U.S. patent application number 10/978050 was filed with the patent office on 2005-03-17 for method of locating conductive spheres utilizing screen and hopper of solder balls.
Invention is credited to Ball, Michael B., Cobbley, Chad A., Waddel, Marjorie L..
Application Number | 20050056682 10/978050 |
Document ID | / |
Family ID | 22612252 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056682 |
Kind Code |
A1 |
Cobbley, Chad A. ; et
al. |
March 17, 2005 |
Method of locating conductive spheres utilizing screen and hopper
of solder balls
Abstract
Apparatus and methods for placing conductive spheres on
prefluxed bond pads of a substrate using a stencil plate with a
pattern of through-holes positioned over the bond pads. Conductive
spheres are placed in the through-holes by a moving feed mechanism
and the spheres drop through the through-holes onto the bond pads.
In one embodiment, the feed mechanism is a sphere hopper which
crosses the entire through-hole pattern. In another embodiment, a
shuttle plate fed spheres from a reservoir and reversibly moves
about one-half of the pitch, moving from a non-discharge position
to a discharge position.
Inventors: |
Cobbley, Chad A.; (Boise,
ID) ; Ball, Michael B.; (Boise, ID) ; Waddel,
Marjorie L.; (Boise, ID) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
22612252 |
Appl. No.: |
10/978050 |
Filed: |
October 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10978050 |
Oct 29, 2004 |
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09576727 |
May 23, 2000 |
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09576727 |
May 23, 2000 |
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09168621 |
Oct 8, 1998 |
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6268275 |
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Current U.S.
Class: |
228/41 ;
257/E21.508 |
Current CPC
Class: |
H01L 2924/01033
20130101; H01L 2924/14 20130101; H01L 2924/00014 20130101; H05K
2203/041 20130101; Y10T 29/49149 20150115; H01L 24/11 20130101;
H01L 24/12 20130101; Y10T 29/49211 20150115; H01L 21/6835 20130101;
H01L 2224/13099 20130101; H01L 2924/01013 20130101; H05K 2203/0557
20130101; H01L 2224/05573 20130101; Y10T 29/49144 20150115; H01L
2224/05599 20130101; H01L 2224/11334 20130101; H05K 2203/0126
20130101; Y10T 29/49222 20150115; Y10T 29/532 20150115; H01L
2224/11003 20130101; H01L 2924/014 20130101; H01L 2924/01032
20130101; H01L 2224/11005 20130101; H01L 2924/00014 20130101; H05K
3/3478 20130101; H01L 2224/05568 20130101; H01L 2924/01082
20130101; Y10T 29/53178 20150115 |
Class at
Publication: |
228/041 |
International
Class: |
B23K 037/00 |
Claims
What is claimed is:
1. An apparatus for placing conductive spheres on a substrate,
comprising: a stencil plate with a first pattern of a plurality of
through-holes, the stencil plate configured to place a plurality of
conductive spheres in the first pattern on a surface of a
substrate; a shuttle plate parallel to the stencil plate and
proximate thereto, the shuttle plate having a second pattern of
through-holes corresponding to the first pattern; apparatus for
moving the shuttle plate from a first position wherein the first
and second patterns are axially aligned to a second position
wherein the first and second patterns are non-aligned; and
conductive sphere supply means for placing the conductive spheres
in the first pattern of through-holes.
2. The apparatus of claim 1, wherein the supply means is configured
to place the conductive spheres in the first pattern of
through-holes when the shuttle plate is in the second position.
3. The apparatus of claim 1, wherein the supply means is configured
to place the conductive spheres in the first pattern of
through-holes when the shuttle plate is in the first position.
4. The apparatus of claim 1, wherein the first pattern corresponds
to a pattern of bond pads on the substrate.
5. The apparatus of claim 1, wherein the sphere supply means
comprises a bottomless container with side walls extending downward
to proximate the movable shuttle plate, wherein the spheres drop
into the through-holes of the second pattern as the shuttle is
moved, the side walls encompassing a major portion of the first
pattern.
6. The apparatus of claim 1, wherein the sphere supply means
comprises a container having a bottom with a third pattern of
through-holes corresponding to the second pattern.
7. The apparatus of claim 6, wherein the third pattern is aligned
with the first pattern.
8. The apparatus of claim 6, wherein the third pattern is
non-aligned with the first pattern.
