Our Technology

The growing requirement to protect critical electronic component parts of electrical and electronic equipment from the actions of harsh environmental conditions has fueled the increased application and subsequent high demand for hermetic enclosures. SMG’s glass to metal sealed hermetic feed-through’s and packages create and maintain conditions to protect the component and or the machine from the outside environment helping to ensure its durability and high level of performance. SMG’s glass to metal seal technology possess a number of positive attributes including its resistance to electrical, thermal, mechanical and chemical solicitations which cannot be attained with use of competing solutions, The components in glass to metal seal, made with expansion controlled materials and sinterized glass offer the maximum warranty of being hermetic to (1×10-9) in a wide interval of temperature from -60°C to +300°C.
Glass to metal sealed components can be soldered to containers with tin alloy, brazed, or even can be electrically welded; Packages can be supplied either Tin or Nickel plated or un-plated at the customer request. The practical method of the application and the relatively low cost allow the broad use of the technology in hermetic electronic applications.

In the compression feed through the external metallic part has a higher coefficient of expansion compared to the glass one. The thick metal ring which surrounds the glass exercises a strong compression which gives the seals a high resistance to mechanical and thermal stimulus thus making the seals very suitable for the use involving high pressures.  The metal which is usually used for the external metallic part is either steel or its alloys, such as stainless steel. On the other hand, the conductors are usually made of iron-nickel alloy. In the match technology seals, metallic alloys which have the same coefficient of thermal expansion as the glass one to which they are connected, are used.

Through a convenient choice of such alloys and glass, as well as an appropriate manufacturing technique it is possible to obtain seals in which there are no tensions even in a large temperature interval. The high costly alloys that are used are either iron-nickel or iron-nickel-cobalt. Following below there are the main differences between the two types:
electrical stimulus: in the compression process, due to the impossibility to make the glass overflow, and in order not to create strength differences which could cause its break , these two types of components have a lower electrical insulation, if the dimensions are the same. On the other hand in the match technology process, where a larger superficial path between the electrodes increases the electrical insulation. Between the two different types, we must underline the difference cost-wise: in fact, the compression seals have a lower manufacturing cost compared to the match technology ones. Moreover, mechanical stimulus speaking, have a better reaction.

The assembling of the glass-metal seals is generally achieved through welding. The most widely used welding methods are soft, brazed, projection and arc welding. In the welding, especially those involving the match technology seals, one must be careful not to submit the seals to excessively high temperatures. Prolong exposure to high temperature will cause damage to the parts mechanical strength due to different thermal conductivity between the glass and the metal. This condition can be avoided thanks to the use of an optimized welding technique, improved shape and mass ratio to ensure a faster heat spread.
In soft welding applications it is essential to use carefully-chosen fluxes in order not to alter the superficial resistance of the glass. More particularly, the ones that contain zinc salts must be avoided, because not only do they generate the phenomenon previously mentioned, but they also are corrosive and very difficult to remove from the glass surface. The use of a flux simply made of colophony in alcohol, as well as the welding method involving hot oil described below are among the only means prone to avoid the decay of the glass surface resistivity.

Soldering in hot oil must be done by submering the surface into the oil (usually vegetable) at 250°C followed by another oil at 50°C (e.g. parafin). The surface to be soldered must be tin coated and must receive a certain amount of tin-lead solder. The advantage of this method is its adhesion, the whole cycle takes a few seconds and the possibility of using the soldering alloy without flux allowing to solder more than one feedthrough at the same time.
This type of soldering is widely used for glass-metal seals soldering.
Other more highly skilled technology methods such as brazing, argon welding and resistance welding. The technical staff at SMG is available to help you implement special soldering methods.

At room temperature the specific resistance of the glass is so high than the insulation resistance is practically only function of the superficial resistance which depends on the relative humidity of the ambient and how clean is the glass surface. The specific resistance of the glass instead becomes more important when we deal with high temperature, even in high relative humidity conditions, a high insulation resistance can be obtained by treating the surface of feed-through, with silicon.

Tightness 
For the pressure of about one atmosphere almost all feed through con be considered permanently hermetic: but should we look for higher pressure(even higher than hundred atmospheres) it will be necessary to consider feed through especially developed

Thermal stresses 
Passers-by can be used in the temperature range -65 to +250 °. The sintered glass, unlike ordinary glass, may also be subjected to sudden jumps in temperature without damage.

Mechanical stress 
The resistance to mechanical stresses of traction, torsion, bending and impact is excellent. In some cases, demand extra resistance to bending stresses and torsion (transistors)

Corrosion resistance 
The corrosion resistance is a function only of the features of the metal part constituting the passer. Therefore apply the same tests and the same parameters used for the evaluation of the susceptibility to corrosion of metals such as for example the test in a saline mist chamber.