Gaseous Cleaning Beneath Surface Mounted Components: Evaluation Using a Beam Lead Test Chip

Temperature, humidity, bias (THB) accelerated aging at 85°C, 85 percent relative humidity (RH), and + 10 Vdc bias has been used to evaluate the gaseous, oxidative cleaning beneath surface mounted components. In this instance the component was a Si test chip that had been beam lead bonded to a thin Film header. This work has been performed to investigate the possibility of removing organic contamination from beneath various devices (e.g., chips, chip carriers, etc.) by the use of gaseous, oxidative methods. Current methods involve various combinations of organic solvents, detergents, and/or aqueous solutions of oxidants, and are expensive, difficult to control, and sometimes incompatible with various circuit materials. An integral part of this investigation has been to determine the species responsible for the oxidative removal and then to maximize its production and delivery to the circuits to be cleaned. A most useful tool for accomplishing this is electron paramagnetic resonance (EPR) spectroscopy, which detects the sorts of species involved (atoms and free radicals) both qualitatively and quantitatively. It has been unambiguously determined that
³
P oxygen atoms are the most reactive species with little or no contribution from
¹
\Delta
O
2
. Knowing this, it was possible to develop gas mixtures that increase the atom concentration several-fold, and to find the operating conditions and reactor materials that deliver the most atoms to the reaction site. When these test circuits were cleaned in a system analogous to that used in the EPR studies, their performance under accelerated aging conditions was at least as good as those cleaned using the standard, wet, cleaning procedure. Likewise, circuits cleaned in a conventional plasma processor and using a gas mixture developed the same way, performed as well. Gaseous methods are shown to be viable alternatives to conventional wet cleaning methods currently used for cleaning beneath surface mounted components. Moreover the use of EPR has been shown to yield useful /information about such processes.