9. The apparatus of claim 1, wherein the diameter of the
through-holes of the second pattern are greater than the diameter
of the spheres by up to 1 mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
09/576,727, filed May 23, 2000, pending, which is a divisional of
application Ser. No. 09/168,621, filed Oct. 8, 1998, now U.S. Pat.
No. 6,268,275, issued Jul. 31, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to semiconductor device
manufacturing. More particularly, the present invention is directed
to methods and apparatus for handling solder balls in forming ball
grid arrays (BGAs).
[0004] 2. State of the Art
[0005] Integrated circuit semiconductor devices (ICs) are small
electronic circuits formed on the surface of a wafer of
semiconductor material such as silicon. The ICs are fabricated in
plurality in wafer form and tested by a probe to determine
electronic characteristics applicable to the intended use of the
ICs. The wafer is then subdivided into discrete IC chips or
semiconductor dice, and then further tested and assembled for
customer use through various well-known individual IC die testing
and packaging techniques, including lead frame packaging,
Chip-On-Board (COB) packaging, and flip-chip packaging (FCP).
Depending upon the semiconductor die and wafer sizes, each wafer is
divided into a few dice or as many as several hundred or more than
one thousand discrete die.
[0006] Interconnection of discrete semiconductor packages onto a
substrate such as a printed circuit board (PCB) is often
accomplished with solder preforms having generally a spherical or
other shape. In a process using a ball-grid-array (BGA), spherical
solder balls are attached to prefluxed metallized locations on a
workpiece such as a circuit board or a semiconductor device. The
workpiece is then heated to reflow the solder balls, and the solder
balls become attached to the metallized locations during subsequent
cooling. A semiconductor package or circuit board having a
corresponding but reversed pattern of connection sites may then be
aligned with the BGA and bonded to it by controlled heating in a
reflow furnace.
[0007] The use of flip-chip technology with solder bumps has
numerous advantages for interconnection, it being widely used in
the electronics industry. Flip-chip design provides improved
electrical performance for high frequency processor applications,
such as mainframes, computer workstations, and personal computers
having powerful processors. Ball-grid-array interconnections are of
small size. In addition, easier thermal management and reduced
susceptibility to EMI and RFI emissions are inherent in the use of
BGA technology.
[0008] In addition, surface mount technology (SMT) using solder
"bump" or ball interconnects eliminates the outer package leads
level of interconnection, significantly reducing the cost.
[0009] Solder bumps may be formed on a workpiece by processes of
evaporation, electroplating, stencil printing, and serial methods.
Each of these processes has particular limitations. U.S. Pat. No.
5,672,542 of Schwiebert et al. is an example of a modified stencil
printing process.
[0010] In U.S. Pat. No. 3,716,907 of Anderson, the use of germanium
hemispheres as conductive contacts is disclosed. The germanium
hemispheres are connected to the substrates with solder.
[0011] Relative to other types of interconnections, the use of
solder preforms, in particular spherical or near-spherical balls,
has proven to have significant advantages. One advantage is that
while the solder balls are formed with ball-to-ball size
differences, they may be easily classified by size prior to
application to a workpiece. Thus, a uniform size of solder balls
may be used within a ball-grid-array.
[0012] Various methods have been used for aligning, placing,
retaining and fixing solder balls on an array of sites on a
workpiece.
[0013] In U.S. Pat. No. 5,620,927 of Lee, a template with an array
of through-holes is placed on the workpiece and solder balls are
introduced into the holes by rolling the solder balls across the
workpiece surface. The apparatus may be installed on a tilt table
to encourage filling of all holes. In U.S. Pat. No. 4,871,110 of
Fukasawa et al., a template having an array of holes is placed on a
ball holder with a like array of smaller holes to which vacuum is
applied and over which solder balls are rolled. After the array is
filled with solder balls, the template and ball holder with balls
are removed and the exposed ends of the balls attached to a
substrate by e.g. reflow. The template and ball holder are then
pulled from the substrate, leaving a ball-grid-array ready for
attachment to another substrate or workpiece. A vacuum system is
required, and there is no easy way to replace a solder ball onto a
bond pad to which a ball did not become attached (i.e., missing
ball).
[0014] As shown in U.S. Pat. No. 3,719,981, an array of solder
balls is arranged on the tacky surface of a pressure sensitive (PS)
tape for alignment through a template to solder bumps on a wafer.
