Dow Corning 3-4207 Tough Gel A/B Kit
have been used to isolate circuits from the harmful effects of moisture and other contaminants and provide electrical insulation for high voltages. Another use is providing stress relief to protect circuits and interconnections from thermal and mechanical stresses. Gels are usually applied in thick layers to totally encapsulate higher architectures. More recently, gels have found application in optoelectronics due to their stress relieving capability and high refractive index, as well as the stability of these properties over time. For more information on gels for optoelectronic applications, please refer to the LED Materials family data sheet.
A key characteristic of most gels is a naturally tacky surface after cure. This natural adhesion allows gels to gain physical adhesion to most common surfaces without the need for primers. This tacky nature also results in the unique ability to re-heal if the cured gel has been torn or cut, thereby permitting the use of test probes directly through the gel for circuit testing.
Dow Corning® brand dielectric gels are supplied as solventless, typically low-viscosity liquids. Most are designed as two-part products with 1:1 mix ratios (parts A and B). Others are formulated as one-part products, eliminating the need for mixing. The two-part products generally allow for either room-temperature or heat-accelerated cure. One-part products require heat cure. A few specialized one-part gels allow for very rapid UV cure.
Types of Gels
Dow Corning offers a broad range of products with a wide variety of cure speeds, viscosities, hardnesses, colors and other variables. Characteristics range from our general purpose (standard) gels to certain applications that are uniquely sensitive and require specialized properties.
One-Part, Heat-Cure and Two-Part, Room-Temperature or Heat-Accelerated-Cure Silicone Gels: Although most silicone gels are supplied as 1:1 mix ratio two-part products, for easy processing, one-part gels are also available. One-part gels feature long room-temperature storage lives but require heat exposure to cure and have generally longer curing times. Two-part gels offer more processing flexibility with the options of room-temperature or heat-accelerated cure.
Extreme Low-Temperature Products: Dow Corning® brand silicone gels can typically withstand cold environments down to at least -45°C (-49°F). For even colder uses, there are specialized products that will perform down to -80°C (-112°F).
Tough/Firm Gels: For applications that require gels with added strength, there are tough or firm gel products. These materials have enhanced chemical adhesion, but cure slightly harder than standard gels. Some of these products allow rapid room temperature curing and some contain UV dyes for easy inspection.
Low-Volatility Silicone Gels: For some uses, low-molecular-weight volatiles from the gels can result in problems, such as volatiles re-condensing on surfaces, which can interfere with adhesion or lead to decomposition under high-voltage or very high-temperature conditions. Volatiles may also re-condense and obscure/fog optical surfaces. For these situations, low-volatility silicone gels are recommended.
Low Extractable Gels: Compared to standard gels, a low extractable gel such as Dow Corning® 3-4130 Dielectric Gel offers approximately 25-50 percent less extractables with methyl ethyl ketone (MEK) solvent. (Gel extractables are measured by determining the weight loss of a cured gel after immersion in a solvent. The weight loss represents the gel fraction from the cured material in a swollen state.)
Optically Clear Materials: For optical applications, many of the silicone gels are highly transparent in many wavelengths including the visible range. These materials have some of the highest transmission values of any polymeric materials in selected wavelength ranges. They also provide excellent stress relief and their properties do not vary significantly with time or environmental exposure. For more information on these products, please refer to the LED Materials family data sheet.
One-Part UV-Curing Gels: For applications requiring extremely rapid cure, faster than a traditional room-temperature or heat-accelerable cure product offers, UV-curing gels offer cure within seconds, even in the presence of temperature-sensitive components. However, deep-section cure is generally not possible with these materials.
Solvent-Resistant Gels: Unlike standard silicone gels, which are non-polar and susceptible to swelling in solvents and fuels, fluorosilicone solvent-resistant gels have an increased polar nature and provide improved resistance in applications with solvent and fuel exposure.
Flame-Resistant Gels: For applications requiring UL 94V flammability classification, Dow Corning offers a selection of flame-resistant gels (as listed in section QMFZ2 files E40195, E55519 and E251343). Refer to Underwriters Laboratory website (www.ul.com) for specific details.
Thermally Conductive Gels: Most gels are formulated without fillers. However, for applications that require both heat dissipation and the soft nature of silicone gels, thermally conductive gels include conductive fillers. This significantly increases the thermal conductivity values of these materials to >0.8 watts/meterK. For more information on these gels, please refer to the Thermally Conductive Materials family data sheet.
