GREAT CONNECTOR INVENTIONS: BACKPLANE STIFFENERS David Brearley*
Backplane connectors with large moulded housings existed in the late 1980s but were expensive and very difficult to make. True position for all of the pins had to be accurate or the connector could not be placed easily on the boards and mated. Teradyne Connector Systems found a solution.
T
eradyne Connector Systems (TCS) was a division of Teradyne, the renowned maker of test systems. The connector group was formed to design and tool connectors that Teradyne could not find in the market. Semiconductor testing equipment required large boards with very high pin-count connections to the backplane. Backplane connectors that used large moulded housings existed in the late 1980s, manufactured by Berg, AMP and a few others, but they were expensive and very difficult to make. The primary challenge was to mould a single-piece housing the full length of the daughtercard edge that could be up to 18″ long. The moulds to make these connectors tended to be two-cavity expandable tools that took many hours of set-up before a batch of a particular length could be successfully run. It was especially difficult to keep these very long mouldings straight and flat enough to meet specifications. True position for all of the pins had to be accurate or the connector could not be placed easily on the boards and mated. In the mid-1980s, TCS engineers figured out this problem could be overcome by using smaller right-angle receptacle blocks mounted
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on an extruded stiffener. This connector family was called High Density Plus. The idea was to use the extruded stiffener to group signal modules, guidance and power blocks on a single stiffener. The stiffener was beefy enough to make the assembly straight and each module is precisely located on the stiffener to eliminate cumulative tolerance issues that plagued the long moulded-housing connectors. The stiffeners accepted screws from the bottom of the board, firmly attaching the stiffener to the board and removing any bow or twist in the process. The ‘Plus 2’ version of this connector added ground contacts above and below the signals to provide grounding and shielding. These assemblies on 0.100″ pitch were large and expensive, but the improved true position of the tails eased placement on large boards, and the accuracy of the mating contacts reduced mating forces and improved reliability. AMP used similar extruded stiffeners as well. The real stiffener breakthrough came in the next generation of 2 mm connectors from Teradyne. Extruded stiffeners were expensive, bulky, heavy and occupied a lot of daughtercard space. Also, because these connectors were soldered to the daughtercard, repair
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