USB Specification

USB 3.0 Specifications – Mechanical Layer

USB 3.0 Specifications – Mechanical Layer

The Mechanical Layer defines the form, fit and function of the USB 3.0 connectors and cable assemblies. All implementers should read through this informational manual to understand key concepts of the USB 3.0 Mechanical Layer. This includes:

  • Connector mating interfaces
  • Cables and cable assemblies
  • Electrical requirements
  • Mechanical environmental requirements
  • Implementation notes and guidelines

The intent of this manual is to allow connector, system and device engineers to build, qualify and use the USB 3.0 connectors, cables, and cable assemblies for manufacturing and design elements. Keep in mind the many parts of this specification manual will conflict or differ from the USB 2.0 specification. The SuperSpeed USB 3.0 specification in this case always supersedes the High Speed USB 2.0 specification. Please read through this manual entirely before leaving any and all questions in the comments section. We will respond to all questions and feedback in a timely manner. Thank you.

Objectives

The mechanical layer USB 3.0 specification has been developed with the following objectives in mind:

  • Full support for the 5 Gbps data rate of transfer
  • Backward compatibility with USB 2.0
  • Minimization connector form factor variations
  • Full support for USB OTG (On-The-Go) technology
  • Electromagnetic Interference (EMI) Management
  • Low cost

Connectors

The mechanical layer USB 3.0 specification will define the following connectors:

  • USB 3.0 Standard-A plug and receptacle
  • USB 3.0 Standard-B plug and receptacle
  • USB 3.0 Powered-B plug and receptacle
  • USB 3.0 Micro-B plug and receptacle
  • USB 3.0 Micro-A plug
  • USB 3.0 Micro-AB receptacle

Plugs Accepted By Receptacles

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USB 3.0 Standard A Connector

The USB 3.0 Standard A connector is defined as the host connector, supporting the SuperSpeed mode. It as the exact same mating interface as the USB 2.0 standard A connector, but with additional pins for two more differential pairs and a drain.

This allows the USB 3.0 Standard A receptacle to accept either a USB 3.0 Standard A plug or a USB 2.0 Standard A plug. Likewise, a USB 3.0 Standard A plug can be mated with either a USB 3.0 Standard A receptacle or a USB 2.0 Standard A receptacle. A unique blue color coding on its plastic housing distinguishes the USB 3.0 Standard A connector from the USB 2.0 Standard A connector.

USB 3.0 Standard B Connector

The USB 3.0 Standard B connector is defined for relatively large, stationary peripherals, such as external hard drives and printers. It is defined so that the USB 3.0 Standard B receptacle accepts either a USB 3.0 Standard B plug or a USB 2.0 Standard B plug. Inserting a USB 3.0 Standard B plug into a USB 2.0 Standard B receptacle is physically disallowed.

USB 3.0 Powered B Connector

The USB 3.0 Powered B connector allows a USB 3.0 device to give enough power to a USB adaptor without the need for an external power supply. It is identical to the USB 3.0 Standard B connector in form factor, but has two more pins:

  • Power (DPWR)
  • Ground (DGND)

USB 3.0 Micro B Connector

The USB 3.0 Micro B connector is for small portable USB devices. It is compatible with the USB 2.0 Micro B connector. In other words, a USB 2.0 Micro B plug works in a USB 3.0 Micro B receptacle.

USB 3.0 Micro AB and USB 3.0 Micro A Connectors

The USB 3.0 Micro AB receptacle is similar to the USB 3.0 Micro B receptacle, except for different keying. It accepts a USB 3.0 Micro A plug, a USB 3.0 Micro B plug, a USB 2.0 Micro A plug, or a USB 2.0 Micro B plug. The USB 3.0 Micro AB receptacle is only allowed on OTG products, which may function as either a host or device. All other uses of the USB 3.0 Micro-AB receptacle are prohibited.

The USB 3.0 Micro A plug is similar to the USB 3.0 Micro B plug, except for different keying and ID pin connections. The USB 3.0 Micro A plug, the USB 3.0 Micro AB receptacle, and the USB 3.0 Micro B receptacle and plug all belong to the USB 3.0 Micro connector family since their interfaces differ only in keying. Similar to the USB 2.0 Micro A plug, the USB 3.0 Micro-A plug is defined for OTG applications only.

