U.S. patent application number 15/361947 was filed with the patent office on 2017-05-18 for magnetic field current sensors.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Udo Ausserlechner.
Application Number | 20170138988 15/361947 |
Document ID | / |
Family ID | 46144776 |
Filed Date | 2017-05-18 |
United States Patent
Application |
20170138988 |
Kind Code |
A1 |
Ausserlechner; Udo |
May 18, 2017 |
MAGNETIC FIELD CURRENT SENSORS
Abstract
A magnetic field current sensor including a die having at least
one magnetic field sensing element; a plurality of contacts
disposed in a first plane and coupled to the die; a conductor
comprising first and second contact portions, the first and second
contacts electrically coupled and disposed in a second plane
different from the first plane, and the conductor coupled to and
electrically isolated from the die; and a mold body enclosing the
die, the plurality of contacts, and the first and second contact
portions.
Inventors: |
Ausserlechner; Udo;
(Villach, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
46144776 |
Appl. No.: |
15/361947 |
Filed: |
November 28, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12963817 |
Dec 9, 2010 |
|
|
|
15361947 |
|
|
|
|
12963787 |
Dec 9, 2010 |
9476915 |
|
|
12963817 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2224/48091
20130101; H01L 2924/14 20130101; H01L 2224/48091 20130101; G01R
15/202 20130101; G01R 33/072 20130101; H01L 2224/84801 20130101;
H01L 2224/8485 20130101; H01L 2924/14 20130101; H01L 2924/181
20130101; H01L 2224/37147 20130101; H01L 2924/10253 20130101; H01L
2224/83801 20130101; H01L 43/14 20130101; H01L 24/34 20130101; H01L
2224/84801 20130101; H01L 2224/37147 20130101; H01L 43/06 20130101;
H01L 2924/00014 20130101; H01L 2924/00 20130101; H01L 2924/00
20130101; H01L 2924/00014 20130101; H01L 2924/00014 20130101; H01L
2924/00 20130101; G01R 19/0092 20130101; H01L 2924/00014 20130101;
H01L 2924/181 20130101; H01L 24/37 20130101; H01L 2224/8485
20130101; H01L 43/04 20130101; H01L 2924/10253 20130101; H01L
2224/83801 20130101; H01L 2924/00012 20130101 |
International
Class: |
G01R 15/20 20060101
G01R015/20; H01L 43/14 20060101 H01L043/14; H01L 43/04 20060101
H01L043/04; H01L 43/06 20060101 H01L043/06; G01R 19/00 20060101
G01R019/00; G01R 33/07 20060101 G01R033/07 |
Claims
1. A magnetic field current sensor comprising: a die having at
least one magnetic field sensing element; a plurality of contacts
disposed in a first plane and coupled to the die; a conductor
comprising first and second contact portions, the first and second
contacts electrically coupled and disposed in a second plane
different from the first plane, and the conductor coupled to and
electrically isolated from the die; and a mold body enclosing the
die, the plurality of contacts, and the first and second contact
portions.
2. The magnetic field current sensor of claim 1, further comprising
a ring-shaped seal arranged adjacent the mold body to prevent
creepage current between the first and second planes along a
surface of the mold body.
3. The magnetic field current sensor of claim 2, wherein the
ring-shaped seal comprises an O-ring.
4. The magnetic field current sensor of claim 1, wherein the seal
comprises at least part of a shoulder structure configured for
mounting in a sensor module.
5. The magnetic field current sensor of claim 4, wherein the sensor
module is configured to be mounted to a printed circuit board.
6. The magnetic field current sensor of claim 1, wherein the seal
is arranged between the first and second planes.
7. The magnetic field current sensor of claim 1, wherein the seal
is disposed in one of the first or second planes.
8. The magnetic field current sensor of claim 1, wherein the
plurality of contacts couple the die to a leadframe.
9. The magnetic field current sensor of claim 1, wherein the first
plane is above the second plane.
10. The magnetic field current sensor of claim 9, wherein the die
is between the first and second planes.
11. The magnetic field current sensor of claim 1, wherein the
conductor comprises first and second pillar portions and a
footprint portion, the first and second pillar portions coupling
the first and second contact portions, respectively, to the
footprint portion.
Description
TECHNICAL FIELD
[0001] The invention relates generally to integrated circuits and
more particularly to integrated circuit magnetic current
sensors.
BACKGROUND
[0002] Desired properties of galvanically isolated integrated
circuit (IC) magnetic field current sensors include high magnetic
sensitivity; high mechanical stability and reliability; low stress
influence to Hall sensor elements near chip borders; high thermal
uniformity and low thermal gradients; high isolation voltage;
minimized electromigration issues; and low manufacturing costs.
Conventional current sensors can include one or more features or be
manufactured in ways that aim to address these desired
properties.
[0003] For example, some current sensors use the leadframe as a
current lead. Others also include a magnetic core. Such sensors,
however, can be expensive to manufacture.
[0004] Other current sensors include additional layers, such as
special magnetic layers on top of the silicon die or a thick metal
layer formed on the isolation layer. These sensors are also
expensive, and the former can be sensitive to disturbance fields
and can suffer from drawbacks related to the positioning of the
current leading wire outside of the IC.
[0005] Therefore, there is a need for a galvanically isolated IC
magnetic field current sensor having desired properties while
minimizing drawbacks.
SUMMARY
[0006] In an embodiment, a method of forming a conductor clip for a
magnetic field current sensor comprises forming a footprint
portion; forming first and second contact portions; and forming
first and second pillar portions coupling the first and second
contact portions, respectively, to the footprint portion, the first
and second pillar portions having a constant height and being at
approximate right angles to the first and second contact portions
and the footprint portion.
[0007] In another embodiment, a magnetic field current sensor
comprises a semiconductor die having at least one magnetic field
sensor element; an inorganic insulating layer having at least one
solderable metal plate on a first surface thereof; and a current
conductor coupled to the semiconductor die via the insulating layer
by a solder connection between the current conductor and the at
least one solderable metal plate such that when a current is
applied to the sensor less than about 10% flows through the solder
connection.
[0008] In another embodiment, a method comprises forming a grid of
grooves in a first surface of a copper wafer; coupling the first
surface of the copper wafer to a first surface of a semiconductor
wafer; forming a grid of grooves in a second surface of the copper
wafer, the grid of grooves formed in the first surface aligning
with the grid of grooves formed in the second surface such that a
portion of the copper wafer can be removed to leave a plurality of
copper blocks coupled to the first surface of the semiconductor
wafer; and singulate the semiconductor wafer such that each of the
plurality of copper blocks is coupled to a semiconductor die.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0010] FIG. 1 depicts a current conductor clip according to an
embodiment.
[0011] FIG. 2A depicts sensor components according to an
embodiment.
[0012] FIG. 2B depicts a sensor package according to an
embodiment.
[0013] FIG. 3A depicts a top view of sensor components according to
an embodiment.
[0014] FIG. 3B depicts a side sectional view of the sensor
components of FIG. 3A.
[0015] FIG. 4A depicts a top view of sensor components according to
an embodiment.
[0016] FIG. 4B depicts a side sectional view of the sensor
components of FIG. 4A.
[0017] FIG. 5A depicts a top view of sensor components according to
an embodiment.
[0018] FIG. 5B depicts a side sectional view of the sensor
components of FIG. 5A.
[0019] FIG. 6 depicts simulation results in a partial view of a
current conductor clip according to an embodiment.
[0020] FIG. 7 depicts simulation results of magnetic field versus
z-position of the conductor clip of FIG. 6.
[0021] FIG. 8 depicts simulation results in a partial view of a
current conductor clip according to an embodiment.
[0022] FIG. 9 depicts simulation results in a partial view of a
current conductor clip according to an embodiment.
[0023] FIG. 10 depicts simulation results of flux density of the
conductor clip of FIG. 9.
[0024] FIG. 11 depicts simulation results in a partial view of a
current conductor clip according to an embodiment.
[0025] FIG. 12 depicts simulation results in a partial view of a
current conductor clip according to an embodiment.
[0026] FIG. 13A depicts a top view of sensor components according
to an embodiment.
[0027] FIG. 13B depicts a side sectional view of the sensor
components of FIG. 13A.
[0028] FIG. 14A depicts a top view of sensor components according
to an embodiment.
[0029] FIG. 14B depicts a side sectional view of the sensor
components of FIG. 14A.
