Jerry Tsai, DuPont Performance Polymers
Thermoplastics for Electronics and Handheld Devices
Engineering thermoplastics for electronics play an increasingly vital role in the production of electronic components and devices. Rather than seeking a one-size-fits-all solution, polymer producers such as DuPont are tailoring materials to the specific application with the goal of increasing performance and processing efficiency while lowering costs.
One such product group is the DuPont™ Zytel® HTN family of semi-aromatic polyamides, which offers a combination of properties that make them ideal materials for use in handheld devices.
With built-in shielding, excellent flow, dimensional stability, toughness and strength, Zytel® HTN can reduce the total system cost of thinner and lighter housings for laptop computers, tablet PCs, cell phones and other devices. Zytel® HTN also delivers the right property set for the many electronic connectors, relays, light-emitting diode components and various other electrical and electronic parts contained within these devices. It can withstand high-temperature circuit assembly methods, including those using lead-free solder, has good strength, stiffness and toughness over a wide temperature and humidity range, and is now also available as a halogen-free grade providing conformity with recycling programs for discarded electronic products.
A thinner, lighter laptop housing
A recent testimonial of the design flexibility afforded by Zytel® HTN in handheld devices is provided by the redesigned housing of the Lenovo IdeaPad U550. Weighing in at just 5.3 lbs (2.4 kgs) and measuring just over one inch (2.5 cm) in height, it is remarkably thin and light for a 15.6-inch (40 cm) multimedia notebook. This is partly due to the use of a non-halogen, flame retardant grade of Zytel® HTN for the LCD rear cover assembly (the so-called A cover) and the bottom cover assembly (the D cover). Both covers had been previously produced using a polycarbonate (PC)/ acrylonitrile butadiene styrene (ABS) blend, but by changing to Zytel® HTN it has been possible to reduce their wall thickness from 1.8 mm—the thinnest thickness possible with PC/ABS—to 1.3 mm, a reduction of more than 25 percent.
"Material stiffness is one of the critical requirements for the mechanical stability of a laptop's A cover, which has to protect the sensitive electrical components inside the laptop as well as the LCD screen," explains Aric Dai (Huafeng), research and development director of the IdeaPad product group at Lenovo. "The improved flexural modulus (approximately 17GPa) and flexural strength (approximately 300 MPa) of Zytel® HTN makes it the material of choice for the production of these thinner, lighter and more cost effective covers."
Drop and pressure tests were used to confirm the protective attributes of the laptop housing, including the placing of loads of up to 25 kg (55 pounds) on the A cover. During hands-on consumer reviews, the laptop chassis and lid are described as exhibiting only mild flex when grabbed by the corners and twisted, whilst pushing on the back of the lid does not yield any ripples in the LCD screen—an impressive performance considering its reduced thickness. As well as improved strength, stiffness and impact resistance, the specified Zytel® HTN grade also demonstrates excellent flame retardancy. Whereas a UL-94 V0 rating at 0.8 mm was specified by Lenovo for the application, the halogenfree, flame retardant grade of Zytel® HTN achieves this at just 0.4 mm.
The switch to Zytel® HTN also saw Lenovo adopt Rapid Heat Cycle Molding (RHCM) technology for the production of the highly visible covers. This process can be used to maximize the surface appearance of injection molded parts with a minimal effect on cycle time. Part costs can be reduced using this technology by eliminating the need for secondary operations to hide surface defects, whilst it can also be used to obtain glossy surfaces even with glass-filled materials. The adoption of RHCM technology was made possible by the higher glass transition temperature (around 115°C or 240°F) of Zytel® HTN than that of the previously used PC/ABS blend.
Support in line with the customer's needs
Comprehensive technical support by DuPont assisted Lenovo in its switch to the higher performance and more cost effective material solution, as Aric Dai of Lenovo recalls: "DuPont was able to offer a unique business package including access to its CAE capability during the design phase, on-site technical support, tool and customized gate design and mold-flow simulation, as well as a decoration solution which was in line with our design needs." Indeed, patterns and texture are a defining element of the Lenovo IdeaPad aesthetic, and the U550 is no exception. An extremely fine checkerboard pattern molded onto the A cover makes it feel almost like the texture of knurled metal to the touch. The covers are painted and subsequent adhesion and warpage tests ensure conformity with production standards.