Compliant Cable Assemblies

The USB 3.0 specification defines the following cable assemblies:

  • USB 3.0 Standard A plug to USB 3.0 Standard B plug
  • USB 3.0 Standard A plug to USB 3.0 Micro B plug
  • USB 3.0 Standard A plug to USB 3.0 Standard A plug
  • USB 3.0 Micro A plug to USB 3.0 Micro B plug
  • USB 3.0 Micro A plug to USB 3.0 Standard B plug
  • Captive cable with USB 3.0 Standard A plug
  • Permanently attached cable with USB 3.0 Micro A plug
  • Permanently attached cable with USB 3.0 Powered B plug

A captive cable is a cable assembly that has a Standard A plug on one end and that is either permanently attached or has a vendor-specific connector on the other end. A permanently attached cable is directly wired to the device and it is not detachable from the device. For electrical compliance purpose, a USB 3.0 captive cable (permanently attached or with vendor specific connector on the device end) shall be considered part of the USB 3.0 device.

Raw Cables

Due to EMI and signal integrity requirements, each cable differential pair used for the SuperSpeed lines in a USB 3.0 cable assembly must be shielded. The Unshielded Twisted Pair (UTP) used for USB 2.0 is not allowed for SuperSpeed.

Connector Mating Interfaces

Here we will discuss the connector mating interface, including the connector interface drawings, pin assignments and descriptions.

USB 3.0 Standard A Connector

Noted are the USB 3.0 Standard A receptacle and plug interface dimensions, as well as the reference footprints for the USB 3.0 Standard A receptacle. Keep in mind that only the dimensions that govern the mating interoperability are specified. All the REF dimensions are provided for reference only, not hard requirements.

Although the USB 3.0 Standard A connector has basically the same form factor as the USB 2.0 Standard-A connector, it has significant differences inside. Below are the key features and design areas that need attention:

Besides the VBUS, D-, D+, and GND pins that are required for USB 2.0, the USB 3.0 Standard A connector has five more pins. The basic construction consists of two differential pairs plus one ground (GND_DRAIN). The two added differential pairs are for SuperSpeed data transfer, supporting dual simplex SuperSpeed signaling, while the added GND_DRAIN pin is for drain wire termination, managing signal integrity, and EMI performance.

The contact areas of the five SuperSpeed pins are located towards the front of the receptacle as the blades, while the four USB 2.0 pins towards the back of the receptacle as the beams or springs. In the plug, the SuperSpeed contacts as the beams sit behind the USB 2.0 blades. In other words, the USB 3.0 Standard A connector has a two-tier contact system.

The tiered contact method within the Standard A connector form factor results in less contact area to work with, as compared to the USB 2.0 Standard A connector. The connector interface dimensions take into consideration of contact mating requirements between the USB 3.0 Standard A receptacle and USB 3.0 Standard A plug, the UBS 3.0 Standard a receptacle and USB 2.0 Standard A plug, the USB Standard A receptacle, and the USB 3.0 Standard A plug. Connector designers should carefully consider those aspects in design details.

The connector interface definition comprehends the need to avoid shorting between the SuperSpeed and USB 2.0 pins during insertion when plugging a USB 2.0 Standard A plug into a USB 3.0 Standard A receptacle, or a USB 3.0 Standard A plug into a USB 2.0 Standard A receptacle. Connector designers should be conscious of this when detailing out designs.

There may be some increase in the USB 3.0 Standard A receptacle connector depth (into a system board) to support the two-tiered-contacts, as compared to the USB 2.0 Standard A receptacle. Through-hole footprints and some other footprints, such as SMT (surface mount) are also allowed.

Stacked USB 3.0 Standard A receptacles are not shown in this specification, but they are allowed as long as they meet all the electrical and mechanical requirements defined in this specification. In fact, a double-stacked USB 3.0 Standard A receptacle is expected to be a common application just like the double-stacked USB 2.0 Standard A receptacle that has been widely used in PCs. When designing a stacked USB 3.0 Standard A receptacle, efforts must be made to minimize impedance discontinuity of the top connector in the stack because of its long electrical length. Note that pins 1 to 9 correspond to the lower port, while pins 10 to 18 correspond to the upper port.

Attention must be paid to the high speed electrical design of USB 3.0 Standard A connectors. Besides minimizing the connector impedance discontinuities, crosstalk among the SuperSpeed pairs and USB 2.0 D+/D- pair should also be minimized.