[0030] FIG. 15 is a flowchart of a manufacturing process according
to an embodiment.
[0031] FIG. 16 is a side sectional view of a sensor package
according to an embodiment.
[0032] FIG. 17 is a side sectional view of a sensor package
according to an embodiment.
[0033] FIG. 18 is a side sectional view of a sensor package
according to an embodiment.
[0034] FIG. 19 is a side sectional view of a sensor package
according to an embodiment.
[0035] FIG. 20 is a side sectional view of a sensor package
according to an embodiment.
[0036] FIG. 21 is a side sectional view of a sensor package
according to an embodiment.
[0037] FIG. 22 is a side sectional view of a sensor package
according to an embodiment.
[0038] FIG. 23 is a side sectional view of a sensor package
according to an embodiment.
[0039] FIG. 24 is a side sectional view of a sensor package
according to an embodiment.
[0040] FIG. 25 is a side sectional view of a sensor package
according to an embodiment.
[0041] FIG. 26 is a side sectional view of a sensor package
according to an embodiment.
[0042] FIG. 27 is a side sectional view of a sensor package mounted
to a PCB according to an embodiment.
[0043] FIG. 28 is a side sectional view of a sensor package mounted
to a PCB according to an embodiment.
[0044] FIG. 29 is a side sectional view of a sensor package mounted
to a PCB according to an embodiment.
[0045] FIG. 30A depicts a side sectional view of sensor components
mounted to bus bars according to an embodiment.
[0046] FIG. 30B depicts a top view of the sensor components of FIG.
13A.
[0047] FIG. 31A depicts a side sectional view of sensor components
according to an embodiment.
[0048] FIG. 31B depicts a top view of the sensor components of FIG.
31A.
[0049] FIG. 32 is a top view of clip sheet metal according to an
embodiment.
[0050] FIG. 33 is a top view of clip sheet metal according to an
embodiment.
[0051] FIG. 34 is a top view of clip sheet metal according to an
embodiment.
[0052] FIG. 35 is a flowchart of a manufacturing process according
to an embodiment.
[0053] FIG. 36A depicts a top view of sensor components according
to an embodiment.
[0054] FIG. 36B depicts a side sectional view of the sensor
components of FIG. 36A.
[0055] FIG. 37A depicts a top view of sensor components according
to an embodiment.
[0056] FIG. 37B depicts a side sectional view of the sensor
components of FIG. 37A.
[0057] FIG. 38A is an exploded view of current sensor components
according to an embodiment.
[0058] FIG. 38B is a top view of the current sensor components of
FIG. 38A.
[0059] FIG. 38C is a bottom view of the current sensor components
of FIGS. 38A and 38B.
[0060] FIG. 39 is a perspective view of a current sensor comprising
a copper block according to an embodiment.
[0061] FIG. 40 is a flowchart of a process for manufacturing a
current sensor comprising a copper block according to an
embodiment.
[0062] FIG. 41 is a perspective view of copper blocks mounted on a
piece of silicon wafer prior to singulation according to an
embodiment.
[0063] FIG. 42 is view of a copper block coupled to a silicon die
and a conductor according to an embodiment.
[0064] FIG. 43 is a partial side sectional view of sensor
components according to an embodiment.
[0065] FIG. 44A depicts a top view of a current sensor package
according to an embodiment.
[0066] FIG. 44B depicts a bottom view of the current sensor package
of FIG. 44A.
[0067] FIG. 44C depicts sensor components of the sensor of FIGS.
44A and 44B.
[0068] FIG. 45A depicts a top view of a current sensor package
according to an embodiment.
[0069] FIG. 45B depicts a bottom view of the current sensor package
of FIG. 45A.
[0070] FIG. 45C depicts sensor components of the sensor of FIGS.
45A and 45B.
[0071] FIG. 46A is a perspective view of sensor components
according to an embodiment.
[0072] FIG. 46B is a semi-transparent side sectional view of sensor
components of FIG. 46A.
[0073] FIG. 47 is a side sectional view of sensor components
according to an embodiment.
[0074] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0075] The invention relates to an IC magnetic field current sensor
having a three-dimensional current conductor. In embodiments,
three-dimensional conductors can avoid long lateral dimensions that
increase internal resistance and can also be positioned closer to
the die in order to maximize the magnetic field at sensor element
locations. Additionally, a three-dimensional current conductor
fabricated from a single piece can reduce or eliminate
electromigration issues. Embodiments can also keep the resistance
low, such as on the order of about 100 .mu..OMEGA. in one
embodiment, and provide good galvanic isolation, such as up to
about 10 kV in embodiments. Embodiments can also include current
contacts and low-voltage sensor pins arranged on different levels.
Embodiments can thereby provide significant voltage isolation at
relatively low cost.
[0076] FIG. 1 depicts a current conductor clip 100 according to an
embodiment. In an embodiment, clip 100 comprises a central or
footprint portion 102, a first pillar portion 104, a first contact
106, a second pillar portion 108 and a second contact 110.
[0077] In an embodiment, footprint portion 102 comprises one or
more notches 112. Notch 112 can be configured in size, shape and/or
position to shape and amplify current flow through clip 100 and
near magnetic field sensors. In the embodiment of FIG. 1, notch 112
is about 0.3 mm by about 0.5 mm. As depicted, the internal end of
notch 112 is rounded, though this can vary in other embodiments. In
other embodiments, notch 112 can be longer or shorter, narrower or
wider, non-symmetric, can comprise an aperture through footprint
portion 102, or can have some other configuration.
[0078] Footprint portion 102 is generally sized and shaped such
that it is large enough to make good mechanical contact with a die
on which it is mounted and also to support clip 100 during
manufacturing without causing it to tip or fall, while remaining
smaller than the die as clip 100 should be placed a sufficient
lateral distance from the sawing edge of the die in order to
achieve a desired or required voltage isolation. In embodiments,
the voltage isolation is in a range of about 1 kV to about 10 kV,
with footprint portion 102 separated from the sawing edge of the
die by about 0.1 mm to about 1 mm. As depicted in FIG. 1, footprint
portion 102 is about 1 mm by about 1 mm. If a die on which it is
mounted is about, for example, 2.7 mm by about 2.7 mm, and clip 100
is mounted in the approximate center, the lateral distance between
footprint portion 102 and the sawing edge of the die is about 0.85
mm. Thus, with appropriate mold compound on top of the die, the
distance is sufficient to withstand voltages up to about 10 kV.
[0079] First and second pillar portions 104 and 108 couple
footprint portion 102 to first and second contacts 106 and 110,
respectively and are at approximately right angles to footprint
portion 102 and contacts 106 and 110. In embodiments, first and
second pillar portions 104 and 108 are of a monotonic height such
that they separate the first and second contacts 106 110,
respectively, from the footprint portion by a vertical distance and
are long enough to provide a sufficient distance between contacts
106 and 110 and the sawing edge of the die because one or both of
contacts 106 and 110 can overlap with the sawing edge without
unnecessarily increasing the current path length in clip 100. With
respect to the monotonic nature of the first and second pillar
portions 104 and 108, clip 100 extends from contacts 106 and 110 to
footprint portion 102 only in a single direction, without reversing
direction or bending up and then down. In other words, if contacts
106 and 110 are at a first height and footprint portion 102 is at a
second height, then a function which describes the height versus
lateral dimensions is monotonic in a mathematical sense, meaning
that its derivative does not change sign.
[0080] In the embodiment of FIG. 1, the overall height of clip 100
is about 0.7 mm, with the thickness being about 0.2 mm. Thus, the
vertical distance between contacts 106 and 110 and the sawing edge
of the die on which clip 100 is mounted (which is not shown in FIG.
1) is about 0.5 mm. The height of clip 100 should not be too large,
however, because this can increase the resistance of clip 100 and
consequently the influence the power dissipation and
temperature.
[0081] Contacts 106 and 110 are identical in an embodiment.
