In semiconductor manufacturing, the technologies of stacked semiconductor packaging are important miniaturization strategies in which excellent quality is essential for a good reputation. Yield-based index Cpk has been the most popular tool for successful quality improvement activities and quality program implementation in multichip package processes. For in-plant applications, quality practitioners commonly use the nonconformities in parts per million (NCPPM) table of Cpk to obtain manufacturing yields. However, wire bonding processes are often skewed in multichip package factories. In such situations, the NCPPM table of Cpk is inappropriate to be applied directly. In order to reasonably access manufacturing yield for skewed wire bonding processes, we propose a new yield index Csk. We are the first to modify the index Csk for various skewed distributions for the consistency of NCPPM mapping between indices Cpk and Csk. In addition, bootstrap methods are applied to construct lower confidence bounds which are useful to practitioners for making reliable decisions. An approximated unbiased estimator is also provided. For the purpose of illustration, practical applications are presented.