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Pin Assignments and Description

The usage and assignments of the nine pins in the USB 3.0 Standard A connector are defined as follows:

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USB 3.0 Standard A Connector Color Coding

Since both the USB 2.0 Standard A and USB 3.0 Standard A receptacles may co-exist on a host, color coding is recommended for the USB 3.0 Standard A connector (receptacle and plug) housings to help users distinguish it from the USB 2.0 Standard A connector.

Blue (Pantone 300C) is the recommended color for the USB 3.0 Standard-A receptacle and plug plastic housings. When the recommended color is used, connector manufacturers and system integrators should make sure that the blue-colored receptacle housing is visible to users.

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USB 3.0 Standard B Connector

The USB 3.0 Standard B receptacle and plug interface dimensions are as follows:

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The USB 3.0 Standard B receptacle interfaces have two portions:

  • High Speed USB 2.0 interface
  • SuperSpeed USB 3.0 interface

The USB 2.0 interface consists of pins 1 to 4, while the SuperSpeed interface consists of pins 5 to 9. When a USB 2.0 Standard B plug is inserted into the USB 3.0 Standard B receptacle, only the USB 2.0 interface is engaged, and the link will not take advantage of the SuperSpeed capability.

However, since the USB 3.0 SuperSpeed portion is visibly not mated when a USB 2.0 Standard B plug is inserted in the USB 3.0 Standard B receptacle, users will get the visual feedback that the cable plug is not matched with the receptacle. Only when a USB 3.0 Standard B plug is inserted into the USB 3.0 Standard B receptacle, is the interface completely visibly engaged.

Pin Assignments and Description

The usage and assignments of the nine pins in the USB 3.0 Standard B connector are defined as follows:

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USB 3.0 Powered B Connector

The USB 3.0 Powered B receptacle and plug interface dimensions are as follows:

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Pin Assignments and Description

The usage and assignments of the eleven pins in the USB 3.0 Powered B connector are defined as follows:

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USB 3.0 Micro Connector Family

The USB 3.0 Micro connector family is made up of the USB 3.0 Micro B receptacle, USB 3.0 Micro AB receptacle, USB 3.0 Micro B plug and USB 3.0 Micro A plug. The USB 3.0 Micro receptacle and plug interface dimensions are as follows:

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The USB 3.0 Micro connector family has the following characteristics:

  • The USB 3.0 Micro B connector may be considered a combination of USB 2.0 Micro B interface and the USB 3.0 SuperSpeed contacts. The USB 3.0 Micro B receptacle accepts a USB 2.0 Micro B plug, maintaining backward compatibility.
  • The USB 3.0 Micro B connector maintains the same connector height and contact pitch as the USB 2.0 Micro B connector.
  • The USB 3.0 Micro B connector uses the same, proven latch design as the USB 2.0 Micro B connector.
  • The USB 3.0 Micro AB receptacle is identical to the USB 3.0 Micro B receptacle except for a keying difference in the connector shell outline.
  • The USB 3.0 Micro A plug is similar to the USB 3.0 Micro B plug with different keying and ID pin connections.
  • There is no required footprint for the USB 3.0 Micro connector family.

Pin Assignments and Description

USB 3.0 Micro B Connector Pin Assignments

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USB 3.0 Micro AB/A Connector Pin Assignments

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Cable Construction and Wire Assignments

Here we will discuss USB 3.0 cables, including their construction, wire assignments, and wire gauges.

Cable Construction

There are three groups of wires:

  • UTP signal pair
  • Shielded Differential Pair (SDP, twisted or twinax signal pairs)
  • Power and Ground wires

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The UTP is intended to transmit the USB 2.0 signaling while the SDPs are used for SuperSpeed, while the shield is needed for the SuperSpeed differential pairs for signal integrity and EMI performance.

Each SDP is attached with a drain wire, which is eventually connected to the system ground through the GND_DRAIN pin(s) in the connector.

A metal braid is required to enclose all the wires in the USB 3.0 cable. The braid is to be terminated to the plug metal shells, as close to 360° as possible, to contain EMI.

Wire Assignments

Here are the wire number, signal assignments, and colors of the wires for the SuperSpeed USB 3.0 specification.

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Wire Gauges and Cable Diameters

This specification chooses not to specify wire gauges. Table 5-8 lists the typical wire gauges for reference. A large gauge wire incurs less loss, but at the cost of cable flexibility. One should choose the smallest possible wire gauges that meet the cable assembly electrical requirements.