Contacts 106 and 100 should be large enough to offer a sufficient
surface and, desirably, be larger than the die. Thus, as depicted
in FIG. 1, contacts 106 and 110 can overlap the sawing edge of the
die (not depicted) and are about 3 mm by about 1.2 mm
[0082] As previously mentioned, the thickness of clip 100 in FIG. 1
is about 0.2 mm. Clip 100 should be thick enough to ensure
mechanical stability during assembly and during subsequent
operation of the device. A thicker clip also reduces the internal
resistance of the clip. On the other hand, the thickness of clip
100 is limited by the manufacturability of the clip: clip 100 is
punched and pressed, bent or otherwise formed into shape and needs
to be done so with reasonable accuracy, which limits the overall
thickness. Further, if clip 100 comprises notch 112, the width of
notch 112 typically is equal to or greater than the thickness of
clip 100, regardless of whether notch 112 is formed by punching,
etching or some other methodology. Thus, clip 100 is about 0.2 mm
thick in the embodiment of FIG. 1, which the same as the width of
notch 112 as depicted. For large current ranges, however, clip 100
need not include notch 112, and the omission of notch 112 can
simplify manufacturing and allow for thicker clips, such as up to
about 1 mm or more in embodiments.
[0083] In general, clip 100 comprises a material that is a good
electrical and thermal conductor and nonmagnetic, such as having
ferromagnetic impurities that are less than 0.1%. It is helpful for
the material to be soft enough to facilitate punching, forming,
pressing, trimming and other steps during manufacturing. In one
embodiment, clip 100 comprises copper. In another embodiment, clip
100 comprises aluminum.
[0084] FIG. 2 depicts a sensor package 200 comprising clip 100.
FIG. 2A depicts package 200 before molding, while FIG. 2B depicts
package 220 after molding.
[0085] In FIG. 2A, clip 100 is coupled is coupled to a die 202,
which in turn is coupled to a base plate or die paddle 203. In
embodiments, die 202 is coupled to die paddle 203 by an adhesive,
solder paste or some other suitable means. Die paddle 203 is a
conductive base plate, and because the magnetic field in clip 100
can induce eddy currents in the die paddle, die 202 is made as
thick as possible in an embodiment to maximize the distance between
clip 100 and die paddle 203. As depicted, clip 100 is coupled to a
top of die 202, though in other embodiments the bottom of die 202
can be used. In an embodiment, a galvanic isolation layer 204 is
between clip 100 and die 202. Also depicted in FIG. 2A are signal
output, ground and supply voltage reference pins 206a, 206b and
206c and related bond wires 208a, 208b and 208c, as well as two
capacitors: 210a between signal pin 206a and ground pin 206b, and
210b between ground pin 206b and supply pin 206c.
[0086] In FIG. 2B, sensor package 200 is depicted after molding. A
mold body 212 encloses the components of sensor package 200, with
contacts 106 and 110 and sensor pins 206a, 206b and 206c remaining
external to mold body 212.
[0087] FIG. 3 depicts clip 100 and die 202. FIG. 3A is a top plan
view, and FIG. 3B is a cross-sectional view taken along A-A' shown
in FIG. 3A. Die 202 includes a plurality of magnetic field sensors
214a, 214b and 214c. In an embodiment, magnetic field sensors 214a,
214b and 214c are Hall plates, which are sensitive to the magnetic
field component perpendicular to the surface of die 202. The active
volume of sensors 214a, 214b and 214c is typically about 20 .mu.m
to about 200 .mu.m in length and width and less than about 10 .mu.m
thick, such as about 3 .mu.m in an embodiment. To remove offset, a
spinning current technique is utilized, such as with Hall plates
having geometries that are 90 degrees symmetric.
[0088] Magnetic field sensors 214a, 214b and 214c are positioned on
die 202 at locations which the current through clip 100 experiences
extreme values, for example along the boundary of clip 100. If clip
100 comprises one or more notches 112, an optimum position for a
magnetic field sensor 214a, 214b and/or 214c is adjacent an end of
notch 112, as notch 112 causes strongly inhomogeneous current
density and consequently the magnetic field is more effectively
localized near an end thereof. More information regarding notch 112
and this effect can be found in co-owned U.S. patent application
Ser. No. 12/711,471, which is incorporated herein by reference in
its entirety.
[0089] If the distance between the active volume of magnetic field
sensors 214a, 214b and 214c and the opposing surface of clip 100 is
small, such as about 5 .mu.m to about 50 .mu.m in embodiments, half
of the active volume should overlap clip 100 in an embodiment. In
another embodiment comprising notch 112, the active volume can be
positioned predominantly or entirely adjacent notch 112, such that
only a small part or no part of magnetic field sensor 214a, 214b
and/or 214c overlaps the conductive material of clip 100.
[0090] To remove undesirable background magnetic field effects on
magnetic field sensors 214a, 214b and 214c, higher order
differential field measurements can be used, such as are described
in co-owned U.S. patent application Ser. No. 12/630,596, which is
incorporated herein by reference in its entirety. In essence,
magnetic field sensors 214a, 214b and 214c need not each be located
at magnetic field extremes, though it can be advantageous for each
to experience a strong magnetic field. This is not always possible,
however, absent complicated chip design and increased ohmic
resistance of clip 100. Therefore, another viable option is to
position less than all magnetic field sensors 214a, 214b and 214c
at points of maximum field from current through clip 100. Such a
configuration is the one depicted in FIG. 3, with magnetic field
sensor 214b positioned with respect to the end of notch 112 and
magnetic field sensors 214a and 214c positioned on either side
thereof, after and before sensor 214b with respect to the direction
of current flow in clip 100.
[0091] FIG. 4 depicts another embodiment of clip 100 and die 202,
in which the axis of magnetic field sensors 214a, 214b and 214c is
rotated 90 degrees on the surface of die 202. As can be seen in
FIG. 4A, the distance between magnetic field sensors 214a and 214b
is less than the distance between magnetic field sensors 214b and
214c. In embodiments, these distances can be chosen arbitrarily so
that the positions of magnetic field sensors 214a, 214b and 214c
match with one or several locations of strong or extreme magnetic
field due to current in clip 100.
[0092] For compatibility with higher current ranges, clip 100 omits
notch 112 which increases the resistance of clip 100, as depicted
in FIG. 5. The configuration of magnetic field sensors 214a, 214b
and 214c is similar to that of the embodiment depicted in FIG. 4
but with the addition of a fourth magnetic field sensor 214d. Two
magnetic field sensors 214b and 214c are arranged near the middle
of clip 100, and the signals of magnetic field sensors 214a, 214b,
214c and 214d can be combined as follows:
Total signal=(d-a)-3*(c-b)
where a refers to the signal of magnetic field sensor 214a, b
refers to the signal of magnetic field sensor 214b, etc., and the
magnetic field sensors 214a, 214b, 214c and 214d are equidistantly
spaced.
[0093] If magnetic field sensors 214a, 214b, 214c and 214d are not
equidistantly spaced, each signal is then multiplied by an
appropriate scaling factor, such as is described in previously
mentioned U.S. patent application Ser. No. 12/630,596, which has
been incorporated herein by reference.
[0094] As can be seen, at least one advantage relates to the
versatility of embodiments of clip 100 and the package concept.
Small changes in the thickness, width, notch geometry and/or other
characteristics of clip 100 can adjust or customize the resistance
of clip 100. Further, as illustrated by FIGS. 3-5 in particular,
the number and configuration of the magnetic field sensors can also
be customized for signal processing, such as by selecting the
desired sensor or sensors by dedicated metal masks, fusible links,
zener zapping, memory such as EEPROM, or in some other suitable
way. The isolation hardness may also be adjusted. For example, for
low isolation requirements, such as for about 1 kV, inexpensive
layers like polyimide can be used. For more moderate isolation,
such as about 4 kV, thicker polyimide or thin nitrides or oxides
can be used. For maximum isolation, such as up to about 10 kV,
silicon dioxide, such as about 15 .mu.m thick in an embodiment, can
be used. In general, therefore, it is possible to manufacture an
entire family of current sensors with full scale current ranges of,
for example, about 5 A to about 500 A, at very low cost.
[0095] FIG. 6 depicts simulation results for an embodiment of clip
100. Only half of clip 100 is depicted, and notch 112 is omitted in
this embodiment. Clip 100, which comprises copper, is coupled to a
bus bar 602, which is about 5 mm wide by about 1 mm thick. The
narrow portion of clip 100 is about 1 mm wide and about 0.2 mm
thick, current streamlines therethrough are shown in FIG. 6. 0 V is
defined at the left side of clip 100, while 0.5 mV is defined at
the right side of bus bar 602, and the current is 5.5365 A. Power
dissipated by clip 100 is 4.2556 mW, and the resistance of clip 100
in the embodiment of FIG. 6 is 140 .mu..OMEGA.. The magnetic flux
density 50 .mu.m below clip 100 is about 2.05 mT, or about 370
.mu.T/A. At a full current range of 75 A, the magnetic field (B) is
about 27.8 mT at each side of clip 100. FIG. 6 depicts the Bz field
at z=-50 .mu.m. The bottom surface of clip 100 is at z=0 mm.
