Arun Chandrasekhar

Determination of the complex permittivity of packaging materials at millimeter-wave frequencies

The focus of this paper is the determination of the complex permittivity of chip packaging materials at millimeter-wave frequencies. After a broad overview of existing measurement techniques, three methods will be presented that have been established for the dielectric property determination of substrate, as well as mold materials (encapsulants, under-fill, etc.) in the millimeter-wave frequency range. First, the open resonator used here will be briefly described. It allows accurate determination of the dielectric constant and loss of thin sheet substrate materials from below 20 GHz to above 100 GHz. Second, a filled waveguide method is explained in detail. The setup used here can determine the complex dielectric properties of mold materials from 70 to 100 GHz. Third, the method based on covered transmission lines will be described in detail. The used lines allow measurements from below 40 GHz to approximately 90 GHz. Verification of all three methods will be provided by inter-comparison and comparison to values from the literature. Additionally, results for several typical substrate and mold materials that are available for millimeter-wave packaging will be shown and discussed.

Characterisation, modelling and design of bond-wire interconnects for chip-package co-design

This work is a comprehensive experimental investigation of chip to package wirebond interconnects for chip-package co-design. Wirebonds are interconnect bottlenecks in RF design, but are difficult to avoid due to their low cost and manufacturing ease. We have shown measurements on wirebonds in coplanar configuration with different return paths and also the cross coupling. We have also extracted lumped and distributed models and demonstrate the excellent agreement with measurements atleast upto 15GHz. We have proposed multi-wirebonds as a potential solution for better impedance matching. Different types of inductors with Q-factors of upto 100 have also been illustrated. We show influence of encapsulant on wirebonds and finally we also demonstrate a methodology to extract the time-domain response from S-parameters.

The influence of packaging materials on RF performance

Abstract At frequencies beyond 1 GHz, every component of the IC package contributes to the RF performance, whether required or not. In this work, we study the effects of packaging materials namely, the substrate and the globtop/underfill material on RF performance. We have measured interconnects on two area-array CSPs, the ball grid array and the polymer stud grid array using IMEC’s MCM-D technology. The measurements on the package interconnect show that the losses in the package substrate material account for about 50% of the total losses at 1.8 GHz and this drops to less than 20% at 5.2 GHz. The losses due to impedance mismatch dominate the losses especially below 10 GHz and considerable improvement in performance cannot be obtained by using an improved/expensive substrate. The other study is about the influence of globtop/underfill materials on wirebonds (through 3D EM simulations) as well as on standard 50 Ω MCM-D transmission lines (through experiments). While a higher value of dielectric constant of the globtop/underfill material is better on wirebonds, the influence of loss tangent is felt only above values of 0.1. The influence of seven different globtop/undefill materials on 50 Ω transmission lines has been used to extract their dielectric constant and loss tangent values at 30 GHz. These results are very valuable since one can hardly find the properties of globtop/underfill materials beyond 1 GHz.

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 /spl Omega/.

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

The thin film multilayer multichip module-deposited (MCM-D) technology of IMEC is used for characterising the RF electrical performance of two types of chip scale packages (CSPs). The measurement technique called MCM-on-package-on-MCM (MoPoM) enables accurate measurements and de-embedding in the gigahertz (GHz) range of frequencies. Wafer processing of the MCM-D technology allows for several design structures to be integrated on a single mask. The packages chosen are a 120-pin plastic ball grid array (PBGA) and an 80-pin polymer stud grid array (PSGA). Lumped element models extracted from measurements and three-dimensional simulations show good agreement with the measurements up to 6 GHz for the BGA and 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 at 5.2 GHz both the packages exhibit a return loss of lower than -10 dB and hence cannot be used in most cases without design improvement. We also show that the influence of encapsulant is significant while transmission line detuning due to the package is not significant at microwave frequencies. We also briefly mention about the crosstalk effects. We demonstrate the significant degradation in the performance of a 5.2 GHz MCM-D low noise amplifier (LNA) after packaging. A significant improvement in package performance is observed by conjugate matching the package interconnects.

A new in-situ approach to flip-chip interconnect characterization up to millimeter wave frequencies

In this paper we present the performance of flip-chip interconnects up to 40 GHz based on an alternative non-destructive measurement technique. The presented method unfolds the raw flip-chip interconnect, excluding any launch structures for an actually mounted silicon chip. A preliminary modeling approach for chip-package co-design is outlined.