U.S. patent application number 12/728947 was filed with the patent office on 2011-09-22 for electrical component thermal management.
This patent application is currently assigned to Honeywell Intenational Inc.. Invention is credited to Rainer Blomberg, Michael J. Gillespie, Lance L. Sundstrom.
Application Number | 20110228484 12/728947 |
Document ID | / |
Family ID | 44486298 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110228484 |
Kind Code |
A1 |
Sundstrom; Lance L. ; et
al. |
September 22, 2011 |
ELECTRICAL COMPONENT THERMAL MANAGEMENT
Abstract
Thermal management features are described for use with
electrical components. In some examples, an assembly includes a
printed board that includes a thermally conductive thermal attach
pad thermally connected to a heat sink, an electrically conductive
attach pad that is separate from the thermally conductive attach
pad, and an electrically conductive trace electrically connected to
the electrically conductive attach pad. An electrical component can
be electrically connected to the electrically conductive attach pad
and the electrically conductive trace of the printed board. A
thermal interface material is disposed adjacent at least a portion
of a side surface of the electrical component and in contact with
the thermally conductive attach pad. In this manner, the assembly
may provide a thermally conductive pathway from an electrical
component to the heat sink.
Inventors: |
Sundstrom; Lance L.;
(Pinellas Park, FL) ; Blomberg; Rainer; (Palm
Harbor, FL) ; Gillespie; Michael J.; (Seminole,
FL) |
Assignee: |
Honeywell Intenational Inc.
Morristown
NJ
|
Family ID: |
44486298 |
Appl. No.: |
12/728947 |
Filed: |
March 22, 2010 |
Current U.S.
Class: |
361/718 ;
174/252; 29/832 |
Current CPC
Class: |
H01L 23/42 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101; H01L 2924/0002
20130101; Y10T 29/4913 20150115; H01L 23/36 20130101 |
Class at
Publication: |
361/718 ;
174/252; 29/832 |
International
Class: |
H05K 7/20 20060101
H05K007/20; H05K 1/00 20060101 H05K001/00; H05K 3/30 20060101
H05K003/30 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with Government support under
Contract Number 4080 awarded by Lockheed Martin Corporation. The
Government has certain rights in the invention.
Claims
1. An assembly comprising: a printed board that includes a heat
sink, a thermal conductive attach pad thermally connected to the
heat sink, an electrically conductive attach pad that is separate
from the thermally conductive attach pad, and an electrically
conductive trace; an electrical component electrically connected to
the electrically conductive attach pad and the electrically
conductive trace of the printed board, wherein the electrical
component defines a side surface; and a thermal interface material
disposed adjacent at least a portion of the side surface of the
electrical component, wherein the thermal interface material is
thermally connected to the thermally conductive attach pad and the
heat sink.
2. The assembly of claim 1, wherein the thermally conductive attach
pad is electrically isolated from the electrically conductive
attach pad and the electrically conductive trace.
3. The assembly of claim 1, wherein the printed circuit board
comprises a plurality of conductive layers, the electrically
conductive trace being defined by at least one of the conductive
layers, and wherein the heat sink is defined by at least one of the
conductive layers.
4. The assembly of claim 1, further comprising a thermal bridge
that surrounds at least a portion of the side surface of the
component, wherein the thermal interface material is disposed at
least partially between the thermal bridge and the electrical
component.
5. The assembly of claim 4, wherein the thermal bridge surrounds at
least a portion of a top surface of the electrical component.
6. The assembly of claim 4, wherein the thermal bridge comprises at
least one of copper, a copper alloy, tin plated steel, tin plated
copper, or nickel plated copper.
7. The assembly of claim 4, further comprising a housing defining a
cavity in which the electrical component is disposed, wherein the
thermal bridge at least partially surrounds the housing and the
thermal interface material is disposed between the thermal bridge
and the housing.
8. The assembly of claim 1, wherein the printed board further
comprises a thermally conductive via thermally connected to the
heat sink and thermally connected to the thermally conductive
attach pad.
9. The assembly of claim 8, further comprising an electrically
conductive via electrically isolated from the thermally conductive
via.
10. The assembly of claim 8, wherein the thermally conductive via
extends through an entire thickness of the printed board.
11. The assembly of claim 1, wherein the heat sink comprises a
thermal core heat sink.
12. The assembly of claim 1, wherein the electrical component
comprises at least one of a transistor, diode, resistor, capacitor,
inductor or integrated circuit.
13. The assembly of claim 1, wherein the thermal interface material
comprises a thermal conductivity greater than approximately 10
Watts/meter-Kelvin.
14. An assembly comprising: a printed board that includes a heat
sink, a thermal conductive attach pad thermally connected to the
heat sink, an electrically conductive attach pad that is separate
from the thermally conductive attach pad, and an electrically
conductive trace; an electrical component electrically connected to
the electrically conductive attach pad and the electrically
conductive trace of the printed board, wherein the electrical
component defines a side surface; and a thermal bridge that
surrounds at least a portion of the side surface of the electrical
component; and a thermal interface material disposed at least
partially between the thermal bridge and the electrical component,
wherein the thermal interface material is thermally connected to
the thermally conductive attach pad.
15. The assembly of claim 14, wherein the electrically conductive
attach pad is electrically isolated from the thermally conductive
attach pad.
16. The assembly of claim 14, wherein the thermal bridge defines a
fill port through which the thermal interface material is
introduced between the thermal bridge and the electrical
component.
17. A method comprising: electrically connecting an electrical
component to an electrically conductive attach pad of a printed
board, wherein the printed board further comprises a thermally
conductive attach pad thermally connected to a heat sink, and
wherein the thermally conductive attach pad is separate from the
electrically conductive attach pad; and introducing a thermal
interface material adjacent at least portion of a side surface of
the electrical component so the thermal interface material is
thermally connected to the thermally conductive attach pad.
18. The method of claim 17, wherein electrically connecting the
electrical component to the electrically conductive attach pad of
the printed board comprises soldering the electrical component to a
solder pad on a top surface of the printed board, wherein the
solder pad is electrically connected to an electrically conductive
trace disposed in the printed board.
19. The method of claim 17, further comprising attaching a thermal
bridge to the printed board so the thermal bridge surrounds at
least a portion of the side surface of the component, wherein
introducing the thermal interface material comprises introducing
the thermal interface material so the thermal interface material is
disposed at least partially between the thermal bridge and the
electrical component.
20. The method of claim 19, wherein the thermal bridge defines a
fill port, and introducing the thermal interface material comprises
introducing the thermal interface material into the fill port.
Description
TECHNICAL FIELD
[0002] This disclosure relates to electrical components and, more
particularly, to electrical components mounted on a printed
board.
BACKGROUND
[0003] A printed board assembly (PBA) can be fabricated using many
different techniques. One technique is a through-hole mounting
technique that utilizes individual electronic components with
mounting lead pins. The lead pins of the individual components can
be inserted into through-holes from a first side of a printed board
and then soldered from an opposite side of the printed board (PB).
Another technique for coupling electrical components to a printed
board utilizes surface mount technology (SMT). SMT involves
mounting a surface-mount device (SMD) or surface-mount component
(SMC) directly onto conductive attach pads of a PB.
SUMMARY
[0004] In general, this disclosure relates to an assembly that
includes one or more thermal management features for managing heat
generated by an electrical component and techniques for forming the
assembly. The electrical component is disposed on a substrate
(e.g., a printed board) that includes at least one electrically
conductive electrical attach pad and at least one thermally
conductive thermal attach pad that is thermally connected to a
thermal heat sink. In some examples, a printed board includes the
heat sink, which can be, but need not be, separate from the
electrically conductive trace. In other examples, the heat sink is
external to the printed board. In some examples, the substrate
includes a thermal via that is thermally connected to the thermal
attach pad to the heat sink. The thermal attach pad is separate
from the electrical attach pad. In addition, in some examples, the
thermal attach pad is electrically isolated from the electrical
attach pad to which an electrical component is electrically
coupled.
[0005] Various thermal management features of the assembly may
provide a dedicated pathway for transferring heat away from an
electrical component. In some cases, for example, the thermal
attach pad is thermally connected to the electrical component,
e.g., via a thermal interface material alone or in combination with
a thermal bridge, which defines a thermally conductive pathway from
the electrical component to the heat sink. Thus, the thermal
interface material and thermal pad help to transfer heat from the
electrical component to the heat sink. In further cases, a
thermally conductive attach pad, thermal via, and heat sink provide
a dedicated pathway for conducting heat away from the electrical
component.
[0006] In one aspect, the disclosure is directed to an assembly
comprising a printed board that includes a heat sink, a thermal
conductive attach pad thermally connected to the heat sink, an
electrically conductive attach pad that is separate (e.g.,
physically spaced away from, does not overlap with, or separated by
a substrate material) from the thermally conductive attach pad, and
an electrically conductive trace. The assembly further includes an
electrical component electrically connected to the electrically
conductive attach pad and the electrically conductive trace of the
printed board, where the electrical component defines a side
surface. In addition, a thermal interface material is disposed
adjacent at least a portion of the side surface of the electrical
component, and is thermally connected to the thermally conductive
attach pad. For example, the thermal interface material can contact
the thermally conductive attach pad.
[0007] In another aspect, the disclosure is directed to an assembly
comprising a printed board that includes a heat sink, a thermally
conductive attach pad thermally connected to the heat sink, an
electrically conductive attach pad that is separate from the
thermally conductive attach pad, and an electrically conductive
trace. The assembly further includes an electrical component
electrically connected to the electrically conductive attach pad
and trace of the printed board, where the electrical component
defines a side surface, and a thermal bridge that surrounds at
least a portion of the side surface of the electrical component. In
addition, a thermal interface material is disposed at least
partially between the thermal bridge and the electrical component,
and is thermally connected to the thermally conductive attach
pad.