Thixotropic Gels: Unlike traditional gels supplied as low-viscosity liquids, thixotropic gels are formulated to reduce the tendency to flow and allow the gels to be more easily contained in specific areas of a module.
Fast Formulation of Custom Gels: Dow Corning manufactures a wide variety of dielectric gels to meet the needs of most application and process situations, and we are continuously expanding the product offerings in each of these families to ensure that there are specific products to meet your needs. However, if you can’t find a match for your needs, Dow Corning can modify any of our existing products to help meet your exact needs through our Fast Formulation process. Examples of Fast Formulation options include modification of a product’s cure schedule, rheology, viscosity or conductivity – all in a timely manner.
Product Finder: Dow Corning features a unique interactive product finder on our website that can help you pick the right materials for your applications. You can access the product finder at www.dowcorning.com/electronics by selecting “Technical Data” on any of our product family pages.
Production of Prototype Printed Boards or Process Design: We can produce printed boards or test patterns for early evaluation of a material’s abilities. Based on our extensive industry experience, we can advise you on the best methods and conditions for your process.
Analytical, Environmental and Physical Testing: We have expertise to share to monitor quality, perform specialized testing for troubleshooting, or simulate accelerated service conditions.
Equipment Recommendations: Through many years of providing electronics materials, Dow Corning has developed strong alliances with key equipment suppliers worldwide. Save time and expense by taking advantage of these alliances to ensure the optimum integration of material and processing.
Consultation with Technical Experts: Have our experts visit your facility or join us at one of our global application centers to work together on your material and processing needs. We can provide seminars and training for your personnel to allow them to work more knowledgeably. With material, process and equipment integration solutions from Dow Corning, you can manufacture more modules and assemblies in less time, at less cost, with fewer shutdowns and fewer customer rejects.
Special Packaging: Our products are supplied in a variety of standard package types and sizes but if these will not meet your need, let us know. We also have a number of authorized repackagers we can call upon to help.
Tutorials: Gel materials tutorials, including an overview and a processing tutorial, can be found on our website (dowcorning. com/electronics). The tutorials are accessible from the product family pages or the left-hand navigation bar under Technical Library.
HOW TO USE
Mixing Two-Part Gels: Some gels are supplied in bladder packs that avoid direct air contact with the liquid gel components, allowing use of air pressure over the pack in a pressure pot for dispensing. Do not apply air pressure directly to the liquid gel surface (without the bladder pack) as the gel can become supersaturated with air and bubbling can occur when the material is dispensed and cured. Use of bladder packs prevents bubbling, maintains cleanliness and avoids gel contamination.
In general, gels are supplied as two-part products that are mixed in a 1:1 ratio (Parts A and B); one-part gels are available that eliminate the need for mixing. Gels can be dispensed manually or by using one of the available types of meter mix equipment. Typically, the two components are of matched viscosities and are readily mixed with static or dynamic mixers, with automated meter-mix normally used for high volume processes. For low-volume applications, manual weighing and simple hand mixing may be appropriate.
Inaccurate proportioning or inadequate mixing may cause localized or widespread problems affecting the gel properties or cure characteristics. If possible, the potential for entrapment and incorporation of gas (typically air) should be considered during design of the part and selection of a process to mix and dispense the gel. This is especially important with higher-viscosity and faster-curing gels. Degassing at >28 inches (10-20 mm) Hg vacuum may be necessary to ensure a void-free, protective layer.
Working Time and Cure: Working time (or pot life) is the time required for the initial mixed viscosity to double at room temperature (RT). For two-part, addition-cure products, the cure reaction begins when Parts A and B are mixed. As the cure progresses, viscosity increases until the material becomes a soft gel. For one-part, addition-cure and UV-cure products, the viscosity either increases at a much lower rate or does not change significantly at RT. Cure conditions for each product are shown in the typical properties table. Cure is defined as the time required for a specific gel to reach 90% of its final properties. Gels will reach a no-flow state prior to full cure. Addition-cure silicone gels may be RT and heat cure or exclusively heat cure. Adding heat accelerates the cure reaction.
