Cu Core Ball Solder Joint Heat Cycle Resistance
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Solution Overview
Problem
Solder bumps used in high-density semiconductor packaging face challenges in maintaining strength against impacts and heat cycles, particularly when using Cu core balls, which often result in short circuits due to weight collapse and reduced strength against heat cycles compared to Ag-containing solder alloys.
Innovation Solution
A Cu core ball with a Cu ball covered by an Ag-free solder alloy, specifically a Sn-Cu alloy with a diffusion prevention layer, is developed to enhance dropping strength and heat cycle resistance, while minimizing radioactive impurities and ensuring high sphericity to prevent software errors and improve mounting uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Ag-free solder alloy is used to reduce cost, then manufacturing cost is reduced, but dropping strength and heat cycle resistance deteriorate
Solution Approach 1:
The invention uses a composite structure with a Cu core and Sn-Cu solder alloy shell. The Cu core provides high strength and heat cycle resistance, while the Sn-Cu solder alloy shell provides soldering functionality. This composite material approach achieves both cost reduction (by eliminating Ag) and maintained reliability (through the strong Cu core).
Solution Approach 2:
The invention changes the compositional parameters of the solder alloy by limiting Cu content to 0.1-3.0% in the Sn-Cu alloy shell. This parameter optimization ensures the solder layer maintains adequate strength and soldering properties while the Cu core provides the necessary mechanical support, achieving both cost efficiency and reliability.
2Quantity of substance
If Cu core ball with Sn-Cu solder alloy is used instead of Ag-containing solder, then Ag content is reduced to 0.1-3.0% Cu, but dropping strength and heat cycle resistance may deteriorate
Solution Approach 1:
The invention creates a composite material system where the Cu core (providing strength) is combined with a Sn-Cu solder alloy shell (providing soldering properties). This composite structure replaces Ag-containing solder while maintaining or improving dropping strength and heat cycle resistance through the synergistic combination of materials.
Solution Approach 2:
The invention applies local quality by having different material compositions in different regions: the Cu core provides high strength and heat cycle resistance, while the Sn-Cu solder alloy shell (with 0.1-3.0% Cu) provides soldering functionality. Each region is optimized for its specific function, achieving overall reliability without Ag.
3Reliability
If solder layer with higher Cu content is used, then heat cycle resistance is improved, but manufacturing cost increases
Solution Approach 1:
The invention optimizes the Cu content parameter in the Sn-Cu solder alloy shell to the range of 0.1-3.0%. This parameter optimization achieves adequate heat cycle resistance while controlling manufacturing cost, avoiding the need for higher Cu content that would increase cost without providing proportional benefits.
Solution Approach 2:
The composite structure allows the Sn-Cu solder alloy shell to have lower Cu content (0.1-3.0%) while the Cu core provides the necessary heat cycle resistance. This material distribution optimizes cost by placing Cu only where it provides maximum benefit, rather than requiring high Cu content throughout the entire solder bump.
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 Cu core ball achieves desired levels of dropping strength and heat cycle resistance, preventing weight-induced collapse and software errors, and maintains high sphericity for uniform solder bumps, thus supporting high-density packaging without the drawbacks of Ag-containing alloys.
Implementation Method 1
a Cu core ball in which a Cu ball is covered by an Ag-free solder alloy... a Sn-Cu alloy with a diffusion prevention layer
Implementation Method 2
the semiconductor package can be supported by the Cu ball which is not molded at the melting point of the solder even if the weight of the semiconductor packages is applied to the solder bumps
Implementation Method 3
a solder paste using the Cu core ball, a formed solder using the Cu core ball, and a solder joint using the Cu core ball
Data Source
AI summary
Provided are a Cu core ball and a cu core column, which achieve dropping strength and strength against heat cycle. The Cu core ball (1) contains a Cu ball (2) made of Cu or a Cu alloy and a solder layer (3) which is made of a solder alloy composed of Sn and Cu and covers the Cu ball (2). The solder layer (3) contains not less than 0.1% through not more than 3.0% of Cu and the remainder is composed of Sn and impurities.