Common Causes of Bubble Formation in Solar Panel Adhesives

  • Post last modified:March 11, 2026

Common Causes of Bubble Formation in Solar Panel Adhesives

The solar energy industry is under constant pressure to increase efficiency and extend the lifespan of photovoltaic (PV) modules. While much of the focus remains on the purity of silicon wafers or the efficiency of thin-film cells, the structural integrity of the module is equally critical. Solar panel adhesives play a vital role in bonding frames, junction boxes, and encapsulating cells. However, one of the most persistent challenges in the manufacturing process is the appearance of voids or bubbles within these adhesive layers. Understanding the common causes of bubble formation in solar panel adhesives is essential for quality control, long-term durability, and maintaining the rated power output of the module.

Bubbles are more than just an aesthetic defect; they represent a failure in the continuity of the bond. In the harsh environments where solar panels operate—characterized by extreme UV exposure, temperature fluctuations, and moisture—these small pockets of air or gas can lead to catastrophic failures. This comprehensive guide explores the technical triggers for bubble formation and provides actionable insights for engineers and manufacturers to mitigate these risks.

The Impact of Bubbles on Solar Module Reliability

Before diving into the causes, it is important to understand why the industry spends significant resources trying to eliminate them. In solar applications, adhesives and encapsulants serve as both a mechanical bond and a protective barrier. When bubbles are present, several negative outcomes can occur:

  • Thermal Hotspots: Air is a poor conductor of heat. Bubbles trapped near solar cells can act as insulators, preventing heat from dissipating. This leads to localized overheating, or “hotspots,” which can permanently damage the cell and reduce the overall efficiency of the string.
  • Moisture Ingress: Voids often create pathways for moisture to penetrate the module. Once moisture reaches the metallic interconnects or the cells themselves, it triggers corrosion, leading to premature power degradation.
  • Delamination: Bubbles reduce the effective surface area of the bond. Under thermal cycling (the expansion and contraction caused by day-night temperature shifts), these voids act as stress concentrators, eventually causing the adhesive to peel away from the substrate.
  • Electrical Arcing: In high-voltage solar arrays, air gaps within the insulation or adhesive layers can lead to partial discharge or arcing, posing a fire hazard and system failure.

1. Surface Contamination and Substrate Preparation

One of the most frequent common causes of bubble formation in solar panel adhesives is improper surface preparation. Adhesives require a clean, high-energy surface to wet out properly. When a surface is contaminated, the adhesive cannot form a continuous molecular bond, leading to “micro-voids” that expand during the curing process.

Oils and Fingerprints

In a manufacturing environment, even trace amounts of skin oils or machine lubricants on the glass or backsheet can prevent the adhesive from spreading evenly. As the adhesive cures, it may pull away from these contaminated spots, leaving behind air pockets.

Dust and Particulates

Solar panels are often manufactured in large-scale facilities where airborne dust is a factor. A single speck of dust can act as a nucleation point for a bubble. During the application of the adhesive, air can become trapped underneath or around the particle, creating a void that is difficult to remove once the adhesive begins to set.

Chemical Residues

Cleaning agents used on the glass or aluminum frames must be fully evaporated before adhesive application. If solvents are trapped under the adhesive bead, they will eventually volatilize, creating “gas bubbles” as the chemical transitions from a liquid to a vapor state during the curing cycle.

2. Improper Mixing of Two-Component Adhesives

Many high-performance solar adhesives, such as certain epoxies and urethanes, are two-component systems (Part A and Part B). The process of combining these two materials is a critical stage where air is frequently introduced.

High-Speed Agitation

When mixing two components, using a high-speed mixer can whip air into the viscous liquid. This creates a “frothy” mixture filled with micro-bubbles. Unlike larger bubbles that might rise to the surface, these micro-bubbles often remain suspended due to the material’s viscosity.

Incorrect Mixing Ratios

If the ratio of resin to hardener is off, the chemical reaction may not proceed as intended. In some cases, an excess of one component can lead to an exothermic reaction that is too intense. The resulting heat can cause the adhesive to “boil” at a microscopic level, leading to internal gas formation.

To prevent these issues, manufacturers often utilize vacuum degassing chambers after mixing or employ static mixers in automated dispensing systems that are designed to blend components without introducing air. If you are experiencing issues with manual mixing, you may want to [Contact Our Team](https://www.incurelab.com/contact) for guidance on automated dispensing solutions.

3. Outgassing of Substrates and Adhesives

Outgassing is a phenomenon where a solid or liquid material releases a gas. In the context of solar panel manufacturing, this is a major contributor to bubble formation during the lamination or curing phase.

Substrate Outgassing

Certain backsheet materials or plastic components in the junction box may contain moisture or volatile organic compounds (VOCs). When the panel is heated during the lamination process, these volatiles are released as gases. If the adhesive has already begun to skin over or cure, these gases become trapped, forming large, visible bubbles.

Adhesive Byproducts

Some adhesives, particularly certain types of silicones (acetoxy cure), release byproducts like acetic acid during the curing process. If the adhesive is applied in a thick layer or in a confined space where the byproduct cannot escape, it can form bubbles within the bond line. This is why “neutral cure” silicones are generally preferred in the solar industry, as they produce less volatile byproducts.

4. Environmental Factors: Humidity and Temperature

The environment of the production floor plays a massive role in the behavior of industrial adhesives. Variations in humidity and temperature can change the chemical dynamics of the bonding process.

High Humidity

Urethane-based adhesives are particularly sensitive to moisture. The isocyanate component in the adhesive can react with water vapor in the air to produce carbon dioxide (CO2) gas. This chemical reaction is a notorious cause of “foaming” or bubbling in polyurethane bonds. If the production facility is not climate-controlled, high-humidity days can lead to a spike in defective modules.