Magnetic field sensors, such as Hall elements, would be positioned
about 20 .mu.m to about 50 .mu.m below this point in an
embodiment.
[0096] FIG. 7 depicts the decline of the magnetic field versus
z-position near the edge of clip 100 (i.e., at about y=-0.5 mm).
For example, if z changes by about 0.1 mm, the magnetic field
decreases from about 2 mT to about 1.5 mT, or about 0.3%/.mu.m. If
the adhesive layer and thickness of clip 100 change, such as due to
temperature changes or humidity, so too can the vertical distance
change, possibly leading to errors in the calibration of the
current sensor. Because the absolute value of the thicknesses is
also small, however, any percentage change will be correspondingly
small. Therefore, material expansion is not a significant problem
in view of the thin layers used.
[0097] FIG. 8 depicts simulation results for another embodiment of
clip 100, this time comprising a notch 112. Notch 112 is about 0.2
mm wide in this embodiment, such that the remaining cross-section
for the current at the most narrow point of clip 100 is about 0.5
mm by about 0.2 mm, or about 0.1 mm.sup.2. The current is 4.361 A,
and the dissipated power in clip 100 is 3.56 mW. The resistance of
clip 100 in this embodiment is about 187 .mu..OMEGA., which
corresponds to a full-scale current of up to about 53.5 A. The
magnetic field 50 .mu.m below footprint 102 of clip 100 and near
notch 112 is 3 mT, whereas the magnetic field is only about -2 mT
near the opposite edge of clip 100. If a first magnetic field
sensor, such as a Hall plate, is arranged near the tip of notch 112
and second magnetic field sensor on the other side of the narrow
portion of footprint 102, and if the total signal is calculated as
the difference therebetween, the result is 5 mT/4.361 A. If each
magnetic field sensor has a stochastic residual offset error of 50
.mu.T, the offset error in the total signal is about 71 .mu.T, and
the ratio of signal over offset is about 16.2*A.sup.-1. Thus, the
offset error of the sensor is about 0.062 A. The embodiment of FIG.
8 can also be used for a 25 A full-range because the full-scale
magnetic field is about 20 mT. Comparing the embodiment of FIG. 8,
in which clip 100 comprises notch 112, and the embodiment of FIG.
6, which omitted notch 112, the magnetic field in the embodiment of
FIG. 8 is nearly double that of the embodiment of FIG. 6, whereas
the increase in resistance is only 187/140, or about 134%.
[0098] FIG. 9 depicts simulation results for another embodiment of
clip 100 in which notch 112 in footprint portion 102 comprises an
aperture. Such a configuration can be suitable for lower currents,
when an even narrower constriction in footprint portion 102 can be
beneficial, and offer advantages over an embodiment in which a very
long, narrow notch is used, as such a notch can reduce the
mechanical stability of clip 100. In the embodiment of FIG. 9, the
two connecting portions 902 of footprint portion 102 have
cross-sections of about 0.08 mm.sup.2. The current in clip 100 is
about 4.43 A, power dissipation about 3.6 mW, internal resistance
about 185 .mu..OMEGA., comparable to other embodiments discussed
herein above. The magnetic field, however, is lower, with extremes
being about 340 .mu.T/A. Refer also to FIG. 10.
[0099] If four magnetic field sensors are used, such as in the
embodiment of FIG. 5, and positioned at y=-0.6 mm, -0.2 mm, 0.2 mm
and 0.6 mm, the total signal is about 10.2 mT. If each magnetic
field sensor has a stochastic residual offset of 50 .mu.T, the
overall offset in the signal is about 224 .mu.T, and the signal to
offset ratio is 10.3*A.sup.-1. Thus, the offset error of the
embodiment of FIG. 9 is about 0.1 A. In general, the embodiment of
FIG. 9, with an aperture 902 in footprint portion 102, has about
the same resistance, 61% more offset error, better crosstalk
suppression and greater mechanical stability than an embodiment
having a notch longer than at least half the width of footprint
portion 102.
[0100] Another embodiment of clip 100 is depicted in FIGS. 11 and
12, in which clip 100 is thicker, as can be suitable for higher
currents. Clip 100 is also wider, such as about 5 mm at contact
areas 106 and 110 and about 2.3 mm at footprint portion 102. Clip
100 can be coupled to a die that is about 2 mm by about 3.5 mm,
with a lateral separation distance of about 0.5 mm. In this
embodiment, the current is about 16.42 A and the power dissipation
is about 9.74 mW, with an internal resistance of about 36
.mu..OMEGA.. Such an embodiment can be suitable for a current range
of at least about 277 A. The magnetic field 50 .mu.m below
footprint portion 102 of clip 100 is about 2.5 mT at 16.42 A for
152 .mu.T/A, or about 42 mT at 277 A. If two magnetic field sensors
are used, positioned left and right of footprint portion 102 at a
distance of about 2.5 mm, the resulting signal is about 304
.mu.T/A. If the stochastic residual offset of each magnetic field
sensor is 50 .mu.T, the offset error of the sensor is about 71
.mu.T, which is equivalent to about 0.23 A, or 0.084% of the
full-scale current of 277 A. The current density in the solder
joint between the bus bar and the contact portions of clip 100 is
about 100 A/mm.sup.2 to about 300 A/mm.sup.2.
[0101] Because clip 100 is 400 .mu.m thick in this embodiment, it
is not necessary to keep the isolation layers less than 50 .mu.m
thick. Therefore, it is possible to attach clip 100 to the rear
side of the die if the die is thin, such as about 60 .mu.m in one
embodiment. Refer, for example to FIG. 13, which depicts a thinner
example embodiment of die 202.
[0102] In the embodiment of FIG. 13, isolation layer 204 is applied
to the bottom side of die 202, and magnetic field sensors 214a,
214b, 214c and 214d are arranged at the top side of die 202, as
depicted. This provides a new perspective for manufacturing the
current sensor, as a single leadframe can be used, which comprises
clip 100 and the leads (refer, for example to FIG. 2) of the
sensor. This can simplify manufacturing by utilizing only one
curing process to attach die 202 to clip 100. Further, footprint
portion 102 can be larger because there is little or no risk of a
short between clip 100 and the bond wires (refer, for example, to
FIG. 2) because they are now on opposing sides of die 202. The
placement of bond pads on die 202 should be chosen so that the bond
pads are supported by footprint 102 of clip 100. If the bond pads
would be near the perimeter of die 202, which as previously
mentioned can extend over clip 100, the forces during the wire
bonding process could damage or break die 202.
[0103] FIG. 14 depicts another embodiment of clip 100 and die 202,
which comprises two magnetic field sensors 214a and 214b. It can be
seen in FIG. 14A that magnetic field sensor 214a is positioned at
the center of clip 100, and magnetic field sensor 214b is
positioned nearer the edge of clip 100. This embodiment
demonstrates that a high degree of symmetry is not necessary, and
the magnetic field sensors need not be symmetric with respect to
the center line of clip 100.
[0104] Advantages of arranging two magnetic field sensors closer
together than the width of clip 100, as in FIG. 14, include better
rejection of background magnetic fields; less effect on total
signal of small tolerances in position due to inaccuracies during
the die attach process; and potential availability of positions
underneath clip 100 where the magnetic field strength depends less
on frequency, which could be found via numerical simulation
techniques. A disadvantage, however, is smaller magnetic fields
from the current through clip 100. In general, however, if some
sensitivity can be sacrificed, magnetic bandwidth of the system can
be increased.
[0105] FIG. 15 is a flowchart of an exemplary manufacturing process
1500 for embodiments of a sensor package as discussed herein above.
At 1502, a leadframe with sensor pins and an elevated die paddle
are provided. In an embodiment, the die paddle has a smaller
surface area than the die such that the sawing edge of the die
extends beyond the die paddle along its perimeter by at least about
several tenths of a millimeter.
[0106] At 1504, a die is provided. The die can have a thickness of
about 60 .mu.m in an embodiment, though this can vary in other
embodiments.
