UBM Metal Pad Sidewall Insulation Against Indium Diffusion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current electronic chip assembly methods using Under Bump Metallization (UBM) face challenges with indium diffusion into gold layers, leading to chip degradation due to the formation of gold-indium intermetallic alloys, especially when soldering materials come into contact with the sidewalls of the metal pads, which can compromise the mechanical integrity of the chip.
Innovation Solution
Incorporating an electrically insulating barrier layer made of zinc sulphide or silicon dioxide on the sidewalls of the metal pad, in contact with the conductive barrier layer, to prevent contact between the soldering material and the gold layers, thereby blocking indium diffusion and maintaining chip integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrically insulating barrier layer is added on the sidewalls of the metal pad to prevent indium diffusion, then chip reliability is improved, but device complexity increases
Solution Approach 1:
An electrically insulating barrier layer is introduced as an intermediary substance between the soldering material (indium) and the gold layers. This insulating layer acts as a mediator that prevents direct contact and diffusion between indium and gold, thereby protecting the chip structure while allowing the soldering material to be deposited on the metal pad surface.
Solution Approach 2:
The protection mechanism transitions from a two-dimensional surface coating to a three-dimensional structure by adding vertical sidewall coverage. The insulating barrier layer is deposited on the sidewalls of the metal pad, creating a protective envelope that extends into the vertical dimension and prevents indium from reaching the gold layers through lateral diffusion paths.
2Productivity
If a single photolithography step is used for manufacturing, then manufacturing cost and time are reduced, but manufacturing precision may be compromised
Solution Approach 1:
Multiple manufacturing operations are merged into a single photolithography step. The process combines the definition of the metal pad pattern and the formation of the insulating barrier layer structure in one alignment cycle, eliminating the need for separate photolithography steps and intermediate processing stages.
Solution Approach 2:
The single photolithography step performs multiple functions simultaneously: it defines the metal pad geometry, determines the coverage area for the insulating barrier layer, and ensures proper alignment all in one operation. This multi-functional approach replaces what would traditionally require multiple specialized steps.
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 insulating barrier layer effectively prevents indium from reacting with the gold layers, reducing the risk of chip degradation and allowing for a single photolithography step in manufacturing, eliminating the need for precise double alignment and reducing costs.
Implementation Method 1
an electrically insulating barrier layer is disposed on, and in contact with, the sidewall of the first metal layer over the entire periphery of the metal pad... to prevent contact between the soldering material and the gold layers, thereby blocking indium diffusion
Data Source
AI summary
An electronic chip including a substrate and, on the side of one face of the substrate, a metal pad intended to receive a soldering material, the pad including, in order from said face of the substrate, a first metal layer, an electrically conductive barrier layer, and a second metal layer, wherein an electrically insulating barrier layer is arranged on, and in contact with, the sidewall of the first metal layer over the entire periphery of the metal pad.