Vacuum Insulated Glazing Technical Series: Vacuum Insulated Glazing Edge-Sealing (Part II)

Vacuum Insulated Glazing Edge Sealing: An Investigation

Introduction:

In Part I we reviewed the structural principles and structural-strength differences of the three most common edge seals.

In Part II we will further examine the three edge seals, covering environmental resistance, environmental compliance, safety, and edge thermal performance.

1. UV Resistance

Residual organics in the edge-sealing material reduce VIG thermal performance under ultraviolet exposure.

1. The root cause of the problem

In glass-frit and silver-paste edge sealing,

organic resin solvents are often added to help with coating and forming.

In theory, these organic solvents should fully decompose and volatilize during sintering,

but incomplete decomposition can occur.

Residual organics + ultraviolet exposure

↓

↓

decomposition into CO₂ and H₂O

↓

↓

CO₂ → absorbed by getters

H₂O → cannot be absorbed by getters

↓

↓

Vacuum pressure rises → thermal performance decreases

2. UV Resistance

1) Glass-Frit Edge Sealing: High Risk

1. With a sealing temperature of around 400°C, organic decomposition is the least complete, and more residual content remains.

2. Under long-term UV exposure, residual organics can decompose and generate water vapour that cannot be absorbed.

3. If residual organics form connected pathways, decomposition may create gas-leakage channels.

2) Silver-Paste Edge Sealing: Medium Risk

Silver paste goes through the approx. 700°C tempering process, so organic decomposition is more complete than in glass-frit edge sealing.

However, silver-paste sealing may leave residual organics that affect thermal performance:

Thermal performance of VIG using silver-paste edge sealing:

With an evacuation port, heating, and gas ionization:

U-value = 0.42 W/m²·K

Without an evacuation port:

U-value ≈ 0.6 W/m²·K

Differences:

• The evacuation-port unit removes air more effectively

• Combined with heating and gas ionization, it can remove H₂O molecules from the double-glazing cavity.

• By contrast, without an evacuation port, H₂O cannot be removed and continues to affect the vacuum.

3) Solder Alloy Sealing can fix this

It does not use organic solvents.

No harmful gases or organic residues are produced.

➢ No organic-decomposition issues

➢ No CO₂ or H₂O

➢ Resists UV irradiation, long-term sun exposure, and high-temperature/high-humidity conditions.

2. Acid/Alkali Corrosion Resistance

How good are the three sealing methods at resisting acid/alkali corrosion?

Key point: The Ag₃Sn silver-tin intermetallic phase in silver-paste edge sealing can undergo electrochemical corrosion in humid acidic environments. This is a risk that requires particular attention for coastal and high-humidity regions.

3. Environmental and Safety Compliance

As global environmental regulations become more stringent, compliance certification for VIG seals has become a prerequisite for market entry.

Two of the strictest global environmental compliance systems:

1. RoHS: restricts hazardous substances in electrical and electronic equipment

including lead, mercury, cadmium, and hexavalent chromium.

2. REACH: EU regulation on registration, evaluation, authorization and restriction of chemicals

with broader scope and stricter requirements.

Leaded glass-frit edge sealing is being phased out by economies such as the EU and Japan.

Solder alloy seals are compliant with RoHS and REACH.

4. Compatibility with Tempered Glass

Tempered glass is safer and sometimes a necessity for glass used in construction.

How Tempered Glass Works

Tempered glass is produced by heating and rapid cooling.

This process forms a surface compressive stress layer on the glass surface (≥90 MPa).

When broken, it fragments into small blunt particles.

Consequently: The sealing temperature must stay below the stress-relief or annealing temperature of tempered glass.

Compatibility comparison:

• High-Temperature Glass-Frit Edge Sealing: Not compatible

  Its sealing temperature exceeds the stress-relief temperature of tempered glass.

• Low-Temperature Glass-Frit Edge Sealing: Probably not compatible

  Initial surface compression must be raised >140 MPa. Needs precise temperature control. And…

⚠️More:

Ideal tempered-glass surface compression: ≥90 MPa ✅

Low-Temperature Glass-Frit Edge Sealing tempered-glass surface: 64 MPa < Q < 90 MPa

This is unsafe.

because it does not break into small particles like tempered glass,

nor does it shatter like ordinary glass.

The breakage pattern could be unpredictable.

Silver-Paste Edge Sealing & Solder Alloy Edge Sealing: Compatible with Tempered Glass

Both use low-temperature solder alloys. The sealing temperature is far below the stress-relief point.

5. Edge Thermal Performance

Concern:

Since solder alloy edge seals have high thermal conductivity, will they create an edge thermal bridge and reduce overall insulation performance?

Using LBNL THERM, a professional thermal-simulation tool, we modelled and analysed the edge thermal performance of three edge-sealing materials:

Simulation:

Edge-seal width: 8 mm

Edge-seal thickness: 0.3 mm

Thermal conductivity of each material at room temperature:

Glass-frit solder: 1 W/m·K

SAC305 alloy: 54 W/m·K

Active alloy solder: 30 W/m·K

Results:

Conclusion: they are almost identical.

In other words: solder alloy edge sealing does not sacrifice edge thermal performance.

6. In Sum

Notes

RoHS compliance: Depends on formulation.

REACH compliance: Depends on formulation.

Depends on process temperature and surface compression.

7. Added Value of Solder Alloy Sealing

✅ Longer Service Life

A chemical-metallurgical bond gives the seam 5.8 times the shear strength of glass-frit edge sealing. It greatly improves resistance to thermal expansion/contraction and mechanical impact.

✅ Long-Term Stable Performance

With no organic residues and resistance to ultraviolet degradation, the vacuum remains stable longer.

✅ Compatible With Tempered Glass

Lower process temperature.

✅ Hazardous-Material Compliant

RoHS & REACH compliance. Access to higher-end markets.

✅ Usable in Coastal and High-Humidity Regions

Impervious to electrochemical corrosion, and hence safe to use in coastal and high-humidity regions.

✅ No Edge Thermal Performance Loss

The edge thermal performance of our products is almost identical to that of glass-frit edge sealing.

✅ Higher Yield

Our solder alloy sealing process has a higher yield.

Terms (Part II)

About Super Tech & SuperVIG
Fujian Super Tech Advanced Material Co., Ltd. focuses on R&D and manufacturing of high-performance thermal insulation materials and is a major player in the vacuum insulation... (to be completed)
Solder Alloy VIG Sealing is a proprietary technology of SuperVIG.
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