Salt atmosphere testing normally consists of a 5 % salt fog
at 35°C for 48 hours, nonoperating. Failure criteria normally consists of
inability to meet end-of-life performance.
Since military equipment specifications normally require
conformal coating with a low permeability insulating material, all salt
atmosphere test data that has been gathered involves assemblies protected in
that manner. The data includes results with a number of different conformal
coat materials. Many conformal coat materials perform satisfactorily on both
MIBs and polymer-glass multilayer boards.
Completed modules fabricated with DIP and flatpack ICs on
polymer-glass MLBs and with LCC and other surface-mounted devices on MIBs with
both noble metal and copper thick film conductor systems--all conformal
coated--have been subject to salt atmosphere tests. Data on the polymer-glass
modules is extensive, while that on the ceramic modules is limited. However,
in no case has there been any failure attributed to the mounting or