Views: 0 Author: Site Editor Publish Time: 2025-12-08 Origin: Site
In crystalline silicon photovoltaic (PV) module manufacturing, one of the most critical and delicate steps is soldering the thin silicon solar cells into strings. The thermal budget in this step determines not only electrical performance and long-term reliability, but also scrap rate and overall line throughput. Quartz infrared (IR) heating lamps have become a widely used heat source in modern tabber-stringer equipment because they deliver intense, controllable, non-contact heat exactly where it is needed.
This article looks at solar wafer soldering from a process engineer’s point of view: how the line runs, where heat is required, how quartz IR can be integrated or retrofitted, what kind of configurations are realistic, and where IR is – and is not – the right tool.
In a standard crystalline silicon module line, the cell interconnection process typically includes:
Cell loading and inspection
– Cells (often M6–M12, 166–210 mm) are loaded from cassettes and checked for cracks, color, and orientation.
Flux application
– Flux is applied to the busbars or pads on the cell surface and sometimes to the copper ribbons to promote solder wetting and oxide removal.
Ribbon placement and alignment
– Tinned copper interconnect ribbons are positioned onto the busbars by the tabber-stringer machine, often under vacuum or mechanical support.
Soldering / bonding (tabbing & stringing)
– Heat is applied to reflow the solder coating on the ribbon (and sometimes additional solder paste) to form a metallurgical joint with the cell busbar.
Cooling and string handling
– The joint is cooled in a controlled way while the string is transported, then strings are laid up for bussing and lamination.
Throughout this sequence, heating is concentrated in the soldering zone, but preheating and controlled cooling are also critical to avoid thermal shock and mechanical stress on thin wafers.
Key locations where precise heating is required:
Preheating zone
– Bringing cells, ribbons, and solder above ambient (typically to 80–150 °C) before peak reflow.
– Reduces thermal gradients and thermal shock when entering the main soldering zone.
Main soldering / reflow zone
– Raising busbar/solder interface to above liquidus (commonly 210–240 °C depending on alloy) for sufficient time to achieve full wetting and intermetallic formation.
Post-solder thermal conditioning
– Avoiding abrupt cooling that can induce microcracks or warpage, especially with larger/thinner cells.
Any non-uniformity in temperature across the cell area or from cell to cell will directly translate into:
Incomplete solder wetting or “cold” joints.
Local overheating, discoloration, or microcracks.
Lower string yield and higher rework/scrap.
Many tabber-stringer lines in the field still rely on older or mixed heating technologies. The most common are:
Contact soldering tips / shoes
Heated belts or hot plates
Hot air or convection tunnels
Conventional IR panels with slow response
Each has characteristic limitations in the context of high-throughput, high-precision PV cell soldering.
Contact tools apply heat by conduction. Typical issues:
Mechanical stress and risk of cracking
– Even finely controlled pressure can stress thin wafers, especially with small non-planarities or foreign particles.
Non-uniform contact
– Slight variations in planarity or contamination cause local under- or over-heating.
Slow thermal response
– Large metal masses are slow to heat and cool, making it difficult to adjust the temperature profile quickly for new products or recipes.
Maintenance and contamination
– Solder build-up and flux residues require regular cleaning, which impacts uptime.
Hot air or convection systems heat both the product and surrounding air:
Low energy efficiency
– Much of the energy goes into heating air and metal fixtures rather than the ribbons and cells.
Limited local control
– It is difficult to create sharp temperature peaks or narrow zones; heat spreads beyond the target region.
Potential for flux disturbance
– Airflow can disturb flux distribution or introduce contamination.
Some lines use older IR panels with ceramic emitters or slow-response lamps:
Slow response to setpoint changes
– Not ideal for fast recipe changes or dynamic power modulation.
Limited zoning
– Coarse zoning may not match modern multi-busbar or multi-wire layouts.
Size and footprint
– Larger furnaces occupy more line length, which conflicts with compact, high-throughput layout requirements.
These limitations have driven many engineers and machine builders to adopt quartz infrared heating lamps as the primary or supplemental heat source in modern soldering zones.
Quartz IR lamps deliver intense, radiant energy directly to the cell and ribbon surfaces without physical contact. In PV soldering lines, they are typically integrated in three roles: preheating, boosting, and full IR soldering.
An IR preheating module is usually placed just before the main soldering point:
Function
– Pre-warm cells and ribbons to 80–150 °C, depending on solder system and cell design.
– Reduce the temperature step between ambient and reflow, minimizing thermal stress.
Implementation
– 1–2 rows of short-wave or fast-response medium-wave quartz lamps above (and sometimes below) the transport path.
– Zoning along the direction of travel to shape a gentle temperature ramp.
Preheating with IR is particularly effective when retrofitting older lines that run close to their temperature limit and struggle with scrap due to cracking.
Instead of relying solely on contact tips or hot plates, many modern designs use IR to provide the sharp reflow peak:
Boost from below or above
– Lamps are positioned to focus on the busbar/ribbon area while minimizing heating of non-critical regions.
