Sloped Sidewall UBM Build-up for Solder Joint Reliability
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Solution Overview
Problem
The challenge is to minimize the under bump metallization (UBM) footprint while maintaining solder joint reliability, as large UBM pads can lead to voids and product defects, and consuming more area, which is counter to the goal of smaller feature sizes in semiconductor devices.
Innovation Solution
A method of forming a semiconductor device that includes a substrate with a first insulating layer, a conductive layer, and a UBM build-up structure with sloped sidewalls, which allows for a smaller footprint without compromising solder joint reliability by increasing the metal contact area and redistributing stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UBM pad size is increased to improve solder joint reliability through more metal contact area, then solder joint reliability is improved, but the UBM footprint increases and voids may form in the solder joint
Solution Approach 1:
The patent transitions from a two-dimensional flat UBM pad to a three-dimensional build-up structure with sloped sidewalls. This vertical dimensionality change increases the metal contact area between UBM and solder bump without expanding the horizontal footprint, directly resolving the contradiction between reliability and area consumption.
Solution Approach 2:
The build-up structure is confined within the footprint of the underlying UBM layer, creating a nested configuration where the extended metal structure is contained within the original boundary. This nesting approach allows increased contact area while maintaining compact footprint.
2Reliability
If the UBM pad size is increased to improve solder joint reliability, then metal contact area is increased, but voids develop in the solder joint causing product defects
Solution Approach 1:
By creating a three-dimensional build-up structure with controlled sloped sidewalls, the patent increases metal contact area vertically rather than horizontally. This dimensional change provides adequate contact area for reliability without creating the large flat surfaces that lead to void formation during soldering.
Solution Approach 2:
The patent modifies the geometric parameters of the UBM structure by introducing sloped sidewalls with specific angles and build-up heights. These parameter changes optimize the balance between contact area and void prevention, allowing reliable solder joints without the harmful voids associated with large flat pads.
3Productivity
If smaller die size is achieved through front-end process improvements, then device performance and efficiency are improved, but the UBM footprint consumes valuable area
Solution Approach 1:
The patent utilizes the vertical dimension to increase functional metal area while maintaining a compact horizontal footprint. This allows smaller die sizes to achieve adequate solder joint reliability without sacrificing area to large flat UBM pads, supporting continued device miniaturization.
Solution Approach 2:
The build-up structure concentrates the metal material where it is most needed - at the interface with the solder bump - creating a localized enhancement of contact area. This local quality improvement provides sufficient reliability for small devices without requiring proportionally large UBM footprints.
Data Source
AI summary
A semiconductor device has a first conductive layer formed over a substrate. A first insulating layer is formed over the first conductive layer. A second conductive layer is formed over first insulating layer and first conductive layer. A third insulating layer is formed over the second insulating layer and second conductive layer. An under bump metallization layer (UBM) is formed over the third insulating layer and second conductive layer. A UBM build-up structure is formed over the UBM. The UBM build-up structure has a sloped sidewall and is confined within a footprint of the UBM. The UBM build-up structure extends above the UBM to a height of 2-20 micrometers. The UBM build-up structure is formed in sections occupying less than an area of the UBM. A solder bump is formed over the UBM and UBM build-up structure. The sections of the UBM build-up structure provide exits for flux vapor escape.