U.S. patent application number 12/582637 was filed with the patent office on 2010-07-01 for method for depositing solder material on an electronic component part.
Invention is credited to Kenneth J. Huth, Lawrence C. Monterulo, John C. Sugrue.
Application Number | 20100163608 12/582637 |
Document ID | / |
Family ID | 38228892 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100163608 |
Kind Code |
A1 |
Huth; Kenneth J. ; et
al. |
July 1, 2010 |
Method for depositing solder material on an electronic component
part
Abstract
A method for accurately depositing a required volume of solder
material on a specific area of a lead frame, substrate or other
part (4) of an electronic component to be bonded by reflow of
solder material to another part into a reliable, void-free
connection during a subsequent assembly step comprises the
following steps. Minute particles (3) of solder material whose
cumulative volume corresponds to the total volume to be deposited
are loaded into a cavity (2) cut into a fixture (1) made from a
material such as graphite. The cavity delineates the specific area
of deposit. The part (4) is then laid upon the fixture and
immobilized thereon by a cover (7) made from a material such as
graphite. The fixture and its enclosed part are then subjected to
solder material melting temperature under a controlled atmosphere
in a furnace. The cavity is patterned and dimensioned to
accommodate the right number of uniformly dimensioned particles
necessary to precisely create the desired deposit of solder
material.
Inventors: |
Huth; Kenneth J.; (Whitsett,
NC) ; Monterulo; Lawrence C.; (Yonkers, NY) ;
Sugrue; John C.; (Stratford, CT) |
Correspondence
Address: |
CHARMASSON, BUCHACA & LEACH, LLP
2635 Camino Del Rio South, Suite 102
SAN DIEGO
CA
92108
US
|
Family ID: |
38228892 |
Appl. No.: |
12/582637 |
Filed: |
October 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12418845 |
Apr 6, 2009 |
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12582637 |
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12159682 |
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PCT/US06/49669 |
Dec 29, 2006 |
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12418845 |
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11523895 |
Sep 19, 2006 |
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12159682 |
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11323444 |
Dec 30, 2005 |
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11523895 |
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Current U.S.
Class: |
228/256 |
Current CPC
Class: |
H05K 2203/0338 20130101;
H05K 2203/041 20130101; H05K 3/3478 20130101; H05K 2203/0113
20130101 |
Class at
Publication: |
228/256 |
International
Class: |
B23K 1/20 20060101
B23K001/20; B23K 31/02 20060101 B23K031/02 |
Claims
1. A method for accurately depositing a metered volume of solder
material of a given melting point on a delineated area of an
electronic component part, said method comprising the steps of:
providing a fixture having a top surface shaped and dimensioned for
intimate contact with said area, and a melting temperature
substantially higher than said melting point; carving into said top
surface a cavity shaped to be congruent with said area; placing
into said cavity a number of particles of said solder material;
positioning said part against said top surface and said particles
in contact with said area; and exposing said fixture and part to a
temperature at least equal to said melting point; whereby the
material of said particles melts and adheres to said area.
2. The method of claim 1 which further comprises securing said part
upon said fixture with a cover.
3. The method of claim 1, wherein said fixture is made of a
material comprising high density graphite.
4. The method of claim 1, wherein said solder material comprises a
metal alloy selected from the group consisting of gold alloys, tin
alloys, lead alloys, copper alloys, and silver alloys.
5. The method of claim 1, wherein said solder material comprises a
metal alloy selected from the group consisting of AuSn, AuGe, AuSi,
AuAgCu, AgCu, and PbSnAg.
6. The method of claim 1, wherein said delineated area comprises an
electronic package lead frame.
7. The method of claim 1, wherein said delineated area comprises a
marginal, peripheral area of a microelectronic package lid.
8. The method of claim 1, wherein said cavity is segmented into a
plurality of ditches.
9. The method of claim 8, wherein two of said plurality of ditches
are differently dimensioned.
10. The method of claim 1, wherein said particles are laid in a
single row into said cavity.
11. The method of claim 1, wherein said particles are substantially
uniform.
12. The method of claim 1, wherein said particles are laid in a
plurality of rows into said cavity.
13. The method of claim 1, wherein said particles are symmetrical,
and have calculated dimensions.
14. The method of claim 1, wherein said particles are spherical,
and have a calculated diameter and radius.
15. The method of claim 1, wherein the cumulative volume of said
particles is equal to said metered volume.
16. The method of claim 14, wherein said cavity has a constant
depth greater than said diameter.
