Innovations needed by the connector industry have consistently stimulated the development of engineering plastics. The proliferation of different resins has been incredible as suppliers work to develop the right materials to match evolving needs of the connector industry and its customers.
Important features to the end customers include:
- Ruggedness—they cannot break or be damaged in normal use or even abusive circumstances
- Dimensional precision is needed to ensure excellent mating and true position of pins
- Performance over a wide range of temperatures and humidity from the arctic to the equator
- Resistance to environmental exposure
- Heat, especially during reflow or wave soldering processes
- Chemical or UV exposure in the field
- Long life (at least as long as specified for the equipment.) In my experience, plastic degradation is one of the most common failure modes causing us to throw away a piece of equipment. This is OK for a cheap consumer product, but certainly not OK for much else.
- Many connectors have plastic parts that must move, for example, latches for mating, contact retention, and snapping together multiple components
- Plastic cost is seldom a significant cost element to the end consumer
- In addition to holding all the contacts together, plastic also provides insulation between contacts and protects fragile mating springs from abuse
Connector manufacturers also need:
- Ability to mold with high output levels (short mold cycles) and very high yields
- Ability to reliably fill the thinnest walls; especially important for high-density, tight-pitch parts
- Molded parts must come out of the mold straight in all directions, and must stay that way over life
Of the hundreds of plastic resins available, a few have come to dominate connector applications, including the following:
In general terms, a connector manufacturer will choose a resin that gives them the lowest cost product that meets all of the end-use specifications. The lowest cost includes the cost of the resin, yield, and productivity. Many of these resins can be reground and mixed with virgin resin to yield more parts per pound of resin. This practice is common and is accomplished by mixing a fixed amount all the time. One of the differentiators between first tier connector manufacturers and third world knock-off producers is in how they manage regrind. The best will completely purge the process on a regular basis so that regrind is well controlled. The worst might use 100% reclaimed material.
PBT Polyester and Nylon dominated up until the 1980s when the industry went to reflow soldering. The reflow process involves exposure to temperatures > 214°C for long enough to melt all of the solder on the board. Under this condition, the housings would soften, causing unacceptable distortion and compromising spring performance.
The answer was the quick emergence of LCP materials. These are quite stable at high temperatures and also flow well to fill very fine features in the connector housings with excellent cycle rates. These advantages overwhelmed the cost disadvantage and now the majority of connectors seeing reflow on PCBs tend to be LCP.
In recent years, multistep over-molding of wafers has become common. Many of these resins are formulated to provide just the right electrical impedance. This combined with clever designs using just the right combination of air and plastic as dielectrics have enabled new connectors transmitting speeds we did not think were possible a few years ago.
Innovation and development continues as more specialty resins emerge to meet specific industry requirements:
- Sealing resins for medical, military, industrial, and cable applications
- Resins loaded with conductive material that absorb high frequency radiation
- Custom resins with finely tuned dielectric constants have been added to the menu
- Low temp over molding resins used to strain relieve solder or weld joints in cable connections
- High temp resistance and chemical resistance to enable use in automotive, aerospace, and medical applications
- Resins that can be electroplated and mixed with non-plateable materials to enable MIDs (Molded Interconnect Devices) that can replace connectors, wires, and PCBs in high-volume applications, especially in the LED lighting industry
Our thanks to the giants in the chemical industry, including DuPont, GE, Ticona, SABIC, Chevron-Philips, and Celanese, who have invested the R&D necessary to enable the rich innovation in plastics that continues to fuel continued innovation in the connector business.