This paper presents a study on warpage for the base (bottom) package of Package-on-Package (PoP) stacking. Today’s consumer electronics demand higher performance from smaller form factors. 3-Dimensional (3-D) Packaging has been widely adopted in many compact applications, such as cellular phones and digital cameras. Especially, Original Equipment Manufacturers (OEMs) are insisting on the rapidly expanding PoP stacking because it provides the space-savings of 3-D technology with the added flexibility not present in traditional stacked die package. OEM can choose the top package provided by multiple suppliers. The challenge is to develop the base package of PoP which the top package is mounted on. For the base package, warpage is a critical item in order to enable package stacking with high yield. It is difficult to control the warpage of the base because the manageable parameters are very limited such as very thin and small mold cap and thin substrate which make the package flexible and causes rather large warpage by CTE mismatch of each material. Furthermore, the requirements to meet the warpage spec at both room temperature and reflow temperature put more constraints on the design. We systematically studied the warpage control for the bottom package by both experiments and finite element simulations with all possible design parameters and material sets. We did design of experiment (DOE) and measured the actual warpage of package at room temperature and also at reflow temperature using shadow moiré method. In parallel, finite element model simulation were carried out to correlate with the empirical results and help understand the effects of critical package parameters for warpage control. By optimizing design parameters and material set, the package warpage could be well controlled within specifications. In the paper, we will present the warpage test data and simulation data. The effects of die size, mold compound material and thickness, substrate thickness, and die attach material will be discussed in depth.
展开▼
