CHARACTERISATION OF OUTGASSING CONTACT MATERIALS FOR MINIATURE RELAYS L. Koller, M. Bizjak and S. Spruk Institute for Electronics and Vacuum Technology Ljubljana, Slovenia * Iskra STIREL, Ljubljana, SLovenia Keywords: miniature relays, electromagnetic relays, hermetical relays, component parts, vacuum outgassing, contact properties, Au electroplating, contact resistance, profesional electronics, testing, experimental results, AES, Auger electron spectroscopy Abstract: Systematic investigations of vacuum outgassing for hermetic relays with AgCdO/AGPHOR and PdAg30 Au electroplated contacts were done The experimental vacuum system constructed and built at our institute was additionally equipped with quadrupole mass spectrometer tor residual gas analysis. Prior to the final encapsulation the relays were baked at the constant temperature of 125 C and outgassed in vacuum 1 x10 mbar for several hours. The residual atmosphere was analysed every hour; in residual gas mixture, hydrogen, carbon monoxide, carbon dioxide water vapour and remanents of cleaning chemical agents (ethanol, trichlorethylene) and hydrocarbons were found. Residual gas analysis showed that the concentration of impurity gases depends on materials and their treatments in different technological phases. Karakterizaclja razplinjenega kontaktnega materiala za miniaturne releje Ključne besede: releji miniaturni, releji elektromagnetni, releji hermetični, deli sestavni, razplinjevanje vakuumsko, lastnosti kontaktov, pozlatitev elektrokemijska, upornost kontaktna, elektronika profesionalna, preskušanje, rezultati eksperimentalni, AES Auger spektroskopija elektronska Povzetek- Sistematično smo raziskovali hermetične releje z AgCdO (AGPHOR lot folija) in PdAg30 elektrokemijsko pozlačenimi kontakti. Eksperimentalni vakuumski sistem, ki smo ga uporabljali, je bil konstruiran in narejen na našem inštitutu. Dodatno smo ga opremili s kvadrupolnim masnim spektrometrom za analizo preostale atmosfere v relejih. Pred dokončno inkapsulacijo smo preiskovane releje razplinjevali nekaj ur pn konstantni temperaturi 125°C v vakuumu 1x10"® mbar. Vsako uro smo analizirali atmosfero v relejih. V izmerjeni mešanici plinov smo odknli vodik, ogljikov monoksid, ogljikov dioksid, vodno paro, ostanke kemijskih čistil (etanola in tnkloretilena) in klorovodike. Analiza je pokazala, da je koncentracija plinskih nečistoč odvisna od materialov samih pa tudi od njihove obdelave v različnih tehnoloških postopkih. 1. INTRODUCTION Contamination film formed on the surface of electric contacts is one of the most serious causes of failure of hermetic relays. It deteriorates the contact resistance and device reliability. The most common types of contamination films are oxides and othercorrosion products particles, layers formed by thermal diffusion processes, debris produced by mechanical wear and fretting, further evaporation outgassing, and condensation on contact surlaces of volatiles from isolation materials and those originating from manufacturing processes (1-9). Systematic investigations of vacuum outgassing of hermetic relays are done. The experimental vacuum setup was designed and assembled at Institute for Electronics and Vacuum Technique, Ljubljana. It has been additionally equipped with quadrupole mass spectrometer for residual gas analysis. 2. EXPERIMENTAL The experimental set up, designed and assembled specifically for vacuum outgassing of hermetic relays is shown in Fig. 1. The vacuum system consists of rotary Fig. 1a: Experimental vacuum system (scheme) for outgassing process for hermetic reiays: 1-vacuum chamber, 2-vacuum system, 3-PNG head, 5-mass spectrometer, 6-piate vaive, Z-A/a chamber for finai hermetic relays incapsulation Fig. 1b: Experimental vacuum system (photograph) vane pump and turbomolecular pump enabling to attain a vacuum of at least 1x10 ® mbar. The vacuum chamber which can be baked up to 300°C is equipped with a resistive heater. A thermocouple Fe-CuNi, 0.5 mm in diameter, is in thermal contact with one of the outgassed relays in the middle of the vacuum chamber. For residual gas analysis the quadrupole mass spectrometer Leisk 1000 M with AMU 2-100 has been used. Prior to the final hermetic incapsulation the relays are baked at constant temperature of 125°C in a vacuum of 1x10'^ mbar for several hours. The residual atmosphere has been analysed every hour. 3. RESULTS AND DISCUSSION The first analysis of residual atmosphere was made in an empty and unbaked stainless steel chamber after a few days of continuous pumping. The base pressure in chamber was 2x10"® mbar. Mass spectrum in Fig. 2 shows the outgassing products in the empty chamber. This spectrum is typical for a standard vacuum system with very small air leaks and no unusual gas sources; it shows that the most prominent outgassing product in the empty vacuum chamber is a mixture of water vapour, CO and N2; small quantities of hydrogen and some hydrocarbons are also released in the empty chamber at this temperature as expected. The spectrum in Fig. 3 was obtained after one hour's baking of the empty chamber at 125°C. This spectrum I II Ü Fig. 2: Mass spectrum showing the outgassing products of the empty chamber 0.5 41 29 57 55 m/e Fig. 3: Mass spectrum of the outgassing products of the empty chamber after one hour baking shows the main outgassing product consisting of water