[0107] At 1506, an insulation layer is provided between the die
paddle and the bottom side of the die. In an embodiment, the
insulation layer is applied to the die surface during a
semiconductor manufacturing process on wafer level, before
singulation of the dies. The insulation layer can also comprise a
ceramic, porcelain, or glass platelet or a KAPTON foil in
embodiments. The insulation layer is larger than the die paddle, or
even larger than the die, in an embodiment to ensure voltage
isolation between the die paddle and the sawing edge of the
die.
[0108] At 1508, the die is coupled to the die paddle with an
interstitial isolation layer. In embodiments, the coupling is by
adhesive, soldering or some other suitable means. The top side of
the die includes magnetic field sensors and bond pads and is spaced
further from the die paddle than from the bottom side of the
die.
[0109] At 1510, the bond pads are coupled to the pins of the
leadframe. In an embodiment, the coupling is by bond wires.
[0110] At 1512, the die and a portion of the sensor pins are
enclosed with mold compound, such as by transfer molding.
[0111] At 1514, the pins of the sensor excluding the ground pin are
cut from the leadframe, and at least one of two contacts for the
current clip is cut from the leadframe in an embodiment.
End-of-line testing and calibration of the current sensor are
performed, and remaining connections between the sensor package and
the leadframe are cut.
[0112] Various customizations are also possible according to
embodiments. For example, the contacts can be elongated if it is
desired to vary the distance between the solder joints and the
magnetic field sensors. It can be necessary to do this if the
solder joints need to be plated with nickel, which is magnetic and
can therefore affect the magnetic fields and thus the calibration
of the current sensor. The magnetism of the nickel can be reduced,
for example, by alloying with phosphorous, or the nickel-plated
surfaces can be laterally shifted until they are sufficiently
distal with respect to the magnetic field sensor element and to the
regions of increased magnetic field.
[0113] There are also many possibilities for configuring the
current contacts and sensor pins. In FIG. 16, sensor package 200 is
configured for a through-hole application, and in FIG. 17 for a
surface-mount application. In the embodiments of FIGS. 16 and 17,
die paddle 203 is configured such that sensor pins 206 are at about
the same height as die 202 so that bond wires 208 may be made
essentially flat in order to have pillar portions 104 and 108 as
short as possible. This can be particularly helpful in
surface-mount applications in which the bond wires "dive"
underneath the clip contacts. In the embodiment of FIG. 16,
contacts 106 and 110 are not at right angles with pillar portions
104 and 108; rather, contacts 106 and 110 are extensions of pillar
portions 104 and 108 extending through mold body 212.
[0114] In FIG. 18, clip 100 is rotated 90 degrees, as compared to
the embodiment of FIG. 16, in order to provide a larger creepage
distance and more significant clearance between sensor pins 206 and
contacts 106, 110 of clip 100. FIG. 19 depicts a similar rotation
of clip 100 with respect to the embodiment of FIG. 17.
[0115] Contacts 106 and 110 and sensor pins 206 can be accessible
on the same surface of package 200 or on different surfaces, as
depicted in FIGS. 20 and 21. Such a package 200 can be mounted, for
example, in a hole of a printed circuit board (PCB), with sensor
pins 206 accessible from the top side of the PCB and clip contacts
106, 110 from the bottom side of the PCB. The PCB can be used to
increase the creepage and clearance distances between sensor pins
206 and clip contacts 106, 110. On the bottom side of the PCB, the
high current rail and power devices of the system can be mounted,
whereas the control and low voltage components are mounted on the
top side of the PCB, in embodiments.
[0116] In other embodiments, current contacts 106, 110 can project
from mold body 212, as depicted in FIG. 22, or can be flush with
it, as depicted in FIG. 23, as a so-called "leadless" package. In
the embodiment of FIG. 22, the projecting contacts 106, 110 can be
fixed to current rails bolting or ultrasonically welded to a bus
bar or otherwise suitably coupled.
[0117] In embodiments, pillar portions 104 and 108 need not be
configured at ninety degrees with respect to the surface of die
202. Angles closer to 90 degrees, however, can be more easily
manufactured, such as by pressing sheet metal. Another advantage of
pillar portions 104, 108 being perpendicular to the surface of die
202 is that pillar portions 104, 108 are then shorter, which can
minimize electrical and thermal resistance between footprint
portion 102 and contact portions 106 and 110. Yet another advantage
is smaller lateral size of the spacing between contact portions 106
and 110, which can save space, increase the number of devices per
strip during production and consequently reduce the cost of
manufacturing.
[0118] FIG. 24 depicts an embodiment in which pillar portions 104
and 108 are not perpendicular with respect to the surface of die
202 but are at angles close to 90 degrees. For example, a can be
within a range of about 50 degrees to about 130 degrees in various
embodiments. In general, a should be selected such that the
dielectric strength between clip 100 and die 202 is maximized, with
two paths of dielectric breakdown to be considered: through the
bulk of mold body 212 and along an interface of mold body 212 to
isolation layer 204. The latter is often the weaker; therefore, it
should typically be longer. In FIG. 24, the bulk breakthrough is
illustrated as the distance between E and C, whereas the
breakthrough along the interface is illustrated as the distance
between E and F.
[0119] Referring to FIG. 25, if there are bond pads on the surface
of die 202, which are not typically covered by insulating layers,
and if there are bond wires 208 which are also not coated by an
insulating film, then the distance E-F between footprint portion
102 and the edge of die 202 is not the worst case for dielectric
breakdown, rather the distance between F, and the nearest bond wire
208 along the interface between mold body 212 and isolation layer
204 and the distance between C and the nearest bond wire 208
through mold body 212.
[0120] To increase the voltage isolation between clip 100 and bond
wires 208 and bond pads, a spray coating isolation, such as
benzocyclobutane (BCB), maybe applied after bond wires 208 are
installed between the bond pads and leads. Additionally or
alternatively, the surfaces of clip 100 that face bond wire 208 and
the bond pads can be coated with a dielectric isolation film.
[0121] In FIG. 26, clip 100 comprises a footprint portion 102 that
comprises, at the point of contact with die 202, a slim volume,
which reduces the length of the current path to a minimum. In a
strictly mathematical sense, the contact between footprint portion
102 and isolation layer 204 is no longer an area in the embodiment
of FIG. 26 but rather a line of contact that extends over a certain
length, the width of clip 100, into the drawing plane of FIG. 26.
Nevertheless, footprint portion 102 of clip 100 can still be
considered to be parallel to the surface of die 202, because the
contact line is parallel to the surface in a mathematical sense.
Embodiments optionally can comprise a support structure(s), such as
support studs 2602, to support die 202 given the narrow
configuration of footprint portion 102. The support structure or
studs 2602 can be conductive or insulating in various
embodiments.
[0122] Referring to FIG. 27, if clip 100 is coupled to the back
side of die 202, die 202 can be contacted in a flip-chip
configuration with solder bumps 218 on leadframe 203. In
embodiments, die 202 should be thin because magnetic sensor
elements 214 are on the top of die 202 and clip 100 is below die
202. Package 200 can comprise a shoulder 220 around its
circumference to help improve the voltage isolation between the top
and bottom, such as for when inserted in a PCB 222. In FIG. 27, a
sealing rim 226 between package 200 and PCB 22 is also included,
which can reduce creepage between clip 100 and sensor pins. Sealing
pastes or grease and adhesives can also be applied to the rim of
PCB 222, for example. Solder contacts 224 couple pins 206 to traces
of PCB 222.
[0123] In another embodiment, shoulder 220 is omitted such that
mold body 212 fits within the hole in the PCB 222, as in FIG. 28.
In the embodiment of FIG. 28, sensor package 200 comprises a
bracket 230 to couple pins 206 to PCB 222. In an embodiment,
bracket 230 is coupled to a top surface of PCB 222 at solder
contacts 224. Given that the sealing is along a rim 226 on the
perimeter of package 200, a tighter tolerance is needed between
mold body 212 and the hole in PCB 222 in embodiments such as FIG.
28 when compared with the embodiment of FIG. 27 comprising shoulder
220.
[0124] Another embodiment is depicted in FIG. 29 in which PCB 222
is configured such that no shoulder is needed on mold body 212, as
in FIG. 27, and package 200 is positioned within a recess of PCB
222. Sealing rim 226 is positioned at the top surface of package
200, with sensor pins 206 are positioned inside. Solder joints 232
couple pins 206 to PCB 222.
