Photovoltaic Cell Solder Strip Welding With Thin Solder Layers
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Solution Overview
Problem
The existing welding methods for photovoltaic cells result in small contact areas between solder strips and electrode pads, leading to low welding tension, increased risk of tin sweating, and reduced reliability due to thick fluxing layers and high temperatures.
Innovation Solution
A method involving the application of a thin first solder layer on the substrate, followed by lapping the solder strip onto this layer to enhance contact area and tension, using a combination of first and second solder layers with specific thickness and wetting angle ratios to improve weldability and reduce the thickness of the solder strip, thereby reducing production costs and increasing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a thick fluxing layer (15 μm - 20 μm) is used on the solder strip, then the solder strip can cover the electrode pad, but the actual contact area between the fluxing layer and the electrode pad remains small, resulting in low welding tension and increased risk of tin sweating
Solution Approach 1:
The solder strip structure is segmented into three distinct layers: a base layer, a fluxing layer (3-8 μm), and a solder metal layer. This segmentation allows each layer to perform its specific function optimally, with the solder metal layer providing direct contact with the electrode pad to ensure high welding tension, while the fluxing layer provides necessary fluxing action without excessive thickness that would reduce contact area.
Solution Approach 2:
The thickness of the fluxing layer is changed from the conventional 15-20 μm to 3-8 μm, and the solder metal layer thickness is controlled at 2-5 μm. These parameter changes optimize the contact area between the solder strip and electrode pad, improving welding tension while preventing tin sweating defects.
2Quantity of substance
If the fluxing layer is thick, then it can provide sufficient fluxing coverage, but large tin sweats are easily formed after heating, affecting product reliability
Solution Approach 1:
The fluxing layer thickness is reduced from 15-20 μm to 3-8 μm, which provides sufficient fluxing coverage while preventing excessive molten solder formation that causes tin sweating. The solder metal layer (2-5 μm) is specifically designed to control molten solder volume and reduce surface tension, further preventing tin sweating defects.
Solution Approach 2:
The solder strip uses a composite structure with a base layer, fluxing layer, and solder metal layer. This composite material design allows the fluxing layer to be thin yet effective, while the solder metal layer provides controlled molten solder behavior that prevents tin sweating during welding.
3Quantity of substance
If conventional welding methods are used with thick fluxing layers, then the solder strip can be applied, but the contact area with the electrode pad is small, requiring higher welding temperatures and longer welding times
Solution Approach 1:
The fluxing layer thickness is reduced to 3-8 μm and solder metal layer thickness is 2-5 μm, creating a thinner overall solder strip structure that achieves better contact with the electrode pad. This allows welding to be completed at lower temperatures and shorter times, improving production efficiency.
Solution Approach 2:
The segmented structure with a dedicated solder metal layer (2-5 μm) ensures optimal contact area with the electrode pad, enabling efficient heat transfer and faster welding cycles, thereby improving overall productivity.
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
This method increases the contact area between the solder strip and electrode pads, stabilizes welding tension, reduces the risk of defects like rosin joints, and decreases silver paste consumption by 70%, while maintaining reliable bonding and reducing the risk of cracking and tin sweating.
Implementation Method 1
heating the coating member in such a manner that the substrate is coated with the first solder to form the first solder layer
Implementation Method 2
in a molten state, a ratio of a thickness of the second solder layer to a thickness of the first solder layer is 3:7
Implementation Method 3
lapping one end of the solder strip on the first solder layer of the first cell, lapping another end of the solder strip on the first solder layer of the second cell, and connecting the first cell and the second cell together by welding
Implementation Method 4
in a molten state, the second solder layer has a wetting angle smaller than 90°
Data Source
Figure 1~3
Figure 4
AI summary
Disclosed are a welding method for a photovoltaic cell and a photovoltaic module. First and second cells are adjacent to each other and welded to each other by a solder strip. The welding method includes providing a substrate of each of the first cell and the second cell, and providing a first solder layer at a preset position of the substrate where an electrode pad of the substrate is located; and lapping one end of the solder strip on the first solder layer of the first cell, lapping another end of the solder strip on the first solder layer of the second cell, and connecting the first cell and the second cell together by welding. A lower welding temperature is required, over-welding and de-welding are reduced, a contact area between the solder strip and the first solder layer is larger, the tension is stable, and better reliability is achieved.