## 1 Introduction  
Integrated-circuit (IC) packaging is a procedure in which a processed wafer is cut into dies and then coated in materials such as resin, ceramics, and metal. The small volume of ICs means that electronic components are very close together, but this allows circuits to work faster and more reliably and protects the crystallites from external contamination. Thus, ICs are fundamental components of electronic products [1]. The cluster effect in the electronics industry in Taiwan has resulted in a complete information and communication technology industry chain with a firm position in the global electronics industry [2; 3; 4]. At present, the output values of Taiwan's wafer foundry industry and IC packaging and testing industry take up the largest shares of the global market (approximately 70% and 50%, respectively). Companies in Taiwan also provide vertically integrated services including design, research and development (R&D), component supply, assembly, and original equipment manufacturer (OEM) manufacturing, such as MediaTek's IC design services, Taiwan Semiconductor Manufacturing Company (TSMC)'s wafer foundry services, and Foxconn's assembly and production services [5]. During the production process, the quality of all components and the assembly must be ensured so as to provide consumers with safe products of good quality and performance. For this, process capability indices (PCIs) are useful and convenient tools used to determine whether the process quality reaches the customer's requirements [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. A number of researchers have examined the relationship between PCIs and Six Sigma quality levels [5; 16; 17; 18].  
As ICs are the key components of modern electronic products, a package is required to protect the die so that it does not take on any physical or chemical damage during component and circuit production processes. The molding process in IC packaging has three crucial smaller-the-better (STB) quality characteristics: (A) lead frame deformation, (B) wire sweep, and (C) package warpage. Excessive lead frame deformation, wire sweep, or package warpage will affect subsequent IC product processes or the functions of the final product. Moreover, a PCI contains unknown parameters, \(\mu\)and \(\sigma\), which means that it requires sample data for estimation. In this paper, we investigate the relationships between the process quality levels \(\omega\) and the value of a Six Sigma quality index (SSQI) \(Q_{PU}\) for the three STB quality characteristics. We propose a novel, confidence interval based fuzzy testing method using the upper confidence limit of SSQI \(Q_{PU}\) to evaluate the quality of the IC packaging molding process. Because this approach is grounded on confidence intervals, it reduces the risk of misjudgment caused by sampling errors and also increases the accuracy of decision-making in measuring the quality of the IC packaging molding process.  
The remainder of this paper is organized as follows. Section 2 proposes an SSQI for the IC packaging molding process. Estimators of index accuracy and index precision are used to derive confidence interval based fuzzy numbers of SSQIs as well as the membership function for the development of a fuzzy evaluation model. Section 3 presents an example of a practical application. Finally, conclusions are provided in Section 4.