17. The method of claim 1, wherein said step of positioning
comprises inverting said fixture and part.
18. The method of claim 14, wherein said cavity has a constant
depth lesser than said diameter.
19. The method of claim 1, which further comprises pressing said
part against said fixture.
20. The method of claim 14, wherein said cavity has an arcuate
bottom of a radius commensurate with the radius of said
particles.
21. The method of claim 14, wherein said cavity has a series of
spaced-apart bottom separators dimensioned to intimately nest said
particles.
22. The method of claim 21, wherein said separators are regularly
spaced-apart at a calculated interval.
Description
PRIORITY APPLICATION
[0001] This is continuation of U.S. patent application Ser. No.
12/418,845, filed Apr. 6, 2009, a continuation of U.S. patent
application Ser. No. 12/159,682, filed Jun. 30, 2008, a 371 of
PCT/US06/49669 filed Dec. 29, 2006 which is a continuation-in-part
of U.S. patent application Ser. No. 11/323,444 filed Dec. 12, 2005
and a continuation-in-part of U.S. patent application Ser. No.
11/523,895 filed Sep. 19, 2006.
FIELD OF THE INVENTION
[0002] This invention relates to microelectronic assemblies and
packaging, and more particularly to the deposition of soldered
strips or other shaped patches on electronic component parts such
as lead frames, package lids, or substrates for later reflow and
connection.
BACKGROUND
[0003] The extensive miniaturization of electronic circuits and
their packaging requires the accurate deposition of minute,
accurate quantity dabs, lines, or other shaped patches of solder
over delineated areas of a component surface for future connecting
of leads, lids and other parts by reflow.
[0004] The solder must be applied in controlled quantity and
precisely on target in order to avoid bridging or unwanted gaps
with other soldered points or circuit parts.
[0005] In the prior art, stamped soldered preforms are tack-welded
to, or solder strips are laid on the electronic assembly or package
in order to hold the solder in place for later remelting.
[0006] This invention results from attempts to devise a more
precise method for depositing minute, accurate amounts of solder in
precise locations without portions coming out of the demarcated
area.
SUMMARY
[0007] The instant invention provides a method for more accurately
depositing a specified amount of solder material on a precisely
delineated area on a surface of an electronic component part that
will be subsequently subjected to reflow.
[0008] In some embodiments the method can used in order to
establish a reliable and void-free connection with another
component part. In some embodiments the component part may be a
lead frame, package lid, substrate or other part. In some
embodiments the volume of required solder material is calculated as
the product of the area to be covered by the solder material times
the desired height of the solder patch or strip. In some
embodiments this volume is used to calculate the number or amount
of solder material particles which are loaded into a cavity cut in
the exposed surface of a fixture made of high density graphite or
other crucible-type material having a melting temperature
substantially higher than the melting point of the solder material.
In some embodiments the delineated area of the part upon which the
solder material is to be deposited can be positioned against the
exposed surface of the fixture, and the combined fixture and part
are exposed to a temperature at least as high as the melting
temperature of the solder material in a batch or belt furnace under
a controlled atmosphere.
[0009] In some embodiments the top surface of the fixture can be
shaped and dimensioned for intimate contact with the solder
material deposit area. In some embodiments the cavity carved into
said exposed surface can be shaped to be congruent with the deposit
area when the part is positioned against the fixture with the
particles in contact with said area.
[0010] In some embodiments the part can be secured upon the fixture
with a cover of the same high melting point material.
[0011] In some embodiments the particles can be laid in one or more
rows into the cavity. In some embodiments the particles can be
selected to have the same calculated, uniform range of dimensions
and can be symmetrical, spherical, cylindrical or other shapes.
[0012] In some embodiments the cumulative volume of all the
particles is equal to the total metered volume of solder material
to be deposited.
[0013] In some embodiments the cavity has a constant depth which is
greater than the diameter or size of the particles. In some
embodiments the fixture and part are inverted prior to introduction
into the furnace so that the particles drop into contact with the
area of deposit.
[0014] In other embodiments the cavity has a depth that is lesser
than the diameter or other appropriate size dimension of the
particles and pressure is applied to the cover to hold the
particles in position and assure a better adhesion of the solder to
the part. In some embodiments the fixture may or may not be
inverted during heating depending on the flow characteristics of
the materials involved.
[0015] In some embodiments the cavity has an arcuate bottom whose
radius is commensurate with the radius of the particles.
