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Dense Connector Contact Geometry

IP.com Disclosure Number: IPCOM000109063D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 9 page(s) / 241K

Publishing Venue

IBM

Related People

Gillett, JB: AUTHOR

Abstract

There is a growing need to create very dense, low noise, controlled impedance electrical connections between flexible insulating films carrying strip lines and multi-layer circuit boards. The object of this article is to demonstrate a contact arrangement which can be varied to achieve the tightest theoretical density at one extreme, to a very reliable connection with redundant contacts at another extreme. There is an intermediate case which provides some degree of redundancy while maintaining a very simple and dense wiring arrangement on the flex film.

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Dense Connector Contact Geometry

       There is a growing need to create very dense, low noise,
controlled impedance electrical connections between flexible
insulating films carrying strip lines and multi-layer circuit boards.
The object of this article is to demonstrate a contact arrangement
which can be varied to achieve the tightest theoretical density at
one extreme, to a very reliable connection with redundant contacts at
another extreme.  There is an intermediate case which provides some
degree of redundancy while maintaining a very simple and dense wiring
arrangement on the flex film.

      It is a common practice to use crossed cylinders which make
good electrical contacts by concentrating the applied forces at a
point, producing a high Hertz stress and low contact resistance.
This invention extends that principle, but could equally apply to
crossed bars.

      Fig. 1 shows the structure of a single contact as it would be
fabricated on a printed circuit card, board or ceramic module.  A
circuit trace from an internal wiring or power plane is brought to
the surface through a conducting via, and a land plated on the
surface to connect to the via.  A photoresist mask is then applied
and personalized to expose a bar on the land which is then plated up
to a semicylindrical shape.  The surface of the plated bar is noble
metal suitable for electrical contacts.  The resistive mask is left
in place so that only the contact bar is exposed at the surface of
the card.

      The tolerances on the relative placement of contacts on the
film to contacts on the card, when brought into operating position,
can be decomposed into two orthogonal components, x tolerance and y
tolerance.  Fig. 2 shows that, for maximum theoretical density of
contacts for a given x and y tolerance, and the separation between
contact strips is equal to the y tolerance.  There is also a minimum
space required between nearest neighbor contacts to avoid short
circuits caused by manufacturing tolerances of the card.

      The flex film has a similar contact structure orthogonal to
that on the card, as seen in Fig. 3.  The flex film carries a
stripline (to maintain an impedanc...