emi gasketing, passivated options
NEDC manufactures gaskets of all sorts. Our arena of play in the gasket world usually is high value gasketing materials. For that reason, a lot of the build to print items we see include “SILVER FILLED” or “SILVER – COPPED FILLED” A question we get very often, is “What is the difference between PASSIVIATED SILVER ALUMINUM, and SILVER ALUMINUM FILLED”. Great question.
Difference between Passivated/Non-Passivated EMI Gaskets:
Each conductive gasket has metal particles that fill it. These metal particles are filled at a high percentage. This varies from manufacturer to manufacturer. However, the percentage of fill ranges from 60% to 80% by volume. This is an important detail because now you know- by volume most of this gasket is filled with these type particles.
What is Passivation?
PASSIVATED SILVER ALUMINUM fluorosilicone gaskets is essentially a coating on the particles of silver- aluminum. It is designed to make the gasket more inert to weathering/salt-spray than other types of gaskets.
Why is Passivation important for EMI Gaskets?
Here’s the thing. The government has this salt-spray test to test corrosion resistance. This test is usually a 168 Hour Salt Spray/ Salt Fog test. There are a few salt spray/salt fog tests. The main one used is ASTM B117 Salt Fog. Another one of these tests is MIL-STD-810 METHOD 509.5 SALT FOG. Essentially, these gaskets are exposed to an atmosphere that is full of salt fog that would essentially be present near the sea/ocean, and it uses that to show how galvanic corrosion of surfaces may occur in real applications. These are mainly used to test galvanic corrosion. Galvanic Corrosion occurs when two dissimilar metals are joined in the presence of an electrolyte. Note: Since the advent of these type gaskets- other types of gasket have also come out that are good for galvanic corrosion such as nickel-plated aluminum.
Why are not all EMI/RFI Gaskets are this way?
Two Reasons:
- Passivated Silver Aluminum is going to cost you more for sure. I see some OEM manufacturers who charge 50% more for their passivated silver aluminum gaskets than their normal silver aluminum gaskets.
- Passivated Silver Aluminum is something that came out in the early 90’s AFTER the regular silver aluminum filled gaskets came out when these technologies were first created. For that reason, many customers have always used the non-passivated versions, and got by just fine. So this created a legacy of having plain silver aluminum gaskets in applications, and in memories, testing.
emi/rfi corroded flange gasket interface
Types of Passivated Silver Aluminum Fluorosilicone Gasketing by Manufacturer
Cho-Seal 1298, by Parker Chomerics- certified to Type D, MIL-DTL-83528
SSP-550-70, by Specialty Silicone Products- certified to Type D, MIL-DTL-83528
SAS Sealtron 1157 by SAS Industries- certified to Type D, MIL-DTL-83528
5000-F-P by East Coast Shielding- certified to Type D, MIL-DTL-83528
More Information on Passivated EMI Gaskets
NEDC waterjet-cuts, knife-cuts, and die-cuts EMI gaskets all the time. These gaskets are also available with an adhesive backing for ease in application if required. For more information on EMI conductive gaskets, or you believe you have an application that could utilize EMI gaskets, please contact sales@nedc.com.