[0125] In general, therefore, embodiments of current sensors
benefit from good isolation between current contacts and contact
pins. Even if good isolation is achieved by the mold compound and
isolating layer with high dielectric strength, clearance distance
between the contacts and pins as well as creepage can still present
challenges. Standardization rules generally call for certain
dimensions, which in applications at more than about 5 kV can
result in large packages. In embodiments, however, if the sensor
package can offer two planes, one for the current contacts and
another for the pins of the low-voltage leads, with some form of
sealing therebetween, the sensor package can be very small with
creepage and clearance requirements met after the package is
installed in the module, such as a PCB in embodiments. In
embodiments, the package can also comprise some means, such as tape
or a clip, for mechanically coupling the package to the PCB during
the assembly process.
[0126] Referring to FIG. 30, another embodiment of clip 100 is
depicted. Resistance of clip 100 can be reduced if current
streamlines do not need to bend around sharp corners, but an
external bus bar 240 (incoming) and 242 (outgoing) is typically
much wider than clip 100, resulting in inevitable current flowline
bending. Areas of potential discontinuities are circled in FIG. 30,
of which FIG. 30A is a side perspective view and FIG. 30B is a top
view.
[0127] An option for reducing or eliminating the discontinuities is
to reduce the width of bus bar 240, 242 and clip 100 at a constant
angle, one embodiment of which is depicted in FIG. 31. FIG. 32
depicts the sheet metal 101 of clip 100 before it has been formed
into clip 100. The vertical black lines denote edges along which
sheet metal 101 is bent to form clip 100. The thin dashed lines
denote virtual circles that define the edge of sheet metal 101 in
order to avoid sharp bends in the current lines. In the embodiment
of FIG. 32, footprint portion 102 omits notch 112. FIGS. 33 and 34
depict alternate shapes of sheet metal 101, with the embodiment of
FIG. 34 providing the smallest resistance. In general, the radius
of the circles should be larger than the height of clip 100, with
the height being the vertical distance between contact area 106 or
110 and the top surface of the die. The circle can also degenerate
to an ellipse.
[0128] In operation, it is important that clip 100 remains securely
coupled to die 202. To accomplish secure coupling, embodiments can
use adhesive, soldering or some other suitable technique. Regarding
soldering, diffusion soldering between footprint portion 102 and a
metal layer on top of the surface of die 202 can be used. This
metal layer can be isolated from the rest of die 202 by a
dielectric isolation layer, comprising polyimide, silicon dioxide
or silicon nitride, in embodiments, and, in general, serves merely
a mechanical purpose related to adhesion with no electrical
function.
[0129] In embodiments, however, this on-chip metal layer can be
used for alignment of clip 100 with respect to die 202. The on-chip
metal layer is typically aligned very accurately with respect to
die 202 because of the high accuracy of the semiconductor
manufacturing processes. If clip 100 is soldered to this layer, the
solder can pull a slightly eccentrically mounted clip 100 into the
center of the on-chip metal layer through the action of its surface
tension.
[0130] Because the area of footprint portion 102 is small,
challenges can be presented during assembly. For example, the
adhesive force of solder paste or adhesive applied to the bottom of
clip 100 and/or the top of die 202 can be too small to hold clip
100 in place before the solder or adhesive has developed full
strength, such as after curing. Therefore, it can be advantageous
in embodiments to not attach individual clips 100 to individual
dies 202 but rather to have several clips 100 arranged in a second
leadframe. Dies 202 are attached to a first leadframe according to
conventional semiconductor manufacturing techniques, and the second
leadframe is then placed on top of the first leadframe. FIG. 35 is
a flowchart of an embodiment of a manufacturing process 3500
according to such an embodiment.
[0131] At 3502, adhesive is applied to the die paddles of the first
leadframe.
[0132] At 3504, the semiconductor dies are placed on the die
paddles. The adhesive is cured.
[0133] At 3506, the sensor pins are coupled to the bond areas on
the dies by bond wires.
[0134] At 3508, adhesive is applied to the dies and/or footprint
portions of the clips.
[0135] At 3510, a second leadframe having the clips is placed on
the first leadframe having the dies. In an embodiment, this is
carried out such that the footprint portions of the clips are
placed at or near the magnetic field sensor elements on the top
surfaces of the dies. In another embodiment, the first and second
leadframes can also be connected via secondary means, for example
along their circumferential frames. This can be helpful or
necessary if the cumulative area of the footprints of all of the
devices per strip is too small to take up the mechanical load
during the handling process. These additional means can comprise
mechanical fixtures such as rivets or nuts; chemical joints such as
gluing or soldering; or physical joints such as spot welding, among
others. The adhesive between the dies and clips is cured.
[0136] At 3512, the mold bodies are molded.
[0137] At 3514, the clips of the second leadframe are stamped out,
either completely or only on the current input or output side. The
sensor pins except for the ground pins of the first leadframe are
also stamped out. If an isolation test in which a voltage of
several kVs is applied between the current rail and the sensor pins
is desired or required, all low voltage pins of the sensor can be
stamped out such that no connection to the primary conductor
exists. Step 3514 can be omitted or carried out only partly if the
devices are large, with full stamping carried out at 3518.
[0138] At 3516, end-of-line testing and calibration of the sensor
devices are carried out.
[0139] At 3518, the remaining sensor pins are stamped out to
singulate the sensor devices.
[0140] If the contact portions of the clips are large when compared
to the size of the footprint portion, in particular if the
footprint portions are mechanically fragile because they include
one or more notches to shape the current path, it can be helpful or
necessary to add non-conducting support structures to the clips.
This can be, for example, an adhesive foil attached to the contacts
portions, or those parts of the footprint portions not in contact
with the isolation layer after clip coupling can be molded in a
plastic encapsulation in embodiments.
[0141] In other embodiments, the clip comprises multiple layers,
such as a contact layer and a footprint layer. Each layer can be
stamped out separately from sheet metal and coupled by soldering or
welding, such as UV welding, in embodiments. In another embodiment,
the contact layer is stamped from sheet metal while the footprint
portion is galvanically grown on top of the contact layer, such as
via electrolytic deposition. This avoids other materials, such as
solder, and can establish a full surface contact between the
layers, avoiding spot welding. Advantages include a smaller
separation distance, even less than the layer thickness, between
the contacts, and the possibility of having different thicknesses
of the two layers. Layer thickness is important for voltage
isolation, because the thickness of the footprint portion is
identical to the vertical distance between the bottom surface of
the contacts and the die surface. Also, the current density is
related to the ratio of the thicknesses of the contacts and the bus
bar. If the bus bar is thick and the contacts are thin, the current
is inclined to flow vertically through the central parts of the
contacts, leading to strong peaks in the current density
distribution near the center of the solder area, as depicted in
FIG. 36. Areas of high current density in solder layer 3602 between
bus bar 602 and the contact layer of contact portions 106 and 110
are also illustrated.
[0142] If bus bar 602 is thinner than the contact layer, the
current is included to flow laterally through the contact layer,
which reduces the excessive current densities in solder layer 3602
between bus bar 602 and the contact layer because the current is
spread more evenly over solder layer 3602. As depicted in FIG. 37,
the current density is nearly homogeneous in solder layer 602.
[0143] In embodiments, contact portions 106 and 100 can overlap
bond pads on die 202, or not. The length, height and other
characteristics of the bond loops can be adjusted in these various
embodiments for sufficient vertical distance and isolation. The
thickness of the contact layer can be less than or greater than the
thickness of the footprint layer in order to pull the peak current
density in solder layer 602 out of the vertical center plane, in an
embodiment.
[0144] Another embodiment is depicted in FIG. 38, in which package
200 is configured for insertion into a hole in a PCB, with a bus
bar on a first (high voltage, high current) side of the PCB and
sensor pins 206 on the second (low voltage, low current) side of
the PCB, with a sealing ring between. FIG. 38A is an exploded view
of clip 100, a reinforcement mold 3802, isolation layer 204, die
202, contact pads and sensor leads 206. In embodiments,
reinforcement mold 3802 comprises a suitable insulating material,
such as a mold compound material in an embodiment.
[0145] Clip 100 can be formed from a contact layer, with each
contact portion 106 and 110 separately stamped. Contact portions
106, 110 can then be mounted in a mold cavity, where reinforcement
mold 3802 is cast to fill the gap between the portions 106 and 110.
The footprint layer, comprising footprint portion 102, can then be
electrolytically grown on top. Die 202 can then be mounted, with
isolation layer 204 in between. In an embodiment, this
manufacturing is carried out with the contact layer fixed in a
frame. The frame can then be placed into another mold tool to cover
die 202 with mold body 212, which is shown in FIG. 38B.
