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Reducing Stack Height with Low-Profile SMT Connectors
By Glenn Goodman, Senior Development Engineer, Advanced Interconnections Corp. T
o fit more functionality into tighter spaces, multiple circuit boards are typically needed.
These multiple boards require some form of board-to-board electrical interconnections to link the different functions of each board. Numerous choices are available for these board- to-board interconnections, each with its own mechanical and electrical properties. However, the size con- straints of today’s high-density, com- pact packages are driving a demand for lower-profile connectors.
PCB connectors are typically
Low-profile SMT connector system consisting of a receptacle (left) and a header (right), designed to mate with minimal force.
configured as two-piece interconnec- tion systems, with a header and a receptacle or socket. Most are de - signed to provide paths for signals and power between boards, with con- figurations spanning from single contacts to large numbers of contacts for complex power/signal connec- tions. One-piece PCB connectors are also available, with a connector mounted on one board making con- nections with a secondary board through compression of the contacts on the second board. PCB connectors are specified by
TECHNICA, U.S.A. Fulfilling Manufacturing Needs Throughout the Electronics Industry
the number of positions or number of circuits that they can support. The contacts, also called terminals or pins, are defined by pitch — the distance from the center of one contact to the center of the next contact. The typical pitch for PCB connectors ranges from 0.5 to 1.27 mm (0.02 to 0.05 in.), with contacts arranged in one, two, three, or four rows. Engineers challenged with designing low-profile packages continually balance these mechanical design options with electrical and per- formance requirements.
Stacking PCBs Many connector systems pro-
vide secure interconnections between circuit boards, but also add size to the final assembly. One way to reduce the overall size of a multi- board circuit assembly is by stacking boards. In some cases, the final height of a board assembly can be critical because of limited available space in a particular system. An example of such a limited-
space requirement is an integral tun- able laser assembly (ITLA) that is part of an optical transceiver for a telecommunications system. In this application, the layout requires either a micro cable-to-board or board-to- board solution to provide power to the laser without adding height to the small form-factor pluggable (SFP) transceiver module. A connector system with special
requirements is needed for the ITLA. Minimum stack height is important to allow the connector assembly to fit into the system design; off-the-shelf connector components did not meet the mechanical and electrical demands of such a tight-fitting circuit board assembly. Because space is limited, a con-
Finest achine arts Compact Design Easy aintenance
German Engineering Modular Design Flexible and Scalable
nector system with a fine pitch is required. However, the contacts also need to be robust, to meet the demands of a telecommunications sys- tem for long operating lifetime with minimal performance degradation. The compact laser package only
allowed for a connector with a length less than 8 mm (0.31 in.), a minimal board stack height of 4 mm (0.16 in.) and compatibility with automated assembly equipment for attaching the connectors to circuit boards. The costs and difficulty of
Available exclusively through Technica, U.S.A. 1-800-909-8697 •
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assembling circuit boards with any connector system increase when spe- cial tooling or assembly equipment is required. Ideally, a connector system that enables stacking of circuit boards with reliable low-profile SMT inter- connections can be supplied in tape- and-reel format in support of auto-
Continued on page 72
May, 2017
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