Materials Science and Engineering A 380 (2004) 231–236 Application of electronic speckle-pattern interferometry to measure in-plane thermal displacement in flip-chip packages Baik-Woo Lee a,∗ , Woosoon Jang a , Dong-Won Kim a , Jeung-hyun Jeong a , Jae-Woong Nah b , Kyung-Wook Paik b , Dongil Kwon a a School of Materials Science and Engineering, Seoul National University, San 56-1, Shinrim-dong, Kwanak-gu, Seoul 151-744, Republic of Korea b Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Taejon 305-701, Republic of Korea Received 12 January 2004; received in revised form 22 March 2004 Abstract Electronic speckle-pattern interferometry (ESPI) was applied for noncontact, real-time evaluation of thermal deformation in a flip-chip package. The spatial resolution of ESPI was increased to submicron scale by magnifying the areas studied in order to measure the deformation of such small-scale components as the solder in the flip-chip package. Thermal deformation in the horizontal and vertical directions around the solder joints was measured as two-dimensional mappings during heating from 25 to 125 ◦ C. ESPI was successful in obtaining information on the complicated deformation field around the solder joints. Furthermore, the shear strain could also be calculated using the measured thermal deformation around each solder joint. The applicability of ESPI to flip-chip packages was verified by comparing the ESPI results with those of finite-element analysis (FEA). © 2004 Elsevier B.V. All rights reserved. Keywords: Electronic speckle-pattern interferometry (ESPI); Flip-chip package; Shear strain; Finite-element analysis (FEA); Coefficient of thermal expansion (CTE) 1. Introduction Flip-chip packages are produced by an interconnection technique in which the active area of a chip is mounted by various interconnecting materials on a multilayer substrate [1]. While flip-chip technologies have progressed rapidly and are now widely used, they present special reliability con- cerns [2–4]. A large thermal expansion mismatch between the chip and the substrate increases the likelihood of fatigue failure in solder joints under cyclic thermal loading [2,3]. In addition, the thermal mismatch often results in the delam- ination of interfaces between two materials, which eventu- ally leads to mechanical and/or electrical failure [4]. Thus, it is of great interest to measure the thermomechanical de- formation of flip-chip packages. Noncontact optical methods are desirable in measuring such thermomechanical deformation because they allow real-time, whole full-field measurement during operation. ∗ Corresponding author. Tel.: +82-2-880-8404; fax: +82-2-886-4847. E-mail address: hotline1@plaza.snu.ac.kr (B.-W. Lee). Different but complementary optical methods include holo- graphic interferometry [5], moiré interferometry [4–6] and electronic speckle-pattern interferometry (ESPI) [5,7]. Among these methods, ESPI is one of the most promising for measuring thermal deformation in a flip-chip package in that it requires little or no special specimen preparation and can measure in-plane and out-of-plane deformation with high sensitivity. It is based on the interference of two speckle-patterns recorded before and after deformation. The speckle-patterns arise by the interference of two incident beams, an object beam and reference beam; here the ob- ject beam is reflected on the specimen and then goes to a CCD camera, while the reference beam goes directly to the camera. As the specimen deforms, the resulting surface de- formation changes the phase difference between the object and reference beam and thus alters the speckle-pattern. Sub- tracting the deformed speckle-pattern from the undeformed one produces correlation fringes that yield a displacement field through the well-known relationship between fringe order and displacement. An ESPI system was applied to measure in-plane ther- mal displacement in a flip-chip package consisting of a Si 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.03.068