Rigid-flex board with anisotropic interconnect and method of manufacture

A rigid-flex circuit board construction comprising:

• (a) Two rigid circuit boards each comprising at least one conductive layer, which has a conductive pattern and a plurality of contact pads defined thereon, at least one contact pad being designated an interconnecting pad disposed on a rigid insulating substrate;
• (b) a flexible jumper having a first and a second connecting terminus for electrically and mechanically connecting to the rigid circuit boards, the flexible jumper comprising a flexible insulating substrate and at least one conductive layer, each conductive layer having a conductive pattern and a plurality of contact pads defined thereon, at least one contact pad on each terminus of the flexible jumper being designated an interconnecting pad, each interconnecting pad on the flexible jumper having a corresponding interconnecting pad on the corresponding rigid circuit board;
• and
• (c) an electrically interconnecting adhesive layer on each terminus of the flexible jumper, each adhesive layer interposed between a conductive layer of the flexible jumper and a conductive layer of the corresponding rigid circuit board for mechanically connecting the two conductive layers in a superposed relationship with a connected area therebetween, and for electrically connecting corresponding interconnecting pads on the two conductive layers, the interconnecting layer being conductive across a thickness thereof and being non-conductive throughout a coplanar direction thereof, and being disposed substantially throughout the connected area of the two conductive layers, the interconnecting layer comprising a non-conductive adhesive having a plurality of deformable conductive metallic particles of size in the range of about 100 mesh to 500 mesh dispersed substantially uniformly throughout the adhesive such that each particle is electrically insulated from substantially every other particle, the particles and the insulating substrates connected by the adhesive having coefficients of thermal expansion such that the difference between the coefficient of the particles and the coefficient of each substrate is within 25% of the coefficient of the particle, and the maximum particle diameter is about 90-110% of the distance between two conductive layers, and wherein 80% of the particles have a diameter within about 20% of a mean diameter;
• wherein the flexible jumper is bent such that the rigid boards are in close planar proximity of each other.

A rigid-flex circuit board construction comprising:

• (a) a rigid circuit board including a conductive layer disposed on a rigid insulating substrate, the conductive layer having a conductive pattern with a plurality of contact pads defined thereon, at least one contact pad being designated an interconnecting pad;
• (b) a flexible jumper including a conductive layer disposed on a flexible insulating substrate, the conductive layer having a conductive pattern with a plurality of contact pads defined thereon, at least one contact pad being designated an interconnecting pad;
• (c) an electrically insulating coverlayer interposed between the conductive layers on the rigid circuit board and the flexible jumper, the coverlayer including an aperture interposed between the interconnecting pads on the rigid circuit board and the flexible jumper;
• and
• (d) an interconnecting adhesive layer, interposed between the coverlayer and one of the conductive layers, for mechanically connecting the conductive layers in a superposed relationship within a connected area therebetween, and for electrically connecting the interconnecting pads on the conductive layers through the aperture in the coverlayer, the interconnecting layer being conductive across a thickness thereof and being non-conductive throughout a coplanar direction thereof, and being disposed substantially throughout the connected area of the two conductive layers, the interconnecting layer comprising a non-conductive adhesive having a plurality of deformable conductive metallic particles dispersed substantially uniformly throughout the adhesive such that each particle is electrically insulated from substantially every other particle, wherein the particles have a thermal coefficient of expansion which is within 25% of the thermal coefficients of expansion of the substrates of the rigid circuit board and the flexible jumper, and wherein the maximum particle diameter is about 90-110% of the connected distance between the interconnecting pads.