Rectangular Solar Conductor Yield Strength Control
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Solution Overview
Problem
Existing solar battery lead wires face issues with warping and damage due to thermal expansion mismatch with silicon crystal wafers, leading to reduced power efficiency and increased manufacturing costs, particularly when using Cu-clad invar conductors which have high volume resistivity and are expensive.
Innovation Solution
A rectangular conductor with a volume resistivity of 50 μΩ·mm or less and a 0.2% yield strength value of 90 MPa or less, fabricated using materials like Cu, Al, or Ag, and treated to reduce yield strength, combined with a Sn—Ag—Cu based Pb-free solder plating for bonding, to minimize warping and maintain high electric conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If Cu-clad invar is used as the conductor to reduce thermal expansion mismatch, then warping of Si cell is reduced, but volume resistivity increases and electric conductivity decreases
Solution Approach 1:
The patent changes the material parameters by using pure copper or copper alloys instead of Cu-clad invar, and controls the yield strength through heat treatment to achieve optimal balance between thermal expansion compatibility and electrical conductivity. The conductor material is selected from Cu, Cu-Sn, Cu-Zn, Cu-Al, or Cu-Si alloys with specific compositional ranges to maintain low resistivity while achieving appropriate mechanical properties.
Solution Approach 2:
The patent employs composite structure by forming a solder plating film (Sn-Pb or Pb-free solder) on the copper conductor surface. This composite approach allows the copper core to provide excellent electrical conductivity while the solder plating layer provides appropriate thermal expansion characteristics and bonding capability to the Si cell.
2Stability of the object's composition
If Cu-clad invar is used as the conductor to match thermal expansion with Si, then warping is reduced, but manufacturing cost increases due to nickel content
Solution Approach 1:
The patent replaces expensive Cu-clad invar containing 36% nickel with cheaper pure copper or copper alloys. The copper conductor achieves the required performance without the high cost of nickel, making the solar battery more economically viable while maintaining adequate thermal expansion compatibility through the solder plating interface.
Solution Approach 2:
The patent changes the material composition parameters by eliminating nickel-containing invar and using copper-based materials with controlled alloying elements (Sn, Zn, Al, or Si at 0.01-10 mass%). This parameter change dramatically reduces material cost while maintaining the necessary functional properties through proper heat treatment and solder plating.
3Ease of manufacture
If silicon crystal wafer thickness is reduced to lower manufacturing cost, then material cost decreases, but warping and damage risk increases during solder bonding
Solution Approach 1:
The patent changes the mechanical property parameters of the conductor by controlling yield strength to 90 MPa or less through heat treatment. This parameter adjustment makes the conductor more compliant and less likely to cause warping or damage to thin Si cells during bonding, enabling the use of thinner, more cost-effective silicon wafers.
Solution Approach 2:
The patent applies local quality by providing solder plating film on specific regions of the conductor surface that contacts the Si cell. This localized soldering approach distributes thermal and mechanical stresses more evenly, reducing the risk of warping and damage to thin Si cells while maintaining bonding effectiveness.
4Strength
If conductor yield strength is high to maintain structural integrity, then mechanical strength is improved, but warping force on Si cell increases during thermal contraction
Solution Approach 1:
The patent optimizes the yield strength parameter to 90 MPa or less through heat treatment, achieving the right balance between mechanical strength and warping control. This parameter optimization allows the conductor to maintain sufficient structural integrity while being compliant enough to minimize warping forces on the Si cell during thermal contraction after solder 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 effectively reduces warping of silicon crystal wafers during bonding, maintains high electric conductivity, and lowers manufacturing costs by using a simpler heat treatment method, resulting in improved solar battery performance and reliability.
Implementation Method 1
a solder plating film formed on a surface of the rectangular conductor, and the solder plating film is used for bonding with the Si cell 51
Implementation Method 2
conducting a heat treatment for the rectangular conductor to have a 0.2% yield strength value equal to or less than 90 MPa in a tensile test
Data Source
AI summary
A rectangular conductor for a solar battery and a lead wire for a solar battery, in which warping or damaging of a silicon crystal wafer is hard to occur at the time of bonding a connection lead wire even when a silicon crystal wafer is configured to have a thin sheet structure, can be provided. A conductor 1 having a volume resistivity equal to or less than 50 μΩ·mm, and a 0.2% yield strength value equal to or less than 90 MPa in a tensile test is formed into a rectangular conductor 10 for a solar battery having a rectangular cross section, and a surface of the rectangular conductor 10 for a solar battery is coated with a solder plating film 13, to provide a lead wire 20 for a solar battery.