A device presenting a gross leak could theoretically pass the fine leak test. Therefore, this test is typically performed after the fine leak test. Also, the wet fluorocarbon could block fine leak paths.
The gross leak test is an inspection test based on boiling points differential of two fluorocarbons. It requires a preconditioning in a pressurized chamber filled with a low boiling point (80°C) fluorocarbon [the Detector]. Under the pressure, the Detector fluid may penetrate the device. After the preconditioning, the device is submerged in a second fluorocarbon fluid with a higher boiling point (125°C) [the Indicator]. When exposed to the high temperature, the detector fluid located within the cavity of the package boils, generating an elevated pressure inside the device causing a bubble stream to emanate from the leak site.
Gross Leak (Simulated Bubbles)