Metal packaging stands out as the preferred choice for high-reliability systems due to the intrinsic impermeability of bulk metals. Whether it's nickel, gold, aluminum, or stainless steel, even thin layers of these metals effectively hinder the transfer of gas molecules across a membrane. The common housing materials, including Kovar, MP35N, and stainless steels (304 and 316 grades), offer robustness and durability for diverse applications. However, achieving a reliable hermetic seal in metal packaging comes with its own set of challenges.

Moisture Challenges

Feed-through seals involve the interconnection of external electrical leads through the package wall to the internal cavity. Typically using materials like Kovar, the lead's coefficient of expansion matches that of the glass material forming the seal. A glass or ceramic bead, heated in a controlled furnace environment, flows to create a seal between the lead and the housing wall. Despite the advantages, challenges emerge, especially concerning moisture.

Moisture Evolution During Firing: study on sealing glasses highlighted three stages of moisture outgassing during firing. The first 30 minutes witness a loss of absorbed moisture on surfaces, followed by a subsequent period of up to 35 minutes involving internal moisture loss as the glass softens. The final stage, occurring between 35 to 50 minutes, sees a loss of chemically bound moisture. Controlling pores and internal moisture alone might not suffice, making glass seals susceptible to physical leak paths.

Hengli furnace's moisture feedback system

Factors Leading to Physical Leaks:

• Poor Surface Preparation:

Adequate oxide finish on the metal package is crucial. An excessively thick oxide layer may be porous or poorly adherent, compromising the seal.

• High Stress in Glass:

Compression or matched seals face challenges. Compression seals, though excellent for many applications, may have thermal cycle performance issues, especially at low temperatures. Matched seals, while better for temperature variations, can lead to glass cracking.

• Mechanical Damage:

Bending stress on the pin can cause glass cracking or detachment of metal from glass.

• Meniscus Issues:

Positive-meniscus joints are vulnerable to damage. Minor flexing of the lead can fracture the thin glass wicked up the lead.

Package and header suppliers are cognizant of these failure mechanisms and employ design strategies to mitigate them, ensuring feed-through systems meet the client's reliability needs. By addressing these challenges, the industry can enhance the integrity of hermetic seals in metal packaging, contributing to the overall reliability of high-performance systems.

HSA Atmosphere Furnace for GTMS 



• 1150 ℃ Maximum Temperature Rating
• Air/Nitrogen/Hydrogen Capable
• <2PPM Gas Tight muffle
• ±1 ℃ Dew point Control
• ±1.5 ℃ Cross Belt Uniformity