Patent Application
20060042827
This invention relates to memory and interface cards for portable computer devices such as personal digital assistants, digital cameras, etc. More specifically it relates to Secure Digital (SD) or Multimedia Memory Card (MMC) type cards that meet existing size standards but have enhanced component packing density.
(Portions of the technical material contained in this section may not be prior art.)
The evolution of component miniaturization in computer technology now allows very small, portable, units that can be carried as personal items, for example, in briefcases, or clothing pockets. There are a variety of such devices available commercially. Among those well known in the trade are PDAs, personal PCs, digital cameras, cell phones, smart phones, etc. For convenience, these portable devices are generically referred to below as PDAs. However, the term should be recognized as referring to any portable electronic device.
To extend the functional capacity of these devices, many have been equipped with slots to accommodate active integrated circuit cards. In so-called SD product technology these slots are designated Secure Digital or SD slots, and the cards as SD cards. When a unit is provided with I/O capability, the cards are referred to as SDIO cards.
A competing technology, MMC storage technology, uses very similar cards as storage media. In the description below, cards that are adapted for use with these technologies, and anticipated new technologies, will be referred to using the generic term “PDA cards”.
In both of the established technologies just mentioned, standards have been established for the form factor of the cards. That allows manufacturers of the portable devices to have a common size and contact pin configuration for the slots in the portable units.
Both the SD standard and the MMC standard prescribe a length×width of 32×24 mm. The SD card thickness standard is 2.1 mm. The nominal MMC card thickness standard is 1.4 mm.
The complexity of the PDA cards and the portable units that use them increases as more functionality is added. These devices now provide audio, picture, video, and document storage capability. They can also interface with wireless LAN using SDIO interface cards. The SDIO card carries an RF integrated circuit. The other applications just mentioned are typically supported with large capacity memory circuits.
The combination of these circuits on a single PDA card presents a challenge for the PDA card designer. The length×width maximums place severe constraints on the design of the integrated circuits (ICs) in the PDA cards. Much of the effort toward more efficient component packing density has centered around these dimensions, i.e. the card area. For example, U.S. patent application Ser. No. 10/839,901 describes and claims PDA card extensions where a portion of the card protrudes outside the slot. That portion has an unconstrained thickness, and various IC structures can be accommodated in the card extension portion.
However, we have recognized that the maximum height within the slot, and the corresponding maximum thickness of the portion of the PDA card contained within the slot, are also limiting. For example, a recent PDA application addition, plug-and-play network interfacing, uses cards having filters and oscillators that are large components, with a height typically in the 0.8-1.2 mm range. Recognizing that it is desirable for many applications to have most of the PDA card and the PDA ICs housed within the slot, and to meet the thickness standard, many versions of current PDA card configurations do not accommodate IC components with heights greater than approximately 0.8 mm.
We have designed a high density PDA integrated circuit card that overcomes in part the height constraint for IC components on the PDA card. We achieve this by building the printed circuit board platform on two levels. We have recognized that the contact pad end of the card should meet the 1.4 mm thickness maximum, while the remaining card portion is only constrained by the 2.1 mm thickness maximum. We take advantage of this difference by forming a tiered platform with two levels. The large IC components are placed on the lower tier of the two-tiered platform. Smaller components are placed on the upper tier. The upper tier portion of the card stays within the 1.4 mm constraint, and the lower tier portion stays within the 2.1 mm constraint. The tiers may comprise two printed circuit boards (PCBs), or a unitary PCB assembly having two tiers.
With reference to
In
The SD and MMC standards bodies have established standard dimensions for PDA cards. While these differ in some cases, dimension f in
In a typical PDA card, dimensions a, b, c, and d, are 0.7 mm, 0.4 mm, 0.8 mm, 0.2 mm, for a total dimension e that meets the SDA maximum of 2.1 mm. The space for components has a height c=0.8 mm. That is sufficient to accommodate devices 16 and 17, but device 18 has a height that exceeds the height of the allowed space at 19.
In some PDA cards, the thickness of the PCB may be less than 0.4 mm. That may allow sufficient space for device 19. However, as PDAs accumulate more and more functionality, the PCB becomes more complex, and thicker multi-layer PCBs are needed. This increases the constraint on dimension c in the PDA card.
To overcome this problem according to the invention, a new PCB configuration is used. This is shown in
In the embodiment of
The tiers of the PCB are physically attached as already shown, and are also electrically interconnected. Again, a variety of approaches may be used to run electrical interconnections between the tiers. Plated through holes, well known in the art, may be used to interconnect a metallization pattern on PCB 21, to contact pads on PCB 23. Recognizing that the PCBs may be multilevel, it is straightforward to route interconnect runners out of both sides of a PCB. This expedient is illustrated in
To realize the benefits of the invention, the tiers should have a significant separation, i.e. height difference. In the context of the dimensions in the current state of the art, a significant advantage may be gained by dropping the lower tier of the PCB by at least 0.1 mm. Moreover, the benefit of the invention is realized when the height of a component on the lower tier exceeds the available height, i.e. dimension c, on the upper tier. It will also be the case that at least one component mounted on the lower tier has a thickness that exceeds the thickness of all of the components on the upper tier.
The PDA card of the invention may be designed to be fully contained in the slot of the PDA device, or may have an extension of the kind described in co-pending application Ser. No. 10/839,901, which application is incorporated herein by reference. In common commercial PDA card designs, the card is longer than the PDA slot, with a portion of the card extending outside the PDA housing. The extension of the PDA card facilitates handling for inserting and extracting the card. In cards designed with a wireless LAN interface, the extended portion of the card may contain an encased RF circuit and an RF antenna.
Whereas the standard PCBs are epoxy resin, for example, FR-4, other PCB types may be used as well. A flexible polymer PCB may be used which, in some cases, may be flexed to provide the two-tiered structure shown in
A particularly useful embodiment of the invention is shown in
The PDA cards described above typically contain one or more IC chips with active devices, e.g. RF chips or memory chips. It also typically has passive components, and/or one or more integrated passive devices (IPDs). The active IC chips, and the passive devices, are referred to by the generic term component(s).
From the foregoing description, it should be evident that according to one embodiment of the invention, a PDA card comprises a first PCB portion with a bottom plastic cover having thickness a1, a PCB having thickness b1, a component space having thickness c1 and a top cover having thickness d1, where a1+b1+c1+d1=e1, and a second PCB portion having a bottom plastic cover having thickness a2, a PCB having thickness b2, a component space having thickness c2 and a top cover having thickness d2, where a2+b2+c2+d2=e2, and wherein e1 is greater than e2, and e1 and e2 are made to conform to an industry standard. It will also be appreciated that whereas at least one of a1+b1+c1+d1 is different from the respective member of a2+b2+c2+d2, others may be the same.
The invention may also be described in terms of the height of the components accommodated by the two tiered PCB. That would be described by a printed circuit board (PCB) having two tiers, a first tier at one level and a second tier at a different level, a cover overlying the PCB forming a first space with height c1 over the first tier and a second space with height c2 over the second tier, where c1 is greater than c2, at least one component attached to the PCB in the first space, the component having a height h1, at least one component attached to the PCB in the second space, the component having a height h2, where h1>c2.
Various additional modifications of this invention will occur to those skilled in the art. All deviations from the specific teachings of this specification that basically rely on the principles and their equivalents through which the art has been advanced are properly considered within the scope of the invention as described and claimed.