[0016] In some embodiments the bottom of the cavity has a series of
spherical depressions, each dimensioned to intimately nest a
particle of solder material. In some embodiments these depressions
are regularly spaced apart at a calculated interval as a function
of the total volume of solder material to be deposited and the
number and size of the particles.
[0017] In some embodiments the cavity is widened and/or segmented
to form one or more variably shaped ditches sized to be filled with
an array of particles.
[0018] Some embodiments provide a method for accurately depositing
a metered volume of solder material of a given melting point on a
delineated area of an electronic component part, said method
comprising the steps of: providing a fixture having a top surface
shaped and dimensioned for intimate contact with said area, and a
melting temperature substantially higher than said melting point;
carving into said top surface a cavity shaped to be congruent with
said area; placing into said cavity a number of particles of said
solder material; positioning said part against said top surface and
said particles in contact with said area; and exposing said fixture
and part to a temperature at least equal to said melting point;
whereby the material of said particles melts and adheres to said
area.
[0019] In some embodiments the method further comprises securing
said part upon said fixture with a cover. In some embodiments said
fixture is made of a material comprising high density graphite. In
some embodiments said solder material comprises a metal alloy
selected from the group consisting of gold alloys, tin alloys, lead
alloys, copper alloys, and silver alloys. In some embodiments said
solder material comprises a metal alloy selected from the group
consisting of AuSn, AuGe, AuSi, AuAgCu, AgCu, and PbSnAg. In some
embodiments said delineated area comprises an electronic package
lead frame. In some embodiments said delineated area comprises a
marginal, peripheral area of a microelectronic package lid. In some
embodiments said cavity is segmented into a plurality of ditches.
In some embodiments two of said plurality of ditches are
differently dimensioned. In some embodiments said particles are
laid in a single row into said cavity. In some embodiments said
particles are substantially uniform. In some embodiments said
particles are laid in a plurality of rows into said cavity. In some
embodiments said particles are symmetrical, and have calculated
dimensions. In some embodiments said particles are spherical, and
have a calculated diameter and radius. In some embodiments the
cumulative volume of said particles is equal to said metered
volume. In some embodiments said cavity has a constant depth
greater than said diameter. In some embodiments said step of
positioning comprises inverting said fixture and part. In some
embodiments said cavity has a constant depth lesser than said
diameter. In some embodiments the method further comprises pressing
said part against said fixture. In some embodiments said cavity has
an arcuate bottom of a radius commensurate with the radius of said
particles. In some embodiments said cavity has a series of
spaced-apart bottom separators dimensioned to intimately nest said
particles. In some embodiments said separators are regularly
spaced-apart at a calculated interval.
[0020] Some embodiments provide a method for accurately depositing
a volume of solder of a given melting point to a given height on a
delineated area of given superficies on the face of an electronic
component, said method comprising the steps of: providing a slab of
material having a bottom surface shaped and dimensioned for
intimate contact with a zone of said face including said area, and
a melting temperature substantially higher than said melting point;
drilling through said slab at least one bore substantially
perpendicular to said bottom surface and having a lower opening in
said bottom surface falling within said area when said bottom
surface is in contact with said zone; carving into said bottom
surface and around said bottom opening, a cavity at least as deep
as said height and shaped to be congruent with said delineated
area; intimately contacting said face with said slab's bottom
surface; inserting into said bore, a particle of said solder, said
particle having a volume substantially equal to a product of said
superficies times said height; and exposing said component and slab
to a temperature at least equal to said melting point; whereby said
particle of solder melts, flows and deposits accurately over said
delineated area.
[0021] In some embodiments said delineated area is elongated about
an axis; said step of drilling comprises drilling a plurality of
said bores leading to spaced-apart openings along a line parallel
to said axis within said cavity; and said step of inserting
comprises inserting at least one of said particles in each of said
bores, said particles having a cumulative volume equal to said
product. In some embodiments said material comprises high density
graphite. In some embodiments said solder comprise a gold alloy. In
some embodiments said alloy is Au/Sn. In some embodiments said
delineated area comprises an electronic package lead attachment
area on a lead frame. In some embodiments said delineated area
comprises a marginal, peripheral area on an electronic package
lid.
