Brand Dowsil Application Type Pot, Encapsulate 1 Part or 2 Part 2 Part Material Form Liquid, Silicone elastomer Industry Electronics, Optical applications requiring high refractive index, PCB system applications, E-Mobility Solutions, Smart Meters, Electrical applications Manufacturer Dow Chemistry Silicone elastomer, Solvent-free Cure Method 2-Part Cure, Heat Cure Temperature (°C) 100, 150, 125 Cure Time (min) 20, 10, 20 Viscosity (cPs) 19,250, Flowable Color Translucent Ozone Resistance Ozone resistance Chemical Resistance Good High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55, -65 Light Refractive Index (RI) Higher
Technical Data for Dow Dowsil 3-6121 Low Temperature Elastomer
- Pottant / Encapsulant - Pot, Encapsulate
1 Part or 2 Part
- 1 Part or 2 Part - 2 Part
- Part A Name - Base
- Part B Name - Curing Agent
- Elastomer - Silicone elastomer
- Dispenser - Automated metered mixing and dispensing
- 2-Part Cure
Cure Temperature (°C) 100, 150, 125 Test Method Cure Time (min) 20, 10, 20 Test Method Viscosity (cPs) 19,250, Flowable Test Method Linear Shrinkage (%) Minimal shrinkage Work / Pot Time (min) >120 Test Method Mix Ratio 10:1 (by volume), 10:1 (by weight)
General Bond Strength (psi) Good Tear Strength (piw) High, 60 (ppi) Test Method Tensile Strength (psi) High, 625
Ozone Resistance Ozone resistance Chemical Resistance Good UV Resistance UV resistance Environmental Resistance Environmental resistance High Temperature Resistance (°C) 200 Low Temperature Resistance (°C) -45, -55, -65 Moisture/Humidity Resistance Moisture/humidity resistance
Dissipation Factor 0.01000, <0.00100 Test Method Dielectric Strength (V/mil) Good, Durable, 450 Dielectric Constant 2.92, 2.92 Test Method Thermal Conductivity (W/m°K) 0.18, 0.18 Volume Resistivity (O) 4.15 E+14 (ohms/cm)
Shore A Hardness 34 Test Method Elongation (%) 275 Flexibility Flexible
Light Refractive Index (RI) Higher Specific Gravity 1.120 Test Method Coefficient of Thermal Expansion (CTE) 290 (Linear (micron/m °C or ppm ))
Shelf Life Details Shelf life is indicated by the “Use Before” date found on the product label. For best results, Dow silicone encapsulants should be stored at or below 25°C (77°F). 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. Shelf Life Temperature (°F) 77 Shelf Life (mon) 18
Not Good For
Don't Use For Organotin and other organometallic compounds, Silicone rubber containing organotin catalyst, Sulfur, Polysulfides, Polysulfones, Other sulfur containing materials, Unsaturated hydrocarbon plasitcizers, Some solder flux residues
Best Practices for Dow Dowsil 3-6121 Low Temperature Elastomer
Standard silicone encapsulants require a surface treatment with a primer in addition to good cleaning for adhesion while primerless silicone encapsulants require only good cleaning.
In applications requiring adhesion, priming will be required for the silicone encapsulants. See the Primer Selection Guide for the correct primer to use with a given product. For best results, the primer should be applied in a very thin, uniform coating and then wiped off after application. After application, it should be thoroughly air dried prior to application of the silicone elastomer. Additional instructions for primer usage can be found in the information sheets specific to the individual primers.
Dow silicone encapsulants are supplied as two-part liquid component kits. When liquid components are thoroughly mixed, the mixture cures to a flexible elastomer, which is well suited for the protection of electrical/PCB system applications. The 10:1 mix ratio gives one latitude to tune the modulus and hardness for specific application needs and production lines.
Dow silicone encapsulants cure without exotherm at a constant rate regardless of sectional thickness or degree of confinement. Dow silicone elastomers require no post cure and can be placed in service immediately following the completion of the cure schedule.
Thoroughly mixed Dow silicone encapsulant may be poured/dispensed directly into the container in which it is to be cured. Care should be taken to minimize air entrapment. When practical, pouring/dispensing should be done under vacuum, particularly if the component being potted or encapsulated has many small voids. If this technique cannot be used, the unit should be evacuated after the silicone encapsulant has been poured/dispensed. Dow silicone encapsulants may be either room temperature (25°C/77°F) or heat cured. Room temperature cure encapsulants may also be heat accelerated for faster cure. Ideal cure conditions for each product are given in the product selection table. Two part condensation cure encapsulants should not be heat accelerated above 60°C (140°F).
Cure reaction begins with the mixing process. Initially, cure is evidenced by a gradual increase in viscosity, followed by gelation and conversion to a solid elastomer.
Certain materials, chemicals, curing agents and plasticizers can inhibit the cure of addition cure adhesives. Most notable of these include: organotin and other organometallic compounds, silicone rubber containing organotin catalyst, sulfur, polysulfides, polysulfones or other sulfur containing materials, unsaturated hydrocarbon plasitcizers, and some solder flux residues. If a substrate or material is questionable with respect to potentially causing inhibition of cure, it is recommended that a small scale compatibility test be run to ascertain suitability in a given application. The presence of liquid or uncured product at the interface between the questionable substrate and the cured gel indicates incompatibility and inhibition of cure.
In the manufacture of electrical/PCB system assemblies it is often desirable to salvage or reclaim damaged or defective units. With most non-silicone rigid potting/encapsulating materials, removal or entry is difficult or impossible without causing excessive damage to internal circuitry. Dow silicone encapsulants can be selectively removed with relative ease, any repairs or changes accomplished, and the repaired area repotted in place with additional product. To remove silicone elastomers, simply cut with a sharp blade or knife and tear and remove unwanted material from the area to be repaired.
Sections of the adhered elastomer are best removed from substrates and circuitry by mechanical action such as scraping or rubbing and can be assisted by applying Dow brand OS Fluids. Before applying additional encapsulant to a repaired device, roughen the exposed surfaces of the cured encapsulant with an abrasive paper and rinse with a suitable solvent. This will enhance adhesion and permit the repaired material to become an integral matrix with the existing encapsulant. Silicone prime coats are not recommended for adhering products to themselves.
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Cure Temperature Test Methods
|Cure Temperature||Cure Time Test Method|
Cure Time Test Methods
|Cure Time||Test Method|
|20 min||Heat Cure|
|10 min||Heat Cure|
|20 min||Heat Cure|
Viscosity Test Methods
Work / Pot Time Test Methods
|Work / Pot Time||Test Method||Temperature|
|>120 min||Pot life||25°C|
Tear Strength Test Methods
|Tear Strength||Test Method|
|60 (ppi)||Die B|
Dielectric Constant Test Methods
|Dielectric Constant||Test Method|
|2.92||Dielectric constant, 100 Hz|
|2.92||Dielectric constant, 100 KHz|
Dissipation Factor Test Methods
|Dissipation Factor||Test Method|
|0.01000||Dissipation factor, 100 Hz|
|<0.00100||Dissipation factor, 100 KHz|
Shore A Hardness Test Methods
|Shore A Hardness||Shore Hardness Test Method|
Specific Gravity Test Methods
|Specific Gravity||Test Method|