Original 45nm Intel® Core™ Microarchitecture

The Technical Challenges of Transitioning Intel® PRO/Wireless Solutions to a Half-Mini Card

TECHNICAL CHALLENGES AND SOLUTIONS

Shrinking the full-mini card down to a half-mini card

The Intel PRO/Wireless 5300 family of network adaptors is targeted to be offered in two form-factor flavors: (1) the Full-Mini Card and (2) the Half-Mini Card. The Full-Mini Card solution was defined as a single-sided solution with all components on the top side of the PCB. The intent is to support OEM customers who want to make use of the space underneath the Mini Card. With the available room on the top side of the Mini Card, we typically subdivide it into two distinct sections: (1) the high frequency RF section including the Radio Transceiver chip and all the front-end components that reside under an EMI RFI shielded enclosure, and (2) the rest of the circuitry that is not as EMI RFI sensitive and can sit on the board unshielded.

To meet the required functionality of the Intel PRO/Wireless 5300 Network Adaptor, almost all the available area of the Full-Mini Card is populated with hardware components. Therefore, it is fairly obvious that in order to fit on the Half-Mini Card with the same hardware content that is half the board size, some of the components will need to reside on the bottom side of the Half-Mini Card board. We can look at this as if we are taking the Mini Card board and folding it on itself to create a board that is half the length but is now two sided and has components on the top and bottom of the board, as shown in (Figure 5) .

Figure 5: Folding the single-sided Full-Mini Card to yield a dual-sided Half-Mini Card

The actual partitioning of what needs to reside on the top side and what can sit on the bottom side is mainly driven by the z-height limitations of the components and the z-height restriction per the Mini Card specification. The maximum z-height above the board is 2.40mm, while the maximum z-height below the board is 1.35mm. These restrictions remain the same for the Full-Mini Card and the Half-Mini Card even though we used only the top side for our previous-generation solutions. In our case of transitioning to the Half-Mini Card, the RF shielded portion is more suited to sit on the top side of the board, where the extra height is needed, driving almost all other low-profile components to the bottom.

However, based on the Half-Mini Card mechanical specification, the area on the top side that is available to be shielded is actually further limited in comparison to the Mini Card board. This is due mainly to the large mounting hole and antenna interface section at the end of the board that remain the same for both form factors. This section does not scale in size when the board is shortened to half the length. It is only shifted! So, effectively, we have less room for the RF section under the shield of a Half-Mini Card. Knowing this fact a priori drove the development of highly integrated front-end modules to save space and enable all of the RF section, including the Radio Transceiver, to fit inside the shield of the Half-Mini Card board.

With the RF section on top, we are forced to push the rest of the components to the bottom side. This means that they need to comply with the low-profile requirements to ensure that the board complies with the z-height restrictions of the Mini Card specification. Several non-compliant components were identified; specifically the power inductors used in conjunction with the DC DC converters. This fact spurred a search for low-profile substitutes. However, the low-profile substitutes found were three times more expensive than the original part. The team was asked to find some way to place the original component on the top side as part of a cost-saving opportunity. Initially, a solution was proposed whereby the inductors reside on top outside the shielded area because it was feared that the switching noise generated in these inductors would somehow contaminate the RF signals. However, we found that the overhead of this type of solution took up too much of the precious board space needed for the RF section under the shield. We devised a simple Design of Experiment (DoE) whereby we designed a board with the power inductors inside the shielded enclosure. We tested the DoE and proved beyond a shadow of a doubt that noise contamination was not an issue. This became the Plan Of Record, and the original high z-height lower-cost inductors are incorporated within the shielded enclosure area, leaving enough area for the RF components.

We still had more challenges to overcome, however, and these are described in the next sections.

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