Gas permeability of adhesives and their application for hermetic packaging of microcomponents

Abstract

The use of adhesives with low gas permeability in packaging microcomponents provides a simple, lowcost alternative to the standard techniques for hermetic packaging. The permeability to helium of various epoxy resin adhesives was determined by means of a mass spectrometer in reference specimens of de®ned dimensions. The adhesive with the lowest permeability to helium was chosen to bond an evacuated LIGA gyrometer package (¯atpack, volume 1.4 cm 3 ). For comparison, a few packages were closed by laser welding. Subsequently, the pressure rise in the sealed packages due to gas permeation and desorption from the walls was measured by the integrated microsensor, and the permeation rate was determined. The permeation rates of as low as 10 )17 m 3 /s achieved in bonded packages are comparable to those measured in laser welded packages. IntroductionMany applications in microelectronics, micro-optics, and microsensors require hermetically sealed packages either to protect microcomponents from chemical reactions with gases penetrating from the environment [1] or in order to maintain a low overall pressure in an evacuated package, e.g., to eliminate the attenuation by air of movable microcomponents [2].Where standard techniques are used for hermetic sealing, such as glass sealing, soldering, welding [3], anodic or direct bonding [4, 5], a speci®c choice of material is required. These techniques, as a rule, are associated with high process temperatures and high process costs. Adhesives can be employed in packaging technology at low process temperatures and with a large variety of materials [6,7]. Process costs can be reduced also because of the ease of handling.As with standard technologies, the required hermeticity of the package is achieved, on the one hand, by the use of hermetic packaging materials, such as metal, ceramics, and glass. On the other hand, the hermetic tightness of the respective sealing interfaces of the materials so joined is a decisive factor.Modern epoxy resin adhesives have very low gas permeabilities and outgassing rates and, consequently, can be used to join materials for hermetic packages if the package has been designed properly.In this study, the permeability to helium of various epoxy resin adhesives was measured by means of a mass spectrometer in reference specimens of de®ned dimensions, and adhesives were used to seal an evacuated LIGA gyrometer package (¯atpack, volume 1.4 cm 3 ). For comparison, a number of packages were also sealed by laser welding. The overall pressure rise in the sealed packages due to gas permeation and desorption from the walls was measured by the integrated microsensor, and the permeation rate was determined from these readings.

Collection management and study of microscope slides: Storage, profiling, deterioration, restoration procedures, and general recommendations

“…11;Traeger 1976;Hagenmaier & Shaw 1991;Pauly 1999;Gerlach et al 2001;Stern & Fried 2007;Wypych 2012;Pethe & Joshi 2013). The permeability coefficient P of a polymer is defined as: P = (volume of permeating gas) x (effective polymer membrane thickness) x (time)…”

“…Unfortunately, data about the permeability of polymers for gases and vapors is provided in the literature in different units, and the exponent of ten is given sometimes with a positive and sometimes with a negative value, even within one and the same publication (Pauly 1999;Wypych 2012 and references cited therein). Reading Traeger (1976) and Gerlach et al (2001) carefully, the exponent of ten should have a negative value for polymers, and this is corrected in Table 11. It has to be kept in mind that the data provided in Table 11 for homopolymers has to be regarded as only a rough estimation of the order of magnitude of permeability of mounting media and coverslip seals, which are composed of a variety of ingredients (Tabs 5,8).…”

“…The permeability may be reduced by a large amount of filler and in more cross-linked resins in comparison to linear polymers, and it will be increased by a plasticizer (Comyn 1986, pp. 317-318;Pauly 1999;Gerlach et al 2001).…”

“…11; comp. discussion in chapter 3.7.2 Permeability to gases and vapor; Schauff 1985;Gerlach et al 2001;Wypych 2012). Gray (1954, p. 58) and Loveland & Centifanto (1986, p. 184) mentioned that a coverslip seal only retarded oxidation of a medium.…”

Reliability of MEMS packaging: vacuum maintenance and packaging induced stress

“…However, it is generally known that the leakage caused by permeation through the glass and silicon is very low. The permeability coefficient for glass is between 10 À19 and 10 À17 m 2 /(s Pa), and that of silicon and metals is between 10 À20 and 10 À22 m 2 /(s Pa) (Gerlach et al 2001), which is very low compared to other materials. Therefore it is thought that the leakage caused by permeation would be smaller than other leakage sources.…”