For heat-cure products, additional time should be allowed for heating the part to near oven temperature. For 3-4237 Dielectric Firm Gel, even more time at elevated temperature should be allowed to develop full adhesion strength, which builds after the material has cured to a solid gel. The other toughened gels do not require heat to develop adhesion. UV-cure silicone gels may be cured using an H bulb from Fusion UV Systems, Inc.®, or bulbs with similar spectral distributions. If shadow cure is required, Dow Corning® 3-6371 UV Gel features a secondary moisture cure that will convert a 5-mm-thick layer to a nonflow gel after approximately seven days, depending on ambient conditions. Cure schedules should be verified in each new application.
Useful Temperature Ranges
For most uses, silicone gels should be operational over a temperature range of -45 to 150°C (-49 to 302°F) for long periods of time. However, at both the low and high ends of the temperature range, behavior of the materials and performance in particular applications can become more complex and require additional considerations. For low-temperature performance, thermal cycling to conditions such as -55°C (-67°F) may be possible, but performance should be verified for specific parts and assemblies. Factors that may influence performance are configuration and stress sensitivity of components, cooling rates and hold times, and prior temperature history. Specialized products, such as the low-temperature gels, can perform at -65°C (-85°F) and below. At the high-temperature end, durability of cured silicone gels is time and temperature dependent. As expected, the higher the temperature, the shorter the time the material will remain usable.
In the manufacture of electronic devices, salvage or rework of damaged or defective units is often required. Removal of Dow Corning dielectric gels to allow necessary repairs can be assisted by using Dow Corning® brand OS Fluids. Additional information regarding these products is available from Dow Corning. Digestive stripping agents, such as SU100 from Silicones Unlimited, can also be used. In addition, if only one component needs to be replaced, a soldering iron may be applied directly through the gel to remove the component. After work has been completed, the repaired area should be cleaned with forced air or a brush, dried, and patched with additional silicone gel.
Certain materials, chemicals, curing agents and plasticizers can inhibit the cure of Dow Corning dielectric gels. Most notable of these include:
- Organotin and other organometallic compounds
- Silicone rubber containing organotin catalyst
- Sulfur, polysulfides, polysulfones, or other sulfur-containing materials
- Amines, urethanes or amine-containing materials
- Phosphorous or phosphorous-containing materials
- Unsaturated hydrocarbon plasticizers
- Acidic materials (usually organic acids)
- Some solder flux residues
If a substrate or material is questionable with respect to potentially causing inhibition of cure, a small-scale compatibility test should 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 certain situations, toughened gels may appear fully cured but have reduced or no adhesion. This may result from slight inhibition at the interface.
Storage and Shelf Life
Storage conditions and shelf life (“Use By” date) are indicated on the product label.
These products are neither tested nor represented as suitable for medical or pharmaceutical uses.
In general, Dow Corning dielectric gels are available in batch-matched kits containing both Part A and Part B components. Packages that are typically available include 210-mL dual cartridges, one-gallon pails, five-gallon pails, and 55-gallon drums. Not all gels may be available in all packages, and some additional packages and package sizes may be available.
Safe Handling Information
PRODUCT SAFETY INFORMATION REQUIRED FOR SAFE USE IS NOT INCLUDED IN THIS DOCUMENT. BEFORE HANDLING, READ PRODUCT AND MATERIAL SAFETY DATA SHEETS AND CONTAINER LABELS FOR SAFE USE, PHYSICAL AND HEALTH HAZARD INFORMATION. THE MATERIAL SAFETY DATA SHEET IS AVAILABLE ON THE DOW CORNING WEBSITE AT WWW.DOWCORNING.COM, OR FROM YOUR DOW CORNING REPRESENTATIVE, OR DISTRIBUTOR, OR BY CALLING YOUR GLOBAL DOW CORNING CONNECTION.
Health and Environmental Information
To support customers in their product safety needs, Dow Corning has an extensive Product Stewardship organization and a team of Product Safety and Regulatory Compliance (PS&RC) specialists available in each area.
For further information, please see our website, www.dowcorning.com, or consult your local Dow Corning representative.
Limited Warranty Information – Please Read Carefully
The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer’s tests to ensure that Dow Corning’s products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent.
Dow Corning’s sole warranty is that the product will meet the Dow Corning sales specifications in effect at the time of shipment.
Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted.
DOW CORNING SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WARRANTY
OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY.
DOW CORNING DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES.