loaded with additional components for expanded capabilities,
and another that is terminated into, rather than onto, a
PCB—reducing its profile height to a mere 1.8mm.
To be relevant in the smart home market, a device’s user
interface needs to be wireless-compatible. Components
that support this feature, like wireless module cards and
the connectors that accept them, are generally large in size
compared to other board-level components. However, a recent
specification change has enabled significantly smaller form
factors, making use of these components more viable. Formerly
known as Next-Generation Form Factor (NGFF), the M. 2
specification for internally mounted computer expansion cards
and connectors supersedes the Miniature Serial AT Attachment
(mSATA) specification, which uses the PCI Express Mini Card
(PCIe Mini) physical layout and connectors.
Designed for use with a wider range of module widths and
lengths than its predecessor, the M. 2 specification features a
more flexible physical specification and advanced interfacing
capabilities, and also enables smaller computer expansion
cards that operate at faster transfer speeds. Due to the
standard M. 2 criteria for pin count and keying layouts—
depending on which capability the expansion card provides—
these sleek, WiFi, WWAN, and SSD expansion cards can be
inserted into virtually any card edge connector, regardless
of the manufacturer. Connector manufacturers distinguish
themselves by offering different mounting options for this
seemingly universal M. 2 connector design.
Figure 2: Kyocera 6411 Series M. 2 card edge connectors in three
height variations—from top to bottom: 1.8mm, 2.3mm, and 3.2mm—and
the module card location of each relative to the PCB post-insertion.
The different mounting options primarily affect the
connector’s above-board height and the location of the
module’s seating plane, which is where the card edge of
a module enters a connector. Standard M. 2 card edge
connectors measure a slight 2.3mm high, and are designed to
leave just enough space for the bottom of the module card
to clear the mounting surface of the host PCB, but offer
no performance benefits beyond contributing to PCB size
reductions and connecting an M. 2 module card.
To meet the smart home market’s demand for both
reduced PCB size and expanded capabilities, several