Package warpage challenges for LQFP 144 lead CMOS 90 device and it's impact to lead coplanarity

Package warpage or generally referred to as plastic package deformation has become more challenging with larger and thinner package body sizes. The detrimental effects of the package warpage are more prominent in peripheral packages with leads such as fine pitch LQFP (Low Profile Quad Flat Package). As all the leads are embedded in the plastic body, the warpage will displace the leads in the same direction of the warp after the trim and form step. In the first half of the paper, we characterized the warpage of different LQFP packages designs using Akrometrix Thermoire. It was found that larger die size and smaller down set are favorable to reducing package warpage. In the second half of this paper, we explored various factors such as molding process parameters, post mold cure conditions, effects of direct materials properties, and package geometry to determine their impact on the package warpage and lead coplanarity for the LQFP molded package. Molding parameters such as cure time and molding temperature were evaluated in a series of DOEs in attempts to find the most promising factors that can control the warpage. Similar DOEs were also carried out in the post mold cure process coupled with various methods of clamping. As for the direct materials, studies focusing on molding compound properties such as coefficient of thermal expansion (CTE), higher filler content, higher glass transition temperature Tg, and lower mold shrinkage factor have been completed as well. From these series of analyses and experiments, we understood how the leads formed with spring back effect in a warped package will end up with poor coplanarity measures. It is also found that the combination of several material properties that are not optimal will further deteriorate warpage and cause poor lead coplanarity. These findings and results will be shared in this paper and recommendations to correct the issue are presented.