Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR IMPROVED
ELECTRONIC COMPONENT INTERCONNECTIONS
CROSS-REFERENCE TO RELATED APPLICATIONS
[01] This claims benefit of U.S. Provisional Patent Application No. 62/586,815
filed
November 15, 2017, the entirety of which is incorporated herein by reference.
BACKGROUND
Field of the Invention
[02] This relates generally to establishing electrical connection of
components in
electronic circuitry. More particularly, this relates to improved methods for
connecting components to a substrate using anisotropic conductive adhesives.
Description of Related Art
[03] As the modern demands for technology increase, the number of electronic
devices continues to increase, the availability and adoption of such devices
continues to increase, the size of such devices continues to decrease, and the
number of interconnects of electronic components required to manufacture such
devices has vastly increased. Furthermore, in many fields previously analog
devices have all but disappeared as such devices have been replaced by
electronics, and the size of electronic devices has dropped dramatically, even
while the power of those devices has continued to expand rapidly.
[04] As modern components have gotten smaller and more powerful, more
circuitry is present on such components in ever-smaller spaces (i.e. the
density of
the circuitry has increased), with far tighter tolerances between different
aspects
of e.g. a given chip or component (i.e. the pitch has gotten smaller ¨ "ultra-
small
pitch").
[05] Modern components are thus often more susceptible to temperature and
pressure, either of which may result in problems, and even failure of the
component and the entire device of which the component is a part.
Unfortunately current means of creating interconnects between e.g. components
and their substrates all have limitations and drawbacks for particular
applications.
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[06] The skilled practitioner will appreciate that there are a number of means
of
inter-connections (such as traditional solder, anisotropic conductive films
(ACFs),
and anisotropic conductive adhesives (ACAs)) each of which has benefits and
limitations, and each of which provides options that may meet the requirements
for particular interconnections for particular applications, components, or
devices.
[07] Traditional soldering involves exposure of the components being connected
to locally high amounts of heat, and pressure. Exposure of such components to
these unfavorable or untenable conditions can result in outright failure, poor
or
unreliable performance or greatly decreased lifetimes.
[08] As one effort at improving interconnects for various applications, ACFs
have
been developed. These conductive films can reduce the local heat required for
connection by soldering, but they can still require significant heat. In
addition,
both heat and pressure are generally applied to the components, which can be a
significant limitation for sensitive components. ACFs also have a limitation
with
regards to the pitch of interconnections that it is suitable for or can
accommodate.
[09] ACAs have also been developed to provide alternative solutions for
creating
difficult interconnects in particular applications. As with ACFs, these
adhesives
provide electrical conductivity in the Z-axis only. ACAs such as those
produced
by SunRay Scientific comprise magnetically-alignable particles that form
interconnects among components when the particles are aligned along the Z-axis
by exposure to a magnetic field. The adhesive matrix is then cured by e.g.
exposure to heat, to complete and fix the interconnection. No pressure is
required, making ACAs good candidates for pressure-sensitive components.
Further, curing may be accomplished in low heat for temperature sensitive
components. Moreover, ACAs allow finer pitch applications than can be
achieved using ACFs.
[10] Prior art applications of ACAs have generally employed a magnetic field
applied across the entire substrate using an electromagnet. While such a field
covers all components populated on the substrate, it can be disadvantageous in
applications where one or more components on the substrate are sensitive to
magnetic field. In addition, the magnetic field applied over the large area
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includes the entire magnetic field, including flux lines that are not
generally very
perpendicular to the X-Y plane.
[11] While creating interconnects with ACAs is simple and easy, there is
nonetheless a need for improved systems and methods for creating and
optimizing interconnects using ACAs in specific applications.
SUMMARY
[12] The inventor has discovered methods that provide unexpected
improvements in ACA-based electronic interconnects for specific
applications and has developed systems to implement the methods.
The methods provide several advantages based on selecting the proper
ACA properties, using separate magnets positioned for each
component to be interconnected, and selecting the properties of the
magnets used for alignment of the ACA for each specific component
populated on a substrate to optimize the creation of the Z-axis
connections (in terms of the height, number and direction of the Z-axis
columns). The methods allow for the construction of what the inventor
calls a 'magnetic pallet' that provides consistent and optimal alignment
and curing of ACA-based interconnects. The methods can provide
improved consistency of interconnects, reduced failures, improved life
and increased yields of functional connections, as compared to existing
methods of forming interconnects.
[13] In a first aspect, this disclosure provides novel methods of aligning
and curing of ACA-based interconnections in digital devices,
electronics, and the like. The methods for establishing an interconnect
between a substrate and an electronic component populated thereon
using a magnetically-alignable anisotropic conductive adhesive (ACA),
generally comprise the steps of:
[14] a) establishing the dimensions and location on the substrate of
the first electronic component to be placed on and connected to the
substrate;
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[15] b) determining the placement location of the first magnet
corresponding to the dimension and location established for the
component in step a);
[16] c) determining the dimensions and strength of the magnet
required in step b); and
[17] d) mapping the flux lines of the magnetic field for the magnet.