To maximize cable flexibility, all wires are required to be stranded and the cable outer diameter should be minimized as much as possible. A typical USB 3.0 cable outer diameter may range from 3 mm to 6 mm.

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Cable Assemblies

USB 3.0 Standard A to USB 3.0 Standard B Cable Assembly:

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USB 3.0 Standard A to USB 3.0 Standard B Cable Assembly Wiring

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USB 3.0 Standard A to USB 3.0 Standard A Cable Assembly

The USB 3.0 Standard A to USB 3.0 Standard A cable assembly is defined for operating system debugging and other host-to-host connection applications. Below you can see the wire connections for such a cable assembly.

USB 3.0 Standard A to USB 3.0 Standard A Cable Assembly Wiring

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USB 3.0 Standard A to USB 3.0 Micro B Cable Assembly

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USB 3.0 Standard A to USB 3.0 Micro B Cable Assembly Wiring

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USB 3.0 Micro A to USB 3.0 Micro B Cable Assembly

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USB 3.0 Micro A to USB 3.0 Micro B Cable Assembly Wiring

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USB 3.0 Micro A to USB 3.0 Standard B Cable Assembly

A USB 3.0 Micro A to USB 3.0 Standard B cable assembly is also allowed within the USB 3.0 specification. Here we will go over the UBS 3.0 Micro A cable overmold and the USB 3.0 Standard B cable overmold dimensions.

USB 3.0 Micro A to USB 3.0 Standard B Cable Assembly Wiring

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USB 3.0 Icon Location

The USB 3.0 cable assemblies, compliant with the USB 3.0 Connectors and Cable Assemblies Compliance Specification, shall display the USB 3.0 Icons.

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The USB 3.0 Icon is embossed, in a recessed area, on the side of the USB 3.0 plug. This provides easy user recognition and facilitates alignment during the mating process. The USB Icon and Manufacturer’s logo should not project beyond the overmold surface. The USB 3.0 compliant cable assembly is required to have the USB 3.0 Icons on the plugs at both ends, while the manufacturer’s logo is recommended. USB 3.0 receptacles should be orientated to allow the Icon on the plug to be visible during the mating process.

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Cable Assembly Length

This specification does not specify cable assembly lengths. A USB 3.0 cable assembly can be of any length, as long as it meets all the requirements defined in this specification. The cable assembly loss budget and the cable voltage drop budget will limit the cable assembly length.

Electrical Requirements

Here we will discuss the electrical requirements for USB 3.0 raw cables, mated connectors, and mated cable assemblies. USB 3.0 signals, known as SuperSpeed, are governed by this specification. The USB 2.0 signals are governed by the USB 2.0 specification, unless otherwise specified. Refer to the USB 3.0 Connectors and Cable Assemblies Compliance Document for specific D+/D- lines electrical requirements.

Compliance to the USB 3.0 specification is established through normative requirements of mated connectors and mated cable assemblies. SuperSpeed requirements are specified mainly in terms of S-parameters, using industry test specification with supporting details when required. DC requirements, such as contact resistance and current carrying capability, are also specified in this section. Any informative specification for cable and connector products is for the purpose of design guidelines and manufacturing control.

In conjunction with performance requirements, the required test method is referenced for the parameter stated. Additional supporting test procedures can be found in the USB 3.0 Connectors and Cable Assemblies Compliance Document. The requirements in the section apply to all USB 3.0 connectors and/or cable assemblies unless specified otherwise.

SuperSpeed Electrical Requirements

The following sections outline the requirements for SuperSpeed signals. The requirements for the USB 2.0 signals (D+/D- lines) are given in the USB 3.0 Connectors and Cable Assemblies Compliance Document.

Raw Cable

Informative raw cable electrical performance targets are provided here to help cable assembly manufacturers manage raw cable suppliers. Those targets are not part of the USB 3.0 compliance items; the ultimate requirements will be the mated cable assembly performance.

Characteristic Impedance

The differential characteristic impedance for the SDP pairs is recommended to be within 90 Ù +/- 7 Ù. It should be measured with a TDR in a differential mode using a 200 ps (10%-90%) rise time.

Intra-Pair Skew

The intra-pair skew for the SDP pairs is recommended to be less than 15 ps/m. It should be measured with a TDT in a differential mode using a 200 ps (10%-90%) rise time with a crossing at 50% of the input voltage.

