Numerical modeling of warpage induced in QFN array molding process D.G. Yang a , K.M.B. Jansen a , L.J. Ernst a, * , G.Q. Zhang a,b , W.D. van Driel b , H.J.L. Bressers b , J.H.J. Janssen b a Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands b Philips Semiconductors, P.O. Box 30008, 6534 AE Nijmegen, The Netherlands Received 1 February 2005; received in revised form 31 January 2006 Abstract Warpage is a critical issue for QFN array molding process. In this paper, a cure-dependent viscoelastic constitutive model is estab- lished to model the cure-induced warpage in array molding process. For the relaxation modulus functions of the packaging polymer, the equilibrium moduli are modeled with a model based on scaling analysis and the relaxation behavior of the transient part is described by the cure-dependent relaxation amplitude and reduced relaxation times which are based on the time-conversion superposition principle. The cure-dependent parameters are characterized by using an integrated approach of dynamical mechanical analysis (DMA) and differ- ential scanning calorimetry (DSC) measurements. Finite element modeling is carried out for three configurations of a carrier package map mould and the warpage induced during the curing process and cooling down is predicted. The results show that warpage induced during the curing process has significant contribution on the total warpage of the map. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction Thermosetting polymers are widely used as encapsulants in electronic packaging. As one of the major packaging processes, the curing process will introduce residual stress and warpage in the packages due to the polymerization shrinkage and thermal shrinkage in the subsequent cooling down phase. Warpage due to manufacturing processes has long been recognized as an important issue for package reliability. Excessive warpage not only causes device failure issues such as die cracking and interface delamination, but also may cause assembly problems in the subsequent pro- cesses, such as dimension instability, non-coplanarity, etc. Many efforts have been made to predict and/or measure process-induced warpage of packages. Kelly et al. [1] mea- sured the warpage of a plastic power package and indicated that the package was significantly deformed at the molding temperature, which was attributed to chemical shrinkage of the molding compound. In [2], the impact of processing conditions on warpage prediction of a plastic quad flat package (PQFP) was investigated. It was suggested that low temperature and longer molding time or high temper- ature and shorter molding time would result in less war- page. They also showed that the viscoelastic model predicted the warpage more accurately than the thermo- elastic model. In [3], a coupled cure-thermal-stress analysis approach was proposed to predict warpage and stresses during sequential fabrication of electronic packaging struc- tures. However, due to fast and huge change of the mate- rial properties during the curing process, it is still an open and challenging research field to accurately predict the process-induced stress and warpage, especially under complex curing temperature profiles. In this paper, finite element (FE) modeling of map molding process is carried out. First, a carrier QFN pack- age, the map molding process and process-induced war- page issue is described. In Section 3, the material models for describing the behavior evolution during the curing process are presented. In Section 4, the experimental meth- ods for characterization of the cure-dependent properties 0026-2714/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.microrel.2006.09.036 * Corresponding author. Tel.: +31 15 278 6519; fax: +31 15 278 2150. E-mail address: l.j.ernst@wbmt.tudelft.nl (L.J. Ernst). www.elsevier.com/locate/microrel Microelectronics Reliability 47 (2007) 310–318