Rapid advances in technology in several areas have converged to enable small, portable memory cards with vast capacities. Flash memory technologies such as those using electrically-erasable programmable read-only memory (EEPROM) have produced chips storing 128 M-Bytes or more. Small flash-memory cards have been designed that have a connector that can plug into a specialized reader, such as for compact-flash, secure-digital, memory stick, or other standardized formats.
More recently, flash memory cards are being sold that contain a USB connector. Such USB-flash memory cards do not require a specialized reader but can be plugged into a USB connector on a personal computer (PC). These USB-flash memory cards can be used in place of floppy disks. A USB-flash card can have a capacity of more than ten floppy disks in an area not much larger than a large postage stamp.
FIG. 1A shows a prior-art flash-memory card with an industry-standard USB connector. Flash memory chip 12 may be a 128 Mega-byte non-volatile chip or may have some other capacity. Controller chip 14 contains a flash-memory controller that generates signals to access memory locations within flash memory chip 12. Controller chip 14 also contains a USB interface controller that serially transfers data to and from flash memory chip 12 over a USB connection.
USB connector 20 may be mounted on board 10, which is a small circuit board with chips 12, 14 mounted thereon. Multi-layer printed-circuit board (PCB) technology can be used for board 10. A plastic case (not shown) can surround board 10. USB connector 20 is a male connector, such as a type-A USB connector, as it is locked to a female connector (to be discussed later) to transmit data between the flash memory card and a host. The term “male” may be dropped throughout the text to describe the male connector or any components thereon, in situations when there is no ambiguity.
USB connector 20 contains a small connector substrate 16, which is often white ceramic, black rigid plastic, or another sturdy substrate. Connector substrate 16 has four or more metal contacts 18 formed thereon. Metal contacts 18 carry the USB signals generated or received by controller chip 14. USB signals include power, ground, and serial differential data D+, D−.
USB connector 20 contains a metal case 17 that wraps around connector substrate 16. The metal case touches connector substrate 16 on three of the sides of connector substrate 16. The top side of connector substrate 16, holding metal contacts 18, has a large gap to the top of the metal case. On the top and bottom of this metal wrap are formed holes 15.
FIG. 1B shows a female USB connector. Female USB connector 22 can be an integral part of a PC, or can be connected by cable 21. Another female connector substrate 26 contains four metal contact 28 that make electrical contact with the four metal contacts 18 of the male USB connector 20 of FIG. 1A. Female connector substrate 26 is wrapped by a female metal case 27, but small gaps exist between the female metal case 27 and connector substrate 26 on the lower three sides to allow the upper three sides of the male metal case 17 to be inserted.
Locking is provided by metal springs 24 in the top and bottom of the metal case 27. When male USB connector 20 of FIG. 1A is flipped over and inserted into female USB connector 22 of FIG. 1B, metal springs 24 lock into holes 15 of USB male connector 20.
FIG. 2A and FIG. 2B are longitudinal cross-sections highlighting connections between male and USB female connectors. Female USB connector 22 is on the left while male USB connector 20 is being inserted from the right. Male USB connector 20 is flipped over relative to the view of FIG. 1A. Metal contacts 18 are formed on the lower surface of connector substrate 16 on male USB connector 20, while metal contacts 28 are formed on the upper surface of connector substrate 26 on female USB connector 22. The female metal contacts 28 generally are made with flexible metal springs which are placed parallel to the longitudinal direction of the female substrate 26, with their central portion protruded upward into the traveling path of the male USB connector 20. The protruded portion of the metal contact springs 28 will be depressed and deflected downward as the male USB connector is inserted to the female USB connector. Thus the metal contacts face one another to allow for electrical contact when male USB connector 20 is inserted into female USB connector 22 as shown in FIG. 2B.
FIG. 2C is a transverse cross-section illustrating the coupling between male and female USB connectors. This cross-section is perpendicular to the cross-sections shown in FIG. 2A and FIG. 2B. The male USB connector is represented by metal case 17, substrate 16 and four metal contacts 18. The female USB connector is represented by metal case 27, substrate 26 and four metal contacts 28. The external dimensions of the male metal case 17 matches the internal dimensions of the female metal case 27, and the two form an interference fit when fully engaged allowing male metal contacts 18 to be firmly in touch with the female metal contacts 28 to establish electrical connection.
Metal springs 24 formed on the metal case surrounding connector substrate 26 on female USB connector 22 fit into holes on the metal case of male USB connector 20. This helps to lock the connectors together.
FIG. 3 shows a prior-art USB flash memory card using a slim (low-profile) USB connector (based on U.S. Published application No. 2003/0100203 A1). Male USB connector 20 of FIGS. 1, 2 is relatively large. The metal case in particular is cumbersome and increases manufacturing cost. Costs may be reduced by integrating male USB connector 30 with board 32. Board 32 is a PCB that has flash memory chip 12 and controller chip 14 mounted thereon. Board 32 is extended to include male USB connector 30, which has metal contacts 38 formed on end 36 of board 32. The metal case shown in an industry-standard USB male connector does not exist. The edges are raised by a set of juts to prevent the male USB connect from wrongfully engaging to the female USB connector.
The width and thickness of board 32 at end 36 containing male USB connector 30 is designed to approximately match that of connector substrate 16 of FIG. 1A. Plastic case 34 can enclose board 32 but have an opening for metal contacts 38. Plastic case 34 can cover the bottom and sides of male USB connector 30 up to end 36 to emulate potions of the metal case of the male USB connector of FIG. 1A.
FIG. 4A and FIG. 4B show longitudinal cross-sections of the prior-art male slim USB connector being inserted into a standard female USB connector. Board 32 that has male USB connector 30 formed on end 36 is flipped over from the view shown in FIG. 3, and end 36 is inserted into female USB connector 22 from the right side.
Metal contacts 38 are located on the lower surface of male USB connector 30. Plastic case 34 has an opening on the lower surface of male USB connector 30 to expose the metal contacts so they can make electrical connection with metal contacts 28 on the upper surface of connector substrate 26 of female USB connector 22 when inserted as shown in FIG. 4B. The male metal contacts 18 are in touch with the female metal contacts 28 in the full engagement position to establish electrical contact. However, as the male metal case has been removed from the male USB connector, the four metal contacts 18 will be exposed when the male USB connector is disengaged with the female USB connector. As there is no protection for metal contacts, it is likely that these metal contacts can accidentally be touched by human fingers, resulting in contamination and even damage due to electro-static charges. While slim USB connector 30 can be less expensive and smaller than the standard USB connector, it fits less securely into a standard female USB connector. The lack of the metal case removes the mechanical support provided as the male metal case that fit in the gap below connector substrate 26 and the bottom side of the metal case for the female connector. Also, plastic case 34 does not lock into metal springs 24 on the top of female USB connector 22. The result is a noticeable wobble in the up and down direction when a USB flash memory card containing male USB connector 30 is inserted into female USB connector 22. Vertical movement of 3–4 millimeter at the end of a 4-centimeter flash card can occur with slight finger pressure. This vertical play gives the user the feeling that the flash memory card is cheap and unreliable, even when sufficient electrical contact is made.
What is desired is a low-profile male USB connector with reduced vertical wobble which also provides needed protection to the metal contacts in the USB connector. A low-profile male USB connector that more securely fits into a standard female USB connector is desired. A low-profile male USB connector with a more secure fit is desired that can be integrated with the circuit board containing the flash memory chip is also desirable.