Differential Insertion Loss

Cable loss depends on wire gauges and dielectric materials. Keep in mind that the differential loss values should be referenced to 90 Ω differential impedance.

Mated Connector

The mated connector impedance requirement is needed to maintain signal integrity. The differential impedance of a mated connector shall be within 90 Ù +/-15 Ù, as seen from a 50 ps (20%-80%) risetime of a differential TDR.

The impedance profile of a mated connector must fall within the limits shown below. Note that the impedance profile of the mated connector is defined from the receptacle footprints through the plug cable termination area. In the case the plug is directly attached to a device PCB, the mated connector impedance profile includes the path from the receptacle footprints to the plug footprints.

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Mated Cable Assemblies

A mated cable assembly refers to a cable assembly mated with the corresponding receptacles mounted on a test fixture at the both ends. The requirements are for the entire signal path of the mated cable assembly, from the host receptacle contact solder pads or through-holes on the host system board to the device receptacle contact solder pads or through holes on the device system board, not including PCB traces, the measurement is between TP1 (test point 1) and TP2 (test point 2).

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For proper measurements, the receptacles shall be mounted on a test fixture. The test fixture shall have uncoupled access traces from SMA or microprobe launches to the reference planes or test points, preferably with 50 Ù +/-7% Ù single-ended characteristic impedance. The test fixture shall have appropriate calibration structures to calibrate out the fixturing effect. All non-ground pins that are adjacent but not connected to measurement ports shall be terminated with 50 Ù loads.

To be consistent with the USB 3.0 channel nominal differential characteristic impedance requirement of 90 Ù, all measured differential S-parameters shall be normalized with 90-Ù reference differential impedance. Most VNA measurement software allows normalization of measured S-parameters to different reference impedance. For example, in PLTS, one can set the port impedance to 45 Ù to normalize the measured 50-Ù single-ended S-parameters to 45 Ù; this will result in 90-Ù differential S-parameters after the singled-ended-to-differential conversion.

Differential Insertion Loss (EIA-360-101)

The differential insertion loss, SDD12, measures the differential signal energy transmitted through the mated cable assembly. Below you’ll see the differential insertion loss limit, which is normalized with 90-Ù differential impedance and defined by the following vertices: (100 MHz, -1.5 dB), (1.25 GHz, -5.0 dB), (2.5 GHz, -7.5 dB), and (7.5 GHz, -25 dB). The measured differential insertion loss of a mated cable assembly must not exceed the differential insertion loss limit.

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Differential Near-End Crosstalk between SuperSpeed Pairs (EIA-360-90)

The differential crosstalk measures the unwanted coupling between differential pairs. Since the Tx pair is right next to the Rx pair for SuperSpeed, only the differential near-end crosstalk (DDNEXT) is specified referencing to a 90-Ω differential impedance. The mated cable assembly meets the DDNEXT requirement if its DDENXT does not exceed the limit shown below. The vertices that define the DDNEXT limit are: (100 MHz, -27 dB), (2.5 GHz, -27 dB), (3 GHz,-23 dB) and (7.5GHz, -23 dB).

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Differential Crosstalk between D+/D- and SuperSpeed Pairs (EIA-360-90)

The differential near-end and far-end crosstalk between the D+/D- pair and the SuperSpeed pairs (SSTX+/SSTX- or SSRX+/SSRX-) shall be managed not to exceed the limit shown below. The vertices that define the DDNEXT and DDFEXT limit are: (100 MHz, -21 dB), (2.5 GHz, -21 dB), (3.0 GHz,-15 dB) and (7.5 GHz, -15 dB). The reference differential impedance shall be 90 Ù.

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Differential-to-Common-Mode Conversion

Since the common mode current is directly responsible for EMI, limiting the differential-to-common- mode conversion, SCD12, will limit EMI generation within the connector and cable assembly. A mated cable assembly passes the SCD12 requirement if its SCD12 is less than or equal to -20 dB across the frequency range shown below.

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DC Electrical Requirements

Low Level Contact Resistance (EIA 364-23B)

The following requirement applies to both the power and signal contacts:

  • 30 mΩ (Max) initial for VBUS and GND contacts.
  • 50 mΩ (Max) initial for all other contacts.
  • Maximum change (delta) of +10 mΩ after environmental stresses.
  • Measure at 20 mV (Max) open circuit at 100 mA.

Dielectric Strength (EIA 364-20)

No breakdown shall occur when 100 Volts AC (RMS) is applied between adjacent contacts of unmated and mated connectors.

