U.S. patent application number 10/390804 was filed with the patent office on 2003-12-25 for method and apparatus for packaging microelectronic substrates.
Invention is credited to Cobbley, Chad A., Williams, Vernon M..
Application Number | 20030235663 10/390804 |
Document ID | / |
Family ID | 24259500 |
Filed Date | 2003-12-25 |
United States Patent
Application |
20030235663 |
Kind Code |
A1 |
Williams, Vernon M. ; et
al. |
December 25, 2003 |
Method and apparatus for packaging microelectronic substrates
Abstract
A method and apparatus for encapsulating a microelectronic
substrate. In one embodiment, the apparatus can include a mold
having an internal volume with a first portion configured to
receive the microelectronic substrate coupled to a second portion
configured to receive a pellet for encapsulating the
microelectronic substrate. A plunger moves axially in the second
portion to force the pellet into the first portion and around the
microelectronic substrate. The pellet has overall external
dimensions approximately the same as a conventional pellet, but has
cavities or other features that reduce the volume of the pellet and
the amount of pellet waste material left after the pellet
encapsulates the microelectronic substrate. Accordingly, the pellet
can be used with existing pellet handling machines. The mold and/or
the plunger can have protrusions and/or other shape features that
reduce the size of the first portion of the internal volume. In one
aspect of this embodiment, the protrusions can be shaped to fit
within the cavities of the pellet.
Inventors: |
Williams, Vernon M.;
(Meridian, ID) ; Cobbley, Chad A.; (Boise,
ID) |
Correspondence
Address: |
PERKINS COIE LLP
PATENT-SEA
P.O. BOX 1247
SEATTLE
WA
98111-1247
US
|
Family ID: |
24259500 |
Appl. No.: |
10/390804 |
Filed: |
March 17, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10390804 |
Mar 17, 2003 |
|
|
|
09565638 |
May 4, 2000 |
|
|
|
6558600 |
|
|
|
|
Current U.S.
Class: |
428/34.1 |
Current CPC
Class: |
B29C 45/14655 20130101;
B29K 2101/10 20130101; B29C 70/70 20130101; B29K 2063/00 20130101;
Y10T 428/13 20150115; B29C 45/02 20130101; B29C 45/462
20130101 |
Class at
Publication: |
428/34.1 |
International
Class: |
B32B 001/08 |
Claims
1. A method for packaging a microelectronic substrate, comprising:
forming a pellet of uncured thermoset mold compound to have a first
end surface, a second end surface facing opposite the first end
surface, and an intermediate surface between the first and second
end surfaces; forming at least one cavity in the pellet; and at
least partially enclosing the microelectronic substrate by
pressurizing the pellet and flowing the pellet around the
microelectronic substrate.
2. The method of claim 1 wherein forming a cavity in the pellet
includes forming a first slot in the first end surface and a second
slot in the second end surface, further comprising: disposing the
pellet in a chamber having a transverse dimension greater than a
transverse dimension of the first end surface; engaging a plunger
with the first end surface of the pellet; collapsing the first and
second slots without trapping air in the slots by driving the
plunger against the pellet and forcing air from the slots
transversely into the chamber; and exhausting the air from the
chamber through a vent.
3. The method of claim 1 wherein the cavity is a first cavity
formed in the first end surface of the pellet, further comprising
forming a second cavity in the second end surface of the
pellet.
4. The method of claim 1, further comprising forming the cavity to
extend entirely through the pellet.
5. The method of claim 1, further comprising forming the pellet to
have a cross-sectional dimension of between about 13 millimeters
and about 16 millimeters and a length transverse to the
cross-sectional dimension that exceeds the cross-sectional
dimension.
6. The method of claim 1 wherein the microelectronic substrate is a
first microelectronic substrate, further comprising at least
partially enclosing a second microelectronic substrate with the
pellet.
7. The method of claim 1, further comprising selecting the mold
material to include an epoxy.
8. The method of claim 1, further comprising forming the cavity to
have a generally hemispherical shape.
9. The method of claim 1, further comprising forming the cavity to
have a generally cylindrical shape.
10. The method of claim 1, further comprising forming the cavity to
include a slot in the first end surface arranged transverse to the
side surface.
11. The method of claim 1, further comprising forming the pellet to
have a length transverse to the first and second end surfaces that
exceeds a widthwise dimension of the first and second surfaces.
12. The method of claim 1, further comprising selecting the mold
material to include biphenyl, di-cyclo pentadiene, ortho-cresole
novolak and/or a multifunctional material.
13. The method of claim 1, further comprising selecting the
microelectronic substrate to include a DRAM device.
14. The method of claim 1, further comprising curing the mold
material by elevating a temperature of the mold material after
disposing the pellet around the microelectronic substrate.
