Hermeticity Testing of Dual or Multi-cavity Sealed Devices

SiP device may require two or more sealed cavities, and the internal free volumes of these individual cavities often differ. When conducting sealing tests using traditional helium mass spectrum fine leak test, a problem arises if these cavity volumes fall into different classification ranges. If inappropriate bomb conditions from the fixed method procedures are selected, the leak rate criterion for some cavities may be too lenient. For example, in a certain dual-cavity CQFP240 package, the internal free volume of cavity 1 is 0.27 cm³, and the internal free volume of cavity 2 is 0.43 cm³. These volumes fall into the 0.1 \leqslant V< 0.4 and 0.4 \leqslant V< 1.0 classification ranges, respectively. Clearly, the failure criterion for the equivalent standard leak rate L corresponding to cavity 1 is 1×10⁻² Pa·cm³/s, while the failure criterion for cavity 2 is 1×10⁻¹ Pa·cm³/s. If the bomb conditions from the fixed method with the minimum bomb pressure and the longest dwell time, i.e., P_E=206 kPa and t₁=1 h, are selected based on the internal free volume of cavity 2, then the measured leak rate corresponding to the failure criterion for the equivalent standard leak rate L for cavity 1 is 1.93×10⁻⁴ Pa·cm³/s. This value is less than the measured leak rate rejection limit of R₁=3×10⁻³ Pa·cm³/s. This leads to the risk of failed leak detection. This paper discusses the selection of leak rate criteria and bomb conditions for dual or multi-cavity packages. A solution is proposed to extend the bomb conditions used in the fixed method procedures. According to calculation results, by applying the extended bomb conditions for fixed method fine leak testing, the measured leak rates corresponding to the failure criterion of the equivalent standard leak rate L are all greater than the rejection limit R₁. Furthermore, methods for locating the leaking cavity in dual or multi-cavity packages are discussed.