Synchronized with mechanical tools
– IR power is ramped up exactly when ribbons are pressed, then reduced during release and cooling.
This “hybrid” design allows existing mechanical tooling to be retained while sharply improving the thermal profile and reducing cycle time.
In new-build tabber-stringer lines, quartz IR lamps can fully replace traditional heating:
All-IR soldering heads
– Arrays of lamps, often with reflectors and focusing optics, deliver precisely shaped heating patterns to each busbar or wire layout.
Top and bottom heating
– Cells can be heated from both sides to improve uniformity and to compensate for varying ribbon cross-sections.
Independent zones
– Each zone (preheat, reflow, post-heat) is independently controlled, enabling fine tuning for different cell sizes and solder recipes.
This approach eliminates direct mechanical heating, lowers moving mass in the head, and simplifies temperature control logic.
The right configuration depends on cell size, ribbon geometry, flux/solder chemistry, and desired line throughput. Below are typical, non-confidential ranges to illustrate what is realistic.
Common lamp choices for PV soldering include:
Short-wave quartz IR lamps
– Very fast response (on/off in fractions of a second).
– High power density (often 30–60 kW/m² or higher).
– Well suited where tight thermal windows and fast cycle times are required.
Fast-response medium-wave quartz IR lamps
– Slightly longer wavelength, more strongly absorbed by some coatings and flux systems.
– Good balance between penetration and surface heating.
Twin-tube designs with reflectors
– Gold or ceramic reflectors integrated for directional heating and improved efficiency.
For PV soldering, short-wave and fast medium-wave are both used; the choice depends on how aggressively the process needs to respond and on the detailed optical properties of the stack.
Consider a typical stringer with conveyor speeds in the range of 6–15 m/min (depending on cell size and the number of busbars/wires):
Preheat zone
– Power density: 10–20 kW/m² at the product surface.
– Dwell time: 1.0–2.5 s.
– Target cell surface temperature: 80–150 °C.
Reflow / main soldering zone
– Power density: 20–40 kW/m², sometimes higher for very short dwell.
– Dwell time: 0.8–2.0 s above liquidus.
– Peak interface temperature: typically 210–240 °C for common leaded or lead-free solders, within the cell’s safe thermal budget.
Post-heat / controlled cooling zone
– Power density: 5–15 kW/m² (often reduced gradually).
– Dwell time: 1.0–3.0 s to manage cooling gradients.
These values are indicative and must be validated for each combination of wafer thickness, solder alloy, and flux chemistry. Higher throughput (for example > 4,000–5,000 cells/h) generally requires either higher power density, optimized optics, or longer heating path.
Typical lamp distances and arrangements:
Lamp-to-cell distance: usually 80–150 mm, sometimes up to 200 mm for broader, softer heating.
Top-only or top-and-bottom: bottom heating often helps stabilize the profile and reduces the risk of overheating busbar surfaces while cell backs remain too cool.
Zoning across the width: more power over busbar lines, less at cell edges, to avoid hot corners.
Mechanical integration must maintain:
Stable distance despite thermal expansion.
Easy lamp replacement from the side or from above.
Clearances for cameras, sensors, and ribbon handling.
When correctly engineered, quartz IR soldering modules deliver measurable improvements across key metrics.
Better temperature uniformity
– Zoning and lamp layout allow uniform heating across the full cell width and along every busbar.
– Reduces cold joints and solder voids.
Lower microcrack risk
– Non-contact heating and controlled ramps reduce mechanical stress.
– Larger, thinner wafers benefit particularly from gentle preheat + sharp reflow profiles.
Stable, repeatable solder profiles
– Fast response makes it easier to hold a tight process window even when line speed or ambient conditions vary.
The net effect is higher string yields and more consistent module performance in the field.
Higher line speeds
– Higher power density and more focused heating enable shorter dwell times in the reflow zone, supporting higher conveyor speeds (for example moving from 6–8 m/min towards 10–15 m/min, depending on product).
Product changeover
– Recipe-driven power setpoints and zone configurations allow quick switch between different cell formats, busbar counts, or wire geometries.
Compact footprint
– IR modules can provide the required thermal profile in shorter lengths compared to long convection tunnels, freeing valuable floor space.
Quartz IR heating generally improves energy efficiency because:
Radiant energy is directed to the specific surfaces that need heat.
Less mass (air and metal) is heated unnecessarily.
Fast warm-up and cool-down reduce idle losses.
Energy savings vary by line design, but it is common to see reduced energy per watt of module output compared to older hot-air or heavy conduction systems, especially when combined with effective reflectors and zoning.
To get the best results from quartz IR modules, several PV-specific design and tuning aspects must be considered.
Silicon wafers, anti-reflective coatings, solder alloys, and copper ribbons each have different absorption spectra.
Short-wave IR tends to penetrate deeper and can heat both the ribbon and the cell; medium-wave often couples more strongly to certain surfaces and coatings.
In practice, many PV lines use short-wave lamps for the main soldering zone, where aggressive response is desired, and may use medium-wave or lower power for preheat or post-heat zones.
A short feasibility study with actual wafers and ribbons is usually the most efficient way to choose.