[0008] In another aspect, the disclosure is directed to a method
comprising electrically connecting an electrical component to an
electrically conductive attach pad of a printed board, where the
printed board further comprises a thermally conductive attach pad
thermally connected to a heat sink, and where the thermally
conductive attach pad is separate from the electrically conductive
attach pad. The method further includes introducing a thermal
interface material adjacent at least portion of a side surface of
the electrical component so the thermal interface material is
thermally connected to the thermally conductive attach pad.
[0009] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a schematic plan view of an example assembly that
includes two electrical components, a substrate, and one or more
thermal management features.
[0011] FIG. 2 is a schematic cross-sectional view of the example
assembly of FIG. 1 taken along the A-A cross-sectional line shown
in FIG. 1.
[0012] FIG. 3 is a schematic plan view of example attach pads that
can be used to mount two example electrical components and their
respective thermal bridges to a substrate.
[0013] FIG. 4 is a schematic plan view of the two example
electrical components mounted on the attach pads illustrated in
FIG. 3.
[0014] FIG. 5 is a schematic cross-sectional view of another
example assembly that includes one or more thermal management
features.
[0015] FIG. 6 is a flow diagram illustrating an example technique
for forming an assembly with an electrical component, a thermal
bridge and a thermal interface material (TIM).
[0016] FIG. 7 is a flow diagram illustrating another example
technique for forming an assembly with an electrical component and
thermal interface material (TIM).
DETAILED DESCRIPTION
[0017] Thermal management features for an assembly that includes at
least one electrical component are described herein. Some
electronic assemblies include one or more electrical components,
such as one or more discrete components and/or one or more
integrated circuit (IC) components, mounted on a substrate (e.g., a
printed board). Discrete components are individual circuit
elements, such as transistors, diodes, resistors, capacitors,
inductors, and the like. IC components, by contrast, contain two or
more circuit elements in single circuit package. More complex
circuits can be formed by electrically connecting multiple discrete
components, multiple IC components, or a combination of discrete
components and IC components. Regardless of the number,
configuration, or type of electrical components, in some cases it
may be desirable to manage the heat generated by the electrical
components during operation. Better thermal management of
electrical components can help increase the density with which
electrical components can be attached to a printed board and, in
some examples, improve performance of the electrical components by,
for example, reducing their operating temperature.
[0018] FIG. 1 is a schematic plan view of an example assembly 2,
which includes printed board 4, thermal bridges 10, 11, and
electrical components 12, 14. Assembly 2 includes thermal
management features for managing heat generated by electrical
components 12 and 14. Assembly 2 can also be referred to as a
printed board assembly (PBA), printed wiring assembly (PWA), or a
circuit card assembly (CCA). Printed board 4 mechanically supports
electrical components 12 and 14. In addition, printed board 4
includes one or more electrically conductive attach pads and
pathways that can be electrically connected to electrical
components 12 and 14. A plurality of electrically conductive
pathways of printed board 4 can be defined by, for example,
electrically conductive material defining electrically conductive
attach pads, vias, and/or traces within an electrically
nonconductive material.
[0019] In the example shown in FIG. 1, electrical components 12 and
14 are both electrically and mechanically connected to printed
board 4 via a plurality of electrically conductive attach pads 6,
8, examples of which are described in further detail with respect
to FIGS. 3 and 4. However, in other examples, other techniques for
mechanically and electrically connecting electrical components 12
and 14 to printed board 4 can also be used. For example, an
adhesive, such an electrically and/or thermally conductive
adhesive, or another mechanical fixation mechanism (e.g., a screw
or bolt) can be used to mechanically or electrically connect one or
both electrical components 12, 14 to printed board 4. In some
cases, a platform or a package housing can be at least partially
positioned between one or both electrical components 12, 14 and
printed board 4. That is, in some examples, one or both electrical
components 12, 14 can be enclosed within a housing that is attached
to printed board 4.
[0020] In some cases, electrical components 12 and 14 may be
electrically connected to each other via electrically conductive
attach pads, electrically conductive vias, electrically conductive
traces, or a combination of electrically conductive features of
printed board 4. In other cases, electrical components 12 and 14
may not share an electrically conductive pathway provided by
printed board 4 and may instead be merely physically adjacent each
other on a common printed board 4.
[0021] Electrical components 12, 14 can generate heat during
operation. It may be useful to transfer heat away from components
12, 14, and, in some cases, away from printed board 4 in order to
decrease the operating temperature of electrical components 12, 14.
Assembly 2 includes one or more thermal management features that
help transfer heat away from electrical components 12, 14. In the
examples shown in FIG. 1, assembly 2 includes first thermal bridge
10 disposed over electrical component 12 and second thermal bridge
11 disposed over electrical component 14. As described in further
detail below, thermal bridges 10, 11 are attached to thermally
conductive attach pads (also referred to herein as "thermal attach
pads") defined on printed board 4 (not shown in FIG. 1). The
thermal attach pads are separate from the electrical attach pads 6,
8. In some examples, the thermal attach pads are physically
separate from electrical attach pads 6, 8, such that each of the
thermal attach pads defines an outer perimeter that does not
substantially overlap with an electrical attach pads 6, 8. In
addition, in some examples, the thermal attach pads are separated
from an electrical attach pad 6, 8 by a substrate material of
printed board 4, where the substrate material can be electrically
nonconductive.
[0022] Further, the thermal attach pads are thermally connected to
the respective electrical components 12, 14 as well as to a heat
sink of printed board 4. In this way, thermal bridges 10, 11 and
associated thermal attach pads form a thermally conductive pathway
from electrical components 12, 14 to a heat sink. Thermal bridges
10, 11 at least partially surround an outer surface of electrical
components 12, 14 and increase the surface area from which heat is
conducted away from components 12, 14 (e.g., the thermal interface
area) compared to assemblies that do not include a thermal bridge,
and, e.g., rely on an electrical pathway between electrical
components 12, 14 and printed board 14 to transfer heat away from
components 12, 14. The outer surface of an electrical component can
include, for example, a top surface that is opposite the bottom
surface that is closest to printed board 4 when the component is
attached to printed board 4 and a side surface that extends between
the top surface and the bottom surface. Thermal bridges 10, 11 may
be electrically insulated from or electrically connected to
electrical components 12, 14 depending on the application.
[0023] In the example shown in FIG. 1, thermal bridge 10 defines
fill ports 16 and thermal bridge 10 define fill port 18. As
described in further detail below, a thermal interface material
(TIM) can be introduced into a space between an outer surface of
electrical component 12 and an inner surface of thermal bridge 10
via fill ports 16, and a thermal interface material can be
introduced into a space between an outer surface of electrical
component 14 and an inner surface of thermal bridge 11 via fill
port 18. Fill ports 16, 18 can be, for example, openings defined in
a wall of thermal bridges 10, 11, respectively, that extend from an
outer surface of the respective thermal bridge 10, 11 to an inner
surface that faces the respective electrical component 12, 14.
Thermal bridges 10, 11 can each include any suitable number of fill
ports, and the fill ports can have any suitable location. Thus,
while two fill ports 16 at a top surface of thermal bridge 10 and a
single fill port 18 at a top surface of thermal bridge 11 are shown
in FIG. 1, in other examples, fill ports 16, 18 can have any
suitable location in the wall of thermal bridges 10, 11,
respectively. Thermal bridge 10 can include a greater or fewer
number of fill ports and thermal bridge 11 can include a greater
number of fill ports. Moreover, in some examples, thermal bridges
10, 11 do not include fill ports and the thermal interface material
can be positioned between thermal bridges 10, 11 and electrical
components 12, 14 using a different technique.
[0024] Electrical components 12, 14 may each be any generally known
discrete component or IC component, and may even be a combination
of one or more discrete components and one or more ICs. For
example, electrical component 12 and/or 14 may be a transistor,
such as a bipolar transistor, or field effect transistor (FET). In
some cases, a field effect transistor (FET) may be a junction field
effect transistor (JFET), a metal oxide semiconductor field effect
transistor (MOSFET), a metal semiconductor field effect transistor
(MESFET), or a high electron mobility transistor (HEMT). As another
example, electrical component 12 and/or 14 may be a diode, such as
Shottkey diode, dual Shottkey diode, Zener diode, transient voltage
suppression diode, or a thyristor. It should be appreciated,
however, that the preceding examples of discrete components are
intended to be illustrative only, and the assemblies and techniques
of this disclosure are not limited to a particular type of
electrical component or combination of components. Thermal
management of some discrete components can be more difficult than
some IC components because the discrete components may have
significantly smaller surface areas from which heat can be
effectively conducted away from the discrete components. However,
the thermal management features and techniques described herein can
also be used with an assembly that includes one or more IC
components. For example, electrical component 12 and/or 14 may be a
flip-chip, such as a flip-chip that includes balled or bumped
solder die surface, or a flat pack IC package.
[0025] FIG. 2 is a schematic cross-sectional view of assembly 2
illustrated in FIG. 1 taken along line A-A in FIG. 1. Electrical
components 12 and 14 are mounted to printed board 4. Any suitable
number of electrical components can be mechanically and
electrically coupled to printed board 4, which can have any
suitable size. Printed board 4 includes electrically conductive
vias 38A-38D, 54A-B, electrically conductive traces 40 and 44,
thermal core heat sink layer 42, and thermally conductive vias 46A,
46B, 56A, 56B (also referred to as "thermal vias").
[0026] In some examples, printed board 4 may be a twenty-one layer
printed board having ten 1 ounce (oz) (approximately 0.0356
millimeter (approximately 0.0014 inches) thick) and/or 2 oz
(approximately 0.0711 millimeter (approximately 0.0028 inches)
thick copper conductor layers in a top section and a single
approximately 2.794 millimeter (approximately 0.110 inches) thick
copper thermal core layer. A twenty-one layer printed board may
also have ten 1 oz (approximately 0.0356 millimeter (approximately
0.0014 inches) thick) and/or 2 oz (approximately 0.0711 millimeter
(approximately 0.0028 inches) thick) copper conductor layers in a
bottom section, resulting in a centered copper thermal core layer
between equally sized top and bottom sections. A twenty-one layer
printed board may be used for a power supply application and may be
obtained from Time to Market (TTM) Technologies, Inc. (Santa Ana,
Calif.).
