Data processing: measuring – calibrating – or testing – Measurement system – Statistical measurement
Reexamination Certificate
2001-12-14
2004-11-09
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Statistical measurement
Reexamination Certificate
active
06816812
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of moisture absorption in hygroscopic materials, and more specifically to methods and apparatus for predicting moisture absorption in such materials.
BACKGROUND OF THE INVENTION
Certain types of Plastic Encapsulated Microchip (PEM) packages that are exposed to humid air, prior to a reflow soldering process (which attaches these types of components to printed electronic circuit boards), are capable of absorbing significant quantities of water vapor. It is also known that some unprotected PEM packages are capable of absorbing so much moisture, due to their exposure to humidified air, that the rapid heating effect during subsequent soldering causes them to fracture, crack, or explode. “Popcorning” is a term that is often applied to describe this effect. Typically, this kind of damage may cause immediate, or somewhat delayed, fatal defects in the electrical operation of these PEMs. Additional information and much more detail regarding the popcorning effect, as it relates to PEMs, is available in many other previously published papers [e.g., Baluck et al., 1995; Fukuzawa et al., 1985; Gallo and Munamarty, 1995; Gannamani and Pecht, 1996; Holcomb et al., 1994; Hua and Leong, 1998; Hutchins, 1990; Ilyas and Poborets, 1993; Ito et al., 1991; Kitano et al., 1988; Mahajan and Pecht, 1999; McCluskey et al., 1997; Oizumi et al., 1987; Pecht and Govind, 1997; Pecht et al., 1997; Shan et al., 1992; Shook, 1992; Theriault et al., 2000; Totten, 1996A and 1996B; Tubbs and Gallo, 1996; Yalamananchiii et al., 19951].
The specific amount of water vapor that can be absorbed within different types of PEMs depends significantly upon the type and configuration of the plastic encapsulating material that is used to enclose the interior electronic component(s) as well as the exposure time and relative humidity (RH) of the moist air that these devices are exposed to. For these reasons, actual moisture absorption rates, associated with specific PEMs exposed to well defined RH and temperature conditions, must be measured experimentally. And, although there are at least a few experimental studies related to this problem within the extant literature, many of these studies have focused upon moisture absorption measurements involving temperatures and RH conditions that are unlikely, if not (for all practical purposes) impossible within most electronic packaging and assembly environments. However, one of the best previous studies, known to the inventors, involving moisture absorption rates of PEMs and also containing the most realistic operating conditions, was published in a Surface Mount Technology (SMT) Proceedings volume in 1992 [Chong et al., 1992]. In that paper, the lowest controlled operating temperature and relative humidity condition was at 30 C and 60% RH. In addition, theoretical equations allowing predictions at other temperatures and RH conditions were developed. The dried PEMs studied during that work were also exposed for long time periods (up to 1,000 hr) to high humidity test atmospheres. However, although moisture pick up behavior could be estimated at ambient temperature conditions, that behavior was not measured directly.
Related art may be found in the following, some of which are referred to herein:
ANSI/IPC-SM-786A, Procedures for Characterizing and Handling of Moisture/Reflow Sensitive ICs. IPC, Northbrook, Ill. Sep. (1994).
Baluck, M. J., Rose, G. L., and Virmnani, Fundamentals of Plastic Encapsulated Microcircuits (PEMs) for Space Applications. NASA TECDOCS (1995).
Chong, D., Dunn, C., Lewis, T., and LeBlanc, J., Moisture Sensitivity of Surface Mount Plastic Packages. Proceedings of the Technical Program: Surface Mount International Conference and Exposition, Edina, Minn. Vol. 1, pp. 421-426 (1992).
Fukuzawa, I., Ishiguro, S., and Nanbu, S., Moisture Resistance Degradation of Plastic LSIs by Reflow Soldering. Proceedings of International Reliability Physics Symposium, pp. 192-197 (1985).
Holcomb, K., Ryan, L., and Suro, E., Moisture in Liquid Epoxy Encapsulant and its Effect on SMDs. Dexter Corporation Technical Paper, Olean, N.Y. December (1994).
Intel Corp., Moisture Sensitivity/Desiccant Packaging/Handling of PSMCs, 1993.
IPC/JEDEC J-STD-020A, Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices. IPC, Northbrook, Ill. (1999).
