Core Solder Bump Structure With Sn Coating Against Oxidation
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Solution Overview
Problem
Existing solder bumps for electronic components are prone to crushing and deformation under the weight of semiconductor packages, leading to short-circuits and appearance defects due to oxidation and discoloration, which affect bonding quality.
Innovation Solution
A core material comprising a Cu core with a Sn-based solder layer and a Sn layer, where the solder layer contains Ag, Cu, Sb, Ni, or other elements, and the Sn layer has a specific thickness ratio relative to the solder layer, preventing oxidation and discoloration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a solder plating layer with high Bi concentration on the inner circumferential side is used, then the solder begins to melt from the inner side first, but the pressure difference caused by volume expansion bursts the Cu core
Solution Approach 1:
The patent changes the concentration distribution parameter of Bi in the solder plating layer from a gradient (high on inner side, low on outer side) to a uniform distribution throughout the layer. This parameter change ensures simultaneous melting of the entire solder layer, preventing pressure differential and core bursting while maintaining controlled melting characteristics.
2Strength
If Ag and Cu content in the solder plating layer surface is increased, then the solder bump strength is improved, but the surface discolors to black and appearance quality deteriorates
Solution Approach 1:
The patent segments the solder plating layer into two distinct layers: a solder plating layer containing Ag and Cu for strength, and an outer Sn layer for appearance quality. This segmentation allows each layer to fulfill its specific function without compromising the other, resolving the contradiction between strength and appearance.
Solution Approach 2:
The patent creates a composite structure by combining the solder plating layer (Sn-Ag-Cu alloy) with an outer Sn layer. This composite material structure integrates the high strength properties of Ag-Cu-containing solder with the oxidation-resistant, appearance-friendly Sn surface layer.
3Manufacturing precision
If the Sn layer thickness is increased, then the appearance quality and oxidation resistance are improved, but the solder layer thickness for bonding is reduced
Solution Approach 1:
The patent optimizes the thickness parameters of both layers within specific ranges: Sn layer thickness of 0.05-5 μm and solder plating layer thickness of 1-20 μm. These parameter changes ensure sufficient Sn coverage for appearance and oxidation resistance while maintaining adequate solder volume for reliable bonding.
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 solution prevents solder bump deformation, reduces oxidation, and enhances bonding quality by maintaining appearance integrity and ensuring reliable connections.
Implementation Method 1
When a relatively large amount of Ag and Cu are contained in the surface of the solder plating layer, Ag and Cu are locally discolored to black... the solder plating layer easily reacts with a sulfur component of the plating liquid and oxygen in the air. As a result, oxidation easily proceeds
Implementation Method 2
forming a bump electrode by heating the mounted core material
Implementation Method 3
A solder layer provided outside the core... being a solder alloy containing Sn and at least any one element of Ag, Cu, Sb, Ni, Co, Ge, Ga, Fe, Al, In, Cd, Zn, Pb, Au, P, S, Si, Ti, Mg, Pd, and Pt
Data Source
Figure 1~2
AI summary
A core material has a core; a solder layer provided outside the core and being a solder alloy containing Sn and at least any one element of Ag, Cu, Sb, Ni, Co, Ge, Ga, Fe, Al, In, Cd, Zn, Pb, Au, P, S, Si, Ti, Mg, Pd, and Pt; and a Sn layer provided outside the solder layer. The solder layer has a thickness of 1 µm or more on one side. The Sn layer has a thickness of 0.1 pm or more on one side. A thickness of the Sn layer is 0.215% or more and 36% or less of the thickness of the solder layer.