[0027] In other examples, printed board 4 can comprise any suitable
type of board. For example, printed board 4 may have a single
conductive layer, dual conductive layers, or a plurality of
conductive layers. Printed board 4 generally includes at least one
electrical trace or electrical trace layer (also referred to as a
conductor layer) and one heat sink layer. However, printed board 4
may have a different number of electrical trace layers, a different
number of heat sinks or heat sink layers, or a different
configuration of electrical trace layers to the heat sink than that
shown in FIG. 2. Moreover, the heat sink can have a different
position relative to the electrical trace layers of printed board
4. For example, the heat sink can be positioned on a top surface or
a bottom surface of printed board 4, or can even be physically
separate from printed board 4.
[0028] In the example shown in FIG. 2, electrical component 12
defines a side surface 13, a top surface 15, a bottom surface 17. A
side surface can be any surface other than a top surface or a
bottom surface, where the bottom surface is closest to printed
board 4 when the electrical component is attached to printed board
4 and the top surface is substantially opposite the bottom surface.
An electrical component may have a single side surface or multiple
side surfaces. In some cases, electrical component 12 may include
leads configured to extend through printed board 4 to mount
component 12 using a through-hole mounting technique. In other
cases, as illustrated in FIG. 2, electrical component 12 may be
electrically and mechanically coupled to printed board 4 via
surface mount technology (SMT) techniques. For example, electrical
component 12 can be electrically and mechanically coupled to
printed board 4 by electrical attach pad 37, as described in
further detail below with respect to FIG. 3. As an example,
interfacial attach pads on component 12 can be mated with
interfacial attach pads of printed board 4, and the attach pads can
be soldered or adhered together. Additional or alternate fixation
mechanisms, such as an adhesive, screw, bolt or the like can also
be used.
[0029] Electrical component 12 can be directly connected to printed
board 4, or may a part of a package (e.g., a housing or a platform)
that is mechanically connected to printed board 4. For example,
electrical component 12 can reside within a package that mounts
directly to conductive patterns on a top surface of printed board 4
using surface mount technology (SMT) techniques. The package
housing may protect electrical component 12 from the environment
(e.g., environmental contaminants), facilitate placement and
fabrication of assembly 2, and, in some examples, help transfer
heat away from electrical component 12.
[0030] As an example, electrical component 12 may reside in a
cavity defined by housing 30. Housing 30 comprises housing bottom
member 34 that defines a surface that is adjacent to printed board
4 when housing 30 is mechanically coupled to printed board 4.
Housing lid 32 can be mechanically coupled to housing 30 to
substantially enclose electrical component 12 within the cavity
defined by housing 30. In some examples, housing lid 32 and housing
30 define a hermetically sealed package, such that electrical
component 12 may be hermetically sealed within housing 30.
[0031] In some cases, electrical attach pads 37 electrically
connect electrical component 12 to printed board 4. For example,
electrical attach pads 37 may be electrically connected to an
electrically conductive pathway defined within housing bottom
member 34, which is electrically connected to electrical component
12. In some examples, electrical attach pads 37 are electrically
connected to at least one of electrical vias 38A-38D. In this way,
electrical component 12 housed within housing 30 can be
electrically connected to electrical attach pads 37 and at least
one electrical via 38A-38D of printed board 4. In other examples,
electrical component 12 can directly electrically connect to
electrical attach pads 37 via respective attach pads, rather than
electrically connecting to attach pads 37 via housing 30, as shown
in FIG. 2. That is, in some examples, electrical component 12 may
not be enclosed within housing 30.
[0032] Assembly 2 also includes electrical component 14. Electrical
component 14 defines a side surface 19, a top surface 21, and a
bottom surface 23. In the example shown in FIG. 2, electrical
component 14 is electrically connected to one of electrically
conductive traces 40 via an electrical attach pad (not shown) that
is electrically connected to at least one of electrical vias 54A,
54B. For example, bottom surface 23 of electrical component 14 can
include an electrical contact (e.g., electrically conductive attach
pad) that electrically connect to an electrical attach pad of
printed board 4. The electrical conductive attach pad of printed
board 4 can be positioned on a top surface of printed board 4 and
can be electrically connect to at least one of electrical vias
54A-54B, which are electrically coupled to at least one of
electrical traces 40 of printed board 4. In the example of FIG. 2,
electrically conductive vias 54A-54B extend through printed board 4
to a plane defined by electrical traces 40, permitting an
electrical connection with one of electrical traces 4. In some
examples, at least one of electrical vias 54A-B may extend through
heat sink 42 and electrically connect to at least one of
electrically conductive traces 44 instead of, or in addition to,
connecting to at least one of electrically conductive traces
40.
[0033] In some cases, electrical component 14 may be configured to
be mounted using either through-hole mounting techniques or surface
mounting technology techniques, as discussed above. As with
electrical component 12, component 14 can be directly connected to
printed board 4, or may be a part of package (e.g., a housing or a
platform) that is then mechanically connected to printed board 4.
For example, electrical component 14 may be a metal electrode
leadless face (MELF) electrical component configured to be mounted
using surface mounting technology (SMT) techniques, such as surface
mounting technology attach pad techniques. A MELF electrical
component may have an electrical component positioned within a
capped cylindrical body that defines a housing.
[0034] Electrically conductive vias 38A-38D are electrically
connected to at least one of electrical traces 40 of printed board
4. In some cases, at least one of electrical vias 38A-38D may
extend through heat sink 42 and electrically connect to at least
one of electrically conductive traces 44 instead of, or in addition
to, connecting to at least one of electrically conductive traces
40. Electrically conductive traces 40, 44 may be discrete traces,
or conductive layers (also known as conductor layers) of printed
board 4. Electrically conductive traces 40, 44 can be used to, for
example, electrically connect electrical components of assembly 2
to each other or to another element separate from assembly 2. In
the example shown in FIG. 2, electrically conductive traces 40, 44
are each shown as a group of ten conductor layers. In the example,
electrically conductive traces 40, 44 are electrically isolated
from each other by an electrically nonconductive material of
printed board 4.
[0035] Electrically conductive traces 40, 44 extend through the
electrically nonconductive substrate of printed board 4.
Electrically conductive traces 40 are closer to top surface 4A of
printed board 4 than bottom surface 4B, and electrically conductive
traces 44 are closer to bottom surface 4B of printed board 4 than
top surface 4A. However, other locations of electrically conductive
traces 40, 44 are contemplated. In the example and configuration
shown in FIG. 2, top surface 4A of printed board 4 is the surface
having the greatest z-axis position (orthogonal x-y axes shown in
FIGS. 1, 3, and 4, and x-z axes shown in FIGS. 2 and 5 for ease of
description only) and bottom surface 4B is the surface having the
smallest z-axis position. Top surface 4A and bottom surface 4B are
located on substantially opposite sides of printed board 4 and face
in substantially opposite directions. Although two groups of ten
electrically conductive traces 40, 44 are shown in FIG. 2, printed
board 4 can include any suitable number of electrically conductive
traces.
[0036] Thermal vias 46A, 46B, 56A, 56B are comprised of a thermally
conductive material. Thermal vias 46A, 46B, 56A, 56B are thermally
coupled to heat sink 42 of printed board 4. Thermal vias 46A, 46B,
56A, 56B are thermally connected to thermal heat sink 42 but are
electrically isolated from electrical traces 40 and 44 disposed in
printed board 4 in the example of FIG. 2. In other examples, at
least some of thermal vias 46A, 46B, 56A, 56B can be electrically
connected to electrical traces 40 and 44 of printed board 4 instead
of or in addition to being electrically connected to heat sink 42.
In this way, in some examples, electrically conductor layers of
printed board 4 in which electrical traces 40 and 44 are defined
can be a heat sink instead of or in addition to dedicated heat sink
42.
[0037] In the example shown in FIG. 2, thermal vias 46A, 46B, 56A,
56B extend between top surface 4A of printed board 4 and heat sink
42 and extend through printed board 4 in a substantially z-axis
direction. In this way, thermal vias 46A, 46B, 56A, 56B define a
thermally conductive pathway between thermal attach pads at top
surface 4A of printed board 4 and heat sink 42, such that heat can
be transferred away from top surface 4A via heat sink 42.
[0038] Heat sink 42 is in a plane substantially parallel to top
surface 4A of printed board 4, whereby electrical components 12, 14
are positioned on top surface 4A of printed board. Heat sink 42 can
be any suitable feature that absorbs and dissipates heat from
electrical components 12, 14, and, in some examples, from printed
board 4. Heat sink 42 can be located in any position suitable for
transferring heat away from electrical components 12, 14. The
specific geometry, orientation, or location of heat sink 42 may
depend on one or more factors, including, for example, the specific
selection and arrangement of thermal management features (e.g.,
thermal bridges 10, 11 and/or thermal interface material), the
thermal conductivities of various materials, and specific type of
electrical components 12, 14 employed.
[0039] As examples, heat sink 42 may comprise one or more
conductive layers of printed board 4, or one or more bonded surface
layers proximate to top surface 4A of printed board 4. Heat sink 42
may be integral to printed board 4, separate from printed board 4,
or may include a combination of features that are both integral to
and separate from printed board 4. Heat sink 42 may also reside on
a surface plane of printed board 4. For example, heat sink 42 may
reside on at least a portion of top surface 4A of printed board 4.
A surface heat sink may be used when thermal attach pads 48, 58 are
provided without corresponding thermal vias 46A-B, 56A-B. In this
manner, thermal bridges 10, 11 and thermal attach pads 48, 58 can
create a dedicated thermal pathway to heat sink 42 without
utilizing thermal vias 46A-B, 56A-B.
[0040] In some examples, heat sink 42 comprises a thermal
conductivity of greater than or equal to approximately 150
Watts/meter-Kelvin, such as greater than or equal to approximately
375 Watts/meter-Kelvin. For example, heat sink 42 can be formed
from an alloy of aluminum that exhibits a thermal conductivity of
approximately 167 Watts/meter-Kelvin, and/or an alloy of copper
that exhibits a thermal conductivity of approximately 385
Watts/meter-Kelvin. Heat sink 42 may be comprised of any suitable
material, such as a metal. In some examples, heat sink 42 comprises
a thermal core heat sink comprising copper (as shown in the example
of FIG. 2), aluminum, or any alloys thereof.
