Monday, March 29, 2021 by
In our recent webinar about electrically conductive sealants and adhesives, our experts covered many topics from electrically conductive filler packages to the physical properties of the materials like adhesive strength, flexibility and working life. Did you miss Introduction to Electrically Conductive Sealants and Adhesives? Watch it now.
The viewer learned the difference between an electrically conductive sealant and an electrically conductive adhesive, why you’d choose one over the other, and the design considerations you need to take now.
During the Q&A portion of the webinar, our experts fielded your excellent questions, so we’ve rounded up our eight top favorites for you below.
- Are there any major chemical incompatibilities that may cause issues with applying an electrically conductive sealant with a non-conductive sealant on apart simultaneously?
With platinum cured silicone systems, sulfur is one contaminant that's known to kill the cure of these materials. There are other materials that kill the cure of silicone materials such as fatty acids. You must be careful when you're using two different types of polymer systems, each with different types of cure systems on the same part. It is something that you want to make sure that there's no interaction between the two systems.
- Can you describe the difference between flame, corona and plasma treatments?
A flame treatment is the use of actual a gas flame right against the surface of the of the part. Flame treatments, corona treatments and plasma treatments all aim to accomplish the same thing: increase the surface energy of the part and improve adhesion.
Plasma treatment usually requires a high energy gas in a vacuum type environment. It's more of a batch process, but that's also very effective in increasing the surface energy of plastics. Corona treatment is the application of an electrical arc on the material. These treatments are usually done right before you intend to cure the material into the part. You want to apply the electrically conductive sealants or adhesive right after these surface treatments, because over time, the surface energy will decrease. And the advantage of the gains that you get by using these surface treatments will be reduced.
- Do electrical properties vary with cure temperature?
The higher the cure temperature, the greater both the mechanical and electrical properties are. With these cross-linking systems, you typically get a more dense and tighter cross-link at the higher cure temperatures, and that's what gives you the better mechanical and electrical properties.
- Is a silver-aluminum filled electrically conductive sealant silver-over-aluminum or aluminum-over-silver?
A silver-plated aluminum particle is on the outside. In many electrically conductive fillers, the outside is either silver or nickel plating over an aluminum particle, a glass sphere, potentially a copper or a graphite particle.
- Over time, is there degradation of conductivity due to oxidation of particles?
With silver-plated copper materials, there can be some degradation over time in oxidation, especially in higher temperature applications. Be sure to note the high temperature limit of the material you’re interested in. Some of our silver-plated copper particles have an organic coating or other stabilizing surface treatment which helps to reduce the oxidation over time. While it is true that there are some silver copper particles that may show degradation or oxidation over time, especially at higher temperatures, specifically, there are other silver-copper fillers that that we offer that don't show that same degradation. It's specific to the filler itself.
- How do you spec an electrically conductive fillers for particle size, shape, and surface area?
For particle size, shape and surface area, we use a Microtrac to characterize the particle size distribution, because most of these particles are not one size. There’s usually a particle distribution for different conductor fillers. The shape of the filler particle also has a huge impact on how it's going to perform in an adhesive or in a sealant. Over years and years of testing and analysis of our conductive fillers, we found out that you don't want to design in a spherical particle for any application where you might see a lot of vibration, like a rotorcraft or aerospace type application, because typically when you vibrate conductive particles that are spherical shape, the electrical performance of the shielding will degrade.
- My products are exposed to terrible conditions such as salt fog, jet fuel, low pressures, high temperature swings, mold, vibration and 30-year lifetime. Any suggestions for keeping our RF covers in place?
Combining electrically conductive sealants or adhesives with an electrically conductive coating will help with these requirements as described above. An electrically conductive coating may help in terms of sealing surfaces and providing a longer field life. Additionally, using an electrically conductive elastomer gasket against fuel splash and salt fog may help protect the internal components, as conductive elastomers are designed for both harsh environments and long field life.
- What effect does a high number of thermal cycles have on RF performance of electrically conductive sealants and adhesives? Specifically, I need performance from 1 - 40 GHz and hundreds of cycles from - 55°C to 105°C.
Our materials are run through thermal cycle testing and we test EMI shielding before and after various thermal cycles. It usually has a lot to do with the type of material and the substrate the material will be applied to. Also, how it will perform after thermal cycling will deepened on how closely the coefficient of thermal expansion is between the compound and the substrate that you're applying the compound to. Other things can influence EMI shielding performance following thermal cycling, like particle size and shape and filler loading of the material. It is important test to the specific substrate that you're going to put these materials on in thermal cycling to determine the outcome.
Did you miss this webinar, or maybe want to watch it again? Watch it for free on-demand now. And so you don’t ever miss another, be sure to sign up for our upcoming webinars.
This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics.