Diagnosing Bubble Defects in Solar Module Lamination: Trapped Air vs. Outgassing

You pull a freshly laminated module from the production line. Under the light, you see it—the frustrating signature of a flawed process: bubbles. These small, scattered defects pose a risk to the module’s long-term reliability and performance. The immediate question is: where did they come from?

Most lamination defects that look like bubbles stem from one of two distinct root causes: trapped atmospheric air or material outgassing. Mistaking one for the other can send your engineering team down a rabbit hole of incorrect fixes, wasting valuable time, materials, and money.

The good news is that you can definitively diagnose the source. The key isn’t to inspect the bubbles themselves, but to analyze their behavior under specific vacuum and pressure profiles during the lamination cycle.

The Two Culprits: A Tale of Two Bubbles

Think of it this way: trapped air is a mechanical problem, while material outgassing is a chemical one. The first involves air that failed to escape; the second involves gases created inside the laminate itself. Understanding this distinction is the first step toward a solution.

Trapped Atmospheric Air: A Race Against the Clock

This is the most common and, fortunately, the easier of the two problems to solve. During the lamination cycle, a vacuum pump removes air from the module sandwich. If the vacuum is applied too quickly (a „fast drawdown“), however, the edges of the encapsulant can melt and seal prematurely.

This creates a seal around the perimeter, trapping pockets of atmospheric air in the center of the module. No amount of vacuum time after this point can remove them. It’s like trying to suck the air out of a food-saver bag after you’ve already sealed three of the four sides.

Material Outgassing: The Hidden Chemical Reaction

Material outgassing is a more complex issue. It occurs when components within the laminate—typically the encapsulant (like EVA or POE) or the backsheet—release volatile organic compounds (VOCs) when heated. These compounds turn into gas, forming bubbles from within the material itself.

This isn’t leftover air; it’s new gas created by a chemical reaction triggered by the lamination temperature. The root cause often lies in the material’s formulation, quality, or even how it was stored before use.

The Diagnostic Power of Pressure and Vacuum Analysis

So, how do you determine whether you’re dealing with a process problem or a material problem? You can turn your laminator into a diagnostic tool by methodically adjusting its vacuum and pressure sequences.

The Vacuum Profile Test: Slowing Down for Clarity

The most powerful diagnostic test involves changing the speed at which you pull the vacuum. Instead of a fast, aggressive drawdown, you run a test cycle with a slow, multi-stage vacuum profile.

Here’s the logic:

1. Run a Baseline Test: Laminate a module using your standard, fast-drawdown recipe and document the bubble formation.
2. Run a Diagnostic Test: On the next module, program a slow, staged vacuum sequence. For example, pull the vacuum down to 200 mbar and hold it for a few minutes, then to 100 mbar and hold, and finally down to the ultimate vacuum level. This gives ample time for all the atmospheric air to escape from the center before the edges have a chance to seal.

The results of this experiment are incredibly telling:

• If the bubbles disappear: The culprit was trapped atmospheric air. The solution is to optimize your vacuum drawdown rate for standard production.
• If the bubbles remain (or even get worse): The problem is almost certainly material outgassing. Since the slow drawdown successfully removed all the atmospheric air, any remaining bubbles must be coming from the materials themselves.

„Many teams immediately blame their materials when they see bubbles, but we often find it’s a simple process-parameter issue,“ notes Patrick Thoma, PV Process Specialist at PVTestLab. „A methodical vacuum profile analysis is the fastest way to get to the truth. By controlling the process, we let the materials tell us what’s really happening.“

What Pressure Sequencing Reveals

While the vacuum test identifies the culprit, pressure sequencing can provide further clues, especially in cases of outgassing. Applying high pressure can force small gas bubbles back into solution within the encapsulant, making them invisible. However, this is just a mask—not a cure. If you find that bubbles only disappear under very high pressure or reappear during subsequent reliability testing (like damp heat tests), it’s another strong indicator of an outgassing problem that needs to be solved at the material level.

Why a Controlled Environment Is Non-Negotiable for Testing

Diagnosing these issues requires precision and repeatability. Material outgassing can be highly sensitive to ambient temperature and humidity. A test run on a cool, dry morning might yield different results than one on a hot, humid afternoon, leading to confusing data.

For this reason, professional diagnostics are performed in a 100% climate-regulated environment. By eliminating environmental variables, you can be certain that any changes you observe result directly from your process adjustments or material selections. This level of certainty is critical when you are building new solar module concepts and need reliable, repeatable data to make key design decisions. Conducting structured experiments on encapsulants under these controlled conditions ensures that your findings are based on science, not circumstance.

Frequently Asked Questions (FAQ)

Can’t I just increase the pressure to get rid of all bubbles?

While high pressure can physically squeeze bubbles and make them disappear, it doesn’t solve the root cause. If the issue is outgassing, those dissolved volatiles can re-emerge later in the module’s life, potentially causing delamination. It’s a temporary cosmetic fix that hides a long-term reliability risk.

Does the type of encapsulant (e.g., EVA vs. POE) affect outgassing?

Yes, absolutely. Different encapsulant formulations have varying chemical compositions and outgassing characteristics. EVA (ethylene vinyl acetate), for instance, produces acetic acid as a byproduct of its cross-linking reaction, which can contribute to outgassing if not managed. POE (polyolefin elastomer) doesn’t have this same reaction but can still contain its own volatile compounds, depending on the grade and additives used.

How do I know if my backsheet is the problem?

You can isolate the backsheet by running a ‚glass-glass‘ lamination test. If you laminate a module using a second piece of glass instead of a backsheet and the bubble problem disappears, the backsheet is a likely contributor to the outgassing.

From Diagnosis to a Lasting Solution

Identifying the source of bubbles in your solar modules is the first and most critical step. Once you know whether you’re fighting trapped air or material outgassing, you can stop guessing and start implementing targeted, effective solutions.

• For Trapped Air: The path forward involves process optimization—fine-tuning your vacuum drawdown rates, checking for leaks in your system, and ensuring your layup is consistent.
• For Material Outgassing: The solution lies in material science—evaluating alternative suppliers, ensuring proper material storage and handling, or running qualification tests on new batches of encapsulants or backsheets.

By using a data-driven diagnostic approach, you can turn a frustrating defect into a valuable opportunity to build a more robust and reliable manufacturing process.

If you are facing persistent lamination challenges and need clear, data-driven answers, get in touch with our process specialists to discuss how a structured analysis can help you find a permanent solution.