[0041] As described above, thermal bridges 10, 11 are positioned to
at least partially surround (or "straddle") electrical components
12, 14, respectively, and each define a thermally conductive
pathway for transmitting heat away from the respective component
12, 14. In the example shown in FIG. 2, thermal bridge 10 extends
substantially entirely around electrical component 12 and is
thermally connected to thermal vias 46A, 46B. In this way, thermal
bridge 10 defines thermally conductive pathway around the entire
outer surface of electrical component 12 not adjacent to printed
board 4 (e.g., by surrounding the entire outer surface of housing
30, in which component 12 is disposed). Thermal interface material
50 is disposed between electrical component 12 and first thermal
bridge 10. In addition, thermal bridge 11 extends substantially
entirely around electrical component 14 and is thermally connected
to thermal vias 56A, 56B. In this way, thermal bridge 11 defines
thermally conductive pathway around the entire outer surface of
electrical component 14 not adjacent to printed board 4. Thermal
interface material 60 is disposed between electrical component 14
and second thermal bridge 11. In the example shown in FIG. 2,
thermal interface material 60 is disposed between an outer surface
of electrical component 14 and an inner surface of second thermal
bridge 11.
[0042] Thermal bridges 10 and 11 thermally couple to electrical
components 12 and 14 to conduct heat away from electrical
components 12 and 14. Accordingly, thermal bridges 10, 11 are each
comprised of one or more thermally conductive materials. In some
examples, thermal bridges 10, 11 are each comprised of a solderable
material. For example, thermal bridges 10, 11 may include copper,
copper alloys, tin plated steel, tin plated copper, nickel plated
copper, and combinations thereof. As described in greater detail
below, thermal attach pads 48 and 58 may thermally and/or
mechanically connect thermal bridges 10 and 11, respectively, to
printed board 4.
[0043] The dimensions of thermal bridge 10, 11 can vary depending
on various factors, such as the size of the electrical component
surrounded, the geometry of bridge selected, and the thermal
conductivity of the thermal bridge and/or thermal interface
material (TIM) selected. In some cases, however, the thermal
bridges 10, 11 each have a minimum wall thickness T of
approximately 500 micrometers (approximately 0.020 inches). Wall
thickness T of thermal bridges 10, 11 defines the dimension of
thermal bridge 10, 11 between an outer surface of the thermal
bridge 10, 11 and the inner surface, whereby the inner surface
faces electrical component 12, 14, respectively. Wall thickness T
can be substantially constant or can vary.
[0044] As illustrated in FIG. 2, thermal bridge 10 surrounds both
side surface 13 and top surface 15 of electrical component 12.
Also, thermal bridge 11 surrounds both side surface 19 and top
surface 21 of electrical device 14. In the example of assembly 2
shown in FIGS. 1 and 2, thermal bridges 10, 11 each have a
generally U-shape in cross-section, such that thermal bridges 10,
11 can each surround at least a portion of the side surfaces and
top surfaces of the respective electrical components 12, 14.
[0045] In some examples, a thermal bridge may surround only a side
surface or only a portion of a side surface of an electrical
component. This type of thermal bridge can be referred to as a
truncated thermal bridge. In other examples, a truncated thermal
bridge can surround only a top surface or only a portion of a top
surface of an electrical component. For instance, a truncated
thermal bridge may be elevated on a support member that is
positioned between printed board 4 and the thermal bridge. In yet
other examples, a thermal bridge may surround at least a portion of
a side surface and at least a portion of a top surface of an
electrical component. In addition, thermal bridges 10, 11 can
surround substantially the entire outer perimeter of the respective
electrical component 12, 14 to substantially enclose the electrical
component, 12, 14, or may only surround part of the outer perimeter
of the respective electrical component 12, 14. Increasing the
interfacial surface area between electrical components 12, 14 and
respective thermal bridges 10, 11 can increase the amount of heat
that thermal bridges 10, 11 transfer away from electrical
components 12, 14, respectively.
[0046] In the example shown in FIG. 2, thermal bridge 10 surrounds
substantially all outer surfaces (e.g., top and side surfaces) of
housing 30 and lid 32 that are exposed when housing 30 is attached
to printed board 4. That is, thermal bridge 10 substantially
surrounds lid 32 and portions of housing 30 that do not face
printed board 4, such as the bottom surface of housing 30.
Similarly, thermal bridge 11 substantially surrounds electrical
component 14, and, in particular, side surfaces 19 and top surface
21 of electrical component 14, which has a substantially
quadrilateral cross-sectional shape when the cross-section is taken
in the x-y plane. However, in some examples, thermal bridge 11 may
surround only one, two, or three side surfaces 19 of electrical
component 14. In addition, in examples in which electrical
component 14 does not have a substantially quadrilateral
cross-sectional shape when the cross-section is taken in the x-y
plane, thermal bridge 11 can surround any portion of the outer
surface of electrical component 14. For example, thermal bridge 11
can leave ends (e.g., as defined by part of the side surface) of
component 14 uncovered by thermal bridge 11.
[0047] In some cases, one or more sides of electrical components
12, 14 not surrounded by thermal bridge 10, 11, respectively, may
be at least partially covered by thermal interface material (TIM)
50, 60, respectively, or a fillet of thermal interface material
(TIM). A thermal bridge may surround at least a portion of an
electrical component using any general shape. For instance, bridge
material may be V-shaped, Y-shaped, or even a rounded shape in
cross-section, rather than substantially U-shaped as shown in FIG.
2, and may surround all or part of the side surfaces of an
electrical component.
[0048] Thermal bridges 10 and 11 illustrated in FIG. 2 are
thermally coupled to thermal attach pads 48, 58, which are
comprised of a thermally conductive material and define a thermally
conductive pathway away from electrical components 12,14. In the
example shown in FIG. 2, thermal attach pads 48, 58 are thermally
connected to at least one of thermal vias 46A, 46B, 56A, and 56B.
As discussed above, thermal vias 46A, 46B, 56A, and 56B extend at
least partially through printed board 4 and are thermally coupled
to thermal heat sink 42. Thermal attach pads 48, 58, thermal vias
46A, 46B, 56A, and 56B, or a combination of thermal attach pads and
thermal vias can provide thermally conductive pathways through
which heat generated by electrical components 12, 14 can be
transferred to thermal heat sink 42. In other examples, thermal
attach pads 48, 58 can be directly thermally connected to heat sink
42, e.g., if heat sink 42 is positioned on top surface 4A of
printed board 4.
[0049] In the example shown in FIG. 2, thermal attach pads 48, 58
are electrically isolated (i.e., not in direct electrical
communication) from electrical attach pads and from electrical
traces 40 and 44 of printed board 4. Also, thermal vias 46A, 46B,
56A, and 56B are electrically isolated from electrical attach pads
and from electrical traces 40 and 44 of printed board 4. In this
arrangement, thermal management features may help transfer heat
away from electrical components 12 and 14 without increasing the
impedance or capacitance of electrical connections of assembly 2.
However, in some examples, thermal attach pads 48, 58 can be
thermally connected to an electrically conductive layer of printed
board 4 that also defines one or more of the traces 40, 44. In
these examples, the electrically conductive layer can act as both
an electrically conductive trace and a heat sink for printed board
4.
[0050] In conventional techniques for thermal management of
electrical components of a printed board assembly, electrical
pathways of the assembly (e.g., electrical attach pads, traces and
vias of the printed board) are used to conduct heat away from an
electrical component. For example, designers have increased the
width and length of electrical traces of a printed board in order
to improve the thermal conductivity of the electrical traces. While
the enlarged electrical traces can improve heat conduction away
from an electrical component, enlarged electrical traces can
increase the capacitance of the trace. In contrast to the existing
thermal management features of a printed board assembly, assembly 2
includes thermally conductive attach pads 48, 58 and heat sink 42
that are dedicated to conducting heat away from electrical
components 12, 14. Thermal vias 46A, 46B, 56A, and 56B are also
provided in the illustrated example of FIG. 2 to enhance thermal
conduction away from electrical components 12, 14 and to thermally
connect thermal attach pads 48, 58 to thermal core heat sink 42.
The thermal management features in assembly 2 are separate from
electrical attach pads, traces 40, 44, and electrically conductive
vias of printed board 4. The dedicated thermally conductive attach
pads 48, 58 and thermal vias 46A, 46B, 56A, and 56B can be used in
addition to or instead of electrically conductive attach pads,
electrically conductive vias 38A-38D, 54A, and 54B, and
electrically conducive traces 40, 44 of printed board 4 to transfer
heat away from electrical components 12, 14.
[0051] By defining dedicated thermal pathways, the thermal
management features of assembly 2 can help manage heat generated by
electrical components 12, 14 without substantially degrading the
electrical performance of assembly 2 by, for example, increasing
capacitance within the assembly. By contrast, in some additional
examples, one or more thermal management features of assembly 2 may
be electrically connected to electrically conductive pathways
within assembly 2 without significantly impacting the electrical
performance of electrical components 12, 14. For example, some
types of electrical components exhibit improved electrical
performance in a high capacitance environment. In these situations,
thermal bridges 10, 11, thermal attach pads 48, 58, at least one of
thermal vias 46A, 46B, 56A, 56B (if included in printed board 4),
heat sink electrical component 12, or a combination of these
features may be electrically connected in assembly 2. Electrical
connectivity may occur through any electrical feature or
combination of electrical features, including electrical attach
pads, electrical vias 38A-38D, 54A-54B, or electrical traces 40,
44.
[0052] Thermal vias 46A, 46B, 56A, and 56B may extend entirely
through a thickness of printed board 4 (whereby a thickness is
measured in a z-axis direction) or through only a portion of
printed board 4. For example, thermal vias 46A, 46B, 56A, and 56B
may truncate at thermal heat sink 42, before reaching electrical
traces 44. In additional examples, one or more of a plurality of
thermal vias may extend different lengths through printed board 4.
