Challenges and Feasibility of Copper Wire bonding for Non-hermetic Packaging

1. Introduction
Wire bonding is still the most widely used interconnection technique for packaging, and likely to retain the dominant position for years to come. Although solder bump, copper pillar, TSV, 3D etc emerging technologies are more and more studied or used for high-end applications, more than 85% of IC packages are still with wire bonding technology. However, due to the explosive growth of gold price during last 5 years (see Fig.l), there is a strong need for conversion to copper wire. With great efforts of last few years from customers, equipment & material suppliers, assembly & packaging house, copper wire conversion has been in great progress. Copper wire bonding has around 25% market share today. As of 2014, copper wire is expected to make up of 60-65% market. The Conversion was lead by consumer products which were most price sensitive and perceived to be least demanding in reliability due to the nature of the application and the relatively short life. For these products, a good track
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Abstract
In the last few years copper wire bonding has undergone a tremendous growth period. The drive behind the growth is the huge cost saving for copper wire compared with gold wire especially for those packages or applications with longer wire connection, more lOs or thicker wire. Copper wire has also other advantages like better electrical performance and mechanical performance. Thinner copper wire can have equivalent performance as the thicker gold wire. Many studies have been done on copper wire bonding for equipment capability, robust process window, and package reliability etc. most of those efforts have been put on molded BGA or leadframe packages etc. hermetic packages, where bБайду номын сангаасnding wire is protected by molding compound. However, there is no much study about copper wire bonding for non-hermetic packages like MEMS microphone, camera module etc where the bonding wires are in cavities and not protected or embedded resin materials. Reliability is a great concern for such applications. The work discussed in this paper focuses on copper wire bonding for non-hermetic packaging. Due to its material properties, copper has much narrow process window for wire bonding than gold wire. It makes the copper bonding even challenging for Non-hermetic packages. With huge of work on the proper wire and capillary selection, and process window optimization, it was found that copper wire bonding is feasible for non-hermetic package, and qualified for camera module and OLGA packages. Yield and productivity are equivalent to gold wire.
Challenges and Feasibility of Copper Wire bonding for Non-hermetic Packaging
ling-en Luan STMicroelectronics Pte Ltd 16, Tao Hua Rd, Futian Free Trade Zone Shenzhen, P.R. China518038 Email: iing-en.luan@
980
2012 International Conference on Electronic Packaging Technology & High Density Packaging 978-1-4673-1681-1112/$31.00 m012 IEEE
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Fig. 1 Gold Price in last 5 years However, for non-hermetic applications like camera modules, OLGAs, or MEMS microphone etc, there are more challenges like copper oxidation, foreign materials and the most concern of reliability, and manufacturability. In this study, wire selection, capillary selection, free air ball assessment, DOE for 1 st bond and 2nd bond parameter optimization were done for a robust cu bonding. �ield and . productivity were also assessed for manufacturablhty. The most critical is reliability test. It is a common sense that reliability for non-hermetic packages should be very challenging due to copper oxidation. The copper oxidation will accelerate under moisture or temperature. Therefore a full reliability tests have been performed like thermal cycling (TC), Temperature Humidity storage (THS), drop test, Tumble test etc. The results show that it is feasible to have copper wire bonding for non-hermetic packaging as long as an optimized process window is achieved.
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