1 9000 Virginia Manor Road, Suite 290, Beltsville, Maryland 20705 |Phone: (301) 474-0607| Fax: (866) 247-9457| www.dfrsolutions.com Temperature Cycling of Coreless Ball Grid Arrays Daniel Cavasin  , Nathan Blattau  , Gilad Sharon  , Stephani Gulbrandsen  , and Craig Hillman   DfR Solutions, MD, USA  AMD, TX, USA Abstract There are countless challenges in making mobile electronics more reliable, including the thin form factor of cellphones and tablets that is forcing mobile computing packages to get thinner. Using coreless ball grid array (BGA) substrates decreases the overall height of the component, but it presents manufacturing challenges and potential reliability concerns when subjected to thermal cycling. This study presents results from tests performed on a coreless 25 mm by 27 mm BGA package with a relatively large die and stiffener ring that survived over 8,000 temperature cycles without failure. In order to investigate the reason behind this robust performance the coefficient of thermal expansion (CTE) of the part was measured using digital image correlation (DIC). The DIC results indicated that this combination of die size, package size, and stiffener ring reduces the CTE mismatch between the BGA package and printed circuit board (PCB). I. INTRODUCTION Standard flip chip substrates are constructed with a 200-800 micron thick core laminate layer with build-up layers on either side. A coreless substrate does not have the core laminate and is only comprised of the build-up layers. A comparison of a standard and coreless substrate is shown in Figure 1, where the coreless substrate lacks the thick glass laminate layer present in the standard substrate. Figure 1: Coreless substrate (left) and standard substrate 1 The use of coreless substrates for BGA packages involves overcoming manufacturing and reliability challenges. They are typically more prone to warpage during assembly than a standard substrate and coreless BGAs have a higher CTE, which may lead to decreased reliability during temperature cycling. In this study, a large BGA package with a large die was subjected to 8,000 temperature cycles without any failures. The robust performance of this part during temperature cycling was unexpected because of the large die dimensions. Therefore, additional experiments were conducted to better understand the fatigue behavior of the package. II. EXPERIMENTAL PROCEDURE The BGA package studied is shown in Figure 2. The die can be seen on the top, the substrate is below, and the stiffener ring is located along the perimeter of the substrate. The package is 25 mm by 27 mm by 1.54 mm (total thickness), and the die is 13.8 mm by 16.5 mm by 0.75 mm. 1 http://www.toppan.co.jp/material/english/semicon/package/fc-bga/coreres/