For instance, a first thermal via may extend to a first thermal
heat sink on a first thermal plane of printed board 4 and a second
thermal via may extent to a second thermal heat sink on a second
thermal plane of printed board 4.
[0053] As described in greater detail below, thermal vias 46A, 46B,
56A, and 56B may be at least partially defined by an attach pad
used to mechanically couple thermal bridges 10, 11 to board 4.
Thermal vias 46A, 46B, 56A, and 56B may be filled or unfilled and
may include thermally conductive materials. For example, thermal
vias 46A, 46B, 56A, and 56B may include copper and copper alloys.
In some cases, thermal vias 46A, 46B, 56A, and 56B can each be
formed by defining openings in printed board 4 and filling the
openings with a thermally conductive material, such as a conductive
epoxy. As a particular example, thermal vias 46A, 46B, 56A, and 56B
can be formed by drilling and copper plating holes in printed board
4. A thermally conductive material may then be introduced into the
copper plated holes to provide additional thermal conductivity. In
further cases, for example where thermal vias 46A, 46B, 56A, and/or
56B are separate from an attach pad, the thermal via can be defined
by an opening within the printed board 4 that remains unfilled. For
example, one or more thermal vias may be drilled, plated with a
thermally conductive material such as copper. The thermal vias can
be left unfilled, allowing thermally conductive plating in the
unfilled vias to help conduct heat from thermal bridge 10, 11 to
thermal heat sink 42.
[0054] In some examples, thermal bridges 10, 11 may directly
contact outer surfaces of electrical component 12 (or housing 30)
and electrical component 14 (or a housing of the component).
However, in the example shown in FIG. 2, thermal bridge 10 is
configured such that once it is positioned around housing 30, there
is a gap between housing 30 and bridge 10. Similarly, thermal
bridge 11 is configured such that once it is positioned around
electrical component 14, there is a gap between the outer surface
of component 14 and bridge 11. The gaps between components 12 (or
housing 30), 14 and the respective bridges 10, 11 can be useful to
provide electrical isolation between the electrical component and
thermal bridge, to allow for manufacturing and assembly tolerances,
and to accommodate expansion and contraction of bridges 10, 11 and
components 12, 14, which can have different coefficients of thermal
expansion. In some examples, gaps G are in a range of approximately
500 micrometers (approximately 0.020 inches) to approximately 1.25
millimeters (approximately 0.050 inches). Gaps G can be the same or
different for thermal bridges 10, 11. In addition, for each of
thermal bridges 10, 11, gap G between the thermal bridge and
respective electrical component can be substantially constant or
may vary.
[0055] While the gaps between components 12 (or housing 30), 14 and
the respective bridges 10, 11 can remain unoccupied, in some
examples, assembly 2 includes thermal interface material (TIM) 50,
60 in at least a portion of the gaps. In the example shown in FIG.
2, assembly 2 includes thermal interface material 50 disposed
between electrical component 12 and thermal bridge 10, and thermal
interface material 60 disposed between electrical component 14 and
thermal bridge 11. In the example shown in FIG. 2, thermal
interface material 50 is disposed between an outer surface of
electrical component 12 and an inner surface of thermal bridge 10,
and thermal interface material 60 is disposed between an outer
surface of electrical component 14 and an inner surface of thermal
bridge 11.
[0056] Thermal interface material 50, 60 is positioned to define a
thermally conductive pathway between electrical components 12, 14,
respectively, and the respective thermal bridges 10, 11. In
examples in which there is an unoccupied space between electrical
components 12, 14 and their respective thermal bridges 10, 11,
thermal interface material 50, 60 at least partially fills the gap
between electrical components 12 and 14 and thermal bridges 10 and
11, respectively. In some examples, thermal interface material 50,
60 completely fills the space between electrical components 12 and
14 and thermal bridges 10 and 11, respectively, while in other
examples, thermal interface material 50, 60 partially fills the
space between electrical components 12 and 14 and thermal bridges
10 and 11, respectively.
[0057] Thermal interface material 50, 60 can comprise any suitable
thermally conductive material. In some cases, thermal interface
material 50, 60 has a relatively high thermal conductivity while
being electrically insulative. For example, thermal interface
material 50, 60 can have a thermal conductivity greater than
approximately 5 Watts/meter-Kelvin, such as greater than
approximately 10 Watts/meter-Kelvin, or greater than approximately
12.5 Watts/meter-Kelvin in some examples. Other thermal
conductivity values are also contemplated. In this manner, thermal
interface material (TIM) 50, 60 provides a relatively low impedence
thermal pathway between electrical components 12 and 14 and thermal
bridges 10 and 11, respectively. In general, any type of thermal
interface material is suitable for use in assembly 2. Specific
examples of thermal interface materials include silicone-based
adhesives and diamond-filled thermal interface materials (TIM). One
suitable thermal interface material is a diamond-filled ME7159 TIM,
available from AI Technology Inc. of Princeton Junction, N.J.,
which has a thermal conductivity of approximately 10.4
Watts/meter-Kelvin. Thermal interface material (TIM) 50 may be the
same as thermal interface material (TIM) 60. Thermal interface
material (TIM) 50 may also be different than thermal interface
material (TIM) 60. A specific type of thermal interface material
(TIM) can be selected based on the type of electrical component
used and desired heat transfer rates.
[0058] Thermal interface material 50 and 60 may be introduced
adjacent electrical components 12 and 14 before or after thermal
bridges 10 and 11 are added to assembly 2. For example, thermal
interface material 50 may be applied to at least a portion of side
surface 13 or top surface 15 of electrical component 12.
Alternatively, thermal interface material 50 may be applied to at
least a portion of housing 30 or housing lid 32. Afterwards,
thermal bridge 10 may be placed over electrical component 12. As
another example, thermal interface material 60 can be applied to at
least a portion of outer surfaces 19, 21 of electrical component 14
prior to the coupling of thermal bridge 11 to printed board 4. In
some cases, thermal interface material 50, 60 can be introduced
between thermal bridges 10, 11 and the respective electrical
components 12, 14 after thermal bridges 10, 11 are placed on
printed board 4 over the respective electrical components 12, 14.
For example, thermal interface material 50, 60 may be introduced
after electrical components 12, 14 and thermal bridges 10, 11 are
solder reflow attached and cleaned. In examples in which one or
both thermal bridges 10, 11 do not surround the entire outer
surface of the respective electrical component 12, 14, thermal
interface material 50, 60 can be introduced through any openings in
the thermal bridge.
[0059] As another example, thermal bridges 10 and 11 may define one
or more fill ports 16, 18 that can be used as an access point for
introducing thermal interface material between thermal bridges 10,
11 and the respective electrical components 12, 14. Fill ports may
be slots, gaps, holes, or other openings that allow a thermal
interface material to be introduced into the space between thermal
bridges 10, 11 and electrical components 12, 14, respectively. In
the example shown in FIG. 2, thermal bridge 10 includes two fill
ports 16. Thermal bridge 11 includes a single fill port 18. Thermal
bridge 10 may be placed over at least a portion of side surface 13
or top surface 15 of electrical component 12. Also, thermal bridge
11 may be placed over at least a portion of side surface 19 or top
surface 21 of electrical component 14.
[0060] After placement of electrical component and thermal bridge
on printed board 4, for example, by solder reflow attachment,
thermal interface material 50 and 60 may be introduced through fill
ports 16 and 18, respectively, so thermal interface material 50 and
60 is disposed between electrical components 12 and 14 and thermal
bridges 10 and 11. In some examples, as shown in FIG. 2, thermal
interface material (TIM) 50, 60 can also be positioned between
electrical components 12, 14, respectively, and printed board 4. In
other examples, thermal bridges 10, 11 can include any suitable
number of fill ports, which can be selected based on, for example,
the size of the thermal bridges 10, 11 and the volume of thermal
material introduced between the thermal bridge and respective
electrical component.
[0061] As noted above, electrical components 12 and 14 may be
attached to printed board 4 using any suitable fixation technique,
such as solder, an adhesive or another fixation mechanism (e.g., a
bolt or screw). In addition, thermal bridges 10, 11 can be
thermally coupled to the respective thermal vias 46A, 46B, 56A, 56B
using any suitable technique, such as thermal attach pads 48, 58
that are in thermal communication with the thermal vias and thermal
bridges.
[0062] In some examples, printed board 4 may include electrical
attach pads to electrically connect electrical components 12, 14,
and thermal attach pads that are thermally connected to a heat
sink. When both electrical attach pads and thermal attach pads are
provided, the different attach pads can be arranged in an suitable
configuration based, for example, the size and positioning of
electrical components 12, 14, and surface area of printed board 4.
Thermal attach pads and electrical attach pads may be adjacently
located and, in cases, may even be abutting. In further cases,
thermal attach pads and electrical attach may be removed from one
another. For example, a thermal attach pad may be separated from
the nearest electrical attach pad by greater than approximately 1
millimeter, such as greater than approximately 1 centimeter, or
greater than approximately 5 centimeters.
[0063] As an example, FIG. 3 is a schematic plan view of
combination electrical component and thermal bridge attach pad
footprints 76, 78, which can be different areas of printed board 4.
Attach pad footprints 76, 78 illustrate an example arrangement of
electrical component attach pads 80, 92 for mounting electrical
components 12, 14 to printed board 4 and thermal attach pads 82, 94
for mounting thermal bridges 10, 11, respectively, to printed board
4. In the example shown in FIG. 3, attach pads 80, 82, 92, and 94
are shown as dashed lines to indicate that the attach pads are
defined as a recess in footprints 76, 78. For example, a recessed
pad may be an aperture within a solder mask area. In some examples,
one or more of attach pads 80, 82, 92, and 94 may be even with a
plane defined by attach pad footprints 76, 78, or may even extend
above the plane defined by attach pad footprints 76, 78.
