Protecting Electronics Connectors Using Silicone Gel Grommet Seals
Electronics connectors have evolved from simple wire-to-wire interface components to those capable of transferring enormous volumes of data required for applications such as video and autonomous driving. Connectors are also being exposed to more demanding environmental conditions such as liquids, noxious gases, extreme temperatures, mechanical shock, and vibration. In order to improve reliability and longevity, many industries including aerospace and automotive have chosen to include flexible thermoplastic gel-pads in designs.
The properties of Resin Designs’ gel-pads make them excellent candidates for sealing electrical connectors. However, in any sealing application, the seal and the item being sealed are a system and cannot be treated independently. This is also the case with gel seals for electrical connectors. The seal and the connector must be compatible and work together to achieve adequate sealing.
What Are Gel Pads and How Do They Work?
Gels combine two effects to create a seal. First, under compression, gels can conform around a variety of objects, such that the surface of the gel is in contact with the entire surface of the object to be sealed. Once the surfaces are in contact, the thermodynamics of the system favors the coating of the surface by the gel versus by air or water. This allows the gel to seal against air and water. It is the combination of the gel's ability to conform around a surface as well as to coat (or wet) the surface that allows it to seal. One effect without the other would not be useful.
A single gel composite seal is used to seal all contact cavities in a connector. They are not used as individual wire seals. Although a gel composite seal will appear to be a solid piece, it is pre-cut at each position where a contact will be inserted. This minimizes the contact insertion force.
The gel grommet seal must be contained and put under pressure to create a seal. A seal recess is required at the rear of the connector to hold the gel seal. The seal recess must fully contain the sides of the gel seal, as this is the primary sealing interface. Compression is applied to the gel by the use of a cap that locks onto the rear of the connector. The gel seal will be compressed between the bottom surface of the connector seal recess and the compression cap. The gap between the bottom surface of the connector seal recess and the compression cap must be designed and controlled to apply the proper amount of compression to the gel.
Contacts are inserted and removed through the gel seal. It is normal for the contacts to pick up gel during insertion and removal. Extensive testing has been done to verify that the gel on the contacts does not impact the electrical performance. Neither the initial contact resistance nor the long-term contact resistance is adversely affected by the presence of gel.
Gel grommets are stamped from sheet stock. The normal delivery method is to provide pre-cut parts on a continuous mylar backing on reels. Other delivery methods to suit the customer’s handling needs could be examined.
What Applications Are Best Suited to Gel Seals?
No material is a universal solution. Gels are not the best sealing solution in all cases. The following charts outline a few of the application features characterized within the automotive connector market. The ability of the gel to seal any given application is characterized by its compatibility with these application features, among others. Here, we will limit our explanation to the areas of “contact type” and “connector type.”
| Connector Type |
Gel Seal Compatibility |
| Cylindrical |
Best - Usually smooth and well-rounded. |
| Box (Lance-less) |
Good - Most are acceptable for use with gel seals. There is a lot of variation in box contact designs. Some are well-rounded and some have sharp edges. |
| Lanced |
Varies - Generally aggressive -- mainly during
extraction. Smaller sizes are more acceptable than larger ones. |
| Cable to Cable |
A lot is gained by small size and high density on high-contact count connectors. |
| Box Interface |
Full range of sizes from a few contacts in a sensor to high contact counts in major electronics.
Size and density are important. |
| Firewall and High Wire Count Cable to Cable |
Medium to high contact count. Size and density are important. |
The following is a list of the basics to be used to analyze your project and the suitability of gel pads for sealing and protection.
Summary of Design Rules
• The connector must have a rear recess to receive the gel
• The connector must have a compression cap capable of applying pressure on the Initial pressure on gel should be Pi = 1 bar (1 kg/cm2).
• The connector compressed height tolerances should not result in Pi > 2 bars or Pi < 0.5 bar.
• A compression curve needs to be generated for every connector
• Total solid gel support should be between 50 and 70 % of total
• Edge support should be ≥ 2
• The contact/cavity cross-section area should be ≤ 55 %.
• The shape of the contact cavity should reflect the shape of the
• The clearance between contact and contact cavity wall should be > 0.15mm all around.
• The contact should be centered during
• Symmetrical latches, for the compression cap, are recommended along the longer side of the connector
• A 45 ° chamfer on the compression cap is recommended for better distribution of stresses.
• Direct impingement of water sprays on gel grommets must be
Conclusion
Silicone gel pads present designers of electrical connectors with unique properties for increased protection and longevity.
LINK:https://blog.resindesigns.com/protecting-electronics-connectors-using-silicone-gel-grommet-seals
