Thin multi-chip flex module
A flexible circuit comprises a folded dielectric sheet having conductive patterns on its surface(s) to which microelectronic device(s) are attached. The dielectric sheet is folded 180° about a selected axis and a bond layer joins the two halves over a portion of their respective surface areas so that a remaining portion of their areas remain unbonded and a bifurcated structure is thereby formed. Electrical contacts are provided on the unbonded or bifurcated portions of the flexible sheets. The flex may be attached to a rigid frame and provided with protective heat spreading covers. The folded flex design is particularly suitable for reel-to-reel manufacturing.
1 . A method for making a multichip module comprising the steps of:
forming a continuous dielectric sheet, said sheet having a conductive pattern on a first surface thereof;
attaching a plurality of microelectronic devices to said first surface so that said microelectronic devices are operably coupled to said conductive pattern;
applying a bonding material to a second surface of said dielectric sheet;
folding said sheet so that said microelectronic devices are on the outer surface of said folded structure; and,
bonding the inner surface of said folded sheet over at least a portion of its area using said bonding material.
2 . The method of claim 1 wherein said sheet further has a conductive pattern on a second surface thereof.
3 . The method of claim 2 wherein said dielectric sheet further contains vias connecting at least a portion of said conductive patterns on said first and second surfaces.
4 . The method of claim 2 wherein a first portion of said conductive pattern on said second surface is configured to engage a second portion of said conductive pattern on said second surface after said dielectric sheet is folded.
5 . The method of claim 1 wherein said conductive pattern included a plurality of contact pads configured to engage an external contact.
6 . The method of claim 1 wherein electrical communication across said inner surface is achieved by bonding the inner surface with a material selected from the group consisting of: solder, anisotropic conductive adhesive, and isotropic conductive adhesive.
7 . The method of claim 1 wherein said microelectronic devices are disposed substantially symmetrically about the axis of said fold, so that the module is substantially symmetrical after folding.
8 . A multichip module comprising:
a flexible dielectric sheet having a conductive pattern on a first surface thereof and a bonding layer on at least a portion of a second surface thereof;
a plurality of microelectronic devices disposed on said first surface so that said microelectronic devices are operably coupled to said conductive pattern;
a 180° fold about a selected axis in said dielectric sheet so that a first portion of said second surface is brought into contact with a second portion of said second surface and bonded thereto.
9 . The multichip module of claim 8 wherein said dielectric sheet is configured for reel-to-reel processing.
10 . The multichip module of claim 8 wherein at least a portion of said dielectric sheet is not bonded, so that a bifurcated portion is formed, and contact pads are formed on said bifurcated portion.
11 . The multichip module of claim 8 wherein said microelectronic devices are selected from the group consisting of: memory circuits, logic circuits, buffer devices, interface devices, optoelectronic devices, and microprocessors.
12 . The multichip module of claim 11 wherein at least some of said microelectronic devices are optoelectronic devices and said dielectric sheet further contains windows configured to allow optoelectronic communication between selected devices after said dielectric sheet is folded.
13 . The multichip module of claim 8 wherein said bonding layer comprises a material selected from the group consisting of: solder, anisotropic conductive adhesive, and isotropic conductive adhesive.
14 . The multichip module of claim 8 further including a substantially rigid frame.
15 . The multichip module of claim 8 further including a heat spreading cover.
16 . The multichip module of claim 15 wherein said heat spreading cover comprises a foldable structure of sufficient size to be folded around said folded dielectric sheet and enclose said microelectronic devices.
17 . A multichip module comprising:
a flexible dielectric sheet having a conductive pattern on a first and a second surface thereof and a bonding layer on at least a portion of said second surface thereof;
a plurality of microelectronic devices disposed on said first surface so that said microelectronic devices are operably coupled to said conductive pattern;
a 180° fold about a selected axis in said dielectric sheet so that a first portion of said second surface is brought into contact with a second portion of said second surface and bonded thereto so that an electrical circuit is completed between said conductive patterns on said first and second portions of said second surface.
18 . The multichip module of claim 17 wherein said bonding layer comprises a material selected from the group consisting of: solder, anisotropic conductive adhesive, and isotropic conductive adhesive.
19 . The multichip module of claim 17 wherein at least a portion of said dielectric sheet is not bonded, so that a bifurcated portion is formed, and contact pads are formed on said bifurcated portion.
20 . The multichip module of claim 17 wherein said microelectronic devices are selected from the group consisting of: memory circuits, logic circuits, buffer devices, interface devices, optoelectronic devices, and microprocessors.