Semiconductor Redistribution Layer Nickel Barrier
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Solution Overview
Problem
Conventional wafer-level chip size packages (WLCSPs) face issues with copper redistribution layers oxidizing during high-temperature processes, leading to reduced contact power and mechanical stress absorption, which affects board-level reliability and solder bonding due to their monotonous structure.
Innovation Solution
A semiconductor device with a redistribution layer comprising a copper plated layer and a nickel plated layer, where the nickel layer provides malleability and ductility to absorb external shocks, prevent cracking, and acts as a barrier to prevent copper from reacting with solder balls, while a dielectric layer covers the redistribution layer to prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monotonous copper plated layer is used for redistribution layer, then electrical characteristics are excellent, but mechanical stress absorption is poor and cracking occurs
Solution Approach 1:
The patent applies composite materials by combining copper and nickel plated layers to form a redistribution layer. The copper layer provides excellent electrical characteristics while the nickel layer contributes superior mechanical properties including stress absorption and crack resistance. This composite structure resolves the contradiction by integrating materials with complementary properties, allowing the redistribution layer to simultaneously achieve good electrical performance and mechanical strength.
2Reliability
If copper plated layer is exposed during high temperature process, then electrical conductivity is maintained, but oxidation occurs reducing contact power
Solution Approach 1:
The nickel plated layer serves as an intermediary between the copper layer and the external environment. It forms a protective barrier that prevents oxygen from reaching and oxidizing the copper layer during high temperature processes. This intermediary layer allows the copper to maintain its excellent electrical conductivity without being exposed to harmful oxidative conditions, thus resolving the contradiction between maintaining electrical conductivity and preventing oxidation.
3Reliability
If solder ball is directly bonded to copper redistribution layer, then electrical connection is achieved, but mechanical stress causes cracking and reliability drops
Solution Approach 1:
The patent uses composite materials by forming a nickel plated layer over the copper plated layer before bonding the solder ball. The nickel layer acts as a buffer that absorbs mechanical stress from the solder ball, preventing stress concentration that would cause cracking in the copper layer. This composite structure enables reliable solder bonding while maintaining crack resistance, resolving the contradiction between achieving electrical connection and ensuring mechanical strength.
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 nickel plated layer enhances the reliability and hardness of the semiconductor device by preventing cracking and oxidation, improving the absorption of mechanical stress and maintaining contact power, thereby increasing board-level reliability and solder bonding strength.
Implementation Method 1
Since the nickel plated layer has excellent malleability and ductility, the nickel plated layer prevents cracking of the first copper plated layer from stress applied to the solder ball
Implementation Method 2
the nickel plated layer provides a barrier layer for preventing the first copper plated layer from reacting with the solder ball
Implementation Method 3
since copper (Cu) easily responds to oxygen in the atmosphere as is widely well known, its surface is easily oxidized during a high temperature hardening process
Data Source
AI summary
A semiconductor device and method of manufacturing the same are provided. The semiconductor device comprises a semiconductor die including a bond pad, a redistribution layer, and a solder ball. The redistribution layer is formed by sequentially plating copper and nickel, sequentially plating nickel and copper, or sequentially plating copper, nickel, and copper. The redistribution layer includes a nickel layer in order to prevent a crack from occurring in a copper layer. Further, a projection is formed in an area of the redistribution layer or a dielectric layer to which the solder ball is welded and corresponds, so that an area of the redistribution layer to which the solder ball is welded increases, thereby increasing bonding power between the solder ball and the redistribution layer.