Insulation Resistance (EIA 364-21)

A minimum of 100 MÙ insulation resistances is required between adjacent contacts of unmated and mated connectors.

Contact Current Rating (EIA 364-70, Method 2)

A current of 1.8 A shall be applied to VBUS pin and its corresponding GND pin (pin 1 and pin 4 of the USB 3.0 Standard A and Standard B/Powered B connectors; pin 1 and pin 5 of the USB 3.0 Micro connector family). Additionally, a minimum current of 0.25 A shall be applied to all the other contacts. When the current is applied to the contacts, the delta temperature shall not exceed +30 °C at any point on the USB 3.0 connectors under test, when measured at an ambient temperature of 25 °C.

In the case of the USB 3.0 Powered B connector, a current of 2.0 A shall be applied to the DPWR pin and its corresponding DGND pin (pin 10 and pin 11 for USB 3.0 Powered-B connector). Additionally, a minimum current of 0.25 A shall be applied to all the other contacts. When current is applied to the contacts, the delta temperature must not exceed +30 °C at any point in the USB 3.0 connectors under test, when measured at an ambient temperature of 25 °C.

Mechanical and Environmental Requirements

The requirements in the section apply to all USB 3.0 connectors and/or cable assemblies unless specified otherwise.

Mechanical Requirements

Insertion Force (EIA 364-13)

The connector insertion force shall not exceed 35 N at a maximum rate of 12.5 mm (0.492″) per minute. It is recommended to use a non-silicon based lubricant on the latching mechanism to reduce wear. If used, the lubricant may not affect any other characteristic of the system.

Extraction Force (EIA 364-13)

The connector extraction force shall not be less than 10 N initial and 8 N after the specified insertion/extraction or durability cycles (at a maximum rate of 12.5 mm (0.492″) per minute).

No burs or sharp edges are allowed on top of locking latches (hook surfaces which will rub against the receptacle shield).

It is recommended to use a non-silicon based lubricant on the latching mechanism to reduce wear. If used, the lubricant may not affect any other characteristic of the system.

Durability or Insertion/Extraction Cycles (EIA 364-09)

The durability ratings listed below are specified for the USB 3.0 connectors.

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Cable Flexing (EIA 364-41, Condition I)

No physical damage or discontinuity over 1 ms during flexing shall occur to the cable assembly with Dimension X = 3.7 times the cable diameter and 100 cycles in each of two planes.

Cable Pull-Out (EIA 364-38, Condition A)

No physical damage to the cable assembly shall occur when it is subjected to a 40 N axial load for a minimum of 1 minute while clamping one end of the cable plug.

Peel Strength (USB 3.0 Micro Connector Family Only)

No visible physical damage shall be noticed to a soldered receptacle when it is pulled up from the PCB in the vertical direction with a minimum force of 150 N.

4-Axes Continuity Test (USB 3.0 Micro Connector Family Only)

The USB 3.0 Micro connector family shall be tested for continuity under stress using the test configurations shown below. Plugs shall be supplied in a cable assembly with a representative overmold. A USB 3.0 Micro B or AB receptacle shall be mounted on a 2-layer printed circuit board (PCB) between 0.8 and 1.0 mm thickness. The PCB shall be clamped on either side of the receptacle no further than 5 mm away from the solder tails. The PCB shall initially be placed in a horizontal plane, and an 8-N tensile force shall be applied to the cable in a downward direction, perpendicular to the axis of insertion, for a period of at least 10 seconds.

The continuity across each contact shall be measured throughout the application of the tensile force. The PCB shall then be rotated 90 degrees such that the cable is still inserted horizontally and the 8 N tensile force will be applied again in the downward direction and continuity measured as before. This test will be repeated for 180-degree and 270-degree rotations. Passing parts shall not exhibit any discontinuities greater than 1 μs duration in any of the four orientations. One method for measuring the continuity through the contacts is to short all the wires at the end of the cable pigtail and apply a voltage through a pull-up to each of VBUS, D+, D-, ID, and the SuperSpeed pins, with the GND pins connected to ground.

When testing a USB 3.0 Micro A plug, all the sense resistors shall stay pulled down for the length of the test. When testing a USB 3.0 Micro B plug, the ID pin shall stay high and the other pins shall remain low for the duration of the test. Alternate methods are allowed to verify continuity through all pins.

