Electrically conductive polymeric compositions, contacts, assemblies, and methods
Electrically conductive polymeric compositions adapted for use in forming electronic devices are disclosed. The compositions are thermally curable at temperatures less than about 250° C. Compositions are provided which may be solvent-free and so can be used in processing or manufacturing operations without solvent recovery concerns. Core-shell conductive particles provide the conductivity of the compositions and devices contemplated herein.
1. An electrically conductive, thermally curable composition comprising:
a. 70 to 92 wt %, based upon weight of the composition, of electrically conductive particles comprising metallic particles, the metallic particles comprising a copper core and a silver shell, having a flake shape with a length of up to about 20 μm and a thickness of up to about 2 μm, and having a tap density of 2.5-4.5 g/cm 3 ; and
b. a thermally curable polymer composition capable of being cured at 250° C. or less, wherein the curable polymer composition is solvent-free, the curable polymer composition comprising:
i) an ethylenically unsaturated monomer or oligomer with hydroxyl groups; and
ii) a blocked isocyanate with an unblocking temperature below 200° C.
2. The composition of claim 1 , wherein the copper core accounts for about 80 to about 98 wt % of each of the metallic particles, and the silver shell accounts for about 2 to about 20 wt % of each of the metallic particles.
3. The composition of claim 1 , wherein the core accounts for about 85 to about 91 wt % of each of the metallic particles, and the shell accounts for about 9 to about 15 wt % of each of the metallic particles.
4. The composition of claim 1 , wherein the electrically conductive particles have a d 50 particle size of from about 2 microns to about 10 microns.
5. The composition of claim 1 , wherein the metallic particles have a surface area of 0.2-5 m 2 /g.
6. The composition of claim 5 , wherein the metallic particles have a surface area of 0.5-2 m 2 /g.
7. The composition of claim 1 , wherein the ethylenically unsaturated monomer or oligomer is a fatty acid modified epoxy acrylate monomer or a fatty acid modified epoxy acrylate oligomer.
8. The composition of claim 1 , further comprising a reactive diluent and a free radical initiator.
9. The composition of claim 8 , wherein the reactive diluent is hexane diol diacrylate.
10. The composition of claim 1 , wherein the electrically conductive particles are used at a concentration of about 84 to about 86 wt %.
11. A method of forming an electrically conductive layer on a substrate, the method comprising;
a. forming a composition comprising:
i. an effective amount of electrically conductive particles, the electrically conductive particles comprising metallic particles, the metallic particles comprising a copper core and a silver shell, having a flake shape with a length of up to about 20 μm and a thickness of up to about 2 μm, and having a tap density of 2.5-4.5 g/cm 3 ;
ii. a thermally curable polymer composition capable of being cured at 250° C. or less, the curable polymer composition comprising:
an ethylenically unsaturated monomer or oligomer with hydroxyl groups; and
a blocked isocyanate with an unblocking temperature below 200° C.; and
b. applying the composition on a substrate to a thickness of from about 1 to about 100 microns; and
c. heating the applied composition to a temperature less than 250° C. to form an electrically conductive layer.