After thermal reflow, the template and tape are removed.
[0015] The use of a template for forming solder bumps or "balls" on
a workpiece from flux and solder pieces is disclosed in U.S. Pat.
No. 5,492,266 of Hoebener et al.
[0016] In U.S. Pat. No. 5,431,332 of Kirby et al., a template is
placed over the bond pads of a substrate, solder balls are poured
over the template, and an air knife "sweeps" the surface free of
excess solder balls.
[0017] The use of a ball pick-up tool with an array of vacuum
suction ball retainers to pull up balls from an underlying
reservoir and place them on a substrate is disclosed in U.S. Pat.
No. 5,088,639 of Gondotra et al., U.S. Pat. No. 5,284,287 of Wilson
et al., U.S. Pat. No. 5,445,313 of Boyd et al., U.S. Pat. No.
5,467,913 of Nemekawa et al., U.S. Pat. No. 5,615,823 of Noda et
al., U.S. Pat. No. 5,680,984 of Sakemi, U.S. Pat. No. 5,685,477 of
Mallik et al., U.S. Pat. No. 5,687,901 of Hoshiba et al., and U.S.
Pat. No. 5,695,667 of Eguchi et al. It is known in the art that
shutting off the vacuum to release each ball onto the substrate is
not always successful, and sometimes balls remain attached to the
pick-up tool. Again, there is no easy way to replace a missing ball
except with a single ball pickup tool.
[0018] U.S. Pat. No. 5,506,385 of Murakami et al. discloses the use
of a single manipulable suction head for picking up a solder ball,
moving it to a position above a fluxed contact pad on a substrate,
and depositing it on the contact pad. Because of the high number of
repetitive actions in separate placement of each ball, ball
placement is time consuming.
[0019] U.S. Pat. No. 5,695,667 shows a single ball suction head
which is used to place a solder ball on a contact pad which is
missing a solder ball of a ball-grid-array.
[0020] The application of flux to solder balls held in a vacuum
apparatus by dipping the balls into a flux reservoir is taught in
U.S. Pat. No. 5,088,639 of Gondotra et al. and in U.S. Pat. No.
5,284,287 of Wilson et al.
[0021] The use of ultrasonic vibration to cause solder ball
movement in the ball reservoir, and to remove excess solder balls
from a vacuum pickup tool, is taught in U.S. Pat. No. 5,687,901 of
Hoshiba et al.
BRIEF SUMMARY OF THE INVENTION
[0022] The invention comprises apparatus and methods for rapidly,
accurately, and reliably placing an array of conductive spheres
such as solder balls on conductive sites, e.g. bond pads, on a
substrate. The substrate may be a circuit board of any composition,
e.g. BT resin, or may be a silicon wafer or even a single
semiconductor die such as an "IC chip". The conductive sites on the
substrate may comprise bond pads which include those which project
from the substrate and those which are recessed into the substrate
surface. Projecting bond pads require a pre-application of flux or
other sticky substance by which the spheres cling to the bond pads.
Use of flux or sticky substance may not necessarily be required
with recessed bond pads.
[0023] The apparatus includes a stencil plate or screen overlying
the substrate, wherein the stencil plate is parallel to and
slightly spaced from the substrate. The stencil plate has an array
of through-holes corresponding to a desired placement pattern of
conductive spheres on the substrate. The invention also includes
ball supply apparatus for providing conductive spheres to the
stencil plate, wherein all through-holes in the stencil plate are
filled with one, and only one, sphere. Spheres placed into the
through-holes of the stencil plate drop by gravity to the substrate
for retention by pre-applied flux or by depressed bond pads. Each
through-hole is slightly larger than a sphere and constrains a
sphere on the substrate until the substrate and stencil plate are
further separated e.g. for solder reflow. The stencil plate
thickness and proximity to the substrate prevent more than one ball
from entering each through-hole of the stencil plate.
[0024] A first embodiment of a ball supplying apparatus is a
sphere-retaining hopper with a lower opening through which spheres
may drop into through-holes of the stencil plate and thence onto
the substrate surface. The hopper is closely spaced from the
stencil plate to maintain control over all the spheres therein.
Sphere placement is accomplished by horizontal movement of the
hopper across the through-hole pattern of the stencil plate,
filling each through-hole with one, and only one, sphere. As the
hopper moves, only the spheres dropping into the through-holes, one
to a through-hole, can escape from the hopper. The numbers of
spheres passing over each through-hole ensure that each hole is
filled, but a higher degree of assurance can be obtained by making
several passes.
