The difference between metal and glass packaging of quartz crystal

We all know that the chip type of quartz crystal packaging cap materials are divided into metal materials and GLASS materials (also known as ceramic packaging), referred to as SEAM series and glass series.

SEAM products are the most widely used, the full range of crystal pecifications are SEAM package; At present, the GLASS market has only a few mainstream specifications, such as 8045,7050,5032,3225,2520 and so on are the most common, then what is the difference between the metal and glass encapsulated crystals, we will introduce them respectively.

1. Structural differences:

The base of SEAM structure has a metal ring of KOVAR material on the ceramic material, which is welded to the base with tungsten and gold plating. The metal cover is KOVAR material with chrome surface.

The top cover of the GLASS structure is the same ceramic material as the base, and the edge of the top cover or the base is combined with high temperature and high purity glass. The thermal expansion coefficient of this glass material is very close to the ceramic special design.

2. SEAM and GLASS encapsulation methods

The encapsulation method of SEAM: the KOVAR and the metal cover are pressed together with a roller electrode, and the pulse direct current of low voltage and high current is combined with the rolling of the electrode, and the upper cover and the base are sealed together with the impedance welding method.

GLASS encapsulation method: The workpiece is moved in the high-purity and high-temperature nitrogen tunnel furnace, and with the appropriate rising and falling temperature curve and the design of the base, the gas is discharged at a lower temperature, and the high-purity nitrogen is inhaled at a high temperature and cooling. The glass melts in the highest temperature area to seal the base and the upper cover, and then becomes one after cooling.

3. EMI analysis and comparison

The main difference between the SEAM package and the GLASS package is the difference between the metal cover and the ceramic cover, which is called the EMI problem of the crystal. Of course, there is no denying that the SEAM package does have MHZ high-frequency radiation in the electric field during vibration, and this high-frequency radiation can be shielded and attenuated after the metal cover of the SEAM package is grounded through the PAD.

And because the miniaturized SEAM package crystal is basically used in the vacuum package, and the GLASS package is the internal use of high purity nitrogen. Vacuum packaging can not reduce the electric field, relatively speaking, GLASS packaging because of its internal nitrogen molecules, but has a better attenuation effect.

In general, the SEAM package has a good shielding effect, but it is important to consider the practical differences between different applications.

In SUMMARY:

In terms of electrical characteristics, SEAM crystal and GLASS crystal are only different in the top cover, and the other designs are exactly the same. Therefore, the electrical characteristics are one sample, and FOOT PAD is the same, so the products of the same specifications can be replaced with each other, which will not cause problems in use.

Due to the factor of the upper cover structure, the GLASS crystal will be slightly higher than the SEAM crystal of the same specification, and the approximate difference is between 0.1 and 0.15.

The reliability of SEAM products and GLASS products is not fundamentally different at the commercial or industrial level. Well-designed GLASS products can also meet the level of reliability required by the automotive industry.

Because GLASS material has certain advantages, so in terms of cost consideration, GLASS has a certain cost advantage. Therefore, for some products with high cost restrictions, such as Bluetooth products, mobile phones and other consumer markets, GLASS series products have certain advantages.