The connector in a hermetic package may seem like minor consideration, but it is a key component that could have serious implications for design, cost, and schedule. Connectors must carry the proper levels of signal and/or power to support the electronic components housed within a package. They must also reliably keep elements from the outside world from entering and damaging mission critical electronics. This article will describe some of the options available and the cost impacts your design decisions may have.
Hermetic connectors have three basic components:
The choices made in each of those areas can have a significant impact on a device’s performance, reliability and costs.
The first consideration for a hermetic connector must take into account the bigger picture: where are you installing it? Housing material selection is application-dependent, but is key to ensure a good match between the connector body and the housing material. Material considerations include:
- Airborne applications, which may push a package design to lower weight metals
- Hot operating environments which would narrow selections to a metal with good thermal resistance
- A corrosive environment which would indicate the need for corrosion resistant materials
The device’s operating environment and method of attach (laser welding vs. solder) will also directly drive material choices. For multi-pin connectors, HSG typically recommends laser welding. For single pin (typically RF) connectors, either laser welding or soldering are the common integration methods.
Hermetic Solutions Group produces hermetic DC connector bodies in:
We also have the unique capability to use our explosive metal welding technology to produce bi-metal connector bodies, typically made of aluminum/stainless or titanium/stainless. These connector bodies feature a stainless steel insert welded into the stainless steel portion of the connector body, with the remainder of the connector body used as a laser weld transition (like metal to like metal) into an aluminum or titanium housing.
These explosively welded connector shells offer an ideal approach to building a high-performance DC connector that will be hosted in a lightweight housing. However, performance does come with a cost. Bi-metal connectors, as described above, will typically add between 25% - 50% to the overall cost vs. solid, single metal options. That said, for decades, our customers have consistently validated the cost/benefit analysis of this approach for high-reliability, light-weight applications. We have thousands and thousands of these connectors operating reliably in a broad spectrum of mission critical applications today. An added benefit to this approach is a greatly simplified replacement process should a connector need to be removed.
Hermetic Connector Format
Hermetic Solutions Group manufactures hermetic connectors in both standard/Mil-Spec configurations and in custom designs. The body material combinations discussed earlier can be used in all of our DC connectors. Unless otherwise stated, all hermetic connectors discussed below are tested for a leak rate of <1x10-9 CC He @ 1 ATM. Available standard styles include:
Sub-D or D-Sub connectors are the largest (and the oldest design) for any standard connector design we manufacture. Although it was first introduced by Cannon in 1952, the design is still in use today, but we typically see it more in legacy applications rather than in new designs.
These are the most common DC connectors that our PA&E Division currently manufactures. They represent an early move toward miniaturization for the D-style connector format. Our Micro-D connectors are built to meet or exceed the requirements of the MIL-DTL-83513 specifications.
This connector design takes the miniaturization trend even further and it is growing in popularity. The Nano-D is a rising star in the defense/aerospace community, where weight and space savings are increasingly important criteria. When made from comparable material, and in the same pin count, a typical Nano-D connector will weigh approximately ¼ that of a comparable Micro-D. It’s a similar story when comparing a Nano-D’s pin spacing (.025”) vs. that of a Micro-D at (.050”). Our Nano-D connectors meet or exceed MIL-DTL-32139.
The 38999 circular connector design can trace it roots back more than 20 years prior to the Sub-D connector’s origination. Hermetic versions of our 38999 compatible connectors are still widely used today in military applications. All aluminum versions of this connector style combine light weight with Beryllium-Copper (BeCu) pins. With this approach, however, thermal cycling can degrade the hermetic performance to the 1x10-5 level.
• CUSTOM CONFIGURATIONS
Hermetic Solutions Group also manufactures DC connectors and feed-thrus based on customer designs. Here, the sky is the limit on design options (within reason), but using standard components can save time and money. Customization will generally add 2x to the cost of a comparable standard connector (this will vary greatly based on quantity purchased).
Standard hermetic connectors have standard non-hermetic mates widely available from our Cristek Interconnects Division. Custom hermetic connectors will likely require a custom mating connector to be built, which can be a cost driver as well.