[18] Steps a) ¨d) are repeated for each additional component to be
placed on and connected to the substrate, so as to determine the
properties and placement location for each additional magnet needed;
[19] The method further comprises the steps of:
[20] f) creating a magnetic tray and securing each magnet in its
respective placement location on the tray;
[21] g) creating an alignment tray and adapting the alignment tray
to retain the substrate during alignment and curing;
[22] h) placing the substrate on the alignment tray;
[23] i) applying the ACA to the substrate in a location suitable for
interconnecting each component to be placed thereon;
[24] j) populating the substrate with the first component and each
additional component where the ACA has been applied;
[25] k) assembling the alignment tray and the magnetic tray;
[26] 1) allowing columns to form in the Z-axis in the ACA; and
[27] m) curing the ACA, thereby establishing the interconnects
between the substrate and the first component and each additional
component.
[28] The alignment tray and the magnetic tray are made of
nonmagnetic material. The magnet tray is adapted to receive and
retain the first and each additional magnet in their respective
placement locations on the tray. The assembled magnet tray (with
magnets in place), and the alignment tray (with substrate populated
with components and ACA) can be placed as an assembly directly into
a curing oven.
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[29] In a second aspect, provided herein are systems for creating
interconnects between a substrate and electronic components attached
thereto using a magnetically-alignable anisotropic conductive adhesive
(ACA). The systems generally comprise a magnet tray comprising a
nonmagnetic tray adapted to receive and retain each of one or more
magnets placed therein in a location that corresponds to the location of
one or more electronic components on a substrate to which the
components are to be connected.
[30] The systems also comprise an alignment tray adapted to retain a
substrate populated with one or more components to be connected
thereto with an ACA during alignment and curing of the ACA.
[31] The systems also include an ACA comprising magnetically-
alignable particles capable of forming interconnections conductive in
the Z-axis.
[32] Both the alignment tray and the magnetic tray are preferably made
of nonmagnetic material. If various embodiments, the substrate can
only be placed in the alignment tray in one orientation.
[33] In presently preferred embodiments, the magnets are permanent
magnets. Generally, for each magnet in the magnet tray, the magnetic
flux lines are substantially parallel to each other and substantially
perpendicular to the X-Y plane in an area corresponding to the area of
the substrate upon which the component and ACA are located. In a
presently preferred embodiment, the magnetic flux lines consist
essentially of lines parallel to each other and perpendicular to the area
of the substrate upon which the component and ACA are located.
[34] In a third aspect, this disclosure provides kit for creating
interconnects between a substrate and electronic components attached
thereto using a magnetically-alignable anisotropic conductive
adhesive. The kits generally comprise:
[35] at least one magnetic tray comprising a nonmagnetic tray adapted
to retain one or more magnets in locations corresponding to a desired
placement of an electronic component on and connection of the
component to a substrate using an ACA;
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[36] sufficient magnets to complete the magnet tray, each magnet of a
desired size and strength for making an interconnection between the
component and the substrate using the ACA;
[37] at least one alignment tray adapted to receive and retain the
substrate and components populated thereon during the alignment
and curing of the ACA to form the interconnect;
[38] and optionally, an ACA suitable for use with the kit to create at
least one interconnect between a component and a substrate using the
kit.
[39] In the kits provided, the magnet tray and the alignment tray are
configured to be oriented vertically with respect to each other. They
are assembled such that an electronic component placed on a substrate
(to be connected thereto with an ACA) on the alignment tray is
brought into vertical alignment with a magnet on the magnet tray
when the magnet tray and the alignment tray are assembled in that
manner. Each component requiring a connection (interconnect) has a
corresponding magnet with which it will be aligned when the trays are
assembled.
[40] In presently preferred embodiments of the kits, the magnets
comprise rare earth magnets, or other permanent magnets.
[41] In yet another aspect, this disclosure provides oven systems
designed for creating interconnections between a substrate and an
electronic component to be placed thereon and connected thereto using
an ACA. The oven systems generally comprise a curing oven and one
or more shelves or racks each comprising
[42] a magnetic tray fitted with one or more magnets each placed in a
location corresponding to the location of an electronic component to be
placed on and connected to a substrate using an ACA; and
[43] an alignment tray adapted to receive and retain a substrate
populated with one or more components to be placed thereon and
connected via an ACA.
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[44] These and/ or further aspects, features, and advantages of the present
invention will become apparent to those skilled in the art in view of this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[45] Fig. 1: A cross-sectional overview of an embodiment of the system for
magnetically aligning and curing ACA interconnects showing a magnet tray with
magnets positioned therein, an alignment tray, substrate and components
populated thereon.
[46] Fig. 2: A flow chart showing the steps of a method of magnetically
aligning
and curing components to substrate using an ACA to create the electrical
connection.
[47] Fig. 3: A drawing showing an embodiment of an alignment tray for use
herewith. The tray contains a plurality of substrates each with a populated
component to be placed on and connected to the substrate.
