You’ve dialed in your lamination recipe. The cycle time is optimized for throughput, the temperatures seem right, and yet you’re still chasing down frustrating defects. Tiny bubbles near the junction box. A slight haze around the cell edges. These aren’t just cosmetic flaws; they’re symptoms of a deeper issue that standard process controls often miss.

The problem? Your lamination recipe might be fighting a battle against the very chemistry of your encapsulant—a battle decided in minutes, sometimes seconds.

Most manufacturers focus on a single metric: total cycle time. But what if the secret to a perfect, void-free, and reliable solar module isn’t about how fast you laminate, but about how the process aligns with the encapsulant’s natural behavior?

This is where understanding curing kinetics comes in. It’s a shift from thinking about time and temperature to understanding the material’s journey from a pliable solid to a fully cross-linked, protective layer.

The Two-Act Play of an Encapsulant

When you heat an encapsulant like EVA or POE, it doesn’t just melt and then harden. It undergoes a critical two-part transformation.

Act 1: The Flow.

As the temperature rises, the polymer chains loosen, and the material’s viscosity drops dramatically. It becomes a liquid designed to flow into every microscopic gap—around cells, ribbons, and junction boxes. This is the crucial stage where true, void-free encapsulation happens.

Act 2: The Cure.

As heating continues, a chemical reaction called cross-linking begins. Individual polymer chains start to form strong, permanent bonds with each other. The material’s viscosity climbs rapidly, and it transforms from a liquid into a durable, solid gel. This is what gives the module its structural integrity and long-term protection.

The problem arises when Act 2 starts before Act 1 is finished. This is called premature cross-linking or premature gelation, and it’s the hidden culprit behind many lamination defects. If the encapsulant starts to solidify before it has filled every space, it traps air and creates voids, setting the stage for delamination and moisture ingress down the line.

Moving Beyond Simple Timers: Meet Scorch Time (ts2) and Cure Time (t90)

To prevent this, we need to speak the encapsulant’s language and know its exact tipping points. While traditional analysis like DSC (Differential Scanning Calorimetry) tells us about the energy of the reaction, it doesn’t tell us about the physical change in viscosity—the factor that truly matters for lamination.

For that, process engineers rely on a tool called a Moving Die Rheometer (MDR). An MDR measures the material’s torque (resistance to shear) as it’s heated over time, giving us a precise map of its journey from liquid to solid.

This map reveals two critical landmarks for any lamination recipe:

• Scorch Time (ts2): This is the „point of no return.“ It’s the moment the cross-linking reaction truly kicks in and the material’s viscosity begins its rapid climb. Before this point, the material is flowing beautifully. After this point, it’s quickly becoming an immovable gel.
• Cure Time (t90): This is the time it takes for the material to reach 90% of its potential cross-linking, the benchmark for a stable, fully cured state that ensures long-term module reliability.

This data tells a story. The initial dip in torque is the encapsulant melting and flowing as its viscosity drops. Then, at the point labeled ts2, the curve turns upward as cross-linking begins. The process is effectively complete when the torque plateaus at the top, and t90 marks the point where we’ve achieved a robust cure.

The Golden Rule of Lamination Recipe Design

Armed with this data, we arrive at the single most important principle for a successful solar module lamination process:

The encapsulant must have enough time to completely flow and fill all voids before Scorch Time (ts2) is reached.

This means your lamination recipe—the combination of temperature ramps, vacuum application, and pressure holds—must be designed to ensure the encapsulant remains a low-viscosity liquid long enough to fully embed the solar cells and components. Only then should the process push the material past its scorch time to achieve a full cure (t90).

Think of it this way:

• A Bad Recipe: Heats up too quickly, triggering scorch time (ts2) while the encapsulant is still trying to flow. The material gels prematurely, trapping air and creating pathways for future failure.
• A Good Recipe: Uses a controlled heating ramp that allows the encapsulant to reach its lowest viscosity and fill every crevice. Once the flow is complete, it holds the temperature to drive the material past ts2 and on to a full t90 cure, locking everything into a perfect, monolithic structure.

By designing your process around the material’s kinetics instead of an arbitrary cycle time, you move from guesswork to predictable, repeatable quality.

Why This Matters More Than Ever

As module designs become more complex—with bifacial cells, half-cut cells, and new backsheet technologies—the geometry inside the module becomes more challenging to encapsulate. There are more nooks and crannies for air to hide.

Ignoring curing kinetics means you are essentially flying blind. You might get away with it on some designs, but you will inevitably run into issues when introducing a new material or a more complex layout. Understanding the t90 and ts2 of your encapsulants is fundamental to successful R&D and is a core component of professional material testing services.

By building your lamination recipes on a foundation of material science, you can:

• Eliminate Voids and Delamination: Ensure complete, bubble-free encapsulation every time.
• Improve Module Reliability: A fully and properly cured encapsulant is the first line of defense against moisture, PID, and mechanical stress.
• Accelerate Innovation: Confidently integrate new materials and designs by knowing exactly how to process them, a critical step when prototyping new solar module designs.

The next time you evaluate your lamination process, look beyond the cycle time on the screen. Ask the deeper question: „Is my recipe working with my encapsulant’s chemistry, or against it?“ The answer could be the key to unlocking the next level of quality and reliability for your products.

Frequently Asked Questions (FAQ)

What is a solar encapsulant?

A solar encapsulant is a polymer-based material, typically Ethylene Vinyl Acetate (EVA) or Polyolefin Elastomer (POE), used to bond the solar cells, glass, and backsheet together into a single, durable unit. Its primary functions are to provide structural adhesion, optical clarity, electrical insulation, and protection from environmental factors like moisture and dirt.

What are the most common causes of voids in a solar module?

Voids are typically caused by trapped air or gases released during the heating process (outgassing). This happens when the encapsulant solidifies (cross-links) before it has had a chance to completely flow into all the gaps within the module layup. A lamination recipe that heats up too aggressively is a primary cause.

Is t90 the same for all encapsulant materials?

No, absolutely not. Every formulation of EVA and POE has a unique chemical makeup, resulting in a different curing kinetic profile. Scorch time (ts2) and cure time (t90) can vary significantly between different suppliers and even between different product grades from the same supplier. This is why testing each specific material is crucial.

Why do we aim for t90 (90% cure) and not t100 (100% cure)?

In polymer chemistry, reaching 100% cross-linking is often impractical and unnecessary. The reaction rate slows dramatically as it approaches completion, meaning the time and energy required to get from 90% to 100% cure is disproportionately large. A 90% cure level (t90) is widely accepted in the industry as the point where the material has achieved the vast majority of its desired mechanical and protective properties for long-term stability. Pushing for t100 would result in excessively long cycle times with little to no added benefit.

How can I find out the t90 and ts2 for my materials?

These parameters are measured experimentally using a Moving Die Rheometer (MDR). Material suppliers sometimes provide this data on their technical datasheets. However, for precise process design, it’s best to perform independent testing under conditions that mimic your production environment. This is a standard procedure in professional solar R&D labs.