L–Thermal Sensor Bonding
Lab Guide & Certification Protocol
1. Overview
For attaching mm-scale thermistors to copper or other substrates under 0–200 °C conditions, three adhesive classes cover many recurring scenarios (under ambient conditions):
Industrial thermal epoxies — for external components, housings, and non-optical mounts
Optics-grade, low-outgassing epoxies — for internal laser/SHG environments
High-temperature sensor-grade epoxies — for occasional >150 °C or structural bonding
⚠️ Laser Safety Reminder: All adhesive work inside laser cavities must only begin once the laser is powered down, locked out, and beam paths secured. Wavelength-specific eyewear is mandatory whenever the enclosure is open. See: Bonding of Optical Components in High-Power Laser Beam Paths for cavity-specific protocols.
1.5 Safety Prerequisites & Protocols
A. Training & Authorization
✓ Completed institutional chemical safety training
✓ Cavity Work: LSO authorization + laser safety certification required
✓ Must review SDS for all adhesives listed in Section 2 (links provided below)
B. Personal Protective Equipment (PPE)
Standard (All Jobs):
Nitrile gloves (6 mil+)
Safety glasses (side shields)
Lab coat
Cavity/Laser Work:
Laser safety eyewear (OD 7+ @ 1064 nm / OD 5+ @ 532 nm)
Thermal Work:
Heat-resistant gloves (for bake-out handling >60°C)
C. Ventilation & Surface Prep
Mixing: Fume hood required for Stycast/EPO-TEK (amine hardeners)
Abrasion Hazards:
Metals: Standard ventilation
Ceramics/Glass/FR-4: N95/P95 dust mask or respirator required. Perform in fume hood or use wet-abrasion to control hazardous dust (silica/glass fibers)
AlN (Aluminum Nitride): Hydrolysis risk (ammonia release) if abrading aged AlN in humid air—use fume hood
D. Chemical & Thermal Response
Skin Contact: Wash with soap + water ≥15 min. NEVER use solvents on skin
Thermal: Cool-down time ≥30 min before touching with thermal gloves; ≥60 min for bare hands
Waste:
Uncured epoxy → Chemical Waste
Solvents → Organic Waste
2. Adhesive Comparison Table
0.67 W/m·K
–55 to 130 °C
Lap shear ~7.7 MPa (Al)<br>Moderate rigidity
Low-waste, occasional external thermistor bonding
0.74 W/m·K
–60 to 200 °C
Shore D > 90 (Very High)<br>Structural standard
Structural, batch bonding on external parts
1.52 W/m·K
Up to 260 °C
High Shear (~18.6 MPa)<br>Requires Heat Cure
High-T external mounting (reserve option)
1.04 W/m·K
–65 to 130/155 °C
CTE matched to Copper<br>Low Outgassing (ASTM E595)
Internal SHG/Laser Cavity bonding near optics
Standards Referenced
ASTM E595: Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment – https://store.astm.org/e0595-15r21.html
3. Use-Case Mapping
A. Internal to Laser/SHG Cavity (Critical Zone)
Use: Stycast 2850FT (Cat 9 or 11) or EPO-TEK H74 Why: Low outgassing (ASTM E595 compliant), CTE match protects optics from stress See also: Bonding of Optical Components in High-Power Laser Beam Paths for surface preparation protocols specific to cavity environments
B. External Parts (Structural)
Use: WEICON Easy-Mix HT 250 Why: Strongest mechanical anchor, reliable to 200 °C, good shelf life
C. Occasional / Low-Waste Jobs
Use: MG Chemicals 8329TCS Why: Minimizes waste for single-sensor jobs
4. Application Protocol
4.1 Bond Line Thickness
Target: 0.05–0.15 mm Reason: Thick epoxy layers act as a "thermal expansion jack," lifting the sensor or cracking the joint during heating.
