PV Basics: Solar Cell Tabber Stringer Machine
PV Basics: Solar Cell Tabber Stringer Machine
In the photovoltaic module manufacturing process, the solar cell tabber stringer machine is one of the core pieces of equipment for building electrical connections between solar cells. Its main function is to solder individual solar cells with interconnection ribbons and connect them in series to form a cell string with a designed voltage output.
A stable stringing process directly affects module power, appearance quality, EL performance, and long-term reliability. For modern PV module factories, especially those producing MBB, half-cell, PERC, TOPCon, HJT, or other advanced modules, the accuracy and consistency of the tabber stringer are very important.
Classification of Solar Cell Tabber Stringer Machines
According to the automation level and soldering process, tabber stringer machines can generally be divided into three types.
Manual Tabber Stringer
A manual tabber stringer requires operators to place solar cells and ribbons by hand. The soldering process is also completed manually or with very simple auxiliary tools.
Main features:
Lower equipment investment cost
Suitable for small-batch production, pilot lines, laboratory testing, or training purposes
Low production efficiency
Lower positioning accuracy
Higher risk of cell breakage and soldering inconsistency
Manual stringing is rarely used in large-scale PV module factories today, but it can still be seen in R&D environments or very small production setups.
Semi-Automatic Tabber Stringer
A semi-automatic tabber stringer automates part of the cell feeding or ribbon soldering process, while some steps still require manual assistance, such as string handling, interconnection, or loading and unloading.
Main features:
Medium production efficiency
Suitable for small and medium-sized production lines
Lower investment compared with full automatic equipment
Higher dependence on operator skill
More variation in soldering quality than full automatic machines
Semi-automatic equipment can be a transitional solution for manufacturers that are upgrading from manual production to automated PV module manufacturing.
Full Automatic Tabber Stringer
A full automatic tabber stringer completes the whole process automatically, including cell loading, cell positioning, ribbon feeding, soldering, string transfer, and connection with the next production process.
Main features:
High positioning precision, commonly around ±0.1 mm depending on machine configuration
High production capacity, often reaching about 6,800 to 8,000 cells per hour for mainstream high-speed machines
Stable soldering quality
Suitable for continuous production lines
Better compatibility with modern PV module technologies such as MBB, half-cell, and high-efficiency cell formats
For mainstream photovoltaic module manufacturers, full automatic tabber stringers have become the standard choice because they support higher capacity, better process control, and lower labor dependence.
Working Principle and Core Process
The working principle of a tabber stringer is based on accurate cell positioning, stable ribbon feeding, controlled soldering temperature, and continuous string formation. Although different machine brands may use different mechanical layouts, the basic process is similar.
Cell Loading and Transfer
Solar cells are first separated from the cell cassette. In many machines, an air knife is used to separate the cells gently and reduce adhesion between thin wafers. Then suction nozzles, belts, or robotic handling systems pick up the cells and send them to the soldering station in sequence.
This step must be smooth and low-stress, because modern solar cells are becoming thinner, and microcracks may appear if handling force is not well controlled.
Vision Positioning System
The vision positioning system normally uses industrial CCD or CMOS cameras to capture the Mark points or reference features on the solar cell. After image processing, the system calculates the cell position and angle deviation.
The motion control system then guides the mechanical arm or positioning platform to adjust the cell to the correct position before soldering. This is essential for avoiding ribbon offset, poor alignment, and hidden soldering defects.
Ribbon Soldering Process
The ribbon soldering process usually includes preheating and soldering.
Preheating:
The soldering fixture or soldering area is preheated through a heating zone, such as a hot plate or heating lamp box. In many processes, the temperature is raised above 110°C before the main soldering stage. Preheating helps reduce thermal shock and improves solder wetting.
Soldering:
The machine places the flux-treated ribbon onto the busbar or grid line of the solar cell. Under controlled pressure and heating temperature, the solder layer on the ribbon melts and forms a firm bond with the silver electrode of the solar cell.
Good soldering should achieve strong adhesion, low series resistance, smooth ribbon alignment, and minimal thermal or mechanical stress on the cell.
Cell String Formation
After soldering, the cells are connected one by one to form a cell string with a preset length, such as 10 cells per string, 12 cells per string, or other configurations depending on module design.
The finished cell string is then transferred to the next process, such as layup, bussing, inspection, or lamination preparation.
Key Technologies in Tabber Stringer Machines
High-Precision Positioning
High-precision positioning depends on both the vision system and motion control algorithm. CCD or CMOS cameras capture the position of the cell, while control algorithms such as PID control help the machine correct movement quickly and accurately.
For high-quality production, the alignment error between the cell and ribbon should generally be controlled within 0.2 mm. If the deviation is too large, common problems may include offset soldering, poor appearance, increased series resistance, or even hidden reliability risks.
Welding Temperature Control
Temperature control is one of the most important factors in string soldering. The soldering temperature must be stable and usually needs to be controlled within a narrow range, such as ±5°C, depending on the process recipe.
Common heating methods include:
Infrared heating: Fast temperature rise, suitable for thin ribbons, especially ribbons with thickness of 0.15 mm or below
Hot plate heating: Better temperature uniformity, suitable for high-reliability soldering and stable mass production
If the temperature is too low, the solder may not fully melt, causing weak solder joints or cold soldering. If the temperature is too high, it may damage the cell, increase thermal stress, or affect long-term module reliability.
Low-Damage Soldering
Modern solar cells are thinner and more fragile than older-generation cells. For thin cells with thickness below 130 μm, mechanical pressure and thermal stress must be carefully controlled.
Many machines use soft-contact soldering systems, such as spring-loaded press heads. The pressure is commonly controlled in a range of about 5 to 15 N, depending on the cell type, ribbon type, and soldering method.
The goal is to achieve enough contact for reliable soldering while avoiding cracks, hidden fractures, edge chipping, or excessive cell bowing.
Practical Applications in PV Module Manufacturing
The tabber stringer is used in the front-end electrical interconnection stage of PV module production. Its performance influences several downstream processes and final module quality.
Typical applications include:
Standard crystalline silicon module production
Half-cell module production
MBB and SMBB module production
PERC, TOPCon, HJT, and other high-efficiency cell module lines
Pilot production lines for new module structures
Factory automation upgrades from semi-automatic to full automatic production
In a complete PV module production line, the tabber stringer must work together with cell cutting, layup, bussing, EL testing, lamination, framing, junction box installation, IV testing, and final inspection systems. A mismatch in capacity or process stability at the stringing stage can easily become a bottleneck for the whole factory.
Ooitech's View
As an equipment supplier working with different PV module production layouts, Ooitech sees the tabber stringer as more than a soldering machine; it is a key process-control point that determines whether a module line can run with stable yield and predictable output. For factories upgrading to MBB, TOPCon, or thinner-cell production, attention should be paid not only to nominal capacity, but also to ribbon control, cell handling stress, temperature uniformity, and compatibility with downstream layup and bussing processes. A good stringing solution should be selected together with the full module line design, otherwise a high-speed stringer may still fail to deliver real production efficiency.