Temperature Fluctuations

If the adhesive is stored in a cold environment and then immediately applied in a warm room, its viscosity will change rapidly. Furthermore, cold adhesives can cause moisture from the air to condense on their surface (the “dew point” effect). Applying an adhesive over this microscopic layer of condensation will inevitably lead to bubbling and adhesion failure.

5. Dispensing and Application Techniques

Sometimes the cause is not chemical, but mechanical. How the adhesive is applied to the solar module matters just as much as the adhesive’s chemistry.

Air Entrapment in the Dispensing Valve

If the dispensing system has a leak or if the fluid pressure is not properly regulated, air can be sucked into the line. This results in “spitting” at the nozzle, where air pockets are injected directly into the adhesive bead as it is laid down on the frame or glass.

Incorrect Nozzle Height and Speed

If the dispensing nozzle is held too high above the substrate, the adhesive “drops” onto the surface, often trapping a pocket of air underneath the bead. Similarly, if the robot moves too quickly, the adhesive bead may break or become thin, allowing air to fill the gaps. A consistent, “wet-out” bead is necessary to ensure that the adhesive displaces all air as it contacts the surface.

Complex Geometries

Junction boxes often have complex shapes with deep channels. If the adhesive is poured too quickly into these areas, it may bridge over corners rather than flowing into them, trapping air in the recesses. This is often referred to as “shadowing” or “bridging.”

6. Viscosity and Rheology Challenges

The flow characteristics (rheology) of the adhesive determine how easily air can escape before the material sets. High-viscosity adhesives are more prone to bubble retention because the internal resistance of the fluid prevents air bubbles from rising to the surface and bursting.

In solar panel manufacturing, there is often a trade-off: a high-viscosity adhesive is needed to maintain the shape of the bead (thixotropy) before curing, but this same thickness makes it harder to eliminate bubbles. If the adhesive “skins over” too quickly, any air trapped inside is locked in place permanently.

7. Curing Profiles and Exothermic Heat

The transition from a liquid to a solid state is a delicate time for any adhesive. If the curing profile is not optimized, it can induce bubbles.

Rapid Curing

In an effort to increase throughput, manufacturers may use high-intensity UV light or elevated temperatures to accelerate curing. However, if the surface of the adhesive cures significantly faster than the bulk material, it creates a “skin.” Any gases generated by the chemical reaction in the center of the bead or any air expanding due to the heat will be unable to escape through the hardened skin, resulting in internal voids.

Exothermic Reactions

Some epoxy resins generate significant heat as they cure. In thick sections, this heat can build up (an exothermic spike), causing the temperature to exceed the boiling point of certain components in the formulation. This leads to a “honeycomb” effect of bubbles throughout the adhesive layer.

Strategies for Preventing Bubble Formation

Identifying the common causes of bubble formation in solar panel adhesives is the first step. The second is implementing robust prevention strategies. Here are the industry best practices for bubble-free solar assembly:

  • Vacuum Degassing: For two-part systems, processing the mixed adhesive in a vacuum chamber before dispensing can remove nearly 100% of entrained air.
  • Automated Dispensing: Using high-precision robotic systems ensures consistent nozzle height, speed, and pressure, minimizing the mechanical introduction of air.
  • Plasma or Corona Treatment: These surface treatments increase the surface energy of substrates like backsheets and frames, allowing the adhesive to “wet out” more effectively and displace air.
  • Environmental Control: Maintaining a cleanroom or a controlled environment with stable temperature and low humidity (typically below 50% RH) is essential for polyurethane and silicone adhesives.
  • Step-Curing: Instead of a single high-temperature blast, using a ramped heating profile allows volatiles to escape slowly before the adhesive reaches its gel point.
  • Material Selection: Work with suppliers to choose adhesives with low-outgassing properties and appropriate viscosities for your specific application.

Diagnostic Methods: Finding the Hidden Voids

Not all bubbles are visible to the naked eye, especially when bonding opaque components like junction boxes to backsheets. Quality control teams often use several methods to detect these hidden issues:

Ultrasonic Testing: High-frequency sound waves can detect changes in density, revealing voids within the adhesive layer without destroying the module.

Thermal Imaging: By applying a heat load to the panel, infrared cameras can identify hotspots caused by the insulating effect of air bubbles.

Cross-Sectional Analysis: During the R&D phase, sample modules are often cut and polished to inspect the bond line under a microscope, ensuring that the dispensing parameters are optimized.

Conclusion

The presence of bubbles in solar panel adhesives is a multi-faceted problem that stems from chemical, mechanical, and environmental sources. From the initial cleaning of the glass to the final curing of the junction box adhesive, every step in the manufacturing process offers an opportunity for air to become trapped. By understanding the common causes of bubble formation in solar panel adhesives—such as surface contamination, improper mixing, and outgassing—manufacturers can implement the necessary controls to ensure their products last for the intended 25 to 30 years in the field.

Reducing voids not only improves the structural integrity of the module but also protects the sensitive electronic components from the elements, ensuring maximum energy yield and a higher return on investment for solar plant operators. As the industry moves toward larger formats and higher-efficiency cells, the precision of adhesive application will only become more critical.

If you are looking to optimize your solar assembly process or are facing challenges with adhesive performance, professional consultation can help bridge the gap between failure and reliability. [Contact Our Team](https://www.incurelab.com/contact) today to discuss your specific bonding requirements and discover advanced adhesive solutions tailored for the solar industry.

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