IPC/JEDEC J-STD-033, Standard for Handling, Packaging, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices. IPC, Northbrook, Ill. (1999).
Gallo, A. A. and Munamarty, R., Popcorning: A Failure Mechanism in Plastic Encapsulated Microcircuits. Dexter Corporation Technical Paper, Olean, N.Y. September (1995).
Gannamani, R. and Pecht, M., An Experimental Study of Popeorning in Plastic Encapsulated Microcircuits. IEEE Transactions on Components, Packaging, and Manufacturing Technology, Part A, Vol. 19, No. 2, pp. 194-201, June (1996).
Hua, F. and Leong, B., A Moisture Induced Failure in FCBGA Packages During Multiple Reflow. Proceedings of the Technical Program: Surface Mount International Conference and Exposition, San Jose, Calif. pp. 14-17 (1998).
Hutchins, C. L., Time and Temperature Requirements for Surface Mount Soldering. Proceedings of the Technical Program: NEPCON West, Anaheim, Calif. pp. 288-297 (1990).
Ilyas, Q. S. M. and Poborets, B., Evaluation of Moisture Sensitivity of Surface Mount Plastic Packages. Proceedings of the ASME Conference, New Orleans, La. pp. 145-156 (1993).
Ito, S., Nishioka, T., Oizumi, S., Ikemura, K., and Igarashi, K, Molding Compounds for Thin Surface Mount Packages and Large Chip Semiconductor Devices. Proceedings of the 39th International Reliability Physics Symposium, pp. 190-197 (1991).
Kitano, M., Nishimur, A., Kawai, S., and Nishi, K., Analysis of Package Cracking During Reflow Soldering Process. Proceedings of the 26th International Reliability Physics Symposium, pp. 90-95 (1988).
McCluskey, P., Munamarty, R., and Pecht, M., Popcorning in PBGA Packages During IR Reflow Soldering. Microelectronics International, Vol. 42, pp. 20-23, January (1997).
Pecht, M. and Govind, A., In-situ Measurements of Surface Mount IC Package Deformations During Reflow Soldering. IEEE Transactions on Components, Packaging, and Manufacturing Technology, Part C, Vol. 20, No. 3, July (1996).
Pecht, M., Ranade, Y., and Pecht, J., Effect of Delamination on Moisture Accelerated Failures in Plastic Encapsulated Microcircuits. Circuit World, Vol. 23, No. 4, pp. 11-15 (1997).
Shan, X., Agarwal, R., Pecht, M., and Evans, J., Effect of Humidity on Reliability of Overlaid High Density Interconnects. Proceedings IEEE Multichip Module age Conference, pp. 106-109, March (1992).
Shook, R. L., Moisture Sensitivity Characterization of Plastic Surface Mount Devices Using Scanning Acoustic Microscopy. Proceedings of International Reliability Physics Symposium, pp. 157-168 (1992).
Totten, C. R., Part I: Managing Moisture Sensitive Devices, Circuits Assembly, pp. 56-64, September (1996A).
Totten, C. R., Part II: Managing Moisture Sensitive Devices, Circuits Assembly, pp. 34-38, October (1996B).
Theriault, M., Carsac, C., and Blostein, P., Evaluating Nitrogen Storage as an Alternative to Baking Moisture/Reflow Sensitive Components. Proceedings of the Technical Program: NEPCON West, Anaheim, Calif. (2000).
Tubbs, T. R. and Gallo, A. A., Accelerated Popcorn Testing of High Solder Reflow Crack Resistant Molding Compounds. Dexter Corporation Technical Paper, Olean, N.Y. April (1996).
Yalamanchiii, P., Gannamani, R., Munamarty, R., McCluskey, P., and Christou, A., Optimum Processing Prevents Popcorning. Surface Mount Technology, pp. 39-42, May (1995).
It is thus desired to provide a method and apparatus for estimating moisture absorption by hygroscopic materials for obtaining a better understanding of the kinetics of the water absorption process that may take place at ambient temperatures, between air saturated (or nearly saturated) with moisture and certain initially dry PEM packages. It is an additional desire to provide
Giacobbe Frederick W.
Pizzo Michael G.
American Air Liquide Inc.
Barlow John
Lau Tung
Russell Linda K.
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