RADIATEUR POUR COMPOSANTS ELECTRONIQUES PORTES PAR DES SUBSTRATS EN MATIERE CERAMIQUE

HEAT DISSIPATION FOR ELECTRONIC COMPONENTS ON CERAMIC SUBSTRATE

Abrégé anglais

ABSTRACT
Disclosed is a heat dissipator for electronic components on a
ceramic substrate. The ceramic plate receives heat from the component at one sur-
face and has a plurality of separate spaced metallic heat-conducting elements
mounted on and extending from the other surface of the plate In a preferred
embodiment the ceramic plate on which the metallic elements are mounted is
separate from a ceramic substrate on which the electronic components are
mounted; the ceramic plate carrying the metallic elements includes adhesive
for adhering it to the ceramic substrate carrying the electronic components;
the metallic elements are cylindrical copper pins; and the pins are connected
to the ceramic plate via solder and metallic pads deposited on the ceramic
plate.

Revendications

-5-
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. The combination of a ceramic substrate carrying
electronic components and a heat dissipator for the electronic
components, said combination comprising
a ceramic substrate carrying electronic components on one
surface and having an opposite surface,
a ceramic plate adjacent to said ceramic substrate and
having a first surface adhered in heat conductive relationship
to said opposite surface of said substrate by a layer of ad-
hesive, said plate having a second surface, and
a plurality of separate, spaced, free-standing, metallic,
cylindrical, heat-conducting elements mounted in an array on and
extending from said second surface of said ceramic plate, said
heat conducting elements being electrically isolated from said
electronic components.
2. The dissipator of claim 1 wherein said metallic
elements are soldered to metallized pads on said second surface.
3. The dissipator of claim 2 wherein said metallic
elements are made of copper.
4. The dissipator of claim 3 wherein said metallized
pads are made of a palladium/silver alloy.

Description

I
1- 920~-96
FIELD OF THE__I_VENTION
The invention relates to dissipating heat from
electronic components on a ceramic substrate.
BACKGROUND OF THE INVENTION
Electronic components can be mounted on a ceramic
substrate and electrically connected to each other through
metallized conductors carried by the substrate. Ire U.S.
Patent No. 4,292,647 discloses a semiconductor package including
a plurality of electronic chips mounted on a ceramic substrate
and provided with individual heat conductive elements mounted
directly above them
SUMMARY_OF_THE INVENTION
I have discovered that heat can he very effectively
dissipated from electronic components through the use of a
ceramic plate that receives heat from the components at one
surface and has a plurality of separate, spaced metallic heat-
conducting elements mounted on and extending from the other surface
of the plate.
According to a broad aspect of the invention there it
provided the combination of a ceramic substrate carrying
electronic components and a heat dissipator for the electronic
components, said combination comprising:
a ceramic substrate carrying electronic components on one
surface and having an opposite surface,
a ceramic plate adjacent to said ceramic substrate and
having a first surface adhered in heat conductive relationship to
I

~23~52~3
-2- 9204-96
said opposite surface of said substrate by a layer of
adhesive, said plate having a second surface, and
a plurality of separate, spaced, free-standing, metallic,
cylindrical, heat-conducting elements mounted in an array on
and extending from said second surface of said ceramic plate,
said heat conducting elements being electrically isolated from
said electronic components.
In a preferred embodiment the metallic elements are
cylindrical copper pins; and the pins are connected to the
ceramic plate via solder and metallic pads deposited on the
ceramic plate.
Because both plates are made of ceramic, there are no
thermal stresses between them. Also, the ceramic plate
diffuses heat well, making the difference in temperature among
the various pins low and promoting efficient heat dissipation.
Finally, the copper pins provide good heat transfer to and low
pressure drop in air passing next to them, and the solder
provides good bond strength and little thermal resistance to heat
passing through it.
DESCRIPTION OF THE PREFERRED EMBODIMENT
I will now describe the structure, manufacture and
operation of the presently preferred embodiment of the
invention after first briefly describing the drawings.
DRAWINGS
Figure 1 is a diagrammatic perspective view,
partially broken away, of a heat dissipator shown attached to a

~2:3~i2~
-pa- 9204-96
ceramic substrate carrying electronic components according to
the invention.
Figure 2 is a bottom plan view of the Figure 1
dissipator.
Figure 3 is a vertical sectional view, taken a-t 3-3
of Figure 1 and upside-down with respect to Figure 1, of a
portion of the Figure 1 dissipator.
STRUCTURE
Referring -to Figure 1, -there is shown ceramic substrate
10, which carries electronic components 12 on

so
-- 3 --
its upper surface and is secured to heat dissipator 14
at its lower surface. Electronic components 12 are
electrically connected to each other by metallization 16
on the upper and lower surfaces of ceramic plate 10, and
the upper surface of plate 10 also carries insulating
coating 18 over metallization 16. Dissipator 14
includes ceramic plate 20 (95~ pure alumina),
thermosetting adhesive layer 22 (5 mix thick and
available from EM under the YN469 or YN568 trade
designations) and metallic heat-conducting pins 24 on
its lower surface.
Referring to Fig. 2, the arrangement of pins 24
on the lower surface of plate 20 is shown. Pins 24 are
mounted on 0.125 by 0.125 inch square palladium/silver
vacuum deposited pads 26, which are spaced from each
other by 0.094 inch in the width direction and 0.108
inch in the length direction. Referring to Fig. 3, pins
24 are approximately 0.1 inch in diameter and I inch
long and include copper core 28 and tin coating 30.
Pins 24 are attached to pads 26 by solder 32,
Manufacture
Heat dissipator 14 is made by securing pins 24
in a jig providing them with the proper arrangement an
applying solder paste to the exposed ends of pins 24.
25 Ceramic plate 20 with pads 26 thereon is placed on the
exposed ends ox pins I and pins 24 and ceramic plate
20 are joined to each other by vapor soldering. After
the pin/ceramic assembly has cooled, adhesive layer 22
is applied, and this is covered with a release layer
30 (not shown), which is removed prior to adhering to
substrate 10. Eta dissipator 14 is easily adhered to
substrate 10 by bringing the lower surface of ceramic
plate 10 in contact with exposed adhesive layer 22,

Lowe 8
.
-- 4 --
.,
which cures in use. Adhesive layer 22 is 5 miss thick
to compensate for irregularities in the plenarily of the
ceramic plate surfaces.
Operation
. . .
In operation, heat from electronic components
12 is conducted through ceramic layers 10, 20 to
heat-conducting pins 24, from which the heat is
transferred to the surrounding air flowing past them.
Because ceramic plate 20 diffuses heat well, the
difference in temperature among various pins 24 is low,
and heat dissipation to the air is efficient. Because
plate 20 and ceramic plate 10 are both ceramic, there
are no thermal stresses between them.` Copper pins 24
provide good heat transfer to and low pressure drop in
air flowing past them. Solder 32 provides good bond
strength and little thermal resistance to heat passing
through it.
Other Embodiments
Other embodiments of the invention are within
the scope of the following claims. For example, pins 24
can be provided directly on the bottom of the ceramic
layer that carries the electronic components if there is
no metallization 16 on the bottom surf e.
_ . _ . _ . . .. . , . . .. _ .. . . .. .