[0025] In a second embodiment, a sphere supply apparatus includes a
shuttle plate with the same through-hole pattern as the stencil
plate. The shuttle plate closely overlies the stencil plate and is
reversibly movable between a first position wherein its
through-hole pattern is aligned with the pattern of the stencil
plate and a second position wherein the through-hole patterns are
non-aligned. In the first position, spheres may drop from the
shuttle plate through-holes into the stencil plate through-holes.
In the latter position, spheres are prevented from entering the
through-holes of the stencil plate. The through-holes of the
shuttle plate may be fed from an overlying open bottom reservoir,
which may be fixed to the shuttle plate or fixed in position. The
linear movement of the shuttle plate is less than the inter-sphere
distance, i.e. pitch, and is generally equal to about one-half of
the pitch.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0026] The following drawings illustrate various embodiments of the
invention, not necessarily drawn to scale, wherein:
[0027] FIG. 1 is a perspective exploded view of exemplary apparatus
of the invention for placing conductive spheres on a substrate;
[0028] FIG. 2 is a sectional side view of a substrate and exemplary
screen for applying flux to the bond pads in a step of a method of
the invention for placing conductive spheres on a substrate;
[0029] FIG. 3 is a sectional side view of a stencil fixture shown
in overlying relationship to a prefluxed substrate ready to receive
conductive spheres in a step of a method of the invention for
placing conductive spheres on a substrate;
[0030] FIG. 4 is a sectional side view of a sphere placement
apparatus of the invention showing spheres placed on the bond pads
of a substrate, as taken along line 4-4 of FIG. 1;
[0031] FIG. 5 is a sectional side view of a substrate having
conductive spheres placed on the bond pads of the substrate in
accordance with a sphere placement method of the invention;
[0032] FIG. 6 is a sectional side view of a substrate having
conductive spheres placed on the bond pads of the substrate and
reflowed in accordance with a method of the invention;
[0033] FIG. 7 is a partial sectional side view of a stencil fixture
of the invention;
[0034] FIG. 8 is a partial sectional side view of another
embodiment of a stencil fixture of the invention;
[0035] FIG. 9 is a partial sectional side view of a substrate with
recessed bond pads having conductive spheres placed thereon, in
accordance with a sphere placement method of the invention;
[0036] FIG. 10 is a cross-sectional end view of another embodiment
of a hopper of the invention, as taken along line 10-10 of FIG.
1;
[0037] FIG. 11 is a perspective exploded view of another embodiment
of the invention for placing conductive spheres on a substrate;
[0038] FIG. 12 is a sectional side view of another embodiment of an
apparatus for placing conductive spheres on a substrate, shown in a
preplacement step in a method of the invention; and
[0039] FIG. 13 is a sectional side view of a sphere placement step
in a method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] The invention comprises an improved method and apparatus for
placing a plurality of conductive spheres 12, such as preformed
solder balls or germanium balls, on conductive sites 14 on a
surface 16 of a substrate 20. The term "substrate" is used in a
broad generic sense herein to include any semiconductor device
including a wafer or a packaged or unpackaged bare die, as well as
traditional substrates including circuitized boards such as printed
circuit boards (PCBs). The method of the invention may be applied
to the placement of conductive spheres 12 on any conductive site
14, whether the site, e.g. a bond pad, projects from the substrate
20 or is recessed therein. The terms "conductive site" and "bond
pad" are used interchangeably herein to denote any site 14 at which
a conductive sphere 12 is to be placed.
[0041] One embodiment of the sphere placement apparatus 10 and the
placement method used therewith are illustrated in drawing FIGS. 1
through 4.
[0042] As depicted in drawing FIG. 1, a placement apparatus 10 for
placing a plurality of conductive spheres 12 on a substrate 20
comprises a stencil plate or screen 30 and a sphere supply
apparatus 50/50A. The substrate 20 is shown with a pattern 22 of
conductive sites or bond pads 14 with an interpad pitch 18, wherein
the pattern 22, in this example, includes all of the bond pads. The
substrate 20 is shown with exemplary registry markers 24 by which
the stencil plate 30 and substrate may be accurately aligned to
each other. The various components of the invention may be aligned
using a mechanical or pattern recognition alignment, or any other
type of accurate alignment apparatus as known in the art.