[48] Fig. 4: A drawing showing an embodiment of an oven employing the
magnetic pallet system. A. Multiple magnet tray and alignment tray assemblies
are shown in a batch oven. The outside dimensions of the alignment and magnet
trays are dictated by the oven dimensions but there is otherwise no
requirement
that each magnet tray or each alignment tray be identical. Thus, a single oven
can be utilized to align and cure a multitude of interconnects for a plurality
of
electronic components on different substrates or devices. B. Shows a magnified
view of an assembly comprising an alignment tray and a magnet tray with the
orientation means (alignment holes). C. A close-up overhead view of a magnet
tray that serves as a rack in the oven.
DETAILED DESCRIPTION
[49] Provided herein are methods and systems for providing improved and more
consistent interconnections for electronic components using ACAs.
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Definitions & Abbreviations
[50] Unless expressly defined otherwise, all technical and scientific terms,
terms of
art, and acronyms used herein have the meanings commonly understood by one
of ordinary skill in the art in the field(s) of the invention, or in the
field(s) where
the term is used. In accordance with this description, the following
abbreviations
and definitions apply.
Abbreviations
[51] The following abbreviations apply unless indicated otherwise:
AC: alternating current;
ACA: anisotropic conductive adhesive;
ACF: anisotropic conductive film;
DC: direct current;
Gs: Gauss, magnetic field units;
NIB: neodymium-iron-boron;
PCB: printed circuit board; and
T: Testa, magnetic field units, SI.
Definitions
[52] As used herein "substantially" may mean an amount that is larger or
smaller
than a reference item. Preferably substantially larger (or greater) or smaller
(or
lesser) means by at least about 10% to about 100% or more than the
corresponding reference item. More preferably "substantially" in such
instances
means at least about 20% to about 100%, or more, larger or smaller than the
reference item. As the skilled artisan will appreciate the term
'substantially' can
also be used as in "substantially all" which mean more than 51%, preferably
more than 60%, 67%, 70%, 75%, 80%, 85%, 90%, or more of a referenced item,
number, or amount. "Substantially all" can also mean more then 90% including
91, 92, 93, 94, 95, 96, 97, 98, 99 or more percent of the referenced item,
number, or
amount.
[53] As used herein, the singular form of a word includes the plural, and vice
versa, unless the context clearly dictates otherwise. Thus, the references
"a",
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"an", and "the" are generally inclusive of the plurals of the respective
terms. For
example, reference to "an electrode" or "a diode" includes a plurality of such
"electrodes" or "diodes".
[54] The words "comprise", "comprises", and "comprising" are to be interpreted
inclusively rather than exclusively. Likewise the terms "include", "including"
and "or" should all be construed to be inclusive, unless such a construction
is
clearly prohibited from the context. Further, forms of the terms "comprising"
or
"including" are intended to include embodiments encompassed by the phrases
"consisting essentially of" and "consisting of". Similarly, the phrase
"consisting
essentially of" is intended to include embodiments encompassed by the phrase
"consisting of".
[55] Where used herein, ranges are provided in shorthand, so as to avoid
having
to list and describe each and every value within the range. Any appropriate
value
within the range can be selected, where appropriate, as the upper value, lower
value, or the terminus of the range.
[56] The formulations, compositions, methods and/ or other advances disclosed
here are not limited to particular methodology, protocols, and/ or components
described herein because, as the skilled artisan will appreciate, they may
vary.
Further, the terminology used herein is for the purpose of describing
particular
embodiments only, and is not intended to, and does not, limit the scope of
that
which is disclosed or claimed.
[57] Although any formulations, compositions, methods, or other means or
materials similar or equivalent to those described herein can be used in the
practice of the present invention, the preferred formulations, compositions,
methods, or other means or materials are described herein.
[58] Any references, including any patents, patent applications, or other
publications, technical and/ or scholarly articles cited or referred to herein
are in
their entirety incorporated herein by reference to the extent permitted under
applicable law. Any discussion of those references is intended merely to
summarize the assertions made therein. No admission is made that any such
patents, patent applications, publications or references are prior art, or
that any
portion thereof is either relevant or material to the patentability of what is
claimed herein. Applicant specifically reserves the right to challenge the
accuracy
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and pertinence of any assertion that such patents, patent applications,
publications, and other references are prior art, or are relevant, and/ or
material.
[59] As used herein, "alignment" means aligning a magnetic material or
composition comprising magnetic particles. Generally, aligning refers to the
arrangement of magnetic particles in the Z-axis under the influence of a
magnetic
field. Alignment is the process by which columns are formed in the Z-axis. As
will be clear from the context, sometimes 'alignment' is also used herein to
refer
to ensuring the proper orientation of two things with respect to each other ¨
such
as the alignment tray and the magnetic tray, or the substrate and the
alignment
tray.
[60] As used herein, "columns" refers to the structures formed by magnetic
particles in a composition in the Z-axis under the influence of a magnetic
field.