[0064] Attach pads 80, 82, 92, 94 can be comprised of any suitable
material, such as tin-lead, silver or gold plated copper. In
general, at least one of thermal attach pads 80, 92 may include a
thermally conductive material, such as copper or a copper alloy, to
facilitate thermal conduction between the at least one thermal
attach pad and a heat sink. Similarly, at least one of electrical
attach pads 82, 94 may include an electrically conductive material
to facilitate electrical conduction between the at least one
electrical attach pad and an electrically conductive trace disposed
in printed board 4. Attach pads 80, 82, 92, 94 may be used, for
example, with surface mounting technology (SMT) techniques for
mounting thermal bridges 10, 11 and electrical components 12, 14 to
printed board 4. Attach pads 80, 82, 92, 94 are disposed at the top
surface 4A (FIG. 2) of printed board 4 and can provide surface to
which thermal bridges 10, 11 and electrical components 12 and 14
can be reflow solder attached.
[0065] In the example of FIG. 3, electrical attach pads 80 define
solder attachment locations on combination footprint 76 for
electrical component 12. Thermal attach pads 82 define solder
attachment locations on combination footprint 76 for thermal bridge
10. As shown in FIG. 3, combination footprint 76 includes
electrical vias 84 and/or 88 that are electrically connected to
electrical attach pads 80 and one or more conductive traces (e.g.,
traces 40 shown in FIG. 2), and thermal vias 86 and/or 90 that are
thermally coupled to thermal attach pads 82 and to a heat sink
(e.g., heat sink 42 shown in FIG. 2). In some examples, combination
footprint 76 may include only in-pad vias 84 and 86, or only
out-of-pad vias 88 and 90, although FIG. 3 illustrates both in-pad
and out-of-pad vias. Electrical vias 84 and/or 88 are electrically
conductive and can each be, for example, a blind hole via that
extends partially through printed board 4 in a z-axis direction
(orthogonal x-y axes are shown in FIG. 3 for ease of description).
Electrical vias 84 can be, for example, similar to electrical vias
38A-38D shown and described with respect to FIG. 2. For example,
electrical vias 84 can be filled vias, as discussed above.
[0066] Thermal vias 86 and/or 90 can be, for example, through-hole
vias that extend through the entire printed board 4 in the z-axis
direction. In other examples, at least one of the electrical vias
84 and/or 88 can be through-hole vias and/or at least one of the
thermal vias 86, 90 can be blind vias. In the example shown in FIG.
3, at least some of thermal vias 86 and/or 90 are electrically
isolated from electrical vias 84 and/or 88, such that the thermal
vias define a dedicated pathway for conduction of heat away from
electrical component 12. Thermal vias 86 and/or 90 can be, for
example, similar to thermal vias 46A, 46B shown and described with
respect to FIG. 2. In cases, one or more thermal vias 86 may be a
filled via while one or more thermal via 90 may be an unfilled
via.
[0067] In the example shown in FIG. 3, electrical vias 84 are
located within electrical attach pads 80 and electrically connected
to electrical attach pads 80, while thermal vias 86 are located
within thermal attach pads 82 and thermally coupled to thermal
attach pads 82. Neither thermal vias 86 nor thermal attach pads 82,
however, are in direct electrical communication with electrical
attach pads 80, and, in some examples, at least some of thermal
vias 86 and thermal attach pads 82 are electrically isolated from
electrical attach pads 80 and electrical vias 84. In other cases,
electrical vias and thermal vias may be located outside of attach
pads 80, 82. For example, assembly 2 may include electrical vias 88
and thermal vias 90, which are positioned such that they do not
overlap with outside attach pads 80 and 82. Although not located
directly in-pad (i.e., in an attach pad), electrical vias 88 are
electrically connected to electrical attach pads 80, and thermal
vias 90 are thermally connected to thermal attach pads 82 through,
for example, peripheral connections not shown in FIG. 3. Electrical
vias 84 located within electrical attach pads 80 and thermal vias
86 located within thermal attach pads 82, as opposed to electrical
vias 88 and thermal vias 90, may, in some cases, improve electrical
and thermal efficiency of printed board assembly 2. As noted,
in-pad electrical vias 84 may be filled with electrically
conductive material, thereby reducing electrical resistance as
compared to electrical via 88, which may be unfilled. Similarly,
thermal vias 86 may be filled with thermally conductive material to
reduced thermal resistance as compared to thermal vias 90, which
may also be unfilled.
[0068] In addition, electrical vias 84 and thermal vias 86 that are
within the attach areas, e.g., substantially overlap with attach
pads 80, 82, respectively, can help reduce a footprint of the
electrical component, thereby increasing the density with which
electrical components can be placed on printed board 4. However,
electrical vias 84 and thermal vias 86 may require filling to
prevent the openings defined by electrical vias 84 and thermal vias
86 from wicking solder away from attach pads 80, 82 during
manufacturing of assembly 2. By contrast, electrical vias 88 and
thermal vias 90, which are located outside of attach pads 80 and
82, can remain unfilled. Unfilled electrical vias 88 and thermal
vias 90 may reduce the cost and time required to create printed
board 4 compared to examples in which printed board 4 includes
filled electrical vias 84 and thermal vias 86.
[0069] Combination footprints 76, 78 may be, for example, sections
of a common printed board 4. Combination footprint 78 may include
features similar to the features of combination footprint 76
discussed above. For example, combination footprint 78 includes
solder mask defined electrical attach pads 92 that defines a solder
attachment location for electrical component 14. Combination
footprint 78 further includes solder mask defined attach pad 94
that defines a solder attachment location for thermal bridge 11.
Combination footprint 78 further includes electrical vias 96, or
100 that define electrically conductive pathways from electrical
attach pads 92 at top surface 4A (FIG. 2) of printed board 4 to one
or more electrically conductive traces of printed board 4.
Electrical vias 96 and/or 100 can be, for example, blind hole or
through-hole vias. Combination footprint 78 further includes
thermal vias 98 and/or 102 that define thermally conductive
pathways between thermal attach pads 94 at top surface 4A of
printed board 4 and, e.g., heat sink 42 of printed board 4.
Electrical vias 96 and/or 100 can be, for example, similar to
electrical vias 54A, 54B (FIG. 2).
[0070] Thermal vias 98 and/or 102 can also be through-hole or blind
hole vias defined through printed board 4. In the example shown in
FIG. 3, at least some of thermal vias 98 and/or 102 are
electrically isolated from electrical vias 96 and/or 100, such that
the thermal vias define a dedicated pathway for conduction of heat
away from electrical component 14. Thermal vias 98 and/or 102 can
be similar to, for example, thermal vias 56A, 56B (FIG. 2).
[0071] Electrical vias 96 are directly electrically connected to
electrical attach pads 92, and thermal vias 98 are in direct
thermal connection with thermal attach pads 94. In other cases,
electrical vias and thermal vias may be located outside of attach
pads 92 and 94, such that the vias are not in either direct
electrical or direct thermal connection with solder pads 92, 94.
For example, assembly 2 can include electrical vias 100 and thermal
vias 102 located outside of attach pads 92 and 94.
[0072] Using a process described in greater detail below,
electrical attach pads 80, 92 may be used to reflow attach
electrical components 12 and 14, respectively, to printed board 4.
FIG. 4 is a schematic plan view of electrical components 12, 14
mounted on respective attach pads 80, 92. As discussed with respect
to FIG. 2, electrical component 12 is enclosed in housing 30 that
includes lid 32. Housing 30 may be configured to mount directly to
conductive patterns on printed board 4 using surface mount
technology techniques and solder pad 80. In the plan view of FIG.
4, lid 32 is shown. Housing 30 and lid 32 are positioned on
combination footprint 76 such that housing 30 does not
substantially overlap with thermal attach pads 82 to which thermal
bridge 10 is configured to connect.
[0073] As FIG. 4 illustrates, electrical component 14 is positioned
on electrical attach pads 92 such that electrical component 14 does
not substantially overlap with thermal attach pads 94 to which
thermal bridge 11 is configured to mechanically attach. Although
not shown in FIG. 4, in some examples, electrical component 14 may
also include a package housing. For example, electrical component
14 may be a metal electrode leadless face (MELF) electrical
component that includes an electrical component positioned within a
capped cylindrical body. The metal electrode leadless face
electrical component may be configured to be mounted using surface
mounting technology techniques.
[0074] After positioning electrical components 12 and 14 over
printed board 4 using electrical attach pads 80, 92, respectively,
thermal bridges 10 and 11 may be positioned over at least a portion
of electrical components 12, 14, respectively, and aligned at least
partially over respective thermal attach pads 82, 94. Electrical
components 12, 14 and thermal bridges 10, 11 can then be
mechanically attached to attach pads 80, 92 and 82, 94,
respectively, using a solder reflow technique. A cleaning operation
may follow reflow attachment to, for example, remove flux residue.
If desired, thermal interface material (TIM) 50 (FIG. 2) can be
introduced between thermal bridge 10 and electrical component 12
before or after thermal bridge 10 is attached to thermal attach pad
82, and thermal interface material (TIM) 60 can be introduced
between thermal bridge 11 and electrical component 14 before or
after thermal bridge 11 is attached to thermal attach pad 94.
[0075] Attach pads 80, 82, 92, 94 are one example of a
configuration of attach pads on printed board 4 and are not
intended to limit to scope of assembly 2. The number, size,
positioning, and configuration of attach pads may vary depending on
the specific electrical components to be attached, the packaging of
the electrical components, and the design of the printed board
arrangement. For example, in some examples, electrical components
12, 14 and/or thermal bridges 10, 11 may not be located on top of
attach pads 80, 82, 92, and 94, but instead one or more of the
attach pads may be in a peripheral area near electrical components
12, 14 and/or thermal bridges 10, 11. In this configuration,
electrical components 12, 14 and/or thermal bridge 10, 11 may
connect to the peripheral attach pads using, for example,
peripheral leads. As another example, attach pads may be reduced in
size if there are no electrical or thermal via, or if electrical or
thermal vias are located outside of are defined by attach pads 80,
82, 92, or 94. As another example, electrical components may be
attached to printed board 4 using, for example, an adhesive. For
example, an electrically conductive adhesive may be used to
electrically and/or mechanically connect electrical components 12,
14 to printed board 4, while a thermally conductive adhesive may be
used to thermally and/or mechanically connect thermal bridges 10,
11 to printed board 4. In some cases, an adhesive may be both
electrically and thermally conductive.