[0043] A stencil plate 30 of the sphere placement apparatus 10 is a
planar plate with upper surface 38 and lower surface 42. An array
of through-holes 34 is arranged in a through-hole pattern 32 which
corresponds to bond pad pattern 22 of the substrate 20.
Through-holes 34 have a diameter 36 which is slightly larger than
the mean diameter 28 of the conductive spheres 12, so that the
spheres may easily pass through, yet be closely constrained in
lateral movement.
[0044] The stencil plate 30 has a thickness 40 which is configured
and positioned for holding conductive spheres 12 on bond pads 14,
such that a sphere supply apparatus 50 moving across the stencil
plate does not intercept the placed spheres, while preventing more
than one sphere from entering each through-hole 34.
[0045] The stencil plate 30 is configured to have its through-hole
pattern 32 aligned with the bond pad pattern 22. Thus,
through-holes 34A, 34B, 34C and 34D are shown vertically aligned by
centerlines 26A, 26B, 26C and 26D with bond pads 14A, 14B, 14C and
14D, respectively.
[0046] Each stencil plate 30 is configured to operate with a
substrate 20 having a particular bond pad pattern 22, a particular
sphere diameter 28, and a given range of bond pad projection height
58 (FIG. 3).
[0047] Referring to drawing FIG. 7, illustrated is a straight
through-hole 34 of a stencil plate 30. As depicted in drawing FIG.
8, the through-hole 34 may have a beveled upper edge 72 which
enhances movement of conductive spheres 12 into the
through-hole.
[0048] The sphere placement apparatus 10 includes a sphere supply
apparatus 50 which in this embodiment is a hopper 50A having a
lower opening 44 (FIG. 4) by which conductive spheres 12 may drop
into through-holes 34 of the stencil plate 30 as the hopper is
moved across the upper surface 38 of the stencil plate. The hopper
50A has inner walls 46 which contain and feed conductive spheres 12
to the stencil plate 30.
[0049] The lower opening 44 has a width 48 equivalent to about two
(2) to about ten (10) sphere diameters 28. Thus, for conductive
spheres 12 having a diameter 28 of 1.0 mm, the lower opening may
have a width 48 of about 0.2 cm. to about 1.0 cm.
[0050] As shown in drawing FIG. 4, the hopper 50A has a lower
surface 60 which is spaced from the upper surface 38 of the stencil
plate 30 by a short distance 62. Distance 62 is less than one-half
(and preferably less than one-third) of the ball diameter 28, and
the stencil plate 30 and hopper 50A may even be in contact. The
hopper 50A is controlled to reversibly move across through-hole
pattern 32 in direction 68 from a first position 64 beyond one side
of the through-hole pattern 32 to a second position 66 beyond the
other side of the pattern, dropping conductive spheres 12 into each
through-hole 34, and thereby onto each bond pad 14 directly
below.
[0051] The substrate 20, stencil plate 30, and hopper 50A are each
manipulated in robotic action to maintain the desired clearances
and alignments, and to move the hopper 50A between positions 64 and
66.
[0052] In the drawings of FIGS. 1-6, the bond pads 14 of substrate
20 are pictured as projecting from the substrate. The sphere
placement apparatus 10 may be used for placing spheres onto
recessed bond pads 14, as depicted in drawing FIG. 9. Depending on
the sphere diameter 28 and the recess depth 74 of the bond pads 14,
the stencil plate thickness 40 may need to be adjusted to achieve a
sufficient plate-to-pad gap 56.
[0053] The hopper 50A may have inside wall surfaces 46 which are
sloping, as in FIG. 4, or parallel, as in drawing FIG. 10.
[0054] Another embodiment of the sphere placement apparatus 10 is
shown in drawing FIGS. 11-13. The substrate 20 and stencil plate 30
are shown as being identical to those already described above.
However, the sphere supply apparatus 50 comprises a shuttle plate
80 which underlies a sphere reservoir 90. Reservoir 90 may be
attached to the shuttle plate 80, or may comprise a separate
structure. Shuttle plate 80 has an upper surface 88 and a parallel
lower surface 92, with a third pattern 82 of through-holes 84. The
third pattern 82 is substantially the same as through-hole pattern
32, although through-holes 84 may be of somewhat greater diameter
86 than the diameter 36 of through-holes 34. The shuttle plate 80
and sphere reservoir 90 may be configured to reversibly move a
short distance in direction 94, i.e. roughly one-half of the
interpad pitch 18. Thus, the shuttle plate 80 moves from a position
where its through-hole pattern 82 is non-aligned with the
through-hole pattern 32 (see FIG. 12) to a position where it is
aligned therewith (see FIG. 13) for dropping the conductive spheres
12 into through-holes 34 and thus onto the bond pads 14.
