Tin Conductive Layer for Post-Passivation Interconnect Adhesion
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Solution Overview
Problem
The interface between bumps and polymer layers in wafer level chip scale packaging (WLCSP) suffers from poor adhesion and moisture attack, leading to delamination issues in post-passivation interconnect (PPI) structures, which limits the reliability and performance of integrated circuits.
Innovation Solution
A conductive layer, typically made of tin or its alloys, is formed over the PPI structure to serve as an anti-oxidation and adhesion layer, preventing copper diffusion and oxidation, and enhancing the interface adhesion between the PPI structure and the polymer layer, thereby improving the bonding strength and reliability of the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polymer layer is formed over the PPI structure in WLCSP, then the package structure is completed and protected, but the interface between the bump and polymer layer suffers poor adhesion and moisture attack leading to delamination
Solution Approach 1:
A tin-based conductive layer is introduced as an intermediary between the copper PPI structure and the polymer layer. This intermediate layer prevents direct contact between moisture and the copper-polymer interface, eliminating the delamination problem while maintaining electrical conductivity and structural integrity.
Solution Approach 2:
The patent converts the harmful effect of moisture by introducing a moisture-resistant tin layer that transforms the vulnerable interface into a protected one. The tin layer acts as a barrier that converts the harmful moisture environment into a benign one by preventing moisture penetration to the copper interface.
2Reliability
If copper is used in the PPI structure, then electrical conductivity is achieved, but copper oxidation and diffusion occur causing reliability issues
Solution Approach 1:
The tin conductive layer serves as a protective intermediary between the copper PPI structure and the external environment. It prevents oxygen and moisture from reaching the copper, thereby eliminating oxidation and diffusion issues while maintaining the electrical conductivity function.
Solution Approach 2:
The patent creates a composite structure where tin and copper work together in a layered configuration. The tin layer provides oxidation resistance and moisture barrier properties, while the copper layer provides electrical conductivity, creating a composite material system with superior overall performance.
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 conductive layer effectively increases the reliability of the package by preventing copper oxidation and delamination, enhancing the adhesion between the PPI structure and the polymer layer, and reducing bump fatigue, thus improving the joint reliability and performance of the semiconductor device.
Implementation Method 1
preventing copper diffusion and oxidation
Implementation Method 2
enhancing the interface adhesion between the PPI structure and the polymer layer
Data Source
AI summary
A method includes coating a passivation layer overlying a semiconductor substrate and forming an interconnect layer overlying the passivation layer. The interconnect layer includes a line region and a landing pad region. The method further includes forming a metallic layer including tin on a surface of the interconnect layer using an immersion process, forming a protective layer on the metallic layer, and exposing a portion of the metallic layer on the landing pad region of the interconnect layer through the protective layer.