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Wrenching Strength (Reference, USB 3.0 Micro Connector Family Only)

The wrenching strength test shall be performed using virgin parts. Perpendicular forces (Fp) are applied to a plug when inserted at a distance (L) of 15 mm from the edge of the receptacle. Testing conditions and method shall be agreed to by all parties. These forces shall be applied in all four directions (left, right, up, down). Compliant connectors shall meet the following force thresholds:

  • No plug or receptacle damage shall occur when a force of 0-25 N is applied.
  • The plug may be damaged, but only in such a way that the receptacle does not sustain damage when a force of 25-50 N is applied.

Lead Co-Planarity

Co-planarity of all SMT leads shall be within a 0.08 mm range.

Solderability

Solder shall cover a minimum of 95% of the surface being immersed, when soldered at a temperature 255 °C +/-5 °C for immersion duration of 5 s.

Restriction of Hazardous Substances (RoHS) Compliance

It is recommended that components be RoHS compliant. Lead-free plug and receptacle materials should conform to Directive 2002/95/EC of January 27, 2003 on RoHS or other regulatory directives.

Environmental Requirements

The connector interface environmental tests shall follow EIA-364-1000.01, Environmental Test Methodology for Assessing the Performance of Electrical Connectors and Sockets Used in Business Office Applications.

Since the connector defined has far more than 0.127 mm wipe length, Test Group 6 in EIA-364-1000.01 is not required. The temperature life test duration and the mixed flowing gas test duration values are derived from EIA 364-1000.01 based on the field temperature per the following.

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Materials

This specification does not specify materials for connectors and cables. Connector and cable manufactures shall select appropriate materials based on performance requirements.

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Implementation Notes and Design Guides

Here we will discuss a few implementation notes and design guides to help users design and use the USB 3.0 connectors and cables.

Mated Connector Dimensions

The distance between the receptacle front surface and the cable overmold should be observed by system designers to avoid interference between the system enclosure and the cable plug overmold. Provisions shall be made in connectors and chassis to ground the connector metal shells to the metal chassis to contain EMI emission.

Mated USB 3.0 Standard A Connector

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Mated USB 3.0 Standard B Connector

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Mated USB 3.0 Micro B Connector

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EMI Management

Systems that include USB 3.0 connectors and cable assemblies must meet the relevant EMI/EMC regulations. Because of the complex nature of EMI, it is difficult to specify a component level EMI test for the cable assemblies. However, connector and cable assembly designers, as well as system implementers should pay attention to receptacle and cable plug shielding to ensure a low impedance grounding path. The following are guidelines for EMI management:

  • The quality of raw cables should be ensured. The intra-pair skew or the differential to common mode conversion of the SuperSpeed pairs has a significant impact on cable EMI performance and should be controlled within the limits of this specification.
  • The cable external braid should be terminated to the cable plug metal shell as close to 360° as possible. Without appropriate shielding termination, even a perfect cable with zero intra-pair skew may not meet EMI requirements.
  • If not done properly, the wire termination contributes to the differential-to-common-mode conversion. The breakout distance for the wire termination should be kept as small as possible for both EMI and signal integrity. If possible, symmetry should be maintained for the two lines within a differential pair.
  • The mating interface between the receptacle and cable plug should have a sufficient number of grounding fingers, or springs to provide a continuous return path from the cable plug to system ground. Friction locks should not compromise ground return connections.
  • The receptacle connectors should be designed with a back-shield as part of the receptacle connector metal shell. The back-shield should be designed with a short return path to the system ground plane.
  • The receptacle connectors should be connected to metal chassis or enclosures through grounding fingers, screws, or any other way to mitigate EMI.

Stacked Connectors

Stacked USB connectors are commonly used in PC systems. This specification does not explicitly define the stacked USB 3.0 Standard A receptacles but they are allowed. The following are a few points that should be taken into account when designing a stacked USB 3.0 connector.

A stacked connector introduces additional crosstalk between the top and bottom connectors. Such crosstalk should be minimized when designing a stacked USB 3.0 connector. The differential NEXT and FEXT should be managed within ~-32 dB (up to the fundamental frequency of 2.5 GHz) between differential pairs in the top and bottom connectors.

Due to the additional electrical length, the top connector will generally not perform as well as the bottom connector. Connector designers should carefully design the top connector contact geometries and materials to minimize impedance discontinuity. Regardless of how many connectors within a stack one may choose to design, the electrical requirements for USB 3.0 must be met.

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