[0022] Some embodiments provide a device for accurately depositing
a volume of solder to a given height on a limited area on the face
of an electronic component which comprises: a slab of material
having a top surface, and a bottom surface shaped and dimensioned
for conformingly resting upon a zone of said face including said
area; said slab having at least one bore having a upper opening in
said top surface and a lower opening in said bottom surface, said
lower opening being positioned above said area when said bottom
surface rests upon said zone; and said slab further having a cavity
in said bottom surface and around said bottom opening, said cavity
having a depth greater than said height, and being shaped to
congruently fit over said limited area. In some embodiments the
device further comprise a plurality of said bores having lower
openings positioned at regularly spaced-apart locations along a
line. In some embodiments said limited area comprises at least one
lead connection spot on an electronic package lead frame. In some
embodiments said limited area comprises a marginal, peripheral area
on an electronic package lid. In some embodiments the device
further comprises a small volume of solder inserted in each of said
bores. In some embodiments said volume is obtained by dividing the
amount of solder to be deposited by the number of bores. In some
embodiments each of said volume consists of a particle of solder.
In some embodiments said particle of solder has a shape selected
from the group consisting of a sphere, a cylinder, and a
quadranglarly sided shape.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a top plan view of the top surface of the
fixture.
[0024] FIG. 2 is a diagrammatical cross-section of the cavity in a
first embodiment of the fixture.
[0025] FIG. 3 is a partial diagrammatical cross-sectional view of
the first embodiment of the fixture placed in a furnace.
[0026] FIG. 4 is a diagrammatical cross-section of a second
embodiment of the cavity section.
[0027] FIG. 5 is a diagrammatical cross-sectional view of the
cavity section in a third embodiment of the fixture.
[0028] FIG. 6 is a perspective partial view of a fourth embodiment
of the cavity section.
[0029] FIG. 7 is a perspective partial view of a fifth embodiment
of the cavity section.
[0030] FIG. 8 is a bottom plan view of a template according to the
invention;
[0031] FIG. 9 is a cross-sectional view taken along line 9-9 of
FIG. 8;
[0032] FIG. 10 is a cross-sectional view taken along line 10-10 of
FIG. 8;
[0033] FIG. 11 is a top plan view of the template applied to a lead
frame;
[0034] FIG. 12 is a bottom plan view of a template for an
electronic package lid; and
[0035] FIG. 13 is a cross-sectional view of a package lid, template
and framing fixture assembly.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0036] Referring now to the drawing, there is shown in FIG. 1 the
top surface of a fixture 1 according to the invention. The fixture
1 is particularly adapted for depositing a strip of solder in a
marginal area around the periphery of the lid of a microcircuit
component. A cavity in the form of an elongate channel 2 carved in
the top surface of the fixture is shaped and dimensioned to be
congruent to the area targeted to receive a deposit of solder
material. The cavity 2 has been filled with a number of uniformly
dimensioned particles of solder material selected in this case to
be in the shape of spheres 3. The cumulative volume of all the
spheres contained within the cavity corresponds to the total volume
of solder material to be deposited. Using uniformly dimensioned
particles allows for precise control of the total volume of solder
material to be deposited.
[0037] As more specifically illustrated in FIG. 2, the cavity 2 has
a constant depth P that is greater than the diameter D of the
spheres 3. The part upon which the solder material is to be
deposited, in this case a microelectronic package lid 4, is held in
a depression 5 in the top surface of the fixture that is shaped and
dimensioned for intimate contact with the lower surface 6 of the
lid. A cover 7 and releasable fastening means such as a clamp C is
used to tightly secure the lid part 4 to the fixture 1.
[0038] The combined fixture, lid and cover is inverted prior to
introducing it into a furnace 8 as shown in FIG. 3. The spheres 3
have dropped within the cavity 2 and come in contact with the lid
4. When the combination is subjected to a temperature at least as
high as the melting temperature of the solder material melts and
adheres to the under surface 6 of the lid.
[0039] In the second embodiment of the cavity illustrated in FIG.
4, the depth Q of the cavity 2 is lesser than the diameter D of the
spheres 3. In this case, it is not absolutely necessary, but will
typically be recommendable to invert the combination fixture lid
and cover prior to introduction into the melting furnace. The
decision whether or not to invert will depend on the
characteristics of the materials involved including wettability of
the lid by the chosen solder material. A pressure A is preferably
applied to the lid to force the spheres in constant contact with
the under surface 6 of the lid, and assure a better adhesion of the
melted solder material to the lid.
[0040] As shown in FIG. 5, the bottom 9 of the cavity 2 is
preferably arcuate with a radius commensurate with the radius of
the spheres 3.