[0146] In embodiments, such a device can be suitable for currents
in a range of about 5 A to about 500 A or more, such as about 1000
A, depending upon the configuration of notch 212 in footprint
portion 102, the thicknesses and configurations of the contact and
footprint layers and the size of the contact surfaces. Voltage
isolation can be up to about 10 kV in embodiments, with the
creepage distance designed by the overlapping parts of the PCB into
which package 200 is inserted.
[0147] In another embodiment of a coreless magnetic current sensor
depicted in FIG. 39, clip 100 is replaced with a copper block 3900.
Embodiments comprising copper block 3900 can present advantages,
including having a low resistance, being positionable close to the
magnetic sensor elements while spaced apart from the sawing edge of
the die, and being relatively inexpensive to manufacture, in part
because of compatibility with conventional semiconductor
fabrication technologies.
[0148] FIG. 40 depicts a process 4000 for manufacturing embodiments
of copper block 3900. In an embodiment, a copper wafer about 400
.mu.m thick is used.
[0149] At 4002, a grid of grooves is formed in a first side of the
copper wafer. In embodiments, the grooves are formed by etching or
sawing. For a 400 .mu.m-thick wafer, the grooves can be about 100
.mu.m deep.
[0150] At 4004, the first side of the copper wafer, now grooved, is
coupled to a silicon wafer. In embodiments, the copper wafer is
coupled to the silicon wafer by soldering, gluing or some other
suitable means. The silicon wafer can include an isolation layer,
onto which the copper block is coupled, in embodiments. In one
embodiment, the isolation layer comprises silicon oxide and is
about 12 .mu.m thick.
[0151] At 4006, a grid of grooves is formed in the second side of
the copper wafer. In an embodiment in which the copper wafer is 400
.mu.m thick, the grooves are 300 .mu.m deep and align with the
first grid of grooves formed in the first side of the copper wafer
such that a frame structure can be released and discarded, leaving
behind an array of spaced-apart copper blocks on the surface of the
silicon wafer. In an embodiment, each copper block is about 1.9 mm
by about 1.9 mm by about 0.4 mm, though these dimensions can vary
in other embodiments.
[0152] At 4008, grooves are optionally formed in the remaining
copper blocks. Such grooves, about 300 .mu.m deep and about 100
.mu.m wide in an embodiment but having other depths in other
embodiments, can be helpful to increase current density in low
current applications. The grooves are formed by a sawing blade in
an embodiment.
[0153] In an embodiment, 4006 and 4008 can be combined, such as if
there is no need to keep a lateral distance between copper block
3900 and the sawing edge of the die. This can be suitable for
embodiments having low voltage isolation requirements.
[0154] At this point, the structure is as is depicted in FIG. 41 in
an embodiment, with a plurality of copper blocks 3900 having
grooves 3902 mounted on a silicon wafer 3904. An isolation layer
3905 is formed on wafer 3904.
[0155] At 4010, bond pads 3906 (FIG. 41) can be cleaned and the
individual chips 3910 singulated. This can be carried out in one or
multiple steps, the particular sequence depicted in FIG. 40 being
but one non-limiting embodiment. After singulation, each chip or
die 3910 is about 2.8 mm by about 2.5 mm by about 0.5 mm in an
embodiment, and each copper block 3900 has a nominal perimeter of
about 300 .mu.m of clearance to the edge of isolation layer 3905,
either to the sawing edge of die 3910 or the bond wires (FIG. 39),
with a strip reserved for bond pads 3906. In an embodiment, the
strip is about 200 .mu.m.
[0156] The embodiment depicted in FIG. 39 can be a part of a
complete sensor, such as is shown in FIG. 44C, with a top surface
left exposed out of a package. Such an embodiment is suitable for
currents up to about 30 A but can be limited above that range
because of electromigration issues.
[0157] At 4012, copper block 3900 can be coupled to a leadframe
3912, such as is depicted in FIG. 42. Leadframe 3912 can be about
0.4 mm thick in an embodiment. Coupling can be effected by gluing,
soldering or other suitable means. For example, in an embodiment
copper block 3900 is coupled to leadframe 3912 by about a layer of
conductive paste or die attach that is about 10 .mu.m thick.
[0158] At 4014, a copper coating can be applied over leadframe 3912
and copper block 3900. In one embodiment, a copper coating about 50
.mu.m thick is uniformly galvanized over leadframe 3912 and copper
block 3900. The copper coating reduces the distance between block
3900 and the sawing edge of silicon die 3910 and bond pads 3906 by
about 50 .mu.m in each direction, while leadframe 3912 becomes
about 100 .mu.m thicker. The depth and width of groove 3902 are
also reduced.
[0159] FIG. 43 depicts an enlarged partial cross-sectional view of
the structure of FIG. 42, with copper coating shown at 3914. Solder
3916 between copper block 3900 and leadframe 3912 affixes one to
the other prior to galvanization but is not necessary for current
transport because electrical contact is made by copper coating
3914. Solder 3916 therefore does not affect electromigration.
[0160] In another embodiment, copper block 3900 can comprise two
distinct portions, if groove 3902 is carried through block 3902. A
metal layer, such as aluminum or power copper, can be formed below
and, if in contact with block 3902, also galvanized, including in
between the portions of block 3900. In this embodiment, arbitrary
thin layers can be grown and also patterned laterally as
desired.
[0161] Advantages of embodiments and process 4000 include the
ability to produce structures more accurately and cheaply than
conventional solutions, in part because the whole silicon wafer can
be used and the structures can be formed more accurately at the
wafer level. In particular, precise position tolerances can be
achieved.
[0162] Other variations are also possible in embodiments. For
example, the copper blocks can be coupled to the front side, back
side or both sides of the wafer. The top sides of the copper blocks
can be prepared for soldering, though electromigration can then
become a current limiter. Large contacts forming part of the
leadframe can be coupled, such as by soldering, to top side of the
copper block. This can be carried out during package assembly. If
diffusion soldering is used, the solder junction can then tolerate
higher current density, such as up to about 60 A. Large contacts
can also be coupled by a conductive glue or other solder and coated
at least partially to ensure good electrical contact with the
copper block, such as in a galvanic bath. In embodiments, the
coating is about 10 .mu.m to about 50 .mu.m thick and comprises a
good conductor, such as copper.
[0163] As previously mentioned, copper block 3900 can be
substituted for clip 100. Thus, embodiments for current sensing
applications comprising copper block 3900 can also comprise at
least one magnetic field sensor. Embodiments can also comprise
amplifiers and signal conditioning circuitry. The magnetic field
sensors can comprise planar Hall plates, which can be disposed near
a straight or curved edge of the copper block and near the part of
the copper block having the smallest cross-sectional area (and
therefore highest current density).
[0164] Following 4008, the die can instead be coupled, such as by
gluing, to a die paddle or a leadframe, with connections then made
between leads and bond pads with bond wires and mold compound
applied.
[0165] An example embodiment is depicted in FIG. 44. FIG. 44A is a
top view of the mold body 4400 and sensor leads 4402. FIG. 44B is a
bottom view of mold body 440 and leads 4402, with copper block 3900
visible. FIG. 44C omits the mold body such that die 3904 and die
paddle 4404 can be seen, as well as bond wires 4406 coupling bond
pads 3906 to leadframe 4408.
[0166] In FIG. 44B, it can be seen that groove 3902 is filled with
mold compound to avoid shorts when the contacts (exposed surfaces
of block 3900) are soldered to busbars, PCBs, or other structures.
In an embodiment, groove 3902 can be made wider at the surface of
the package by first forming groove 3902 with a thick blade and
then sawing deeper with a thin blade. Groove 3902 can also be
formed by etching and then sawing (or in reverse order), in another
embodiment.
[0167] FIG. 45 depicts another embodiment, in which large contacts
are coupled to the copper block. Similar to FIG. 44, FIG. 45A is a
top view, FIG. 45B is a bottom view, and FIG. 45C omits the mold
body. Large contacts 4500 can be part of the leadframe in an
embodiment, such that a separate die paddle is not necessary. This
can increase the bandwidth of the sensor in embodiments. If
contacts 4500 are coupled by a soldering technique having a high
melting point, such as diffusion soldering, the electromigration
limit of the solder junction is also higher than that of the
embodiment of FIG. 44. Similar to the embodiment of FIG. 44, the
gap 4502 between the contacts 4500 is filled with mold compound to
avoid shorts, though the portion of gap 4502 extending beyond mold
body 4400 can be unfilled if the gap width is sufficient.