The process of column formation is sometimes referred to as 'alignment'. The
column properties (e.g. height, diameter, etc.) will be determined by the
strength
of the magnets and the properties of the ACA including the size and amount of
the magnetic particles in the ACA, and the viscosity and other physical
properties of the ACA matrix. Columns can and will form within seconds of
exposure to a suitable magnetic field.
[61] A "magnet" is capable of producing a "magnetic field" which as used
herein
includes any magnetic field whether produced by an electromagnet or a
permanent magnet. The "strength" of a magnet can be measured in Gs (or Ts).
The skilled artisan will appreciate how to determine the strength of any given
magnet, or how to determine the magnetic strength desired for a given magnet.
"Mapping a magnetic field" as used herein means determining the specific shape
of the magnetic field and path of the magnetic field lines. The skilled
artisan will
appreciate how to map the magnetic field of any magnet through various means.
[62] As used herein, a "permanent magnet" means a magnet that does not require
electrical current to flow in order to have a persistent magnetic field.
Permanent
magnets for use herein can comprise iron, nickel, cobalt, and rare earth
metals.
Certain presently preferred embodiments herein utilize rare earth magnets such
as those comprising lanthanoid elements. Magnets comprising neodymium, or
salts thereof, may be useful herein because of their magnetic strength. In one
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embodiment, the magnets comprise neodymium, iron, and boron ("NIB
magnets"). Samarium, gadolinium, and even dysprosium, and salts thereof may
be used for specific applications. Other types of permanent magnets such as
ceramic magnets and other composite magnets, and even flexible magnets may
be suitable for use herein for other specific applications.
[63] As used herein, an "interconnect" is generally a connection between any
two
aspects of a system. Interconnect herein generally reflects an electrical
connection and a physical connection between e.g. two component or a
component and a substrate. "Substrate" is any material used to hold or contain
other electronic components connected thereon for use in an electronic system
or
device, such as a printed circuit board (`PCB'). Substrates can be flexible or
rigid.
Preferred rigid substrates include e.g. PCBs, composites, and rigid polymers;
preferred flexible supports include e.g., flexible polymers.
[64] As used herein, "parallel" means that two lines, such as lines
representing
magnetic flux are always the same distance apart and never touch each other
and
exist in the same plane, i.e. they are at 0 degrees with respect to each
other.
Parallel lines herein are generally reference magnetic flux lines in the Z-
axis,
which are generally perpendicular (i.e. 90 degrees) to the X-Y plane of the
substrate. Because of the difficulty of having perfectly parallel flux lines
throughout entire applications involving multiple magnets, parallel lines in
various embodiments herein may include lines that are "substantially parallel"
to
each other and/ or substantially perpendicular to the X-Y. Such lines may be
positioned at e.g. about -30 to about 30 degrees with respect to each other,
and/ or at about 60 to about 120 degrees with respect to the Z-Y plane. More
preferably such lines are positioned at e.g. about -15 to about 15 degrees
with
respect to each other, and/ or about 75 to about 105 degrees with respect to
the Z-
Y plane. Still more preferably substantially parallel flux lines are
positioned at
e.g. about -5 to about 5 degrees with respect to each, and/ or about 85 to
about 95
degrees with respect to the X-Y plane of the substrate. Even more preferably
the
substantially parallel lines will be positioned within about 0 to about 2
degrees of
each other and/ or within about 0 to about 2 degrees of perpendicular to the X-
Y
plane. The skilled artisan will appreciate that the more the magnetic flux
lines
approximate parallel to each other and perpendicular to the X-Y plane, the
more
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the ACA will form parallel columns during the alignment which will be the
basis
of the interconnect, and the less shorts and other defects that negatively
impact
either the functionality or the durability of the interconnects so formed will
be
present.
[65] As used herein, "Z-axis" means the direction that is perpendicular to the
main
plane in which the substrate lies, i.e. the X-Y plane.
Detailed Description of Illustrative Embodiments
[66] Systems and methods for creating improved and more consistent electronic
interconnects with ACAs in electronic circuits are provided herein. Such
systems
generally comprise individual magnets placed in a location corresponding to
each component being connected. The size and strength of each magnet is
determined based on the component, the substrate, the ACA in use, and the
application in question. Only components being connected with the ACA are
exposed to any magnetic field, meaning sensitive components are not exposed to
unneeded magnetic fields. Preferably, the optimized interconnects provide
better yields, less shorts and other failures, and longer lifetimes/ more
cycles.
The inventors have surprisingly discovered that by employing strategic
selection
of magnet size, strength, and placement, the consistency and quality of
interconnects can be substantially improved. Thus, disclosed herein are
methods
and systems for improving the creation of interconnects using ACAs.
