M. Pacheco, D. Goyal, Intel Corporation, Chandler, AZ

Summary: New Developments in High-Resolution X-Ray Computed Tomography for Non-Destructive Defect Detection in Next Generation Package Technologies. Mario Pacheco, Deepak Goyal Intel Corporation 5000 W. Chandler Blvd. Chandler, AZ, USA 85226 The assembly package development roadmap has been increasing interconnect complexity, component density, the number of stacked dice, material composition, while at the same time reducing critical dimensions. As a result of these trends, the isolation and root cause analysis of defects has become increasingly challenging for traditional analytical tools and techniques. In addition, reduced time-to-information and non-destructive approaches have become critical factors, introducing more challenges into the analytical tools development roadmap. One of these analytical capabilities is 2D x-ray imaging, which is also one of the more extensively used tools in the semiconductor industry to isolate and analyze defects in non-destructive fashion. Some of these capability challenges are the detection of metal migration and dendrite growth, C4 bump non-wetting and cracking, BGA solder fatigue and cracking, wirebonds shorting and die cracking in multi-stacked packages, etc. In this paper, we will demonstrate how next generation x-ray computed tomography (CT) technology [1] can be used to fulfill those analytical gaps. Results and Discussion. As first example of the several compelling case studies that we will present in full paper, we will discuss here a summary of non-destructive detection of non-wets in C4 solder joints. This application is key analytical gap for both root cause analysis and process development. Using 2D x-ray provides information regarding the shape of solder ball indicating non-wetting issues; however, when the shape is such that it is difficult to differentiate between passing and failing bumps due to 2D x-ray imaging limitations, this type of non-wet is known as “invisible”. Figure 1a shows the physical cross section pictures of both passing and non-wet failing solder bumps; this figure also shows that the best 2D x-ray image obtained using high-magnification at an oblique view angle cannot detect these types of non-wet solder bumps. In this case, using x-ray CT fully isolated the defective C4 bump, as can be seen in the virtual planar view of Figure 1a, or in the virtual cross section of Figure 1b. As second example of what we will report in the full paper, we will summarize the detection of cracks and partial cracks in C4 bumps in non-destructive fashion using x-ray CT, with sample sizes of up to 2 inches wide. In this application, destructive techniques like Dye and Pull produce artifacts and cannot be used in packages with underfill and physical cross-sectioning is a tedious and time consuming process. Figure 2 shows a comparison between virtual planar and cross sectional views for both a failing and passing C4 bumps; as can be seen, x-ray CT can provide a clear finger print of cracking issues, either using a virtual plane or a cross-sectional view. The slice surface of a good solder joint looks smooth and uniform; whereas the slice surface of a failing bump looks uneven. A similar situation occurs with the virtual cross-sectional views. One of the compelling capabilities of x-ray CT is the possibility of performing defect inspection during reliability testing to feedback to predictive reliability models, as well as at different steps during production for process development. We will demonstrate in the full paper how x-ray CT has been used to study cracking progression in C4 joints at different readout times in units under reliability testing. Other applications of the x-ray CT will be also included in the full paper, for instance wire bond shorting detection in low density interconnect packages (figure 3), and solder joint cracking detection in second level interconnect (figure 4), among others. The results and discussion in the full paper will demonstrate how the advancement in the x-ray CT technology can be used to fulfill key non-destructive fault isolation gaps in next generation package technologies. Key Words: x-ray, computed tomography, new package technology, fault isolation, failure analysis. [1] D. Scott, F. Duewer, S. Kamath, A. Lyon, D. Trapp, S. Wang, W. Yun, “A novel x-ray microtomography system with high resolution and throughput for non-destructive 3D imaging of advanced packages”, Proc. ISTFA, 2004, pp. 94-98