[0168] Referring to FIG. 45C, the height of bond wires 4406 is as
low as possible in embodiments to the keep the distance between
contacts 4500 and the surface of mold body 4400 larger. Therefore,
in one embodiment wires 4406 are bent downwards so that their top
point is about the same height as the bond pads on die 3904.
[0169] The thickness of contacts 4500 can be similar to that of
sensor leads 4402, which can reduce the price of leadframe 4408. In
an embodiment, leadframe comprises copper with a very low, such as
less than 0.1%, iron content. An advantage of copper block 3900,
however, is that it can be made of high purity copper, which has a
low resistivity, in order to reduce the dissipation and
self-heating of the sensor.
[0170] As previously mentioned in various contexts and with respect
to various embodiments discussed herein throughout, the distance
between the conductor and the magnetic field sensor(s) is also
important, as is the fact that this distance remain stable over the
lifetime of the sensor. Conventional solutions often use thin
conductor layers manufactured during semiconductor fabrication,
which have well-defined positions and are generally stable over
lifetime. Thin conductors, however, are current limiters. Other
conventional solutions for higher current applications fix the
conductor to the die using an adhesive, glue, mold compound or
other material. While such configurations can handle higher
currents, the fixing materials are less stable, susceptible to
moisture, chemical reactions from long-term exposure to high
temperatures and other factors that can alter the material
thickness and thereby affect sensor accuracy.
[0171] Therefore, embodiments can utilize soldering techniques to
couple the primary conductor and semiconductor die, for example in
high current applications in which a massive conductor is used. In
embodiments, solder is not used to carry current but establishes a
mechanical connection between the conductor and the semiconductor
die having the magnetic field sensor elements, with current flowing
in the conductor. The relative position of the conductor with
respect to the magnetic field sensor element(s) is therefore
determined only by anorganic, highly stable materials such as
semiconductors, metal, ceramic, glass, porcelain, solder and the
like.
[0172] Referring to FIG. 46, in one embodiment an insulating layer
4602 is formed on a semiconductor die 4604. Insulating layer 4602
is inorganic in embodiments and can comprise silicon oxide, nitride
or some other suitable material. A metal layer 4606 (FIG. 46B) is
formed on insulating layer 4602 and can comprise copper, aluminum
or some other suitable material. Metal layer 4606 can be formed
and/or prepared such that it is solderable, for example solderable
to a metal part in a package assembly process. Both insulating
layer 4602 and metal layer 4606 can be formed during front-end
semiconductor manufacturing in an embodiment.
[0173] After the individual semiconductor dies 4604 are singulated
during manufacturing, the dies 4604 can each be soldered to a
primary conductor 4608 at metal layer 4606. In the embodiment
depicted in FIG. 46, conductor 4608 comprises a clip. The clip can
comprise a single metal piece or other configurations, such as are
discussed herein above. In other embodiments, conductor 4608 can
comprise other configurations, such as the copper block discussed
herein above. Therefore, the particular configuration of the clip
will not be discussed in detail here, with reference instead made
to the discussion herein above regarding various embodiments.
[0174] Referring in particular to FIG. 46B, insulating layer 4602
and metal layer 4606 can be seen. Insulating layer 4602 can be both
insulating and inorganic, with inorganic being beneficial to avoid
moisture absorption or otherwise alter its composition or
dimensions. In embodiments, insulating layer 4602 comprises silicon
dioxide, nitride or some other suitable material. Metal layer 4606
is positioned on insulating layer 4602 such that layer 4606 does
not contact die 4604 and is electrically floating. In an
embodiment, metal layer 4606 comprises aluminum, copper or some
other suitable material and has been finished such that layer 4606
is solderable. Similar to clip embodiments discussed herein above,
a footprint portion 4610 of conductor 4608 is mechanically coupled
to die 4604 by soldering at metal layer 4606. In embodiments,
conductor 4608 is smaller than metal layer 4606 and metal layer
4606 is sufficiently thick to avoid damage or other effects from
possible manufacturing results including burrs on conductor
4608.
[0175] Another embodiment is depicted in FIG. 47, in which part of
a surface of the semiconductor die is covered by a metal plate or
layer that does not need to be electrically isolated from the die.
FIG. 47 is a partially exploded view for convenience of
illustration. In the embodiment of FIG. 47, solderable metal plates
4702 are coupled to a surface of die 4704, which includes magnetic
field sensor elements 4706 on a top or bottom side of die 4704. The
metal plates 4702 are configured to be coupled to metal plates 4708
coupled to a surface of an insulating plate 4710. Insulating plate
4710 is in turn coupled to a current rail or conductor 4714 by
metal plates 4712. Bond wires 4716 can be coupled directly to die
4704 via bond pads and/or indirectly to die 4704 by traces on a top
surface of plate 4710 and then to leads of a leadframe (not
depicted in FIG. 47).
[0176] In embodiments, insulating plate 4710 comprises ceramic,
glass, porcelain, silicon or some other suitable material.
Insulating plate 4710 can be larger than die 4704 and therefore can
also provide more reliable voltage isolation. Additionally, plate
4710 need not be perfectly flat in embodiments, as plate 4710 can
be profiled by etching or some other technique such that the
perimeter area or a portion thereof is thicker or thinner than the
center area. For example, in an embodiment in which die 4704 rests
in the center of plate 4710, a thicker perimeter portion of plate
4710 can provide increased voltage isolation. In such an
embodiment, metal layer 4708 should not extend to the thicker
perimeter portion.
[0177] In one embodiment of FIG. 47, metal layers 4702 are
positioned at a back side of die 4704, and the electronic devices,
such as magnetic field sensor elements 4706, are on the opposite,
front side of die 4704. Die 4704 can then be coupled to by bond
wires 4716 via bond pads on the front side. In another embodiment,
metal layers 4702 are at the front side of die 4704, as are the
electronic devices, such as magnetic field sensor elements 4706,
and die 4704 is flip-chip mounted on insulating plate 4710.
Contacts can be made via fine conductive traces 4708 and bond wires
4716 to die 4704.
[0178] Metal plates or layers 4702, 4708 and 4712 are prepared to
be solderable and, during manufacturing, the soldering of these
layers 4702, 4708 and 4712 can be carried out in a single step or
in multiple steps. For example, it can be desired in an embodiment
to solder consecutively, using different solder processes at
different temperatures. In embodiments, high-temperature soldering,
such as diffusion soldering, can be used, which is advantageous
because it can be thin and subsequently the package contacts can be
readily solderable at a lower temperature with conductor 4714
remaining stable with respect to the position of die 4704.
[0179] In embodiments, conductor 4714 can comprise a unitary or
plurality of components, for example a clip and leads. At the
surface of die 4704, however, conductor 4714 comprises a single
part.
[0180] Various embodiments of systems, devices and methods have
been described herein. These embodiments are given only by way of
example and are not intended to limit the scope of the invention.
It should be appreciated, moreover, that the various features of
the embodiments that have been described may be combined in various
ways to produce numerous additional embodiments. Moreover, while
various materials, dimensions, shapes, configurations and
locations, etc. have been described for use with disclosed
embodiments, others besides those disclosed may be utilized without
exceeding the scope of the invention.
[0181] Persons of ordinary skill in the relevant arts will
recognize that the invention may comprise fewer features than
illustrated in any individual embodiment described above. The
embodiments described herein are not meant to be an exhaustive
presentation of the ways in which the various features of the
invention may be combined. Accordingly, the embodiments are not
mutually exclusive combinations of features; rather, the invention
may comprise a combination of different individual features
selected from different individual embodiments, as understood by
persons of ordinary skill in the art.
[0182] Any incorporation by reference of documents above is limited
such that no subject matter is incorporated that is contrary to the
explicit disclosure herein. Any incorporation by reference of
documents above is further limited such that no claims included in
the documents are incorporated by reference herein. Any
incorporation by reference of documents above is yet further
limited such that any definitions provided in the documents are not
incorporated by reference herein unless expressly included
herein.
[0183] For purposes of interpreting the claims for the present
invention, it is expressly intended that the provisions of Section
112, sixth paragraph of 35 U.S.C. are not to be invoked unless the
specific terms "means for" or "step for" are recited in a
claim.
* * * * *