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issue: February 2009 APPLIANCE Magazine

Technology Report
Making a Tight Connection

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 Engineers looking to save space can turn to an FPC connector that offers reduced pitch, width, and depth.

New connectors from Molex feature a unique spring on the terminal design that the company plans to add to future connector designs.

 A new 0.25-mm-pitch flexible printed circuit (FPC) connector from Molex Inc. (Lisle, IL, U.S.; www.molex.com) can save up to 40% of space compared with similar 0.30-mm-pitch connectors used in cell phones and other mobile devices. The company says the connectors were designed in direct response to requests from industry engineers. “The industry-standard 0.30-mm-pitch alternatives on the market were not small enough for certain customers’ new phone designs,” says Masayuki Kogashiwam, mobile device industry marketing manager, Molex Micro Products Division (Yamato, Japan). “They were looking for space savings not only in pitch and width, but also in depth. Molex’s 0.25-mm-pitch design has a width of just 2.75 mm, compared with an average of about 3.85 mm on many competitive 0.30-mm-pitch designs.”

The combination of low height, small circuit size, small depth, and the world’s first 0.25-mm pitch makes this the smallest connector on the market, the company claims. “Some customers have introduced 0.20-mm-pitch versions, but the depth is often wider and the circuit sizes often larger to take maximum advantage of the smaller pitch for the length axis,” Kogashiwam says. “Many competitive designs also employ a back-flip-style actuator, which enables the actuator to stay open in the packaging and provide for quicker board assembly. But the back-flip design needs a wider depth than a front-flip design, which is what Molex used.”

The connector’s zero insertion force (ZIF) helps to further save space, while addressing the need for quick assembly. According to Kogashiwam, ZIF functionality makes it easier for an operator to insert the connector and prevents any possible damage to the cable during insertion. “With low insertion force (LIF) FPC connectors, the terminals are not at the same height, which provides some force as the cable is inserted,” he explains. “FPC cable usually has a stiffener near the front to provide stability for the contact area, and in LIF connector designs, sometimes the cable can collapse and become damaged if excessive force is needed to insert it.”

The spring feature on the new connector’s terminal design enables the top and bottom portion of the terminal to be placed slightly further apart, providing more space for the cable to be inserted.

“One challenge with adding a spring feature was to make sure that both the odd and even terminals flexed in the same way to maintain consistent electrical contact,” Kogashiwam notes. “The connector has staggered terminals, which means the solder pads are on opposite sides in order to achieve the small 0.25-mm pitch. This also means the contact point is in a different location for odd/even and that the terminal design needs to be different to accommodate this.”

Molex was able to overcome this design challenge by developing a different spring feature into each terminal that proved it could still maintain consistent electrical contact as the terminals flexed. “The spring feature on both odd and even terminals keeps the terminals at the same height, which helps with maintaining electrical contact and also enables full ZIF functionality,” Kogashiwam explains.

The 0.25-mm-pitch cable has a similar layout and tolerances as 0.30-mm-pitch cable, which the company says makes it more economical and easier to source than 0.20-mm-pitch cables. “Having the same tolerances as 0.30-mm-cable means that the production process of the cable is similar,” Kogashiwam notes. “This makes it easier and more cost-effective for cable manufacturers to produce compared with 0.20-mm-pitch cable, which has tighter tolerances and may have lower production yields. This translates into a higher end-user price.”

A key element during development was making sure the connector design met the same tolerance range as the cable design. “As the pitch gets smaller and with staggered designs, the precision in the terminal design becomes more important,” Kogashiwam says. “Not all competitive designs in this micro range have matching tolerances to the cable.”

The SMT ZIF bottom-contact series is rated at 0.2 A and 50 V and is suited for mobile devices and other applications where space is a concern. A wide area was designed into the housing top to accommodate pick-and-place vacuum nozzles without the need for high-temperature tapes. In addition, front solder tabs under the housing provide space savings, stability, and strain relief for SMT solder joints.

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