If qubits are integrated into semiconductor packages using traditional wire-bonded packaging, then the Josephson junction remains accessible for adjustments, but the package structure limits integration versatility and thermal isolation
Solution Approach 1:
The patent divides the package structure into distinct segments: the substrate with through-holes, the qubit device, and the solder bumps. The through-holes are strategically positioned to provide access paths to the Josephson junction while maintaining the integrity of the integrated package structure. This segmentation allows the Josephson junction to remain accessible for frequency adjustments and thermal/chemical processes while enabling integration into non-wire-bonded packages.
2Adaptability or versatility
If through-holes are added to the substrate to access the Josephson junction, then frequency adjustments become possible, but the substrate structure becomes more complex
Solution Approach 1:
The through-holes in the substrate serve multiple functions simultaneously: they provide mechanical support for the solder bumps during the flip-chip bonding process, and they create access paths for frequency adjustments and thermal/chemical processes to reach the Josephson junction. This multi-functionality reduces the need for additional separate structures, thereby limiting the increase in substrate complexity while enabling frequency adjustment capability.
3Temperature
If solder bumps are used for flip-chip bonding, then thermal isolation is improved, but the bonding process becomes more difficult compared to wire-bonding
Solution Approach 1:
The solder bumps are pre-formed on the substrate with precisely controlled dimensions, shapes, and positions before the flip-chip bonding process. The transfer mold is used to create these solder bumps with high precision, ensuring proper alignment and thermal isolation characteristics. This preliminary preparation simplifies the subsequent bonding process by eliminating the need for complex real-time alignment and bonding parameter adjustments, thereby reducing bonding process difficulty while maintaining thermal isolation benefits.
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 allows for the incorporation of qubits into flip-chip packages, providing thermal isolation and enabling adjustments to the qubit design frequency, overcoming the limitations of traditional packaging methods.
Implementation Method 1
forming a metallic bond between the solder pillar and the wettable pad
Data Source
AI summary
In an embodiment, a method for forming a solder bump includes preparing a transfer mold having a solder pillar extending from a mold substrate and through a first photoresist layer and having a shape partially defined by a second photoresist layer that is removed prior to transfer of the solder. In an embodiment, the mold substrate is flexible. In an embodiment, the transfer mold is flexible. In an embodiment, the method includes providing a device substrate having a wettable pad. In an embodiment, the method includes placing the transfer mold and the device substrate into aligned contact such that the solder pillar is in contact with the wettable pad. In an embodiment, the method includes forming a metallic bond between the solder pillar and the wettable pad. In an embodiment, the method includes removing the mold substrate and first photoresist layer.