[67] In a first aspect this disclosure provides novel methods of aligning
and curing ACA-based interconnections in digital devices, circuit
boards, electronics, and the like. The methods for establishing an
interconnect between a substrate and an electronic component
populated thereon using a magnetically-alignable anisotropic
conductive adhesive (ACA), generally comprise the steps of:
[68] a) establishing the dimensions and location on the substrate of
the first electronic component to be placed on and connected to the
substrate;
[69] b) determining the placement location of the first magnet
corresponding to the dimension and location established for the
component in step a);
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[70] c) determining the dimensions and strength of the magnet
required in step b); and
[71] d) mapping the flux lines of the magnetic field for the magnet.
[72] Steps a) ¨d) are repeated for each additional component to be
placed on and connected to the substrate, so as to determine the
properties and placement location for each additional magnet needed.
The skilled artisan will appreciate that throughout the specification
there are various methods set forth in set herein wherein various steps
are set forth. It should be noted that wherever such steps are not
strictly required to be performed in the stated order, the methods can
equally be performed by conducting the steps in a different order as
best facilitates the achievement of successful interconnections without
changing the overall purpose and result.
[73] The method further comprises the steps of creating a magnetic tray
and securing each magnet in its respective placement location on the
tray; and creating an alignment tray and adapting the alignment tray to
retain the substrate during alignment of the ACA in the Z-axis (i.e.
column formation) and curing.
[74] The substrate is then placed on the alignment tray. The ACA is
applied to the substrate where the components will be placed. The
substrate is then populated with the first and each additional
component.
[75] The alignment tray (including the substrate, components to be
attached, and the applied ACA) and the magnetic tray are assembled
to expose the ACA to the magnets. Sufficient exposure time is
provided allowing columns to form in the Z-axis in the ACA; and the
ACA is then cured, thereby establishing interconnects between the
substrate and the first and each additional component.
[76] Generally, the alignment tray and the magnetic tray are made of
nonmagnetic material, such as aluminum or thermostable materials,
such as plastics or composites. The magnet tray is generally adapted to
receive the first and each additional magnet in their respective
placement locations on the tray. The completed assembly comprising
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the magnet tray with magnets, and the alignment tray with substrate
populated with components and ACA can be placed in a curing oven.
[77] In various embodiments, the magnets comprise permanent magnets. The
magnets comprise rare earth magnets in one presently preferred embodiment.
Rare earth magnets comprising neodymium or NIB magnets are used in one
embodiment.
[78] The inventor has discovered that the size and strength of the magnets for
creating interconnections can be determined empirically for each application
to
optimize the consistency and quality of the interconnects formed. The skilled
artisan will appreciate that selecting the size and strength of a particular
magnet
will relate to the process of column formation, and the magnet selection will
be
influenced by the desired properties of the columns, such as height, diameter,
and the strength of the column. Moreover the connections of the column to both
the component and the substrate are influenced by the magnet properties as
well.
[79] Thus, in certain embodiments, the size and strength of the magnets are
determined to optimize or address the attributes of the column or the final
interconnects. Such attributes may include the height of the columns, the
interconnection strength, the number of resultant shorts, the expected
lifetime of
the completed device or board, the yield of usable product, or the failure
rate or
number of rejects resulting from the process of creating the interconnections.
[80] The inventor has also determined that distinct benefits arise from
utilizing
magnetic flux lines that are substantially parallel to each other and/ or
substantially perpendicular to the X-Y plane in an area corresponding to the
area
of the substrate upon which the component and ACA are located. In various
embodiments the magnetic flux lines consist essentially of such parallel and/
or
perpendicular lines.
[81] In various embodiments, the ACA forms substantially uniform columns in
terms of height and diameter as a result of utilizing the methods provided. In
presently preferred embodiments, the ACA forms substantially uniform columns
that are substantially perpendicular to the X-Y plane of the component and the
substrate.
[82] To optimize the method further, further improve consistency and to make
the
method more foolproof, in one embodiment the geometry of portion of the
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alignment tray that accommodates and/ or retains the substrate is configured
so
that the substrate can only be placed in the alignment tray in one
orientation.
This enables a technician to reproducibly place the substrate in the alignment
tray for production.
[83] In other embodiments, the alignment tray comprise alignment means such as
placement pins, complementary structure, or the like to ensure the magnetic
tray
and the alignment tray can only be assembled in the proper orientation with
respect to each other. Alternatively, the geometry of the alignment and
magnetic
trays only allows assembly in one (proper orientation). The skilled artisan
will
appreciate that there are a number of simply ways to provide for proper
orientation. Again, such features will further increase consistency and allow
any
technician to use the method for production.
[84] As discussed above, generally, the methods allow an assembly comprising
the
positioned magnet tray and alignment tray to be placed directly into a curing
oven. Preferably the alignment tray and the magnet tray comprise materials
that
can withstand curing conditions for curing the ACA. In one embodiment the
trays are aluminum or thermostable, nonmagnetic materials that can withstand
e.g. 50-70 C, 60-80 C, 70-100 C, 75-120 C, 100-140 C, or even greater
temperatures.
It is expected that lower temperature curing methods will continue to be
developed, in which case the materials used to the alignment and magnet trays
can be revised accordingly.
