what kind of material offers reliability and safety in next-generation USB-C connectors?
The Type-C connector supports the new SuperSpeed USB 3.1 format, which offers data-transfer rates as high as 10Gb/s or roughly double the speed of current USB 3.0 versions. It’s still backward-compatible with all the USB 2.0 formats (LS, FS, and HS), so even legacy systems will be able to take advantage of the new connector when it’s designed into dongles.
As a result, the USB-C connector will become the standard design from 2017 on, as decreed by USB Implementers Forum (USB IF), the non-profit corporation founded by the group of companies that developed the original Universal Serial Bus specification.
The USB Power Delivery specification is also being updated to enable USB PD to support the USB-C Cable and Connector specification, for charging up to 100W. USB-C specifications are contained within the overall USB 3.1 standard that also covers data transmission rates.
The various pins on the USB-C connector are spaced with a pitch of just 0.5mm, compared with 0.65mm on a USB 3.0 Micro B connector and 2.0mm on a USB Type A connector. The thinnest insulating wall has been reduced from 1.84mm on the USB Type A to a miniscule 0.12mm on a USB-C connector. It is difficult to successfully design and consistently mold parts with such thin walls and maintain the necessary mechanical and electrical properties.
Many component producers have begun developments in new USB-C connector designs using liquid crystal polymers (LCPs). Traditionally, LCPs are often favored in thin-wall electronics because of their excellent flow properties and because prices of some commodity grades are relatively low, sometimes under $10/kg; LCPs are well-known by USB connector makers, since they have been the favored polymer in previous generations of USB.
But in many cases, USB-C connectors are likely to fail stringent tests regarding their electrical properties, especially resistance to surface tracking, expressed as the Comparative Tracking Index (CTI), and also mechanical properties.
The CTI of the plastic that acts as an insulator as well as a mechanical anchor around the conductors is more than ever a key for product reliability with the USB-C connector. If the insulator does not have sufficiently high CTI, there is a risk that at some point a short circuit will result, damaging the device and possibly even starting a fire. This is not fearmongering – there are various reports of mobile devices catching fire during charging.
There are essentially three routes to reduce risk of fire hazard caused by tracking:
Increasing the creeping distance (defined by conductor pitch and insulator wall thickness)
Lowering the level of environmental pollution (dust, sweat, etc.)
Using an insulation material with a higher CTI
The creeping distance in the connectors is pre-defined and cannot be modified. Reduction of the level of environmental pollution at connector level can only be done by additional sealing, which adds to the cost of the device, so using a material for the insulator with as high a CTI as possible is the most viable solution to increase end-product safety.
Solutions more appropriate than those possible with LCPs or halogen-containing PAs (PA9T or PA6T) can be found with high-performance halogen-free polyamides, such as PA46 and PA4T.
High-performance polyamides 46 and 4T offer the best balance of mechanical and electrical properties and precision molding. Polyamides 46 and 4T already have been approved by several global producers for use in the next generation of USB-C connectors. They answer the need for improved levels of safety and reliability. PA46 and PA4T both have high CTIs of PLC class 0, well above the recommended 400V. They maintain this high performance for twice as long as alternative materials such as LCPs, most of which have CTIs under 400V.
An ideal solution, therefore, is to use PA4T for the first insert molding stage; this has a melting point of 325°C. The second insert molding stage can then be done with PA46, which has a melting point of 295°C.
The most difficult part of a USB-C connector to produce is the plug front housing. Very thin ribs require high flow and tough material, and there is a weld line on the front side, which mandates a material with high welding-line strength.
