You’ve done everything right. The new temperature-sensitive cells are perfectly laid up, the innovative encapsulant is in place, and the module looks pristine coming out of the laminator. But a day later, you see it: a tiny bubble near the busbar. A week later, a corner starts to peel.

This frustrating scenario is painfully familiar to teams working with low-temperature lamination processes. While essential for advanced cell technologies like HJT, these processes operate within a razor-thin margin of error. The good news? Most defects, like delamination and voids, are not random. They are signals from your materials, telling you exactly what needs to change.

This guide will help you interpret those signals. We’ll explore the common root causes behind these defects and share process adjustments—validated through our applied research at PVTestLab—to help you achieve a perfect, durable bond.

The Two Most Common Culprits: Delamination and Voids

Before we dive into solutions, let’s clarify our terms. While they can be related, delamination and voids are distinct issues.

• Delamination: This is a failure of adhesion. It occurs when the encapsulant doesn’t properly bond to the glass, backsheet, or cells, causing layers to separate. It often appears as a milky or hazy area that can be peeled back.
• Voids (or Bubbles): These are pockets of trapped gas or air within the module sandwich. They can range from tiny pinpricks to large, noticeable bubbles, often appearing around ribbons, junction boxes, or cell gaps.

Both problems compromise a module’s long-term reliability and power output, making them critical to solve during the solar module prototyping phase.

Why Your Encapsulant Isn’t Cooperating: The Science of the Bond

Many low-temperature challenges come down to the behavior of specific encapsulants, particularly Thermoplastic Olefins (TPO). Unlike traditional EVA, which undergoes an irreversible chemical cross-linking reaction, TPO functions more like a hot-melt glue. It melts to create a bond and solidifies upon cooling.

This might sound simple, but it creates a very narrow process window.

Our research at PVTestLab has shown that for most TPOs, the magic number is 135°C. If the material doesn’t reach this minimum lamination temperature throughout its entire volume, it simply won’t flow correctly to create a strong, uniform bond. Below this threshold, the risk of delamination rises dramatically.

How dramatically? Our tests show that the risk of TPO delamination increases by 40% for every 5°C drop below the 135°C threshold. This isn’t a gradual decline; it’s a steep cliff. The encapsulant might look like it has melted, but on a molecular level, it hasn’t achieved the deep, interlocking bond needed for 25+ years of durability in the field.

This is why rigorous material testing is not just a preliminary step but a core part of developing a stable production process. You must know your material’s exact thermal requirements before you can build a reliable recipe around them.

5 Validated Process Adjustments to Eliminate Lamination Defects

Understanding the problem is half the battle. The other half is implementing precise, targeted adjustments. Here are five solutions we’ve validated on our full-scale R&D line that address the root causes of voids and delamination.

As PV Process Specialist Patrick Thoma often notes, „The laminator doesn’t see a recipe; it sees a thermal and pressure profile. Your job is to make sure that profile perfectly matches what your specific material needs to achieve a durable bond.“

1. Give Your Encapsulant a Head Start with Preheating

The Problem: Cold TPO is viscous and doesn’t flow easily. When heat is applied quickly, the outer layers can melt and seal the edges before trapped air in the center has a chance to escape.

The Solution: Introduce a preheating step. Bringing the module stack to 80°C before starting the main lamination cycle is remarkably effective. This softens the TPO, dramatically improving its flow properties and allowing air to evacuate more completely during the vacuum phase. Think of it like trying to spread cold butter versus softened butter—one is a struggle, the other is smooth.

2. Slow Down the Ramp-Up for Uniform Heating

The Problem: Voids love to form in „thermal shadows“—areas that heat up slower than the rest of the module, such as regions around a junction box or thick copper ribbons. This uneven heating creates pressure imbalances that trap air.

The Solution: Use a slower initial heating ramp, around 2–3°C per minute. This gives the colder, denser parts of the module assembly time to catch up with the rest. This results in a more uniform temperature distribution, preventing the encapsulant from sealing off air escape routes prematurely.

3. Extend Your Vacuum Phase to Get the Air Out

The Problem: The „pump-down“ or vacuum phase is your one chance to remove air from the module layup. If this stage is too short, residual air will be trapped when the encapsulant melts, creating voids.

The Solution: This is often the simplest fix. Try extending the vacuum phase by an extra 30 to 60 seconds before the heating and pressure stages of the lamination process begin. This ensures the maximum amount of air is removed, leaving less to get trapped later.

4. Apply a Final, High-Pressure Squeeze

The Problem: Even with a perfect cycle, microscopic voids can remain. Over time, these can consolidate and grow, especially under thermal stress.

The Solution: Add a short, high-pressure step at the end of the lamination cycle. After the main heating and pressing are complete, apply a final, higher pressure of around 800 mbar for 5–7 minutes. This final squeeze helps compress any remaining micro-voids into oblivion without putting excessive mechanical stress on the cells.

5. Validate, Validate, Validate

These adjustments are powerful starting points, but they are not a universal magic formula. The ideal recipe depends on your specific combination of cells, encapsulant, backsheet, and equipment. The only way to find your perfect process window is through systematic process optimization.

Testing these parameters in a controlled environment allows you to isolate variables and gather data, turning guesswork into a predictable, repeatable, and scalable manufacturing process.

Frequently Asked Questions (FAQ)

Q: What’s the main difference between TPO and EVA lamination?
A: The key difference is chemistry. EVA undergoes a permanent chemical change called cross-linking, requiring a specific time-at-temperature to cure. TPO is a thermoplastic, meaning it melts to bond and solidifies when it cools—a process that is technically reversible. This is why TPO is more sensitive to precise temperature control than EVA.

Q: Can I use the same lamination recipe for different backsheets?
A: No, this is highly discouraged. Different backsheets have different thermal properties, thicknesses, and compositions. Some may release trace amounts of gas (outgassing) when heated, which can contribute to bubbles if your vacuum cycle isn’t optimized for it. Always treat a new backsheet as a variable requiring process re-validation.

Q: How can I tell if a bubble is from trapped air or moisture?
A: Generally, bubbles from trapped air are sharper and more defined. Voids caused by moisture are often cloudier and can look more like a hazy blister as the water turns to steam during heating. A „bake-out“ step (a low-temperature hold before the main cycle) can help remove residual moisture.

Q: Is more vacuum time always better?
A: Not necessarily. While extending the vacuum is a common fix, there are diminishing returns. An excessively long vacuum phase adds to your cycle time and impacts throughput. The goal is to find the optimal duration that efficiently removes the maximum amount of air.

Your Next Step in Perfecting Lamination

Low-temperature lamination is a process of precision. By understanding how your materials behave and methodically adjusting your parameters, you can overcome the challenges of delamination and voids. The key is to move from trial-and-error to a data-driven approach.

Start by examining your current process. Are there thermal shadows you haven’t accounted for? Could your encapsulant benefit from a preheating step? Answering these questions is the first step toward creating flawless, reliable, and high-performance solar modules.