[0055] In another embodiment of the shuttle plate 80 and sphere
reservoir 90, they are not connected. The reservoir 90 may be kept
in one position while the shuttle plate 80 moves past it for
filling the through-holes 84.
[0056] Turning now to the method of using apparatus 10 for placing
conductive spheres 12 on a substrate 20, we examine drawing FIGS. 2
through 6 in sequence.
[0057] As shown in drawing FIG. 2, a step in the method of the
invention involves the application of a layer 52 of flux or other
sticky substance to the bond pads 14 of the substrate 20. In
drawing FIG. 2, illustrated is an exemplary silk screen 54 by which
the layer 52 is formed, as known in the art. Other methods for
prefluxing the bond pads 14 are also well-known and may be used.
Any method may be used which provides a sticky layer 52 to which a
conductive sphere 12 will adhere. The use of flux, of course,
enhances bonding of solder to a bond pad during reflow.
[0058] After a layer 52 is formed on the bond pads 14, the lower
surface 42 of a stencil plate 30 and the upper surface 16 of a
substrate 20 are aligned to provide a desired plate-to-pad gap 56
(see FIG. 3).
[0059] The hopper 50A, having conductive spheres 12 therein, is
moved in direction 68 across the through-hole pattern 32 of the
stencil plate 30, whereby spheres are dropped into each
through-hole 34 to become adhered to the bond pads 14 (as shown in
FIG. 4).
[0060] At this point in the process, the stencil plate 30 may be
tested, either visually or by other methods known in the art, to
ensure that all through-holes 34 are filled. If any through-holes
34 are unfilled, the hopper movement may be repeated.
[0061] Upon filling of all through-holes 34 with conductive spheres
12, the substrate 20 and/or the stencil plate 30 with hopper 50A
are moved in direction 70, separating the substrate as shown in
drawing FIG. 5 for further manufacturing steps. The next step is
typically one of heating the substrate 20 and conductive spheres 12
to cause a reflow of the solder spheres, resulting in spheres fixed
to the bond pads 14 as shown in drawing FIG. 6. Where the
conductive spheres are not solder, but comprise a metal such as
germanium, the sphere placing method may begin with solder being
placed on each bond pad 14, fluxing of the solder surface, and then
placement of the conductive spheres 12.
[0062] The placement method for the embodiment of drawing FIGS.
11-13 is similar to that of drawing FIGS. 1-4. The steps of
pre-applying a layer 52 of flux or sticky material to the bond pads
14, and aligning of the stencil plate 30 with the substrate 20 are
the same or similar. Once the prefluxed substrate 20 is properly
installed in the apparatus, the shuttle plate 80 and sphere
reservoir 90 are moved from a non-aligned position to an aligned
position, whereby conductive spheres 12 fill the through-holes 84
of the shuttle plate and, upon reaching the aligned position (FIG.
13), are dropped into the through-holes 34 of the stencil plate 30
and onto the prefluxed bond pads 14. The substrate 20 may be then
separated from the stencil plate 30 and the conductive spheres 12
fixed by reflow to the substrate.
[0063] The methods described herein present many advantages to the
BGA formation process, including higher reliability, lower cost,
reduced ball wastage, etc. The apparatus and methods are relatively
simple, yet provide a great deal of flexibility in substrate type,
sphere size, sphere composition, etc. Non-filling of a through-hole
of the stencil plate is easily cured by moving the sphere supply
apparatus through another cycle. There is no need for using a
single-head ball picker to place a single ball as noted in the
prior art.
[0064] This invention may be embodied in several forms without
departing from the spirit of essential characteristics of the
invention. The embodiments as described herein are therefore
intended to be only illustrative and not restrictive, and the scope
of the invention is defined by the appended claims rather than the
preceding description, and all variations that fall within the
metes and bounds of the subject matter claimed, or are equivalent
thereto, are therefore intended to be embraced by the following
claims:
* * * * *