Flip chip interfacial behavior under thermal testing

Abstract

In this study, the interfacial behavior of a flip chip structure under thermal testing was investigated using high sensitivity moire interferometry. The real-time moire interferometry was used to monitor and measure the deformation of the specimen during the test. Two kinds of specimen were prepared: 1) specimen without crack and 2) specimen with horizontal crack at the silicon-epoxy interface. The results show that the maximum shear strain occurs ,at the silicon-epoxy interface. The shear strain variation increases significantly along the interface, with the maximum shear concentration occurring at the edge of the specimen. The creep effect is more dominant in the FR4-epoxy interface. In order to characterize the behavior of the interfacial crack, stress intensity factors KI and Kn, and the strain energy release rate in the vicinity of the crack tip were used to conduct a qualitative study. It was observed that a sharp strain gradient occurred at the crack tip. The stress intensity factors KI and Kn were dependent on temperature.The strain energy release rate with respect to temperature was dominated by KI for the interfacial crack in the specimen. IntroductionThe model package used in this study was a sandwich structure consisting of a silicon chip, epoxy underfill and FR4 substrate. The behaviour of underfillhbstrate and underfillkhip interfaces of the specimen under certain thermal loadings was examined. The thermal deformations of the specimen under thermal cycling tests were obtained by laser moire interferometry and the interfacial behaviour was assessed through analysis of the moire fringe patterns. The main interest of this study was to apply a real-time moire interferometry technique to investigate the variation of thermal strains experienced at the interfaces of the specimen. Upon application of thermal loading to the specimen, the specimen grating deformed along with the specimen, and the resulting interference with the reference grating produced fringes. Based on the fringe patterns captured by a CCD camera, information on the displacements and strains experienced by the specimen was obtained and analyses were carried out.

Thermal strain analysis of an electronics package using the SEM Moiré technique

“…Traditionally, Moiré interferometry is an optical experimental technique and provides high sensitivity deformation measurement (Dally and Riley, 1994;Guild, 1956;Sciammarella, 1982). Optical Moiré fringes are widely employed in experimental mechanics (Graham and Sanford, 1988;Post et al, 1994;Theocaris, 1969;Zhong et al, 2002).…”

Thermal strain analysis of IC packages using various Moiré methods

“…Moiré interferometry is an optical experimental method and provides high sensitivity deformation measurement. Optical Moiré fringes are widely employed in experimental mechanics (Dally and Riley, 1994;Post et al, 1994;Sciammarella, 1982;Theocaris, 1969;Zhong et al, 2002). The Moiré patterns defining the U and V displacement fields are formed by interactions of the x and y families of the specimen grating lines, respectively, with the reference grating lines.…”

“…An optical Moiré interferometer with a mini thermalcycling chamber can be used for real time measurements of thermal deformations and strains of IC packages under thermal testing. This method was used to monitor and measure the deformations and strains of a flip chip structure during thermal cycling (Zhong et al, 2002). Figure 3 shows the shear strain for two thermal cycles measured at an interested point B (the FR4-underfill interface at the specimen edge).…”

Interfacial behavior of a flip-chip structure under thermal testing

“…Recently, AFM (atomic force microscope) Moiré [23] and SEM (scanning electron microscope) Moiré [24] have also been employed to measure thermal strains of electronics packages. However, reports on measurements of thermal deformations and strains of electronics packages under thermal testing using real-time Moiré interferometry are still scarce [25].…”