[0041] In a fourth embodiment of the cavity illustrated in FIG. 6,
a series of holes 10 are carved at regularly spaced intervals I in
the bottom of the cavity 2 to act as a localizer or separator for
spaced apart particles. In this embodiment, each hole 10 is
spherically concave and has the same radius as the spheres in order
to intimately nest one of the spheres 3. It is noted that the hole
radius can be slightly smaller than the spheres and still provide
localization. Although the holes are shown having a partially
spherical shape, other shapes either concave or convex which allow
nesting or other localization of the spheres may be acceptable. The
practicality of the selected shape is generally determined by which
shape is easiest to form during the manufacturing of the fixture.
Depending on the shape of the hole, the intended shape of the
solder patch or strip, and the space formed between the hole
boundaries and a nested particle, the fixture may require inverting
prior to initiating melting.
[0042] In a fifth embodiment of the cavity illustrated in FIG. 7,
the cavity is segmented into one or more ditches 15 having a
specified shape and dimensioning. The size and shape of the
particles is selected to form an array of particles 16 nested
within each ditch and to provide the required amount of solder
material. For example, in a ditch having a rounded corner
rectangular shape in a top plan view, and having a first side
dimension S and an orthogonal side dimension T, spherical particles
are selected having a diameter so that an integer multiple of the
diameter will substantially equal S and another integer multiple
will substantially equal T. Depending on the acceptable range of
volume of solder material, the above equalities need not be exact.
Further, the ditches can be shaped differently from one another
depending on the shape and dimensioning of the delineated area to
receive the solder material.
[0043] In a first step in the disclosed process, the total volume
of solder material to be deposited on the delineated area of a
component part is calculated by multiplying the area of deposit by
the desired height of the solder material strip or patch. The width
of the desired strip or dimensions of the desired patch of
deposited solder material determines the shape and dimensions of
the cavity, whether it is segmented into ditches, whether it uses
particle separating structures, and the size or size range of the
substantially uniformly dimensioned particles. The word
"substantially" is used because the particles may not need to be
exactly uniform but could fall within an acceptable range so that
the completed strip or patch of solder material is adequately
dimensioned. Use of uniformly dimensioned particles provides a
means for precise control of the total volume of solder material to
be deposited. For example, if spherical particles are used, then
the maximum diameter D of the spheres and the number of spheres is
determined by dividing the total volume of solder material to be
deposited by the volume of each sphere. Depending upon that number,
the spheres may be laid in a single row contiguous to each other as
shown on FIG. 1, multiple rows as shown in FIG. 7, or may be
spaced-apart using separator nesting structures 10 shown in the
embodiment of the cavity illustrated in FIG. 6. The interval I
between the nesting structures 10 in a row is determined as a
function of the number of required spheres of solder material and
the total length of that row in the cavity 2. All of the calculated
dimensions are preferably displayed in a spread sheet bearing as
entries the various determinant parameters such as the width and
length of the delineated area to be covered by the solder material,
the desired thickness of the material, the length and width of the
cavity etc. according to well-known techniques for convenient use
by the manufacturer.
[0044] In the embodiments of the cavity illustrated in FIGS. 2-5,
the loading of the spheres into the fixture can be done by pouring
the spheres into the depression 5 in the top surface of the fixture
that is shaped and configured to receive the component part and may
also include a gate for excess sphere removal. Once the cavity has
been filled, the excess spheres can be swept away through the gate,
not shown on the drawing, practiced in the periphery of the
fixture. It is important to note that the loading of particles
having a shape other than spheres can be done through pouring so
long as the groups of particles are flowable. Such flowable groups
of particles can be in the form of nanoparticles or flowable metal
powders made from techniques well known in the electronics
industry. Optionally, the fixture may be vibrated to avoid clumping
of particles and encourage packed nesting.
[0045] The pressure A applied on the lid in the second embodiment
of the cavity illustrated in FIG. 4, is preferably imparted by a
spring pressure clamp in the range of 750 to 1,000 milligrams
(about 1.5 to 2 lbs.).
[0046] The oven is purged of all air and filled with a controlled
atmosphere conducive to reflow of the solder material by being
non-oxidizing and can be for example made of 5 percent hydrogen and
95 percent nitrogen. The temperature of the oven is then raised
above the melting point of the solder material for a period of time
sufficient to melt and join the particles.