[0076] In the examples illustrated in FIGS. 2-4, thermal vias 46A,
46B, 56A, 56B are show as discrete, substantially cylindrical vias
that extend from combination footprints 76, 78 into printed board
4. The assemblies of this disclosure, however, may use a single
thermally conductive thermal via or a plurality of thermally
conductive thermal vias. A thermal via may be discrete, as
illustrated, or may be integrated into a thermal bridge to form a
unitary component. In some cases, a thermal via may be continuous
and substantially coextensive with a length of thermal bridge
disposed on a printed board. In additional cases, a thermal via may
change shape or cross-sectional area across a direction of a
printed board. The dimensions of a thermal via will vary depending
on a selected geometry of the thermal via. In general, the specific
shape or dimensions of a thermal via may not be critical as long as
the thermal via is thermally conductive. In some examples, at least
one thermal via is electrically isolated from electrical attach
pads, electrical vias, and traces in a printed board
[0077] While thermal bridges can be useful for defining a thermally
conductive path between an electrical component and heat sink 42 of
printed board 4, in some examples, an assembly can include a
thermally conductive path between an electrical component and heat
sink 42 that does not include a common thermal bridge that
straddles at least two sides of an electrical component (directly
or indirectly via a housing). FIG. 5 is a cross-sectional view of
an example assembly 110 that includes thermal management features
for managing the heat generated by electrical components, where the
thermal management features do not include a thermal bridge.
However, assembly 110 can also include a thermal bridge in other
examples.
[0078] As with assembly 2 (FIGS. 1 and 2), electrical components 12
and 14 are mounted to printed board 4. Printed board 4 includes
electrically conductive electrical attach pads 80 and electrical
attach pads 92 (not shown in FIG. 5), electrically conductive
electrical vias 38A-38D, 54A, and 54B, and electrically conductive
traces 40, 44. Printed board 4 also includes thermally conductive
thermal attach pads 82, 94 and thermally conductive thermal vias
46A, 46B, 56A, and 56B that extend through printed board 4.
Thermally conductive attach pads 82, 94 may, in some examples, be
more thermally conductive than electrically conductive electrical
attach pads 80. In addition, electrically conductive electrical
attach pads 80 may, in some examples, be more electrically
conductive than thermally conductive attach pads 82, 94.
[0079] Thermal attach pads 82, 94 are thermally connected to heat
sink 42 via thermal vias 46A, 46B, 56A, and 56B. In the example of
FIG. 5, thermal attach pads 82, 94 are electrically isolated from
electrical attach pads 80, 92, electrical vias 38A-38D, 54A, and
54B, and electrical traces 40, 44 disposed in printed board 4.
However, as discussed, in some examples one or more of thermal
attach pads 82, 94 may be thermally connected to one or more of the
electrical features of printed board 4. Assembly 110 further
includes thermal interface material (TIM) 124 and 126, which are
disposed adjacent electrical component 12 and thermal attach pads
82. Assembly 110 also includes thermal interface material 144 and
146, which are disposed adjacent electrical component 14 and
thermal attach pads 94.
[0080] Assembly 110 is similar to assembly 2 shown in FIGS. 1 and
2. However, rather than including thermal bridges 10, 11 that at
least partially surround electrical components 12, 14,
respectively, to help transfer heat away from at least side
surfaces of electrical components 12, 14, thermal interface
material 124, 126, 144, 146 is positioned to help transfer heat
away from electrical components 12, 14. In particular, thermal
interface material 124, 126 is positioned to at least partially
surround electrical component 12 (and, in the example shown in FIG.
5, housing 30) and thermal interface material 144, 146 is
positioned to at least partially surround electrical component 14.
Thermal interface material 124, 126 is thermally connected to at
least a portion of one of the thermal attach pads 82. Further,
thermal attach pads 82 are thermally connected to heat sink 42 via
thermal vias 46A, 46B. Together, these features defined a thermally
conductive path between electrical component 12 and heat sink 42.
Similarly, thermal interface material 144, 146 is thermally
connected to at least a portion of thermal attach pads 94 that are
thermally connected to heat sink 42 via thermal vias 54A, 54B. In
some examples, the thermally conductive paths are electrically
isolated from traces 40, 44 and, in some examples, all electrically
conductive layers of printed board 4.
[0081] Thermal interface material 124, 126, 144, 146 can be
comprised of material similar to thermal interface material 50, 60
described above with respect to FIG. 2. In addition, sections of
thermal interface material 124, 126, 144, 146 can be comprised of
the same or different thermally conductive materials, and each
section of thermal interface material 124, 126, 144, 146 can
comprise one or more layers of thermally conductive material.
Thermal interface material may disposed adjacent at least a portion
of a top surface, at least a portion of a side surface, or at least
portion of both a top surface and a side surface of an electrical
component. In some cases, a plurality of thermal interface
materials may be disposed adjacent a single electrical component
and a thermal attach pad.
[0082] Regardless of the technique used to apply thermal interface
materials 124, 126, 144, 146 to printed board 4, thermal interface
materials 124, 126, 144, 146 are positioned adjacent an electrical
component and printed board 4 such that they provide a thermal path
between the electrical component and one or more thermal attach
pads of printed board 4.
[0083] Thermal interface material 124, 126 can be positioned to
contact any suitable surface area of electrical component 12. As
discussed above, increasing the surface area from which heat is
transferred away from an electrical component can improve the rate
at which heat can be transferred away from component 12, which, in
some cases, can improve electrical performance of the component 12.
Thus, it may be desirable for thermal interface material 124, 126
to contact at least the entire side surface of housing 30, and, in
some examples, regions of housing 30 and lid 32 adjacent to top
surface 15 of component 12.
[0084] In the example shown in FIG. 5, sections of thermal
interface material 124, 126 are disposed adjacent side surface 13
of electrical component 12 on substantially opposite sides of
component 12. In particular, in the example shown in FIG. 5,
thermal interface material 124, 126 is in direct contact with
housing 30, through which heat generated by electrical component 12
dissipates. Thermal interface material can be disposed adjacent to
more than one side of component 12 (if electrical component 12
defines discrete side surfaces) and can be substantially continuous
around at least a portion of an outer perimeter of component 12 or
arranged as discrete sections of thermal interface material that do
not define a substantially continuous surface.
[0085] Thermal interface material (TIM) 124 is thermally coupled to
thermal pad 82 and thermal via 46B, and thermal interface 126 is
thermally coupled to thermal pad 82 and thermal via 46A. In this
way, thermal interface material 124, 126 defines a thermally
conductive path from electrical component 12 to heat sink 42.
Thermal interface material (TIM) 124, 126 comprise a fillet shape
in the example shown in FIG. 5. However, thermal interface material
124, 126 can be deposited to have any suitable shape.
[0086] Sections of thermal interface material (TIM) 144, 146 are
disposed adjacent side surface 19 of electrical component 14.
Thermal interface material 144, 146 can be positioned to contact
any suitable surface area of electrical component 14. In order to
increase the surface area from which heat can be transferred away
from electrical component 14, it may be desirable for thermal
interface material 144, 146 to contact at least the entire side
surface 19 of component 14, and, in some examples, at least a
portion of or the entire top surface 21 of component 14.
[0087] In the example shown in FIG. 5, sections of thermal
interface material 144, 146 are disposed adjacent side surface 19
of electrical component 14 on substantially opposite sides of
component 14. In particular, in the example shown in FIG. 5,
thermal interface material 124, 126 is in direct contact with
component 14. Thermal interface material can be disposed adjacent
to more than one sides of component 14 (if electrical component 14
defines discrete side surfaces) and can be substantially continuous
around at least a portion of an outer perimeter of component 14 or
arranged as discrete sections of thermal interface material that do
not define a substantially continuous surface.
[0088] Thermal interface material (TIM) 144 is thermally coupled to
thermal pad 94 and thermal via 56B, and thermal interface material
(TIM) 146 is thermally coupled to thermal pad 94 and thermal via
56A. In this way, thermal interface material 144, 146 defines a
thermally conductive path from electrical component 14 to heat sink
42. Thermal interface material 144, 146 comprise a fillet shape in
the example shown in FIG. 5. However, thermal interface material
144, 146 can be deposited to have any suitable shape.
[0089] In some examples, thermal interface materials (TIM) 124,
126, 144, 146 may also be formed from an electrically insulative
material. This can be useful for, for example, prevent shorts
between traces 40, 44 or other electrically conductive pathways of
assembly 2.
[0090] FIG. 6 is a flow diagram illustrating an example technique
for forming an assembly that includes an electrical component, a
printed board (or another substrate) and one or more thermal
management features (e.g., a thermal bridge and/or a thermal
interface material). While the technique is described with respect
to assembly 2 (FIGS. 1 and 2), in other examples, a similar
technique can be used to form assembly 110 (FIG. 5). However, the
technique shown in FIG. 6 may be modified such that a thermal
bridge is not coupled to a printed board.
[0091] According to the example technique, solder paste is applied
to printed board 4, e.g., at a plurality of separate attach pads
80, 82, 92, 94 (FIG. 3) (180). The solder paste is deposited and
arranged on printed board 4 at attach pads defined by a solder
mask. Therefore, discrete sections of the solder paste can be
applied over the appropriate electrical vias (e.g., vias 84, 96
shown in FIG. 3) and/or thermal vias (e.g., thermal vias 86, 98
shown in FIG. 3). The appropriate electrical vias and thermal vias
for each solder pad can be determined, e.g., based on the known
locations for each electrical component and thermal bridge or
thermal interface material.