[85] The methods can be more fully appreciated by reference to the figures.
FIG. 2
shows a flow chart for one embodiment 200 of the methods described herein. As
can be seen the methods generally start with an understanding of the substrate
and the components to be placed thereon and connected thereto using the ACA
as noted in step 210. The dimensions and location of each component can be
mapped out to allow the design of a magnet tray and a determination of the
placement location 220 of each magnet required.
[86] The size and strength of each magnet can be determined 225 based on the
specifics of the application. The properties of the magnetic field, e.g. the
magnetic flux lines for each magnet can be determined or mapped out 230. The
skilled artisan will understand how to determine the size, strength, and
magnetic
flux lines for each magnet required. The skilled artisan will also appreciate
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order of the foregoing steps may be altered as might be preferable in a given
application.
[87] The skilled artisan will further appreciate that the properties of the
magnet(s)
will influence the development and formation of the columns in the Z-axis
within
the ACA. Stronger magnets will allow higher columns that form faster, however
it is not desirable to have the magnet be too strong. In various embodiments,
the
ideal properties of the magnets are determined empirically for any given
application.
[88] A magnet tray is created 235 and the magnets selected for the job are
secured
in their respective locations 240. It is understood that the magnet tray is
designed to accommodate each of the magnets in its respective locations by any
useful means that does not alter the position or magnetic field of the magnet
with
respect to the component and substrate. In one embodiment, the magnetic tray
is
made of aluminum with holes cut out at the locations where each of the magnets
is to be placed. The magnets may be secured in place 240 by any means again
provided it does not alter the strength or flux lines of the magnet. Adhesives
can
be conveniently used to secure the magnets in the magnet tray in certain
embodiments.
[89] An alignment tray is created 245 to serve as a carrier for the substrate
and
components and to ensure the substrate and each component populated thereon
aligns with the corresponding magnet in the magnet tray. The alignment tray is
adapted 250 to receive and retain the substrate during the alignment of the
ACA
and the subsequent curing. The tray can be adapted by any mean to secure the
substrate during the process of creating the interconnections. In one
embodiment a recessed area complementary to the shape of the substrate is
created to receive and restrain the substrate passively during the process. In
a
presently preferred embodiment, the substrate can only be received in one
orientation in the alignment tray, thereby minimizing the risk of misalignment
with the magnets in the magnet tray.
[90] The ACA is applied 265 to the substrate at the locations where the
components will be placed 260. In some embodiments contemplated herein the
steps may vary, e.g. the components may be populated and the ACA may be
applied at the same time. The skilled artisan will also appreciate the order
of
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operation here may so vary provided the end result is that each component is
correctly placed on the substrate in the desired location with the desired
amount
of ACA in between the two.
[91] The alignment tray and the magnet tray are then brought into proximity
with
each other. In a presently preferred embodiment, the trays must be brought
into
alignment while positioned vertically with respect to each. This is enforced
by
structure which prevent sliding the alignment tray with the substrate across
the
magnetic fields of the magnets in the magnet tray and initiating improper
column formation. By requiring the magnet tray and the alignment tray to be
brought into proximity in this fashion, the column formation is optimized and
restricted to substantially the Z-axis. The thus assembled trays 270 (the
'assembly' or magnet pallet assembly) can be then be placed in an oven for
curing under appropriate conditions. Because the assembled trays fit together
in
a manner that optimizes formation of Z-axis (i.e. perpendicular) columns that
are
parallel to each other and because the assembly can be moved without
substantially interfering with the columns, the oven may be a batch oven
wherein
the assemblies are manually moved in and out of the oven, or it may be a
semicontinuous or even continuous over, such as a reflow oven wherein the
assemblies travel along a conveyor through the oven. After the ACA has cured
there is little risk of impacting the column structure; i.e. the columns are
stable in
the cured ACA.
[92] It should also be noted that a phenomenon referred to herein as 'chip
flipping' can occur with certain components. If a component is magnetically
polar ¨ i.e. if the component has e.g. two separated magnetic poles, when
exposed to the magnetic field of the magnet tray the component will 'flip' to
align itself with the magnetic field. Because the ACA is not yet aligned or
cured
when the system is exposed to the magnet tray, there is nothing to prevent the
chip(s) from doing so. In extreme cases the component could be pulled entirely
from the substrate. While this only happens with certain components, if
present
it poses a problem. The inventor has developed a simple solution to solve this
issue if such a component is present. It requires including an additional
'tacking'
step to secure the component / chip prior to exposure to the magnet tray.
Generally, the components of concern are secured to the substrate. One useful
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way is to apply a small amount of epoxy to hold the susceptible component in
place in the presence of the magnetic field. Present methods include the use
of
UV-curable epoxy applied as a dab sufficient to secure the component, followed
by a brief exposure to UV light of sufficient intensity and duration to ensure
the
epoxy is cured. The assembly of substrate, component, and ACA can then be
placed in proper proximity to the magnet tray to allow the Z-axis columns to
form without concerns regarding components/ chips flipping.
