Tiny connectors pose big molding challenges.

The challenges of molding new-generation ultra-thin-wall electronic connectors are amply illustrated by two recent applications at Molex Corp. in Lisle, Ill. One new connector requires unusually thin (0.008-in.) walls and fast molding cycles. The other connector has a thin latching mechanism designed for repeated use, as well as a circuit-board header built to take both SMT soldering and through-hole operations.

ULTRA-THIN WALLS

A new Low Force Helix (LFH) connector used in Compaq and IBM notebook computers presented a difficult molding challenge to Molex's Datacomm Div. "The big challenge of the housing was in thin-wall molding," says LFH project manager Craig Bixler. The new connector packs 60 contact pins on 0.050-in. centers into a footprint just 0.70 in. wide and 0.31 in. high. Receptacle walls are only 0.008 in. thick.

The connector cavity is 0.042 in. square and 0.200 in. deep with the 60 metal contacts molded in place. "You have an array of very, very tight, thin walls," says Bixler. In previous connector designs, he says, "There would be occasional walls that thin, but never so many in such a compact array."

The LFH connector needed a structural material with a UL94V-0 flammability rating, as well as good mechanical and dielectric strength. Molex chose a glass-reinforced liquid-crystal polymer, Vectra C130 from Ticona Corp. (formerly Hoechst Technical Polymers) of Summit, N.J. It has higher melt flow than the LCP grade Molex had used to mold other connectors. Prototype connectors were test molded in nylon 46, PCT polyester, and other candidate materials, which either didn't fill the thin walls, took too long to cycle, or flashed, according to Bixler. Vectra C130 reportedly cycles 40-50% faster than alternative materials. It also has essentially zero shrinkage, which maintains accurate centering of the contact inserts.

CONNECTOR WITH SPRING LATCH

The new Micro-Fit 3.0 signal connector was developed by Molex's Commercial Div. to mate an on-board header and wire-end receptacle on printed circuit boards. The dual-row connector has terminals in a dense 3-mm grid, and its wire-end receptacle uses a spring-like latch to engage the ramp molded into the circuit-board header. The receptacle's small size and latching action posed special material and molding challenges.

The Micro-Fit 3.0 comes with two to 24 contacts and is one-third smaller than the previous generation Mini-Fit power connector. The two parts - board header and receptacle - are designed for frequent assembly and disassembly. The receptacle has a positive-action latch that must be depressed to unmate the pair. Pins are on 0.118-in. centers, so walls between the terminals are just 0.018 in. thick, placing unusual demands on the receptacle latch.

When a PBT that Molex uses for other connectors was molded into the new Micro-Fit 3.0, the spring portion or leg would tend to crack or take a set. Molex required a resin with greater resilience that is also UL 94V-0 rated and able to fill thin walls. It opted for Ticona's Celanex 4016 PBT, which has 40% elongation, twice that of comparable unfilled polyesters, along wire twice me impact strength of competitive PBTs. The formulation also uses a non-blooming flame retardant. Molex molds the connectors at its Lincoln, Neb., facility to tolerances of 0.002-0.004 in.

The Micro-Fit circuit-board header, with its latch ramp, has equally thin walls but different requirements. The header must withstand automated SMT soldering at 419-465 F without severe warping. It also needs strength to withstand robotic assembly. Molex picked Ticona's Vectra L130 30% glass-filled LCP. It could fill the thin walls, provide dimensional stability during soldering, and survive automatic assembly. Ticona says its L series cycles about 25% faster than many other LCPs and is UL approved for up to 50% regrind.