Teledyne Interconnect Devices, a custom design house, applies the technology in its Surface-Stack connectors across a wide range of applications. One of these applications, a dual-row, 16-pin connector on 1-mm centers, is designed to connect a keyboard to a pc board in a cell phone (Fig. 4). In this application, the customer wanted to eliminate the assembly of a connector to the keyboard, which the compression contacts permit. This connector's stacking height is 2.3 mm.
Teledyne extended the technology further to develop a single-row, 20-pin connector on 0.5-mm centers with a 2-mm stacking height. This device was designed to mate two flex circuits within a miniature disk drive measuring just 1.5 by 0.75 in.
Unlike traditional blade-on-beam connectors, the contacts in Teledyne's Surface-Stack connectors are molded into the housing. This approach lets connectors be fabricated with tight tolerances and unit-to-unit consistency. A critical element in connector design is the housing material, a liquid-crystal polymer (LCP). Because it becomes highly liquid during the molding process, the LCP can form the delicate features necessary for fine-pitch connectors. This plastic also lends itself to high-cavity-count molds, permitting many connectors to be molded at once.
The surface-stack system can be extended up to about 50 total contacts in a single- or dual-row design, but much higher I/O counts are possible when it's applied in a grid configuration. Teledyne's MicroCon product is a surface-mount microprocessor connector that can achieve 2000 contacts in 50 rows with 1-mm tight contact pitches. According to the vendor, this technology may be scaled down to 0.85 mm. In both the low- and high-pin-count applications, the low mating force of the contacts—about 20 g—is an asset.
AVX Corp. is working with compression connectors as well. The company offers these connectors with 1-mm pitch in its 9158 series. It's also testing 0.8-mm pitch versions. At the same time, AVX is working to reduce package heights from the current 1-mm minimum to 0.6 mm in the next-generation series, the 9160 (Fig. 5).
Tyco Electronics' version of compression technology is called metallized particle interconnect (MPI). It employs a conductive element that's mixed with a polymer and then molded to create a connector of any configuration (Fig. 6). This technology can be applied in board-stacking, backplane-to-daughtercard, LGA, and flex-circuit interconnects.
Along with its inherently adaptable design, the MPI technology provides high I/O density and support for straight routing channels on the pc board. When laying out the board with which the MPI connector will mate, designers may place vias in the middle of the pads, simplifying routing. As a result, MPI lends itself to the development of large (over 2000-pin) interconnect arrays.
The technology is currently available with 1-mm pitch and stacking heights as low as 0.028 in. (0.7 mm). The company has experimented with 0.8-mm pitch for board-to-board connectors, but it hasn't had much demand for this variation. Nevertheless, MPI has found its way into designs where other, finer-pitch connector technologies were tried but ultimately abandoned due to board-routing problems.
Reference:
1."Connector Miniaturization Keeps Pace," Tom Anderson, AVX Corp., Connector Specifier Magazine, December 2001.