Shiny copper ribbons and busbars can reflect IR, causing hot spots if not managed:
Use appropriate reflector geometry (gold, white ceramic, or polished metal) to redirect stray radiation back into useful areas rather than onto sensitive components.
Tilt lamp and reflector assemblies slightly to avoid concentrating reflections at cell edges or corners.
Consider selective shielding where cameras or plastic parts might otherwise see high radiation levels.
A robust soldering profile typically:
Gradually ramps cell temperature in the preheat zone.
Delivers a sharp but controlled reflow peak over a short time.
Allows controlled cooling without sudden quenching.
This can be achieved by:
Configuring multiple zones with stepped power levels instead of a single uniform zone.
Using conveyor speed and lamp power together to tune the time-temperature curve.
Monitoring reference cells/strings with thermocouples or IR pyrometers during commissioning.
For high-end lines, integrating temperature feedback improves robustness:
Attach thermocouples to representative dummy cells or strings at known positions.
Use pyrometers or IR cameras for non-contact monitoring in critical zones.
Feed this information into the IR power control to compensate for ambient variations or lamp aging.
Quartz IR lamps are consumables in a high-duty environment:
Design modules for quick lamp replacement with accessible connectors and guides.
Plan regular cleaning (dust, flux fumes) to maintain efficiency and uniformity.
Track lamp operating hours and power levels to schedule preventive replacement before performance drifts outside the process window.
Even experienced teams can run into recurring issues when adding or upgrading IR modules. Some typical pitfalls include:
If IR heaters are too narrowly focused over the busbar area:
The ribbon and busbar may reach the target solder temperature.
Cell edges remain significantly cooler, leading to partial wetting or weak joints near the cell perimeter.
Mitigation:
Use wider or carefully profiled heating patterns that cover the entire busbar width plus a margin.
Balance top and bottom heating so the complete joint area, not just the top surface, reaches the required temperature.
Driving the reflow zone too hard, or keeping cells above liquidus for too long, can:
Damage anti-reflective coatings.
Cause warpage or microcracks, especially in thin large-area cells.
Accelerate degradation of neighboring materials.
Mitigation:
Validate the complete time-temperature profile with test cells, not just surface temperature readings.
Tune down peak power and/or shorten dwell time while checking solder joint quality (pull tests, cross-sections).
Without careful design:
Reflected IR can hit plastic covers, cables, or sensor housings, causing local overheating.
Cameras or optical sensors may be blinded or thermally stressed.
Mitigation:
Incorporate shields and baffles as part of the IR module design.
Verify during commissioning with temperature labels or thermal imaging.
In retrofit projects, it is common to size IR modules based on current operating speeds only:
When production later attempts to increase line speed, the installed power may be insufficient to maintain the same profile.
Mitigation:
Size lamp arrays with headroom for future speed increases (for example 20–30 % above initial design requirement).
Design control systems so that extra power is available but only used when needed.
Standard SMT or wave soldering logic does not always translate directly to PV:
Cells are larger, thinner, and more fragile.
The mechanical support/deformation behavior is different.
Optical and thermal properties of the stack differ from typical PCB assemblies.
Mitigation:
Base design decisions on PV-specific tests and data, not only on general electronics experience.
Involve PV process engineers early when specifying IR modules.
Huai’an Yinfrared Heating Technology works with PV manufacturers and tabber-stringer OEMs from feasibility through to production ramp-up. Typical support includes:
For existing lines:
Review current soldering methods (contact tips, plates, hot air, older IR) and quality/throughput constraints.
Identify where IR preheat, IR boost, or full IR soldering stations can be integrated without major mechanical redesign.
Estimate required power density, zone lengths, and control concepts based on your products and target speeds.
In a controlled environment, Huai’an Yinfrared can:
Test different lamp types, reflector geometries, and mounting distances with your actual wafers, ribbons, and flux/solder systems.
Generate initial time-temperature profiles and solder joint evaluations (visual, electrical, and mechanical).
Provide recommendations on optimal wavelength ranges and zone layouts for your product mix.
Based on the validated concept, Huai’an Yinfrared designs:
Custom quartz IR lamp assemblies (short-wave, fast medium-wave, or mixed) tailored to your tabber-stringer layout.
Reflector and housing designs that manage reflections, protect surrounding components, and simplify maintenance.
Electrical integration plans, including zoning, power supplies, and interfaces to your line control.
Whether the need is a compact retrofit module or a complete IR soldering head for new equipment, the focus is on mechanical compatibility and robust, repeatable heating.
During installation and ramp-up, Huai’an Yinfrared:
Supports on-site tuning of lamp power, zone setpoints, and conveyor speed to achieve the agreed process window.
Trains operators and maintenance teams on inspection, cleaning, and lamp replacement.
Provides long-term supply of replacement lamps and modules, helping ensure stable performance over the life of the line.
By combining quartz IR heating lamps with careful process engineering, PV manufacturers can achieve higher throughput, lower scrap, and more robust module performance – all within a compact, energy-efficient soldering footprint.
Last modified: 2025-12-08