[93] In a second of its several aspects, this disclosure provides systems for
creating
interconnects between a substrate and electronic components attached thereto
using a magnetically-alignable anisotropic conductive adhesive (ACA). The
system comprises a magnet tray comprising a nonmagnetic tray adapted to
receive and retain each of one or more magnets placed therein in a location
that
corresponds to the location of one or more electronic components on a
substrate
to which the components are to be connected.
[94] The system also comprises an alignment tray adapted to receive a
substrate
populated with one or more components to be connected thereto with an ACA.
The alignment tray can retain the substrate during the alignment and curing of
the ACA.
[95] The system also comprises an ACA comprising magnetically-alignable
particles capable of forming interconnections conductive in the Z-axis. The
ACA
formulation can be varied for specific applications as may be dictated by the
electronic components or the nature of the device for which components are
being interconnected. ACAs may be formulated with e.g. different sized
electromagnetic/ conductive particles for applications having different pitch
requirements.
[96] In presently preferred embodiments, the alignment tray and the magnetic
tray are made of nonmagnetic material. In one embodiment the substrate can
only be placed in the alignment tray in one orientation to avoid confusion and
mistakes and to allow nontechnical staff to assist with production.
[97] Generally, the magnet tray and the alignment tray are adapted to be
arranged
together vertically in removable fashion such that the components on the
substrate are vertically aligned with the magnets in the magnet tray and the
ACA
is exposed to the magnetic field such that the flux lines are substantially
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perpendicular to an X-Y plane defining the substrate. Such arrangement is
preferably maintained until curing of the ACA is complete.
[98] In various embodiments of the system the magnets are permanent magnets.
Rare earth magnets are useful for many applications herein, including magnets
that comprise neodymium, such as NIB magnets. These magnets can provide a
strong magnetic field.
[99] An assembly comprising the magnet tray, the alignment tray, and the
substrate populated with components can be placed directly into a curing oven
in
one embodiment. This enables the aligned ACA to be cured with minimal
movement and little risk of disturbing the columns formed in the Z-axis upon
exposure to the magnetic field. In another embodiment the assembly and/ or the
magnet tray serves as a rack that can slide into the oven directly and does
not
requires any supporting shelf or additional rack for use. In other
embodiments,
the assembly can be placed on a conveyor mechanism for use with a
semicontinuous or continuous process oven. In such embodiments the conveyor
may include a multitude of different assemblies with the same of different
configurations of substrates and components ¨ each matched with its own
magnetic tray designed according to the specifics and the components and
substrate to be interconnected.
[100] In various embodiments for each magnet in the magnet tray of the system,
the
magnetic flux lines are substantially parallel to each other and substantially
perpendicular to the X-Y plane in an area corresponding to the area of the
substrate upon which the component and ACA are located. Optimal
interconnections can arise from such arrangements. The ACA forms
substantially uniform columns which are substantially perpendicular to the X-Y
plane of the component and the substrate in various embodiments.
[101] With further reference to the figures, FIG 1 depicts an embodiment 100
of the
system for magnetically aligning and curing ACA interconnects illustrating
certain features of the system. Shown is a cross-sectional view of an
embodiment
for magnetically aligning and curing ACA interconnects showing a nonmagnetic
magnet tray 110 with a plurality of magnets 120 positioned therein. The magnet
tray 110 has openings (not numbered for convenience and clarity) to
accommodate the magnets 120, which may be secured in the magnet tray 110
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using adhesive (not shown) or other means of securing that do not alter the
magnetic flux lines or otherwise interfere with the magnets 120. An alignment
tray 130 has a recess that receives the substrate 140 which is retained in
place
during the alignment and curing of the ACA to form the interconnects.
Substrate
140 has a plurality of electronic components 150 positioned thereon. ACA (not
shown) is applied/ positioned (or likely has been applied) between the
components 150 and the substrate 140. As can be seen, the placement of each of
magnets 120 corresponds to the location of component 150 on substrate 140 so
that the magnets 120 are vertically aligned with the components 150. In this
configuration the magnetic field provides the force to align electromagnetic
particles of the ACA (not shown) to form the Z-axis column. As can be seen,
the
area covered by each of magnets 120 is larger than the area covered by the
corresponding component 150, such that the system 100 provides more optimal
and consistent alignment as compared to prior art electromagnets that cover
the
entire surface of the substrate, or magnets that are the same size as the
component.
[102] Fig. 3 depicts an embodiment of an alignment tray 300 illustrating
various
aspects thereof. The single tray 310 depicted comprises a plurality of
substrates
(not shown), each having a single component 320. In other embodiments (not
shown) depending on the size, a single alignment tray may hold a single
substrate with one or more components. The presence of alignment means 330
are holes in this embodiment allow for proper alignment using e.g. pins or
rods,
with a magnet tray (not shown) such that the magnet tray and alignment tray
are
vertically arranged and the magnets in the magnet tray are aligned with the
corresponding component to be interconnected to the substrate on the alignment
tray. Because proper alignment is important to successful formation of
interconnects, in various embodiments the alignment trays may include simple
features e.g., varying hole geometry, hole patterns or offsets, differing hole
size, a
combination of holes and pins, along with complementary structures in the
magnet tray to ensure the alignment tray and the magnet tray can only be
aligned in a single orientation with respect to each other. The skilled
artisan will
appreciate that there are many art recognized methods for achieving proper
alignment between two such objects.