15. A method for providing a reduced-volume pellet for
encapsulating a microelectronic substrate, the pellet being
suitable for use with a pellet-handling apparatus configured to
handle cylindrical pellets having a selected length, a selected
radius and a selected volume approximately equal to pi times the
selected length times the square of the selected radius, the method
comprising forming an uncured thermoset pellet material into a
pellet body having a first end surface, a second end surface facing
opposite the first end surface and an intermediate surface between
the end surfaces, the pellet body having a maximum length
approximately equal to the selected length, a maximum
cross-sectional dimension approximately equal to twice the selected
radius and a volume less than the selected volume by at least about
5%.
16. The method of claim 15, further forming a cavity in the pellet
body.
17. The method of claim 16 wherein the cavity is a first cavity
formed in the first end surface of the pellet, further comprising
forming a second cavity in the second end surface of the
pellet.
18. The method of claim 16, further comprising forming the cavity
to extend entirely through the pellet.
19. The method of claim 16, further comprising forming the cavity
to have a generally hemispherical shape.
20. The method of claim 16, further comprising forming the cavity
to include a slot in the first end surface arranged transverse to
the side surface.
21. The method of claim 15, further comprising forming the pellet
to have a length transverse to the first and second end surfaces
that exceeds a widthwise dimension of the first and second
surfaces.
22. The method of claim 15, further comprising selecting the mold
material to include biphenyl, di-cyclo pentadiene, ortho-cresole
novolak and/or a multifunctional material.
23. The method of claim 15, further comprising chamfering an edge
between the first end surface and the intermediate surface.
24. The method of claim 15, further comprising forming a chamfered
surface between the first end surface and the intermediate surface,
the chamfered surface having an angle of approximately 45 degrees
relative to both the first end surface and the intermediate
surface.
25. A method for reducing waste material formed while packaging a
microelectronic substrate, comprising: positioning the
microelectronic substrate in a packaging chamber having a first
portion configured to receive the microelectronic substrate and a
second portion coupled to the first portion; providing a pellet of
uncured mold material having an external surface with a cavity and
positioning the pellet in the second portion of the packaging
chamber; and forcing the pellet into the first portion of the
packaging chamber by engaging the pellet with a plunger, inserting
at least a portion of the plunger into the cavity of the pellet,
and moving the plunger against the pellet.
26. The method of claim 25, further comprising heating walls of the
cavity by heating the plunger.
27. The method of claim 25, further comprising receiving a
protrusion of the packaging chamber in the cavity of the
pellet.
28. The method of claim 27, further comprising heating walls of the
cavity by heating the protrusion.
29. A method for packaging first and second microelectronic
substrates, comprising: positioning the first microelectronic
substrate in a packaging chamber; forcing a first pellet of uncured
thermoset mold material having a first length, a first diameter and
first volume into the packaging chamber and around the first
microelectronic substrate by engaging the first pellet with a
plunger; removing the first microelectronic substrate from the
packaging chamber; positioning the second microelectronic substrate
in the packaging chamber; forcing a second pellet of uncured
thermoset mold material having a second length approximately equal
to the first length, a second diameter approximately equal to the
second diameter and a second volume less than the first volume into
the packaging chamber and around the second microelectronic
substrate by engaging the second pellet with the plunger; and
removing the second microelectronic substrate from the packaging
chamber.
30. The method of claim 29, further comprising: selecting the first
pellet to have a first length, a first radius and a first volume
approximately equal to pi times the first length times the square
of the first radius; and selecting the second pellet to have a
second length approximately equal to the first length, a second
radius approximately equal to the first radius and a second volume,
the second volume being less than the first volume by from about 5%
to about 20%.
31. The method of claim 29, further comprising selecting the first
pellet to have one or more first cavities defining a first cavity
volume and selecting the second pellet to have one or more second
cavities defining a second cavity volume larger than the first
cavity volume.
32. A pellet for packaging at least one microelectronic substrate,
comprising: a pellet body formed from an uncured thermoset mold
material and having a first end surface, a second end surface
facing opposite the first end surface, and an intermediate surface
between the first and second end surfaces, the first end surface,
the second end surface and the intermediate surface defining an
internal volume; and at least one cavity wall in the body defining
a cavity in the body.
33. The pellet of claim 32 wherein the cavity is a first cavity in
the first end surface, the second end surface having a second
cavity.
34. The pellet of claim 32 wherein the cavity extends entirely
through the pellet body.
35. The pellet of claim 32 wherein the cavity is completely
enclosed within the internal volume.
36. The pellet of claim 32 wherein the pellet body has a
cross-sectional dimension of between about 13 millimeters and about
16 millimeters and a length transverse to the cross-sectional
dimension that exceeds the cross-sectional dimension.
37. The pellet of claim 32 wherein the pellet body is sized to form
from two to six packaged microelectronic devices.