Material requirements listed below can all be fulfilled by high-performance polyamides PA46 and PA4T:
High flow for 0.12mm wall thickness design
High levels of stiffness, toughness, and welding line strength
High-wear friction strength and high retention force (10,000 times mating/unmating durability test)
Good process window
UL 94-V0 and high CTI (400V) to support USB PD 1.0 and 2.0 standards (up to 5A and 20V)
Good colorability to support consumer electronics market needs
Lead-free reflow soldering
Compatible with high-speed signal transfer up to 10Gb/s
[More details please visit www.dsm.com]
As a result, the USB-C connector will become the standard design from 2017 on, as decreed by USB Implementers Forum (USB IF), the non-profit corporation founded by the group of companies that developed the original Universal Serial Bus specification.
The USB Power Delivery specification is also being updated to enable USB PD to support the USB-C Cable and Connector specification, for charging up to 100W. USB-C specifications are contained within the overall USB 3.1 standard that also covers data transmission rates.
The various pins on the USB-C connector are spaced with a pitch of just 0.5mm, compared with 0.65mm on a USB 3.0 Micro B connector and 2.0mm on a USB Type A connector. The thinnest insulating wall has been reduced from 1.84mm on the USB Type A to a miniscule 0.12mm on a USB-C connector. It is difficult to successfully design and consistently mold parts with such thin walls and maintain the necessary mechanical and electrical properties.
Many component producers have begun developments in new USB-C connector designs using liquid crystal polymers (LCPs). Traditionally, LCPs are often favored in thin-wall electronics because of their excellent flow properties and because prices of some commodity grades are relatively low, sometimes under $10/kg; LCPs are well-known by USB connector makers, since they have been the favored polymer in previous generations of USB.
But in many cases, USB-C connectors are likely to fail stringent tests regarding their electrical properties, especially resistance to surface tracking, expressed as the Comparative Tracking Index (CTI), and also mechanical properties.
The CTI of the plastic that acts as an insulator as well as a mechanical anchor around the conductors is more than ever a key for product reliability with the USB-C connector. If the insulator does not have sufficiently high CTI, there is a risk that at some point a short circuit will result, damaging the device and possibly even starting a fire. This is not fearmongering – there are various reports of mobile devices catching fire during charging.
There are essentially three routes to reduce risk of fire hazard caused by tracking:
Increasing the creeping distance (defined by conductor pitch and insulator wall thickness)
Lowering the level of environmental pollution (dust, sweat, etc.)
Using an insulation material with a higher CTI
The creeping distance in the connectors is pre-defined and cannot be modified. Reduction of the level of environmental pollution at connector level can only be done by additional sealing, which adds to the cost of the device, so using a material for the insulator with as high a CTI as possible is the most viable solution to increase end-product safety.
Solutions more appropriate than those possible with LCPs or halogen-containing PAs (PA9T or PA6T) can be found with high-performance halogen-free polyamides, such as PA46 and PA4T.
High-performance polyamides 46 and 4T offer the best balance of mechanical and electrical properties and precision molding. Polyamides 46 and 4T already have been approved by several global producers for use in the next generation of USB-C connectors. They answer the need for improved levels of safety and reliability. PA46 and PA4T both have high CTIs of PLC class 0, well above the recommended 400V. They maintain this high performance for twice as long as alternative materials such as LCPs, most of which have CTIs under 400V.
An ideal solution, therefore, is to use PA4T for the first insert molding stage; this has a melting point of 325°C. The second insert molding stage can then be done with PA46, which has a melting point of 295°C.
The most difficult part of a USB-C connector to produce is the plug front housing. Very thin ribs require high flow and tough material, and there is a weld line on the front side, which mandates a material with high welding-line strength.
Material requirements listed below can all be fulfilled by high-performance polyamides PA46 and PA4T:
High flow for 0.12mm wall thickness design
High levels of stiffness, toughness, and welding line strength
High-wear friction strength and high retention force (10,000 times mating/unmating durability test)
Good process window
UL 94-V0 and high CTI (400V) to support USB PD 1.0 and 2.0 standards (up to 5A and 20V)
Good colorability to support consumer electronics market needs
Lead-free reflow soldering
Compatible with high-speed signal transfer up to 10Gb/s
[More details please visit www.dsm.com]
