Aluminum nitride filled thermally conductive silicone composition
A composition contains: (a) curable silicone composition including: (i) a vinyldimethylsiloxy-terminated polydimethylpolysiloxane with a viscosity of 30 to 400 mPa*s; (ii) a SiH functional crosslinker; and (iii) a hydrosilylation catalyst; where the molar ratio of crosslinker SiH functionality to vinyl functionality is 0.5:1 to 1:1; (b) alkyl trialkoxysilane and/or a mono-trialkoxysiloxy terminated dimethylpolysiloxane treating agent; (c) filler mix containing: (i) 40 wt % or more of spherical and irregular shaped AlN particles, both having an average size of 30 micrometers or more, the spherical AlN fillers are 40-60 wt % of the weight of the AlN fillers; (ii) 25-35 wt % spherical Al 2 O 3 particles with an average size of 1-5 micrometers; (iii) 10-15 wt % of additional thermally conductive filler with a 0.1-0.5 micrometer average size; and (iv) optionally, BN fillers having an average size greater than 20 micrometers; where filler mix is 90-97 wt % and wt % is relative to composition weight unless otherwise stated.
1 . A thermally conductive composition comprising:
a. a curable silicone composition comprising:
i. a vinyldimethylsiloxy-terminated polydimethylpolysiloxane having a viscosity in a range of 30 to 400 milliPascal*seconds;
ii. a silicon-hydride functional crosslinker; and
iii. a hydrosilylation catalyst;
where the molar ratio of silicon-hydride functionality from the crosslinker to vinyl functionality is in a range of 0.5:1 to 1:1;
b. a filler treating agent comprising one or both of an alkyl trialkoxysilane and a mono-trialkoxysiloxy terminated dimethylpolysiloxane;
c. a thermally conductive filler mix comprising:
i. 40 weight-percent or more aluminum nitride fillers comprising a blend of spherical and irregular shaped aluminum nitride particles, both the spherical and irregular shaped particles having an average particle size of 30 micrometers or more and where the spherical aluminum nitride fillers with a particle size of 30 micrometers or more are present at a concentration of 40 to 60 weight-percent of the total weight of aluminum nitride fillers having a particle size of 30 micrometers or more;
ii. 25 weight-percent to 35 weight-percent spherical aluminum oxide particles having an average particle size of one to 5 micrometers;
iii. 10 weight-percent to 15 weight-percent of an additional thermally conductive filler having an average particle size of 0.1 to 0.5 micrometers; and
iv. optionally, boron nitride fillers having an average particle size of more than 20 micrometers;
where the weight-percent of each thermally conductive filler is relative to composition weight unless otherwise stated and the total amount of thermally conductive filler mix is 90-97 weight-percent of the composition weight.
2 . The thermally conductive composition of claim 1 , wherein the vinyldimethylsiloxy-terminated polydimethylpolysiloxane has a viscosity in a range of 60 to 80 milliPascal*seconds and comprises 1.2 to 1.4 weight-percent vinyl functionality.
3 . The thermally conductive composition of claim 1 , where the silicon-hydride functional crosslinker comprises one or more polysiloxane having chemical structures selected from (II) and (III):
H
(
CH
3
)
2
SiO
-
[
(
CH
3
)
2
SiO
)
]
x
-
Si
(
CH
3
)
2
H
(
II
)
(
CH
3
)
3
SiO
-
[
(
CH
3
)
HSiO
]
y
[
(
CH
3
)
2
)
SiO
]
z
-
Si
(
CH
3
)
3
(
III
)
where subscript x has a value in a range of 10 to 100, subscript y has a value in a range of 3 to 30, and subscript z has a value in a range of 3 to 100.
4 . The thermally conductive composition of claim 3 , wherein the silicone-hydride functional crosslinker has chemical structure (II).
5 . The thermally conductive composition of claim 1 , wherein the alkyl trialkoxysilane is selected from C6 to C12 alkyl trimethoxysilanes and the mono-trialkoxysiloxyterminated dimethylpolysiloxane is selected from mono-trimethoxyterminated dimethyl polysiloxanes having an average chemical structure (IV):
(
CH
3
)
3
SiO
-
[
CH
3
)
2
SiO
]
a
Si
(
OCH
3
)
3
(
IV
)
where subscript a is a value in a range of 30 to 110.
6 . The thermally conductive composition of claim 1 , wherein the composition is free of magnesium oxide fillers.
7 . The thermally conductive composition of claim 1 , wherein the composition is free of boron nitride fillers.
8 . The thermally conductive composition of claim 1 , wherein the additional thermally conductive filler is zinc oxide.
9 . An article comprising the thermally conductive composition of claim 1 on another material.
10 . The article of claim 9 , wherein the thermally conductive composition is between and in thermal contact with a heat generating component of an electronic device and one or more than one of a heat sink, cooling plate and metal cover for the electronic device.