Garth B. Freeman

Use of surface insulation resistance and contact angle measurements to characterize the interactions of three water soluble fluxes with FR-4 substrates

Soldering flux chemistry and its interaction with the printed wiring board have been important reliability concerns for a number of years. Post Vietnam investigation of military hardware revealed corrosion in some areas. The test method most frequently used to assess the corrosion potential of flux residues is surface insulation resistance (SIR) testing. This paper gives some background on surface insulation resistance testing and reports on its application to three different water soluble fluxes. The appearance of surface dendrites is linked to test procedures that allowed water condensation on the board surface. Subsurface conductive anodic filament formation is associated with the use of fluxes which contained polyglycols. The use of contact angle measurements to assess the effect of the soldering flux residues on the board is demonstrated.

Forced flow-thermal gradient chemical vapor infiltration (FCVI) for fabrication of carbon/ carbon

Abstract Carbon/carbon composites with porosities as low as 7% were fabricated within 8–12 hours using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. Preforms consisting of 40 layers of T-300 plain weave carbon cloth were infiltrated with a feed containing a carbon source and a diluent. The carbon sources studied in the present work included propylene, propane, and methane and the diluent was hydrogen. Shorter processing times were obtained when propylene and propane were used as compared to methane. The highest deposition rate obtained in the present study was ~ 3 μm/h which is more than an order of magnitude faster than the typical value of 0.1–0.25 μm/h for the isothermal infiltration process. In the infiltrated composites it was observed that the tows in a cloth were appreciably infiltrated, independent of their position in the preform. Whereas, the coating thickness between the tows and cloth layers strongly depended on the temperature, i.e. position within the preform.

Characterization of Conductive Anodic Filament (Caf) by X-Ray Microtomography and by Serial Sectioning

X-ray microtomography is used to nondestructively section printed wiring boards in which conductive anodic filaments (CAFs) had grown, Quantification of the spatial distribution of copper is compared for microtomography and for serial sections obtained in SEM with backscattered electrons. The agreement between the techniques is excellent and indicates that microtomography may be used confidently to follow the subsurface growth of CAFs.