Gradient Hardness Nickel Layer for Solder Diffusion Control
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Solution Overview
Problem
Existing semiconductor devices face challenges in restraining solder diffusion and stress while maintaining low costs, as thick anti-diffusion layers increase process complexity and costs, and thin layers fail to adequately prevent solder diffusion.
Innovation Solution
A semiconductor device with a nickel layer having distinct hardness regions, where the side facing the solder is harder than the side facing the foundation layer, formed using electroless plating with varying phosphorous concentrations to control hardness, and a thin layer structure to reduce stress and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick anti-diffusion layer (e.g., 70 μm Cu layer) is used to restrain solder diffusion, then solder diffusion prevention is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The nickel layer is designed with spatially varying hardness: the lower portion (near foundation layer) has lower hardness to reduce stress, while the upper portion (near solder) has higher hardness to prevent solder diffusion. This local differentiation allows a thin layer to perform both stress management and diffusion barrier functions that previously required a thick uniform layer.
Solution Approach 2:
The invention changes the hardness parameter of the nickel layer by controlling phosphorous concentration during electroless plating. By varying phosphorous concentration from lower to upper portions, the layer transitions from softer to harder, creating a gradient structure that simultaneously manages stress and prevents diffusion without requiring increased thickness.
2Reliability
If a thick anti-diffusion layer is used to prevent solder diffusion, then solder diffusion prevention is improved, but manufacturing cost increases
Solution Approach 1:
The nickel layer implements local quality variation with hardness increasing from lower to upper portions. This allows the thin layer to provide effective solder diffusion prevention at the upper region while maintaining stress reduction capability at the lower region, eliminating the need for costly thick uniform layers.
Solution Approach 2:
The invention creates a composite structure within the nickel layer itself by incorporating phosphorous at varying concentrations to produce regions of different hardness. This internal composite structure enables multiple functions (stress management and diffusion barrier) in a single thin layer, reducing overall manufacturing cost.
3Ease of manufacture
If a thin anti-diffusion layer is used to reduce stress and cost, then manufacturing cost and stress are reduced, but solder diffusion prevention deteriorates
Solution Approach 1:
The nickel layer compensates for its thin overall structure by implementing local quality variation: the upper portion has higher hardness specifically where solder diffusion prevention is needed, while the lower portion has lower hardness for stress management. This localized property differentiation enables effective diffusion prevention without requiring increased overall thickness.
Solution Approach 2:
The invention changes the hardness parameter within the thin nickel layer by controlling phosphorous concentration distribution. The phosphorous concentration increases from lower to upper portions, creating a hardness gradient that provides enhanced diffusion barrier capability at the solder interface while maintaining stress reduction throughout the layer.
4Ease of manufacture
If a uniform hardness nickel layer is used, then manufacturing process is simplified, but both stress management and solder diffusion prevention cannot be optimized simultaneously
Solution Approach 1:
The nickel layer employs local quality differentiation with hardness varying from lower to upper portions. This allows the single layer to simultaneously optimize for stress management (softer lower region) and solder diffusion prevention (harder upper region), achieving dual functionality that a uniform hardness layer cannot provide.
Solution Approach 2:
The invention implements parameter change within the nickel layer by varying phosphorous concentration from lower to upper portions, creating a hardness gradient. This continuous parameter variation enables the layer to adapt its properties spatially, providing both stress management and diffusion prevention capabilities that a uniform parameter layer cannot achieve.
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
Effectively restrains solder diffusion and stress, reducing the risk of electrical opens or shorts, while maintaining low manufacturing costs and improving reliability through a thin, efficient nickel layer structure.
Implementation Method 1
In order to restrain the diffusion of the solder, an anti-diffusion layer may be used
Implementation Method 2
formed using electroless plating with varying phosphorous concentrations to control hardness
Data Source
AI summary
A semiconductor device includes: a foundation layer that is provided on a substrate and is electrically conductive; a nickel layer provided on the foundation layer; and a solder provided on the nickel layer, the nickel layer having a first region on a side of the foundation layer and a second region on a side of the solder, the second region being harder than the first region.