Extended Under-Bump Metal Layer for Alpha Particle Shielding
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Solution Overview
Problem
Integrated circuits (ICs) using CMOS techniques are susceptible to single-event upsets (SEUs) due to alpha particles emitted from solder bumps or balls, which can cause data corruption, and existing methods to mitigate this issue, such as coating with alpha particle absorbing materials or depositing high-density metal layers, introduce additional manufacturing steps and costs.
Innovation Solution
An under-bump metal (UBM) pad is fabricated on an IC, extending beyond the contact perimeter of the solder bump to block alpha particles, with a thickness of at least 9 microns and a polygonal shape, and is electrically isolated from a UBM field to provide comprehensive alpha particle shielding, ensuring that over 99% of the IC die surface area is protected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional alpha particle absorbing materials or high-density metal layers are deposited on the IC, then alpha particle blocking capability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The under-bump metal pad is extended beyond the solder bump contact perimeter during the existing UBM fabrication process, before final assembly. This preliminary extension creates the alpha particle blocking barrier in advance, eliminating the need for additional post-assembly processing steps while maintaining effective shielding against alpha particles from the solder bump.
2Object-affected harmful factors
If the UBM pad is extended beyond the contact perimeter, then alpha particle blocking is improved, but the area occupied by the UBM pad increases
Solution Approach 1:
The UBM pad is extended only in specific directions beyond the contact perimeter, particularly towards areas where alpha particles would most likely affect sensitive circuit nodes. This localized extension provides targeted protection where needed most, rather than uniformly increasing the pad area in all directions, thus optimizing the balance between shielding effectiveness and area consumption.
3Object-affected harmful factors
If the UBM layer thickness is increased to block alpha particles, then radiation shielding is improved, but material usage and manufacturing complexity increase
Solution Approach 1:
Instead of increasing the thickness of the UBM layer, the solution extends the lateral dimensions of the UBM pad beyond the contact perimeter. This dimensional change from vertical thickening to horizontal extension achieves alpha particle blocking by increasing the path length that alpha particles must travel through the UBM material, thereby reducing the amount of material required while maintaining shielding effectiveness.
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 UBM pad effectively blocks alpha particles, reducing single-event upsets by ensuring that alpha particles are stopped before reaching the underlying semiconductor portion, thereby enhancing the reliability of ICs, especially in smaller node geometries where SEUs are more prevalent.
Implementation Method 1
The UBM pad extends extending beyond the contact perimeter a sufficient distance to block alpha particles emitted from the surface of the solder bump
Data Source
AI summary
An integrated circuit (IC) has an under-bump metal (UBM) pad disposed between a solder bump and a semiconductor portion of the IC. A UBM layer is disposed between the solder bump and the semiconductor portion and includes the UBM pad and a UBM field. The UBM pad has a contact perimeter formed with the solder bump. The UBM pad extends beyond the contact perimeter a sufficient distance to block alpha particles emitted from the surface of the solder bump from causing an upset event in the semiconductor portion. The UBM field is separated from each UBM pad by a gap extending from the UBM pad to the UBM field so as to electrically isolate the UBM field from the UBM pad.