4.2 Surface Preparation
Abrade: Light Scotch-Brite or fine sandpaper (320–600 grit) ⚠️ Wear mask for Ceramic/FR-4 substrates (silica dust hazard)
Clean: IPA or Acetone in Fume Hood See: Cleaning Components After Manufacturing for detailed solvent protocols
Dry: Ensure full evaporation before applying glue (≥5 min air dry)
4.3 Bake-Out (Optics-Grade Only)
Temp/Time: 80–100 °C for 4–12 hours Atmosphere: Vacuum (preferred) or flowing dry N₂ Goal: Drive off volatiles before the part enters the laser cavity
Verification: Visual inspection under magnification (20×) for micro-cracks or haze after cooldown
4.4 Strain Relief
Crucial: Always anchor the cable jacket separately from the sensor head using a cable clamp or secondary glue dot. Do not rely on the thermistor bead to hold the cable weight.
4.5 Substrate Compatibility
Metals (Cu, Al, SS)
Excellent
Bond Aluminium within 1h of abrasion (oxide reformation)
Ceramics (Al₂O₃, AlN)
Good (Stycast matched)
Safety: Dust mask mandatory during abrasion
Glass
Good
Low CTE mismatch with Stycast
Plastics (FR-4, G-10)
Good
Safety: Mask required for fiberglass dust
Difficult (PTFE, PP)
Poor
Require primers (avoid if possible)
5. Dry-Run Training Protocol (Mandatory)
Every user must complete this before their first live cavity installation.
Dry Run A (Mixing): Practice weighing Stycast components (0.01g precision) and mixing without introducing bubbles
Dry Run B (Geometry): Bond a dummy slug. Verify 0.05–0.15 mm thickness and minimal fillet
Dry Run C (Bake-Out): Simulate oven loading and thermal safety (gloves/cooldown)
Dry Run D (Inspection): Use a loupe (10–20× magnification) to check cured dummy for micro-cracks or haze
6. Recommended Lab Stock
MG 8329TCS
Drawer essential (occasional use)
WEICON HT 250
Structural standard
Stycast 2850FT + Cat 9/11
Cavity standard
Precision Scale (0.01g)
Catalyst weighing
Heat-Resistant Gloves
Bake-out handling
Scotch-Brite Pads (7447)
Surface prep
Loupe (10–20×)
Bond inspection
APPENDIX A: Certification Checklist
Trainee: __________ | Supervisor: __________ | Date: _____
PHASE A: Safety & PPE
[ ] PPE: Glasses, Gloves, Lab Coat donned?
[ ] Hazards: Dust mask used for Ceramic/FR-4? Fume hood used for solvents?
[ ] Laser: (If applicable) Lockout and Eyewear protocol demonstrated?
[ ] SDS Review: All four adhesive SDS reviewed? (Circle: Yes / No)
PHASE B: The Mix
[ ] Stycast: Bulk container stirred? Ratio calculated by WEIGHT?
[ ] WEICON: Nozzle purged? Color uniform?
PHASE C: Application & Process
[ ] Prep: Surface abraded (320–600 grit) & solvent cleaned?
[ ] Thickness: Visual check 0.05–0.15 mm?
[ ] Thermal: Bake-out temp set correctly? Thermal gloves used?
[ ] Inspection: Loupe check for cracks/haze?
SIGN-OFF
[ ] Result: Dummy bond is mechanically sound, clean, and safe?
✓ PERMISSION GRANTED FOR LIVE CAVITY WORK
APPENDIX B: Stycast 2850FT Data Card
LAB STANDARD: STYCAST 2850FT (Blue/Black)
Internal Optics / High Vacuum Only
Mix Ratio (Weight)
100 : 3.5
100 : 5.5
Cure
16h @ 25°C
Heat Only: 2h @ 100°C
Max Service Temp
130°C
155°C
ASTM E595 (TML/CVCM)
Pass (<1.0% / <0.1%)
Pass (<1.0% / <0.1%)
CTE (α)
~25 ppm/K
~25 ppm/K
Safety
Fume Hood Recommended
Fume Hood REQUIRED
⚠️ WARNING: Stir bulk resin before weighing. Filler settles!
Source: Stycast 2850FT TDS
Safety Data Sheets (SDS)
All users must review the following before handling:
EPO-TEK H74: https://www.epotek.com/docs/en/SDS/H74%20SDS.pdf
WEICON Easy-Mix HT 250: https://media.weicon.de/fmds/433287/dld:inline and https://media.weicon.de/fmds/433288/dld:inline
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