Borate Glasses: Thermal Expansion Control for Sealing

Overview of Technical Issues:

The borate glass sealing material insufficiently matches the thermal expansion coefficient of the substrate materials during heating-cooling cycles, generating harmful interfacial stress that causes seal cracking, delamination, and hermetic failure; the goal is to optimize borate glass composition to control thermal expansion for reliable sealing performance across operating temperature ranges.

Solution directions generated for this problem

Problem Direction 1 :

ImproveSeal hermetic reliability
VS
ConstraintGlass composition stability

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
Low-oil pharmaceutical emulsion composition containing progestin
Innovative Solution Refine solution

Moisture-shielded borate seal with sacrificial surface reserve

Shield the seal before service
How to solve :
  • Apply 5–15 μm Al2O3-SiO2 barrier on frit by sol-gel or ALD, H2O vapor transmission <10^-4 g/m2·day
  • Pre-fire frit at 380–420°C for 30–60 min in dry N2 dew point ≤-40°C to remove free borate and densify skin
  • Seal at 470–540°C then inspect He leak <1×10^-9 mbar·L/s, coating thickness ±1 μm, CTE drift after 200 cycles ≤0.3×10^-6/K
Expected Effect : Failure <2%/200 cycles, stress <20 MPa, leak rate 10x better, composition tolerance widened to ±1.0 wt%
Risk Control :
  • barrier cracking on cooling
  • pinholes from poor coating wetting
  • overfire causing wetting loss

Problem Direction 2 :

ImproveInterfacial stress resistance
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Method of manufacturing image display device
Innovative Solution Refine solution

Pre-stabilized borate glass with controlled crystallization for stress-tolerant sealing

Pre-treat glass powder to enhance bonding without tight tolerances
How to solve :
  • Pre-heat borate glass powder at 380–420°C for 24–36 hours in controlled humidity (40–60% RH) to induce partial surface hydration and nucleation sites, creating a self-bonding reactive layer that enhances interfacial strength during sealing without requiring ±0.5 wt% composition precision
  • During sealing at 500–580°C, the pre-treated surface layer flows and bonds aggressively to substrate, while bulk glass remains stable — the reactive surface achieves interfacial bonding strength ≥100MPa even with ±1.5 wt% batch composition tolerance
  • Post-seal cooling at controlled rate 2–5°C/min triggers controlled crystallization in the pre-treated layer, locking in a stable microstructure with dispersed crystalline phases (5–15 vol%) that pin cracks and absorb thermal stress over 200 cycles
Expected Effect : Interfacial strength 100MPa achieved; composition tolerance relaxed to ±1.5 wt%; failure rate <3% over 200 cycles; no additional interlayers required
Risk Control :
  • pre-treatment atmosphere control deviation
  • crystallization kinetics variability across batches
  • substrate surface condition sensitivity

Problem Direction 3 :

ImproveGlass composition stability
VS
ConstraintMust not deteriorate

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Multiplexed analyses of test samples
Innovative Solution Refine solution

Pre-stabilization thermal treatment for adaptive borate glass sealing

Pre-stabilize glass via controlled aging then activate during sealing
How to solve :
  • Pre-treat borate glass powder at 380–420°C in 40–60% RH atmosphere for 36–60 hours to induce stable hydration phases and saturate reactive sites, establishing compositional baseline resistant to degradation
  • During sealing at 480–550°C, apply rapid heating rate (15–25°C/min) to temporarily mobilize glass network, enabling adaptive wetting and CTE accommodation at substrate interface while core composition remains locked
  • Post-seal annealing at 320–360°C for 2–4 hours in dry N₂ re-stabilizes surface layer, locking in bonding structure and preventing phase drift over service life — QC via XRD phase fraction ±3%, dilatometry CTE ±0.3×10⁻⁶/K, helium leak rate <1×10⁻⁹ mbar·L/s
Expected Effect : Failure rate <2% over 200 cycles; interfacial stress <18 MPa; composition drift <±0.8 wt% post-treatment
Risk Control :
  • Pre-treatment atmosphere control deviation
  • rapid heating induces micro-cracking
  • annealing incomplete re-stabilization

Problem Direction 4 :

ImproveThermal expansion coefficient matching
VS
ConstraintGlass composition stability

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Nicotine gel
Innovative Solution Refine solution

Process-tuned borate seal with post-lock network stabilization

Tune structure then lock it
How to solve :
  • Use a stable borate base glass with 58-64 B2O3, 18-24 ZnO, 8-12 Al2O3, 6-10 SiO2 wt%, keeping batch tolerance within ±1.0 wt% and powder D50 8-15 μm
  • Seal at 520-560°C for 8-15 min in dry N2 or air dew point below -30°C, then hold 430-460°C for 20-40 min and cool at 1.5-3°C/min to shift boron coordination and lock CTE without changing nominal composition
  • Verify by TMA XRD FTIR helium leak: CTE 25-300°C within substrate match ±0.5×10^-6/K, crystallinity 3-12 vol%, BIII/BIV ratio drift below 10%, seal thickness 80-150 μm, void area below 1%, leak below 1×10^-9 mbar·L/s, 200 cycles from -40 to 200°C with under 2% failures
Expected Effect : CTE match ±0.5×10^-6/K, stress below 20 MPa, failure under 2%, process window widened to ±20°C, about 30-50% lower composition sensitivity than custom multi-oxide tuning
Risk Control :
  • overcrystallization raises brittleness
  • B2O3 volatilization shifts wetting
  • cooling nonuniformity causes CTE scatter

Problem Direction 5 :

ImproveThermal expansion coefficient matching
VS
ConstraintManufacturing precision requirement

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Methods and means for the production of Ig-like molecules
Innovative Solution Refine solution

In-situ thermal gradient tuning of borate glass CTE during sealing process

Use process parameters instead of composition precision to control CTE
How to solve :
  • Apply localized laser scanning (wavelength 1064nm, power 50-150W, scan speed 5-20mm/s) during sealing to create controlled thermal gradients across the glass-substrate interface, inducing differential B-O coordination shifts
  • Implement dual-zone heating profile: substrate preheated to 400-450°C, glass powder heated to peak 550-620°C with ±20°C deliberate variation zones to adjust borate network structure in-situ, shifting CTE by 0.3-0.8×10⁻⁶/K without composition change
  • Use real-time infrared thermography (thermal camera resolution 640×480, frame rate 60Hz) to monitor interface temperature distribution and adjust laser power dynamically, achieving target CTE match within ±0.5×10⁻⁶/K while tolerating glass composition variation up to ±1.5 wt%. Quality control: measure residual stress via photoelastic analysis (acceptance: birefringence <15nm/cm), verify hermetic seal via helium leak test (leak rate <1×10⁻⁹ mbar·L/s), inspect interface via cross-section SEM (no cracks >5μm). Process uses standard borate glass compositions (B₂O₃ 60-75 wt%, SiO₂ 10-20 wt%, alkali/alkaline earth oxides 10-25 wt%) available commercially, eliminating ultra-precise batching.
Expected Effect : Interfacial stress reduced to <20MPa; composition tolerance relaxed to ±1.5 wt%; failure rate <2% over 200 cycles; manufacturing cost -40%
Risk Control :
  • laser-induced microcracking if power exceeds 150W
  • thermal gradient non-uniformity causing localized CTE mismatch
  • infrared monitoring calibration drift
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