Application is a primary driver in pin material selection. BeCu is the most common pin material for typical aerospace DC connectors. This material can reduce the necessary diameter by more than half vs. a pin made from Kovar. BeCu can also carry ~3x the current when compared to a similar-sized Kovar pin. We will touch on this below, but specific sealing/insulator technology is required to use a BeCu pin in a hermetic connector. Glass sealing isn’t an option for BeCu pins, as the sealing temperature of the glass would be higher than this pin material will tolerate. Other pin materials commonly used include:
- Kovar - commonly used in glass-sealed DC and RF connectors
- Platinum/Iridium (Pt/Ir) - common pin material for medical implant devices
- Inconel -widely used in high-pressure, high-temperature (HPHT) applications (Inconel is a cost driver)
The higher the pin count, the higher the cost, but it isn’t just the cost of the additional pins. More pins also mean more labor to assemble and process the connectors and impacts overall connector costs.
As an example, a 37-pin Micro-D could be 2.5X the costs of a 9-pin Micro-D (assuming both are made from the same materials).
Pin size can also be a cost factor. The small pins used in a Nano-D format are typically more expensive than a Micro-D pin because they require additional manufacturing requirements and tolerances.
Most hermetic connectors can include pins with wire-bondable flats at little additional cost. However, wiring pins can add substantial (~2x) cost due to labor and complexity. If we do complete the wiring as part of our manufacturing process, you will probably see shorter overall lead times and a simplified supply chain. In some cases, wiring must be completed before integration into a chassis due to limitations on access, so then it becomes a necessary cost.
Plating is another area that may not immediately come to mind when designing a hermetic connector, but it can impact overall costs.
Selective plating is the prime consideration in this area - it means the relieving of plating (via masking or second machining) to eliminate plating in certain areas. These operations require more labor and therefore result in additional costs.
Plating materials are also a consideration. Some plating materials are becoming obsolete or have been banned. For example, SnPb and Cd plating can be very difficult to source because RoHS and REACH disallow the use of those materials due to toxicity concerns.
Soldering operations typically are completed by using Ni/Au plating, however Ag is also a possibility. Long term exposure to oxygen, temperature, etc. will likely reduce the number of viable plating options here. Nickel plating for corrosion resistance is commonly used, but has poor solderability on its own.
At Hermetic Solutions Group, we use both glass and our Kryoflex® material to seal pins into a connector body. The best approach will be determined by your particular application.
RF applications almost exclusively use glass, while DC applications can use either material. Glass seals deliver good RF dielectric constant, are very chemically resilient, and generally less expensive to process. The main issue with a glass seal is that pin material options will be very limited – typically to an iron/nickel alloy like Kovar. Glass sealed connectors are also susceptible to meniscus cracking/propagation and require very high temperature processing.
Kryoflex provides good dielectric strength, resists propagation of cracks and can seal many compatible (and much more conductive copper alloy) pin material options. We also provide different configurations to support several temperature and body options/combinations. Kryoflex seals, while generally more expensive to process, do deliver more dependable long-term reliability.
As you can see, here are a number of considerations when configuring the right hermetic connector for your application. Those different variables offer design engineers a great deal of flexibility when balancing performance requirements and costs.
Hermetic Solutions Group manufactures many hermetic connector formats, including those adhering to standard military specifications, as well as custom configurations. We look forward to sharing our decades of experience manufacturing both standard and custom hermetic connectors with you.
Get in Touch
Contact us at firstname.lastname@example.org to answer any questions you have on this topic. We look forward to hearing from you.
Nathan Foster currently serves as Vice President of HGS's PA&E division. He is responsible for Program Management, Applications Engineering, and Customer Service. In his nearly 30-year career, Nathan has developed specific expertise in the areas of hermetic electromechanical packages, connectors and applications engineering. While serving as Business Development Manager, Nathan led a team that realized double-digit sales growth from 2011 to 2018. Nathan holds degrees in mechanical design and business management.