Copper Pillar Nickel Cap Etching for Crack Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solder bump and copper pillar manufacturing processes face issues such as stress-induced cracks in low dielectric constant layers and interfaces, leading to reliability concerns due to high leakage currents and structural weaknesses.
Innovation Solution
A method involving the formation of a copper pillar with a nickel cap layer and a carefully controlled etching process to achieve a specific width ratio, reducing stress and improving the interface shape between the copper pillar and the nickel cap layer, along with the use of a buffer layer to absorb stress, and an underfill to enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional solder bump manufacturing process is used, then solder bump can be formed, but undercut of UBM layer occurs inducing stress and cracks in low-K dielectric layers
Solution Approach 1:
A buffer layer is deposited over the UBM layer before forming the solder bump. This buffer layer is preliminarily prepared to prevent lateral etching of the UBM layer during the etching process, thereby preventing undercut formation and subsequent stress-induced cracks in the low-K dielectric layers.
Solution Approach 2:
The buffer layer acts as an intermediary between the UBM layer and the etching process. It protects the UBM layer from direct exposure to the etchant, preventing lateral etching and undercut formation while allowing the etching process to proceed for forming the solder bump.
2Manufacturing precision
If copper pillar manufacturing process is used, then finer pitch is achieved, but stress causes cracks at interface of copper pillar and solder
Solution Approach 1:
A nickel cap layer is deposited over the copper pillar before bonding the electronic component. This nickel cap layer is preliminarily prepared to reduce stress at the interface between the copper pillar and the solder, preventing stress-induced cracks and improving interface integrity.
Solution Approach 2:
The nickel cap layer changes the mechanical properties at the copper pillar-solder interface. It has different mechanical properties compared to copper, which helps to reduce stress concentration and prevent crack formation at the interface during the bonding process.
3Ease of manufacture
If conventional etching process is used, then solder bump is formed, but undercut of UBM layer induces stress causing cracks in low-K dielectric layers
Solution Approach 1:
A buffer layer is deposited over the UBM layer before the etching process. This buffer layer is preliminarily prepared to protect the UBM layer from lateral etching, preventing undercut formation and subsequent stress-induced cracks in the low-K dielectric layers during the etching process.
Solution Approach 2:
The buffer layer serves as an intermediary protective layer between the UBM layer and the etchant. It allows the etching process to proceed for bump formation while preventing harmful lateral etching of the UBM layer, thereby maintaining structural integrity.
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 method effectively reduces stress-induced cracks and improves the reliability of the semiconductor package by maintaining a smooth interface and distributing heat uniformly, thereby enhancing the robustness of the conductive pillar structure.
Implementation Method 1
a nickel cap layer is formed over a copper pillar
Implementation Method 2
the use of a buffer layer to absorb stress
Implementation Method 3
distributing heat uniformly
Data Source
AI summary
An embodiment of the disclosure includes a conductive bump on a semiconductor die. A substrate is provided. A bond pad is over the substrate. An under bump metallurgy (UBM) layer is over the bond pad. A copper pillar is over the UBM layer. The copper pillar has a top surface with a first width and sidewalls with a concave shape. A nickel layer having a top surface and a bottom surface is over the top surface of the copper pillar. The bottom surface of the nickel layer has a second width. A ratio of the second width to the first width is between about 0.93 to about 1.07. A solder material is over the top surface of the cap layer.