AES studies of surface phenomena on liquid indium solder

Abstract

Fluxless vacuum soldering is widely used in optoelectronics for hermetic encapsulation in the production of second and third generation image-intensifier tubes. Extremely clean surfaces are indispensable for obtaining good wetting with liquid solder in this sophisticated sealing technique. A new sensitive investigation method based on Auger Electron Spectroscopy for studies of surface phenomena on liquid indium solder has been developed. An Auger Spectrometer is adapted to study the following phenomena: • -surface oxidation of crystalline and liquid indium in the temperature range from 298 K to 523 K in a vacuum at constant oxygen pressure of 5×10 −5 mbar with oxygen time exposure up to 100 min; • -isothermal dissociation of In 2O 3 thin film on liquid indium surface described by reaction: In 2 O 3( c)+4 In(1) = 3 In 2O(g) at the temperatures of 633 K, 675 K, 750 K and 820 K in a vacuum below 1×10 −9 mbar. The equation for In 2O vapour pressure calculation log p( In 2 O) = (−12536/ T)+12.75 was obtained from thermodynamic functions for bulk materials and from equilibrium of the afore-cited reaction.