Thermally conductive pre-applied underfill formulations and uses thereof
Provided herein are thermally conductive underfill compositions which have a combination of melt viscosity, glass transition temperature (Tg), coefficient of thermal expansion, and/or transparency that renders such materials useful for the preparation of a variety of electronic devices, such as flip chip packages, stacked dies, hybrid memory cubes, through-silica via (TSV) devices, and the like. In certain embodiments of the invention, there are provided assemblies comprising a first article permanently adhered to a second article by a cured aliquot of a formulation as described herein. In certain embodiments of the invention, there are provided methods for adhesively attaching a first article to a second article. In certain embodiments of the present invention, there are provided methods for improving heat dissipation by electronic devices assembled employing thermally conductive, but electrically non-conductive adhesive.
1. A formulation comprising:
a thermosetting resin composition comprising an epoxy resin, a (meth)acrylate resin, and one or more of a maleimide, a nadimide, or an itaconamide resin,
a curing agent,
a fluxing agent, and
a filler in the range of about 20 vol % up to about 60 vol. % which imparts sufficient thermal conductivity to said formulation such that said formulation, upon cure, has a bulk thermal conductivity of greater than 0.5 W/mK, as measured by the laser flash method,
wherein:
said formulation, as a B-staged film, has a minimum melt viscosity of <40,000 P, as measured by Ares Rheometer at 10 Rad frequency with a 10° C./min ramp rate using a sample 1 inch in diameter and 1 mm thick and said formulation, as a B-staged film, after cure, has a Tg greater than 80° C.; a coefficient of thermal expansion below Tg (CTE1) of less than 60 ppm/° C. and a coefficient of thermal expansion above Tg (CTE2) of less than 160 ppm/° C.; and a transmittance of at least 10% at a wavelength of 555 nm or longer.
2. The formulation of claim 1 further comprising one or more flow additives, adhesion promoters, rheology modifiers, toughening agents, conductivity additives, or mixtures of any two or more thereof.
3. The formulation of claim 1 further comprising a non-reactive diluent therefor, which comprises in the range of about 10 up to about 70 wt %, based on the total weight of the formulation.
4. The formulation of claim 3 wherein said diluent is selected from the group consisting of aromatic hydrocarbons, saturated hydrocarbons, chlorinated hydrocarbons, ethers, polyols, esters, dibasic esters, alpha-terpineol, beta-terpineol, kerosene, dibutylphthalate, butyl carbitol, butyl carbitol acetate, carbitol acetate, ethyl carbitol acetate, hexylene glycol, high boiling alcohols and esters thereof, glycol ethers, ketones, amides, heteroaromatic compounds, and mixtures of any two or more thereof.
5. The formulation of claim 1 wherein said thermosetting resin composition further comprises a member selected from the group consisting of a cyanate ester, a vinyl group-containing resin, a cyclic ester, a benzoxazine, an oxetane, a silicone resin, a polyester, a polyurethane, a polyimide, a melamine, an urea-formaldehyde, a phenol-formaldehyde, and mixtures of any two or more thereof.
6. The formulation of claim 1 wherein said curing agent is a free radical initiator and/or an epoxy hardener.
7. The formulation of claim 1 wherein said filler is a non-electrically conductive filler having a thermal conductivity greater than silica.
8. The formulation of claim 1 wherein said filler is selected from the group consisting of aluminum oxide (Al 2 O 3 ) magnesium oxide (MgO), zinc oxide (ZnO), aluminum nitride (A1N), boron nitride (BN), carbon nanotubes, diamond, clay, aluminosilicate, and mixtures of any two or more thereof.
9. The formulation of claim 7 wherein said thermally conductive filler is aluminum oxide (Al 2 O 3 ).
10. The formulation of claim 7 wherein said thermally conductive filler is boron nitride (BN).
11. The formulation of claim 7 wherein said filler has a particle size in the range of about 0.005 μm up to about 20 μm.
12. The formulation of claim 1 wherein said formulation, upon cure, has a thermal conductivity of at least about 1.0 W/mK.
13. The formulation of claim 1 wherein said thermosetting resin composition comprises at least one epoxy.
14. A B-staged aliquot of the formulation of claim 1 .
15. A cured aliquot of the formulation of claim 1 .
16. A curable film comprising a B-staged layer of the formulation of claim 1 on a suitable substrate thereof.
17. A film comprising a cured layer of the formulation of claim 1 .
18. An assembly comprising a first article permanently adhered to a second article by a cured aliquot of a formulation according to claim 1 .
19. A method for adhesively attaching a first article to a second article, said method comprising:
(a) applying an aliquot of the formulation of claim 1 to said first article,
(b) bringing said first and second articles into intimate contact to form an assembly
wherein the space between said first article and said second article is substantially completely filled by the formulation applied in step (a), and thereafter
(c) optionally subjecting said assembly to conditions suitable to cure said formulation.
20. A package comprising a plurality of dies adhered by the formulation of claim 1 .