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Laser Weldable, Hermetic Radio Frequency Case Study

Laser Weldable, Hermetic Radio Frequency Case Study

Customer Challenge

A customer contacted Winchester Interconnect in need of a solution to repair a hermetically sealed RF package that had failed in the field. The failure identified was a loss of hermeticity in the solder joint at an RF feedthrough connector location. Solder reflow was not an option with a fully populated unit as the temperature of the soldering process would cause harm to electronic components within the package.

Challenge Review

RF and Microwave packaging is a high-performance product often used in high-cost of failure applications. These products are used in aerospace and space communications systems requiring optimal performance across various environments, temperatures, and altitudes. While more expensive than other packaging techniques, hermetic packaging provides the conditions needed for optimal performance in any environment.

Typically, hermetic RF connectors are manufactured with glass sealing technology because of the ability of the glass to perform at high frequency, in some cases up to 100 GHz. Glass-to-metal hermetically sealed RF connectors have been traditionally integrated into hermetic packages using solderable technology, solder being the only reliable technology available to bond the glass seals to the electronic chassis metallurgically. Glass-to-metal RF connectors are typically sealed using low coefficient of thermal expansion (CTE) materials such as Kovar. Integrating Low CTE materials into high CTE materials, e.g., Kovar into Aluminum, using solderable technology presents challenges including but not limited to:

  • Long-term reliability of the hermetic seal
    • Many applications require electronic packaging to function at high and low temperatures ranging from above 100°C to below 0°C. Sealing low CTE material into high CTE material presents high-stress conditions during temperature changes. The stress on the glass seal/solder joint causes the seals to separate and lose the hermetic seal over time.

  • Inability to rework / repair connector locations
    • Typically solderable RF connectors are sealed using 80/20 AuSn, with a melting point of 280°C. After packages are integrated with sensitive materials which cannot withstand the AuSn reflow temperatures, connector replacement is not an option.
  • Additional sub-assemblies are needed to adapt the required interface (SMP, SMPM, SMA, etc.)
    • Glass seals are manufactured by sealing a center contact to a ferrule and soldered in a chassis. After installing the glass seal, a bolt-on flange mount adapter is required to allow mating of the RF cable to the connector.

Winchester Solution

Winchester Engineers proposed a rework option to replace the solderable RF connector with a laser-weldable RF connector. The damaged connector was removed using precision machine processing and replaced with a laser weldable connector. The small heat-affected zone (HAZ) of a laser weld process would not harm electronic components within the package.

Winchester’s laser-weldable feedthroughs can match CTE across the glass-sealed RF connectors materials to the package’s material using Winchester’s explosion-bonded material technology. The match of CTE gives the package long-term reliability across a wide spread of environments, temperatures, and altitudes. Laser weldable RF connectors manufactured by Winchester can transition low CTE material of glass seals, Kovar, to many materials including but not limited to Aluminum, titanium, and stainless steel.

Customer Improvement

By choosing Winchester’s laser-weldable RF connector technology, the customer can expect these improvements to their design:

  • Adaptable to high CTE alloys, which provides long-term reliability during thermal shock.
  • Ability to replace connectors if damaged during manufacturing.
  • Isolates the glass seal of the RF connector to not only protect against thermal expansion and any mechanical stress applied to the package.
  • Many interface options can be designed directly into the connector, eliminating the need for bolt-on adapters.