[0092] The solder paste may be applied using any suitable
technique, such as, for example, a stencil or screen printing
process. In some cases, the solder paste may be applied such that
it is limited to one or more attach pads on printed board 4. The
solder paste may be comprised of any suitable material, such as a
paste that includes particles of solder (e.g., a tin-lead
alloy).
[0093] An electrical component (e.g., component 12 or 14 shown in
FIG. 2) is then placed on the solder paste disposed on printed
board 4 (182). For example, electrical component 12 can be placed
on solder paste at attach pads 80 (FIG. 3) and electrical component
14 can be placed on solder paste at attach pads 92. Any suitable
number of electrical components can be attached to printed board 4.
The electrical components can be placed using any suitable
technique, such as manually or via a computer controlled pick and
place robot.
[0094] The electrical component may be positioned on printed board
4 to electrically connect to an electrically conductive attach
pads. The electrically conductive attach pad may be electrically
connected to electrical vias and traces disposed in printed board
4. For example, electrical component 12 can be placed on solder
paste at attach pads 80 (FIG. 3), which overlie electrically
conductive vias 84 (FIG. 3) that are in electrically conductive
contact with one or more electrically conductive traces 40, 44. As
another example, electrical component 12 can be placed on solder
paste at electrical attach pads 80 (FIG. 3), and positioned such
that electrical contacts of component 12 or housing 30 are in
electrical communication with (e.g., direct or indirect electrical
contact) electrically conductive vias 88, which are in electrical
communication with one or more electrically conductive traces 40,
44.
[0095] As another example, electrical component 14 can be placed on
solder paste at attach pads 92, which overlie electrically
conductive vias 96 (FIG. 3) that are in electrically conductive
contact with one or more electrically conductive traces 40, 44. In
addition or alternatively, electrical component 12 can be placed on
solder paste at attach pads 92 (FIG. 3), and positioned such that
electrical contacts of component 14 are in electrical communication
with (e.g., direct or indirect electrical contact) electrically
conductive vias 100, which are in electrical communication with one
or more electrically conductive traces 40, 44.
[0096] After placing electrical components on printed board 4, one
or more thermal bridges are placed on the solder paste disposed on
printed board 4 (184). For example, thermal bridge 10 can be placed
on printed board 4 in alignment with thermal attach pads 82 (FIG.
3), such that the ends of thermal bridge 10 are at least partially
and, in some examples, entirely positioned on thermal attach pads
82. In addition, thermal bridge 11 can be placed on printed board 4
in alignment with thermal attach pads 94, such that the ends of
thermal bridge 11 are at least partially, and, in some examples,
entirely positioned on thermal attach pads 94. Thermal bridges 10,
11 are positioned on printed board 4 (184) such that thermal
bridges 10, 11 surround at least a portion of a side surface of the
respective electrical components 12, 14, e.g., as shown in FIG.
2.
[0097] Electrical components 12, 14 and thermal bridges 10, 11 are
reflow solder attached to printed board 4 (186). For example,
printed board 4, along with the electrical components 12, 14, and
thermal bridges 10, 11 that have been attached to printed board 4
can be introduced into a reflow oven. The reflow oven may operate
at a temperature high enough to melt solder particles in the solder
paste at the attach pads, thereby binding the electrical component
and thermal bridge to the printed board. Following the reflow
attachment of one or more electrical components and one or more
thermal bridges to printed board 4, all solder flux or other
residues from printed board 4 may be cleaned off using, for
example, a chemical solvent (188).
[0098] In the technique shown in FIG. 6, a thermal interface
material (TIM) is introduced adjacent an electrical component
(190). In examples in which a thermal bridge was positioned at
least partially around a side surface of the electrical component,
the thermal interface material (TIM) can be introduced into a space
between an inner surfaces of the thermal bridge and outer surfaces
of the electrical component or housing in which the electrical
component is positioned. For example, thermal interface material 50
can be introduced through one or both fill ports 16 defined by
thermal bridge 10, such that thermal interface material 50 is
disposed between thermal bridge 10 and housing 30 of electrical
component 12. Utilization of two or more fill ports 16 may be
useful if thermal bridge 10 is relatively large. As another
example, thermal interface material 60 can be introduced through
fill port 18 defined by thermal bridge 11.
[0099] The thermal interface material may be introduced through one
or more fill holes in the thermal bridge or at a different
location, as discussed above. Introduction of the thermal interface
material into the space between a thermal bridge and electrical
component around which the thermal bridge is placed may be
accomplished using any suitable technique. For example, a flowable
thermal interface material, such as a liquid, paste, or grease can
be introduced into the space between the thermal bridge and
respective electrical component via an introduction tool, such as a
syringe, pipette, nozzle, or similar apparatus. The introduction
tool can introduce a predetermined volume of thermal interface
material into the space between a thermal bridge and respective
electrical component. In other examples, however, thermal interface
material may be introduced into the space between the thermal
bridge and respective electrical component until thermal interface
material protrudes out of a fill port, out of an end of a thermal
bridge where the thermal bridge does not cover a side surface of an
electrical component, or out of both locations.
[0100] In some examples, additional thermal interface material is
applied to one or more electrical components of assembly 2 (194).
For example, a fillet of thermal interface material may be attached
to a side surface or a top surface of an electronic component not
covered by thermal bridge material. In this manner, an electrical
component may be entirely encased with thermally conductive
material. The thermal interface material adjacent the one or more
electrical components may be cured (196). The parameters of curing,
as well as the necessity of curing may depend on the type and
volume of thermal interface material used. In some cases, curing
may include oven curing that heats the thermal interface material
to a temperature of at least approximately 150.degree. C. for
approximately one hour.
[0101] FIG. 7 is a flow diagram of an example technique for forming
an assembly including a thermal interface material (TIM) that is
thermally connected to an electrical component and a heat sink of a
printed board. While FIG. 7 is described with reference to assembly
110 of FIG. 5, in other examples, the technique shown in FIG. 7 can
be used to assemble another assembly. As with the technique shown
in FIG. 6, solder paste is applied to printed board 4 at one or
more solder mask defined attach pads to which one or more
electrical components can be attached (180). One or more electrical
components are positioned on printed board 4 and aligned with at
least one attach pad (182). Thereafter, the one or more electrical
components are reflow solder attached to printed board (186), e.g.,
using the techniques described above, and the printed board
assembly is cleaned to remove solder flux or any other residues
(188).
[0102] Thermal interface material is deposited on printed board 4
such that it is adjacent to, and, in some examples, in direct
contact with, at least a portion of a side surface of an electrical
component and a thermal attach pad to provide thermal communication
between the electrical component and the thermal attach pad (198).
For example, with respect to assembly 110 (FIG. 3), thermal
interface material 124 can be deposited on printed board 4 such
that it is adjacent side surface 13 of electrical component 12 and
adjacent thermal attach pad 82. As another example, thermal
interface material 126 can be deposited on printed board 4 such
that it is adjacent (e.g., in direct contact with) side surface 13
of electrical component 12, adjacent thermal attach pad 82, and in
thermal communication (e.g., direct or indirect contact) with
thermal via 46B. In some examples, thermal interface material (TIM)
124 is physically separated from thermal interface material 126,
while in other examples, thermal interface material (TIM) 124 is
substantially contiguous with thermal interface material (TIM) 126.
In addition, thermal interface material (TIM) 144, 146 can be
deposited on printed board 4 such that it is adjacent (e.g., in
direct contact with) side surface 19 of electrical component 14 and
adjacent (e.g., in direct contact with) thermal attach pad 94. In
some examples, thermal interface material (TIM) 144, 146 can be
deposited on printed board 4 such that it is adjacent side surface
19 of electrical component 14, adjacent thermal attach pads 94, and
in thermal communication (e.g., direct or indirect contact) with
thermal vias 56B, 56A.
[0103] Thermal interface material (TIM) can be applied to printed
board 4 using any suitable technique. In one example, thermal
interface material is preshaped into a discrete element and has a
predetermined volume. This preshaped piece of thermal interface
material is then placed adjacent at least a portion of a side
surface of an electrical component that is attached to printed
board 4 and in thermal communication with one or more thermal vias
of printed board. In another example, thermal interface material is
injected or otherwise flowed or poured into the space on printed
board 4 near a thermal via and adjacent at least a portion of a
side surface of an electrical component that is attached to printed
board 4. In some examples, depending on the type of the thermal
interface material utilized, the thermal interface material may
maintain its shape prior to curing. However, in other examples, the
thermal interface material may be partially cured prior to being
deposited on printed board 4. After depositing thermal interface
material (198), the thermal interface material can be cured (196),
e.g., as described above with reference to FIG. 6.
[0104] Although two adjacent electrical components are illustrated
and described in relation to FIGS. 1-5, this disclosure is not
limited a particular number or a particular configuration of
electrical components on a printed board. The thermal management
features (e.g., a thermal interface material alone or in
combination with a thermal bridge, a thermal attach pad in thermal
communication with a heat sink, and, in some examples a thermal via
in thermal communication with a heat sink) are applicable to an
individual component or a plurality components. The plurality of
components may be mounted on a printed board adjacently or
non-adjacently.
[0105] The assemblies of this disclosure may be capable of
providing a number of advantages over conventional thermal
management techniques for printed board assemblies. For example,
the assemblies may include a relatively low impedance thermal path
between an electrical component and one or more heat sinks In some
cases, a thermal bridge and a thermal interface material may
efficiently conduct heat away from a relatively large surface area
of an electrical component to a thermal bridge attach pad. For
example, a thermal bridge that includes copper may efficiently
transfer heat away from a high power electrical component. In
further cases, a fillet of thermal interface material located at a
periphery of an electrical component may efficiently transfer heat
away from the electrical component. For instance, a fillet of
thermal interface material may transfer heat to a thermal bridge
attach pad even without a thermal bridge. Because thermal paths in
the assemblies of this disclosure may be electrically isolated from
an electrical component, a designer may separately optimize thermal
and electrical conduction pathways using the thermal management
features described herein.
[0106] Various embodiments of the invention have been described.
These and other embodiments are within the scope of the following
claims.
* * * * *