Accurate RF electrical characterisation of CSPs using MCM-D thin film technology

The thin film multi-layer MCM-D (multi chip module-deposited) technology developed at IMEC is used for characterising the RF electrical performance of two CSPs (chip scale packages). The measurement technique, called MoPoM, (MCM-on-package-on-MCM) enables accurate measurements and de-embedding, apart from allowing for different measurement structure designs on a single mask. The packages chosen are a 120-pin PBGA (plastic ball grid array) and an 80-pin PSGA (polymer stud grid array). Lumped element models extracted from measurements and 3D simulations show good agreement with the measurements up to 6 GHz for the BGA and 5 GHz for the PSGA. The electrical performance of the packages is compared at 1.8 GHz (GSM), 2.4 GHz (Bluetooth) and 5.2 GHz (HiperLAN) and it can be seen that at 5.2 GHz, both packages cannot be used without design modifications. We also show that the influence of encapsulant is significant, while package loading is not, at microwave frequencies and also briefly mention the crosstalk effects. We demonstrate significant degradation in the performance of a 5.2 GHz MCM-D low noise amplifier (LNA) after packaging. A drastic improvement in package performance is observed by matching the package interconnects to 50 Ω.