vapour, CO and N2 and unusual peaks typical for ethanol, trichlorethylene (mass 31, 45, 60) supposedly remanents from cleaning processes; some hydrocarbons are also released. The spectrum in Fig. 4 was obtained after 24 hours baking of the empty chamber at the same temperature. Total pressure attained was 1.3x10® mbar. This spectrum is similar to that shown in Fig. 2, which shows the empty chamber without baking. Finally, the mass spectrum represented in Fig. 5 shows the outgassing products of miniature relays baked at 125°C. The system pressure in this case was 1x10'® mbar. The spectrum was registered 30 minutes after bringing the miniature relays up to the temperature. In the spectrum considerable partial pressures of ethanol. Fig. 4: Mass spectrum of the outgassing products of the empty chamber after 24 hours baking 0.5 32 31 43 57 55 45 60 I Fig. 5: rn/e Mass spectrum of the outgassing products of miniature relays (contacts PdAg30/Au) at 125"C in a vacuum of 1x10 mbar after 30 minutes hydrocarbons, oxygen and CO2 can be seen. Other spectra indicate also appreciable concentrations of water vapour, CO and N2. Residual atmosphere was analysed every hour. After 24 hours of relay outgassing process the spectrum in Fig. 6 was registered. The background system pressure was 3x10"® mbar. A comparison of this spectrum with that shown in Fig. 4forthe empty vacuum chamber at 125°C, reveals that both spectra are quite similar, indicating that the baked relays are ready for final incapsulation. The most useful and often the simplest method for detecting contamination on an electric contact surface is to determine its contact resistance. Contact resistance of vacuum outgassed relays with PdAg30/Au contacts was measured immediately after hermetic incapsulation and later in constant time intervals of 7, 14, 21 and 42 days. For a comparison the contact resistance of nonoutgassed relays was measured. The results are collected in Table 1. Initial contact resistances of nonoutgassed and outgassed relays were very similar. However, the difference in 0.5 28 41 57 Fig. 6: UlLLiLl^ m/e Mass spectrum registered after 24 hours of the relay (contacts PdAgSO/Au) outgassing process Sample no. nonoutgassed relays 1 2 3 4 5 6 7 8 9 10 R (mQ) after incapsulation 65 70 55 60 70 55 65 70 60 55 R (ma) after 7 days 120 130 110 140 100 90 120 145 100 90 R (ma) after 14 days 205 180 175 250 200 150 170 220 205 195 R (mü) after 21 days 230 190 175 255 205 160 170 230 210 205 R (mO) after 42 days 250 300 210 280 250 210 180 245 230 220 Sample no. outgassed relays 11 12 13 14 15 16 17 18 19 20 R (mQ) after incapsulation 70 60 55 75 70 60 60 50 60 65 R (mi2) after 7 days 70 60 55 80 70 60 60 50 60 65 R (mil) after 14 days 70 60 55 85 70 60 65 50 60 65 R (mQ) after 21 days 70 60 55 85 70 60 65 50 60 65 R (ma) after 42 days 70 60 60 85 70 60 65 50 65 65 Table 1: Contact resistance of nonoutgassed and vacuum outgassed relays (contacts PdAg30/Au) measured immediately after hermetic incapsulation and in constant time intervals after 7, 14, 21 and 42 days itbllSIH, Fig. 7a: at m a r increase was noticed. Therefore some relays were opened and their contacts analysed (Fig. 7a and 7b). Dark spots found on the contacts probably caused the increase of contact resistance. It seems that the relays mentioned were not sufficiently outgassed. Detailed examination of the phenomenon is planed in the near future. ♦ m *. L S * 'A r ' '.f k Fig. 7b: Pictures of the contaminated contact after outgassing contact resistance was as early as after 7 days enormous. In relays which were not treated with vacuum outgassing contact resistance increased higher than it is qualified in current standards for miniature hermetic relays (0.1 ohm max). When contact resistance of miniature relays with AgCdO contacts was measured after outgassing considerable 4. CONCLUSIONS The experimental vacuum system set up was designed and assembled specifically for vacuum outgassing of hermetic miniature relays. Systematic investigation of vacuum outgassing of hermetic relays were done. Residual gas analysis shows that outgassing products consist of remanents of cleaning chemical agents (ethanol, trichlorethylene), a mixture of water vapour, CO, N2 and some hydrocarbons originating from rotary pump oil. The results of experiments described above show clearly that the outgassing process is indispensable and should be included in the technology for producing of reliable hermetic relays qualified to MlL-R-3906 and MIL-R-5757 standards. REFERENCES 1. F.H, Reid and W. Goldig, Gold als Oberfläche, Eugen G. Lenze, Saulgau (Wuert) (1982). 2. S. Sinharoy, W.J. Lange, C.B. Friedhoft, J. Vac. Sei. Technol. A8, 2 (1990) 930. 3. A,G. Zalužin, Atomnaja Energ. 47 (1979) 113. 4. H.D. Fischer, Analysis of Volatile Contaminants in Microcircuits, Solid State Technology 1978. 5. R. Holm, Electric Contacts Handbook, Springer, New York 1967. 6. R.G. Alefeld, J. Foike, Vodorodv metallah, Mir, Moskva 1981. 7. M. Wutz, H. Adam, W. Walcher, Theorie und Praxis der Vakuum^ technik, Friedr. Vieweg und Sohn, Braunschweig, Wiesbaden 1982. 8. J.H. Leck, Pressure Measurements in Vacuum Systems, Chapman and Hall, London 1964. 9. N. Yushimura, T. Sato, S, Adachi, T. Kanezawa, J. Vac. Sei. Technoi. A8,2(1990)924, Prispelo (Arrived): 18.01.94 Sprejeto (Accepted): 16.02.94 Lidija Koller Inštitut za elel