The Mass Spectrometry technique involves the ionization and separation of gas molecules as they flow from the package cavity followed by a measurement of their relative abundance (ppmv) as a function of their mass-to-charge ratio (m/z).
Hermetic devices are loaded on the instrument one at a time. The inlet chamber (cf. scheme below) is then subjected to high vacuum before the pin punctures the device, thereby releasing the gaseous content into the system.
By controlling the size of the transfer passage, the gases flow into the analyzer at a predetermined rate. Under the energy of an electron beam, gas molecules eject electron(s), form ions, and fragment to some degree. Each substance has its own unique fracture pattern which is dependent on its chemical structure and instrument settings. As the ions enter the quadrupole mass filter, they are manipulated by electrical attraction and repulsion allowing a differentiation according to their mass-to-charge ratio (m/z). They are then sequentially counted over a given period of time.
The relative ionic abundance (or intensity) of each fragment is measured over several scans, which gives individual pump-out curves for each Atomic Mass Unit (AMU).
Pump-out curve for an AMU
This raw data is corrected from the background level and integrated to form the mass spectra of the gas sample (peak intensities for each detected AMU).
Mass Spetra of the Gas Sample
Substance recognition is then performed on the entire mass spectra. Recognized substances are then quantitated (volume concentrations are expressed in % or ppm), taking into account overlapping peaks and instrument sensitivity.
Typical IVA Test Report
For substance recognition we are using a proprietary library dedicated to substances generally found in hermetic microelectronic packages : constituents of air, common solvents and cleaning agents, leak testing substances, etc ...
For unknown organic compounds a NIST mass spectra database (with more than 140 000 substances listed) is used to assist in their identification.
Identification of low level residual substances can be difficult, as the signal intensity is generally low (trace gases). Additional techniques are available to positively identify the unknown organic compound(s) : Outgassing Studies and GC/MS.
Find out more about the IVA analysis technique by reading the IVA Test Sequence article.