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Description for Dow Dowsil 3-6651 Thermally Conductive Elastomer
Two-part, grey, low modulus, low viscosity, good thermal conductivity, UL 94 V-0 rating.Brand Dowsil Chemical Resistance Good chemical stability Application Type Encapsulate 1 Part or 2 Part 2-Part Material Form Liquid, Polydimethylsiloxane elastomer Industry Protection of electrical applications where heat dissipation is critical., Sensors, Protection of PCB system assembly applications where heat dissipation is critical., High voltage transformers, Smart Meters, E-Mobility Solutions, Smart Home Devices, Heat sinks Manufacturer Dow Chemistry Polydimethylsiloxane elastomer Cure Method 2-Part Cure, Heat Cure Cure Temperature (°C) 120, 100, 150, 70 Cure Time (min) 60, 15, 30 Viscosity (cPs) Low, Flowable, 32,000, 13,350 Color Gray Ozone Resistance Resistant to ozone High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55 Volume Resistivity (O) 8.8E+14 (ohm*cm) Key Specifications UL (Underwriters Laboratory), ULC (Underwriters Laboratories of Canada), NFPA (National Fire Protection Association): UL 94: UL 94 V-0 -
Technical Data for Dow Dowsil 3-6651 Thermally Conductive Elastomer
Overview
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Chemical Resistance
- Chemical Resistance - Good chemical stability
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Application Type
- Pottant / Encapsulant - Encapsulate
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1 Part or 2 Part
- 2-Part
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Material Form
- Elastomer - Polydimethylsiloxane elastomer
- Liquid
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Industry
- Smart Meters
- Smart Home Devices
- E-Mobility Solutions
- Electronics - Protection of electrical applications where heat dissipation is critical., Heat sinks
- Sensors
- Printed Circuit Board (PCB) - Protection of PCB system assembly applications where heat dissipation is critical.
- Transformers - High voltage transformers
- Power Supplies - Power converters
- Industrial - Gap fill
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Chemistry
- Silicone - Polydimethylsiloxane elastomer
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Application Method
- Dispenser - Manual Dispense, Automated meter-mix
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Cure Method
- Heat - Heat Cure
- 2-Part Cure
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Color
- Gray
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Key Specifications
- UL (Underwriters Laboratory), ULC (Underwriters Laboratories of Canada), NFPA (National Fire Protection Association) : UL 94 : V0 - UL 94 V-0
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Brand
- Dowsil
Specifications
Cure Specs
Cure Temperature (°C) 120, 100, 150, 70 Test Method Cure Time (min) 60, 15, 30 Test Method Viscosity (cPs) Low, Flowable, 32,000, 13,350 Test Method Work / Pot Time (min) 6 Test Method Mix Ratio 1:1 (by volume), 1:1 (by weight) Bond Strength
Tensile Strength (psi) 85 Material Resistance
Ozone Resistance Resistant to ozone UV Resistance Resistant to ultraviolet degradation Environmental Resistance Barriers against environmental contaminants High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55 Vibration Resistance/Shock Resistance Barriers against stress-relieving shock, Barriers against vibration absorbers Conductivity
Dissipation Factor 0.00300, <0.00010 Test Method Dielectric Strength (V/mil) Durable dielectric insulation, 325 Dielectric Constant 4.10, 4.10, 4.13, 4.13 Test Method Thermal Conductivity (W/m°K) Good, 1.10, 1.15 Volume Resistivity (O) 8.8E+14 (ohm*cm) Hardness
Elongation (%) 2 Shore OO Hardness 53, 50 Flexibility Flexible Modulus (psi) Low, 3 (Compression at (10%, psi)) Other Properties
Specific Gravity 2.400, 2.370 Test Method Coefficient of Thermal Expansion (CTE) 175 (ppm/°C) Test Method Flash Point (°F) 392.0 Business Information
Shelf Life Details Shelf life is indicated by the “Use By” date found on the product label. For best results, Dow Corning thermally conductive materials should be stored at or below the maximum specified storage temperature. Special precautions must be taken to prevent moisture from contacting these materials. Containers should be kept tightly closed and head or air space minimized. Partially filled containers should be purged with dry air or other gases, such as nitrogen. Any special storage and handling instructions will be printed on the product containers., Shelf life is indicated by the “Use By” date found on the product label. For best results, Dow thermally conductive materials should be stored at or below the maximum specified storage temperature. Special precautions must be taken to prevent moisture from contacting these materials. Containers should be kept tightly closed and head or air space minimized. Partially filled containers should be purged with dry air or other gases, such as nitrogen. Any special storage and handling instructions will be printed on the product containers. Shelf Life Temperature (°F) 86 Shelf Life Type From date of manufacture Shelf Life (mon) 12, 12 Not Good For
Don't Use With non-reactive metal substrates, non-reactive plastic surfaces, Teflon, polyethylene, polypropylene. -
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Best Practices for Dow Dowsil 3-6651 Thermally Conductive Elastomer
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Mixing
Upon standing, some filler may settle to the bottom of the liquid after several weeks. To ensure a uniform product mix, the material in each container should be thoroughly mixed prior to use. Two-part materials should be mixed in the proper ratio either by weight or volume. The presence of light-colored streaks or marbling indicates inadequate mixing.
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Deairing/Degassing
Automated airless dispense equipment can be used to reduce or avoid the need to de-air. If de-airing is required to reduce voids in the cured elastomer, consider a vacuum de-air schedule of > 8 inches Hg (or a residual pressure of 10–0 mm of Hg) for 10 minutes or until bubbling subsides.
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Curing
Addition-cure adhesives should be cured at 100°C (212°F) or above. The cure rate is rapidly accelerated with heat. Thin sections of less than mils may be cured in 15 minutes at 150°C (30°F). For thicker sections, a precure at 70°C (158°F) may be necessary to reduce voids in the elastomer. Length of precure will depend on section thickness and confinement of adhesive. It is recommended that 30 minutes at 70°C (158°F) be used as a starting point for determining necessary pre-cure time. Addition-curing materials contain all the ingredients needed for cure with no byproducts from the cure mechanism. Deep-section or confined cures are possible. Cure progresses evenly throughout the material. These adhesives generally have long working times.
Cure reaction begins with the mixing process. Initially, cure is evidenced by a gradual increase in viscosity, followed by gelation and conversion to its final state. Pot life is defined as the time required for viscosity to double after Parts A and B (base and curing agent) are mixed.
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Cure Temperature Test Methods
Cure Temperature | Cure Time Test Method |
---|---|
120°C | Heat Cure |
100°C | |
150°C | |
70°C |
Cure Time Test Methods
Cure Time | Test Method |
---|---|
60 min | Heat Cure |
15 min | |
30 min |
Viscosity Test Methods
Viscosity | Test Method |
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Low | |
Flowable | |
32,000 cPs | |
13,350 cPs | Mixed |
Work / Pot Time Test Methods
Work / Pot Time | Temperature |
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6 min | 25°C |
Dielectric Constant Test Methods
Dielectric Constant | Test Method |
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4.10 | 100 Hz |
4.10 | 100 KHz |
4.13 | 100 Hz |
4.13 | 100 KHz |
Dissipation Factor Test Methods
Dissipation Factor | Test Method |
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0.00300 | 100 Hz |
<0.00010 | 100 KHz |
Coefficient of Thermal Expansion (CTE) Test Methods
Coefficient of Thermal Expansion (CTE) | CTE Test Method |
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175 (ppm/°C) | (by TMA) |
Specific Gravity Test Methods
Specific Gravity | Test Method |
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2.400 | |
2.370 | Cured |

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