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[103] In yet another aspect, the disclosure provides kits for creating
interconnects
between a substrate and electronic components attached thereto using a
magnetically-alignable anisotropic conductive adhesive. The kits generally
comprise:
[104] at least one magnetic tray comprising a nonmagnetic tray adapted to
retain
one or more magnets in locations corresponding to a desired placement of an
electronic component on and connection of the component to a substrate using
an ACA;
[105] sufficient magnets to complete the magnet tray, each magnet of a
desired
size and strength for making an interconnection between the component and the
substrate using the ACA; and
[106] at least one alignment tray adapted to receive and retain the
substrate and
components populated thereon during the alignment and curing of the ACA to
form the interconnect.
[107] Optionally, the kits further comprise an ACA suitable for use with
the kit to
create interconnects between components and the substrate using the kit.
[108] The magnet tray and the alignment tray are generally configured to be
oriented vertically with respect to each other and can be assembled such that
an
electronic component placed on a substrate on the alignment tray is brought
into
vertical alignment with a magnet on the magnet tray when the magnet tray and
the alignment tray are so oriented and assembled. This configuration is used
for
both the alignment and curing process in various embodiments.
[109] In a presently preferred embodiment the oriented and assembled magnet
tray
and alignment tray ("the assembly") can be placed into a curing oven. In one
embodiment, the magnet tray or the assembled trays function as a rack in the
oven, or a rack for conveying into a semicontinuous or continuous oven such as
a
reflow oven, or a curing tunnel.
[110] In various embodiments, when the magnet tray and alignment tray are
assembled together, for each magnet in the magnet tray, the magnetic flux
lines
are substantially parallel to each other and substantially perpendicular to
the X-Y
plane in an area corresponding to the area of the substrate upon which the
component is located. Generally, an ACA positioned between the substrate and
a component thereon forms substantially uniform columns that are substantially
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perpendicular to the X-Y plane of the component and the substrate when the
trays are oriented and assembled.
[111] In a still further aspect, the disclosure provides oven systems for
creating
interconnections between a substrate and an electronic component to be placed
thereon and connected thereto using an ACA. The systems operate generally as
described above for other systems described herein and in accordance with the
methods. Generally the oven systems comprise a curing oven and one or more
shelves or racks each comprising a magnetic tray fitted with one or more
magnets each placed in a location corresponding to the location of an
electronic
component to be placed on and connected to a substrate using an ACA; and an
alignment tray adapted to receive and retain a substrate populated with one or
more components to be placed thereon and connected via an ACA.
[112] The magnets in one embodiment are permanent magnets. Rare earth magnets
are useful for many applications herein, including magnets that comprise
neodymium, such as NIB magnets.
[113] In various embodiments of the oven systems, for each magnet in the
magnet
tray of the system, the magnetic flux lines are substantially parallel to each
other
and substantially perpendicular to the X-Y plane in an area corresponding to
the
area of the substrate upon which the component and ACA are located. The ACA
forms substantially uniform columns, which are substantially perpendicular to
the X-Y plane of the component and the substrate in various embodiments.
[114] An embodiment 400 of the oven system is shown in FIG 4. As can be seen
each assembly 450 of a magnet tray 410 and an alignment tray 420 can serve as
a
rack 425 in the batch oven 401 which is generally designed to accommodate a
plurality of such racks 425. A magnified view of an assembly 450 is shown as
inset Fig 4B, which comprises an assembled magnet tray 410 and alignment tray
420 retaining the substrate, components and the ACA (generally, 430) during
alignment of the columns in the Z-axis, and throughout the curing process. The
alignment holes 435 ensure that the assembly can only be put together in the
proper orientation. Inset Fig 4C, shows a separate magnet tray 410 showing a
plurality of permanent magnets 415 in place.
[115] The scope of the invention is set forth in the claims appended hereto,
subject,
for example, to the limits of language. Although specific terms are employed
to
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describe the invention, those terms are used in a generic and descriptive
sense
and not for purposes of limitation. Moreover, while certain presently
preferred
embodiments of the claimed invention have been described herein, those skilled
in the art will appreciate that such embodiments are provided by way of
example
only. In view of the teachings provided herein, certain variations,
modifications,
and substitutions will occur to those skilled in the art. It is therefore to
be
understood that the invention may be practiced otherwise than as specifically
described, and such ways of practicing the invention are either within the
scope
of the claims, or equivalent to that which is claimed, and do not depart from
the
scope and spirit of the invention as claimed.
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