Smart cards having thin die

Abstract

Thin semiconductor die, approximately 0.004 to 0.007 inches thick, are positioned substantially on the neutral plane of a smart card, the neutral plane defined as the plane of substantially no mechanical strain during flexure of the smart card, thereby providing smart cards having improved resistance to mechanical flexure, and / or smart cards having improved RF performance.

Description

CROSS-REFERENCE TO RELATED APPLICATIONRelated subject matter is disclosed in the co-pending, commonly assigned U.S. patent application of E. Suhir--1, Ser. No. 08 / 551,241, filed on Oct. 31, 1995, entitled "Data Carriers Having An Integrated Circuit Unit", in the co-pending, commonly-assigned U.S. patent application of Clifton-Flynn-Verdi 4-6-15, Ser. No. 08 / 558,579, filed on Oct. 31, 1995, entitled, "Smart Card Having a Thin Die", and in U.S. Pat. No. 5,480,842 issued on Jan. 2, 1996 to Clifton, Flynn, and Verdi.BACKGROUND OF THE INVENTION1. Field of the InventionThis invention relates generally to semiconductor devices, and more particularly to semiconductor die that are used in the manufacture of smart cards.2. Background ArtExisting smart cards may fail when, due to applied mechanical stress, the semiconductor die of the smart card breaks. Mechanical stress is inherent in typical smart card operational environments, such as point-of-sale terminals, electronic cash machines, credi...

AI Technical Summary

Benefits of technology

Improved smart card semiconductor die are provided that have a thickness of approximately 0.004 to 0.007 inches. These die are positioned at or near the neutral plane (i.e., plane of substantially zero mechanical strain during flexure) of a smart card, thereby providing smart cards having improved resistance to mechanical flexure and / or enhanced performance at RF frequencies.

Problems solved by technology

Existing smart cards may fail when, due to applied mechanical stress, the semiconductor die of the smart card breaks.

To this end, note that it is not feasible to use semiconductor die that are about 0.030 inches thick.

Semiconductor die thinner than 0.011 inches are typically not used in smart cards, as such die have traditionally been difficult to handle during the manufacturing process, and the resulting manufacturing expenses are relatively high.

Furthermore, conventional wisdom dictates that, as the thickness of a die is decreased, the die become increasingly vulnerable to mechanical failure.

A shortcoming of existing 0.011-inch die is that the die do not provide sufficient immunity to mechanical flexure.

When such die are used to fabricate smart cards, breakage and card failure may result if the smart card user bends or flexes the card.

Another shortcoming of existing smart card semiconductor die designs is that little, if any, consideration is given to RF (radio frequency) performance issues.

Although transponder devices and pagers have been developed for use at higher frequencies, such devices occupy a much larger physical volume than is available within the confines of a smart card.

That same lead, used at 500 Mhz, provides an inductive reactance of several hundred ohms, which may severely disrupt desired circuit operations at higher frequencies.

Moreover, when an existing semiconductor dice having a thickness of 0.011 inches is used to fabricate active semiconductor device, these devices provide electron transit times on the order of several tenths of microseconds, effectively limiting device operation to frequencies less than about 10 Mhz.

Unfortunately, the methods and systems described in the Miller patent are only practical when used to construct discrete transistor devices.

The use of tweezer-based devices to construct smart cards is impractical because it would be much too labor-intensive, time-consuming, and expensive.

Note that existing smart card packaging techniques place the semiconductor die near the surface of the card, due to tight packaging and interconnect requirements, and also because the thickness of the die represents a substantial portion of the thickness of the actual smart card package.

Therefore, if a user bends a smart card back and forth, the semiconductor die, being situated near the surface of the card, is subjected to relatively high levels of mechanical stress.

However, semiconductor die material functions as a lossy dielectric, attenuating RF signals that are incident thereupon, including the signals that are used to couple data to and from the smart card.

This attenuation limits the maximum coupling distance between a smart card and a smart card reader, and also restricts the position in which a smart card must be held relative to a smart card reader / writer, in order to successfully read and write data from and to the smart card.

Images