[0047] In most applications, the delineated area of the component
part upon which the solder material must be deposited is coated
with gold for best adhesion with a solder material consisting of a
gold alloy such as AuSn, AuGe, AuSi, and AuAgCu, or other alloys
such as AgCu, PbSnAg or other known solder or brazing material
which can include some metal alloys of gold, tin, lead, copper, and
silver. The oven should be raised to a temperature that will melt
the solder, such as about 340 degrees Celsius for AuSn solder, for
approximately 15 minutes in order to assure complete melting and
joining of the solder material and best adhesion to the component
part.
[0048] Referring now to FIGS. 8-11, there is shown an alternate
embodiment in which a soldering guide or template 101 particularly
adapted to deposit a series of short strips, patches or spots 102
of solder, illustrated in dotted lines in FIG. 11 and oriented
along an axis X-X', upon a lead frame 103. The strips 102 will be
later used by reflow process to connect outside leads to an
electronic package. The template 101 is constituted by a slab of
material having a melting temperature substantially higher than
melting point of the solder such as a gold alloy solders such Au/Sn
solder, preferably, a high density graphite.
[0049] The bottom surface 104 of the template is machined to
intimately match and rest upon the zone into which the areas
wherein the solder is to be deposited are located; in this case,
the flat top surface 105 of the lead frame. A series of cavities
106 cut into the bottom face 104 of the template are shaped and
dimensioned to congruently fit over the areas to be occupied and
delineated by the solder strip 102. The depths D' of the cavities
must be at least as great as the desired height of the solder strip
102. A series of sets 107 of channels or bores 108 are drilled from
the upper surface 109 of the template toward the cavities 106. Each
set 107 of bores terminates into a number of lower openings 110
regularly spaced-apart in the roof 111 of a cavity along a line
substantially parallel to the axis X-X' of the cavities.
[0050] It should be understood that if the limited area that will
receive the solder is a small spot, the cavity may be circular and
be fed by a single channel or bore.
[0051] As illustrated in FIGS. 12 and 13, a quadrangular template
112 is specifically intended for use in depositing a continuous
bead 113 of solder along a marginal, peripheral area of an
electronic package lid 114 in accordance with the present
embodiment. A cavity 115 matching the outline of the desired bead
113 is cut into the bottom surface 116 of the template 112. Bores
17 have their lower openings distributed at regularly spaced-apart
locations along the roof of the cavity 115.
[0052] FIG. 13 illustrates the positioning of the template 112 over
the package lid 114 within a special jig or fixture 118. A solder
particle 119 of a defined volume shape such as a sphere and
constituted by a metered volume of solder is inserted in the upper
opening 120 of each bore.
[0053] The whole assembly 121 comprising the fixture 118, the
package lid 114 and the loaded template 112 is then placed into an
oven and exposed to a temperature sufficient to melt the solder
under a controlled atmosphere. When melting, the solder from the
particles flows into the cavities and deposits very accurately in
the area limited by the overhead cavity 115. The solder is
distributed evenly in a continuous strip to a thickness that
depends upon the size and number of the solder particles 119.
[0054] After a cooling period, the template 112 is removed leaving
a narrow bead of solder on the periphery of the lid 114 for future
reflow attachment when the lid is installed upon an electronic
package.
[0055] The particles 119 of solder are preferably manufactured
according to processes well-known to people skilled in the art of
metal particle fabrication.
[0056] The size of the particles and the diameter of the bores are
determined by first calculating the total volume of the soldered
strip or spot, that is, the product of superficies of the targeted
area times the desired height of the solder deposit. This total
volume is then divided by the number of bores leading to the cavity
capping that area.
[0057] In many electronic package assembly applications where the
width of the soldered traces falls within the range of about 0.3
millimeter (12 mils) and about 0.7 millimeter (28 mils), the
particles can be spheres having a diameter between about 0.35
millimeter (14 mils) and about 0.65 millimeter (26 mils) with
spacing between the bores of approximately 1 millimeter (40 mils).
It should be understood that the particles can be provided in
shapes other than spheres, such as cylinders, quadrangularly sided
shapes such as blocks, or other readily manufactured shapes having
a defined volume.
EXAMPLE
[0058] For the common Au/Sn solder, the electronic component and
template assembly is preferably exposed to a temperature of
approximately 360 degrees Celsius for thirty minutes in an oven hot
zone under an atmosphere of 5% hydrogen and 95% nitrogen with a gas
flow of 10 cubic feet per hour. The assembly is then moved to a
cool zone for 20 minutes under continuous gas flow to prevent oxide
formation.
[0059] While the preferred embodiments of the invention have been
described, modifications can be made and other embodiments may be
devised without departing from the spirit of the invention and the
scope of the appended claims.
* * * * *