Determination of the Mechanical Properties OP Integrated Circuit Packaging Materials using a Focused Acoustic Beam Techn
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DETERMINATION OF THE MECHANICAL PROPERTIES OF INTEGRATED CIRCUIT PACKAGING MATERIALS USING A FOCUSED ACOUSTIC BEAM TECHNIQUE DE ZHANG * AND GABRIEL M.CREAN National Microelectronics Research Centre, Prospect Row, Cork, Ireland ABSTRACT A novel method for the measurement of the mechanical properties of integrated circuit interconnection and packaging materials using a conventional acoustic microscope lens, is presented in this paper. This technique allows the simultaneous generation and detection of longitudinal (LW) and shear (SH) acoustic waves in a material system based upon acoustic mode conversion principles at a water-solid interface. Experimental results obtained using a 50 MHz acoustic lens are presented for a range of ceramic materials and compared with published data. Acoustic ray propagation theory is employed to analyse the experimental results. INTRODUCTION A wide range of material systems are currently under investigation for high performance integrated circuit packaging applications. The incorporation of such novel materials or process steps within a specific packaging technology is determined by a number of competing requirements relating to thermal, electrical and mechanical integrity criteria. The trend towards multilayer interconnect structures and large area die attach has posed significant mechanical integrity problems and has led to the rapid use of finite element computer aided stress modelling codes for optimum package reliability [1,2]. However the accuracy of such simulations depend critically upon the accurate determination of the physical mechanical properties of the constituent material systems input into the code. At present several techniques exist for the determination of bulk and thin film material mechanical properties including Xray diffraction [3], optical [4], ultrasonic [5] and mechanical indentation [6] . This paper presents a novel method for determination of solid layer mechanical properties using a focused acoustic beam, which is particularly suitable for the determination of the mechanical properties of small dimension IC packaging structures. PRINCIPLE
OF
THE
TECHNIQUE
The technique is based upon mode conversion phenomena [7] which occur when an acoustic wave impinges upon a water-solid or solid-water interface. Both longitudinal and shear acoustic waves can be transmitted into a layer when a focused acoustic *
De
Zhang
is
on
leave
from
Nanjing
University,
Mat. Res. Soc. Symp. Proc. Vol. 239. 01992 Materials Research Society
China
282
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Fig.1 Acoustic ray path insystem
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Reflected acoustic pulse train received by lens transducer
beam is incident at a water-solid interface from water, and subsequently reflected from the bottom of this layer. Figure 1 shows a typical acoustic ray path in the lens, coupling fluid and layer material. The reflected acoustic pulse
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