38. The pellet of claim 32 wherein the mold material includes an
epoxy.
39. The pellet of claim 32 wherein the first and second end
surfaces are generally circular and the intermediate surface is
generally cylindrical.
40. The pellet of claim 32 wherein the cavity has a generally
hemispherical shape.
41. The pellet of claim 32 wherein the cavity has a generally
cylindrical shape.
42. The pellet of claim 32 wherein the cavity includes a slot in
the first end surface arranged transverse to the side surface.
43. The pellet of claim 32 wherein a length of the pellet body
transverse to the first and second end surfaces exceeds a widthwise
dimension of the first and second surfaces.
44. The pellet of claim 32 wherein the thermoset mold material
includes biphenyl, di-cyclo pentadiene, ortho-cresole novolak
and/or a multifunctional material.
45. The pellet of claim 32 wherein the pellet body has a generally
right-cylindrical shape with a chamfered corner between the first
end surface and the side surface, the chamfered corner forming an
angle of approximately 45 degrees with both the first end surface
and the side surface.
46. The pellet of claim 32 wherein the cavity extends into the side
surface of the pellet body.
47. A pellet for packaging a microelectronic substrate, comprising:
a pellet body formed from an uncured thermoset mold material and
having a first generally circular end surface, a second generally
circular end surface opposite the first end surface and a generally
cylindrical intermediate surface between the first and second end
surfaces; a first generally spherical cavity wall defining a first
generally spherical cavity in the first end surface, the first
cavity having an opening in first end surface; and a second
generally spherical cavity wall defining a second generally
spherical cavity in the second end surface, the second cavity
having an opening in the second end surface.
48. The pellet of claim 47 wherein the pellet body has a
cross-sectional dimension of between about 13 millimeters and about
16 millimeters and a length transverse to the cross-sectional
dimension that exceeds the cross-sectional dimension.
49. The pellet of claim 47 wherein the mold material includes an
epoxy.
50. The pellet of claim 47 wherein a widthwise dimension of the
first end surface and a lengthwise dimension of the intermediate
surface describe a cylindrical volume, and the cavities have a
volume of from about 5% to about 20% of the cylindrical volume.
51. The pellet of claim 47 wherein a length of the pellet body
transverse to the first and second end surfaces exceeds a widthwise
dimension of the first and second surfaces.
52. The pellet of claim 47 wherein the pellet body has a generally
right-cylindrical shape with a chamfered corner between the first
end surface and the side surface, the chamfered corner forming an
angle of approximately 45 degrees with both the first end surface
and the side surface.
53. A pellet for packaging a microelectronic substrate, comprising:
a pellet body formed from an uncured thermoset mold compound and
having a first generally circular end surface, a second generally
circular end surface opposite the first end surface and a generally
cylindrical intermediate surface between the first and second end
surfaces; a first slot wall defining at least one first slot in the
first end surface; and a second slot wall defining at least one
second slot in the second end surface.
54. The pellet of claim 53 wherein the pellet body has a
cross-sectional dimension of between about 13 millimeters and about
16 millimeters and a length transverse to the cross-sectional
dimension that exceeds the cross-sectional dimension.
55. The pellet of claim 53 wherein the mold compound includes an
epoxy.
56. The pellet of claim 53 wherein the first and second end
surfaces are generally circular and the intermediate surface is
generally cylindrical.
57. The pellet of claim 53 wherein a length of the pellet body
transverse to the first and second end surfaces exceeds a widthwise
dimension of the first and second surfaces.
58. The pellet of claim 53 wherein the pellet body has a generally
right-cylindrical shape with a widthwise dimension and a lengthwise
dimension describing a cylindrical volume, the slots having a slot
volume of from about 5% to about 20% of the cylindrical volume.
59. A reduced-volume pellet for packaging a microelectronic
substrate, the reduced-volume pellet being useable with a pellet
handling apparatus configured to handle cylindrical pellets having
a selected length, a selected radius transverse to the selected
length, and a selected volume approximately equal to pi times the
selected length times the square of the selected radius, the
reduced-volume pellet comprising a pellet body formed from an
uncured thermoset mold material, the pellet body having a maximum
body length approximately equal to the selected length and a
maximum body cross-sectional dimension approximately equal to twice
the selected radius, the pellet body further having a volume of
uncured mold material at least 5% less than the selected
volume.
60. The pellet of claim 59 wherein the pellet body has a cavity
that forms a void in the uncured mold material.
61. The pellet of claim 60 wherein the cavity is a first cavity in
the first end surface, the second end surface having a second
cavity.
62. The pellet of claim 60 wherein the cavity extends entirely
through the pellet body.
63. The pellet of claim 60 wherein the cavity is completely
enclosed within the internal volume.
64. The pellet of claim 60 wherein the cavity includes a slot in
the first end surface arranged transverse to the side surface.
65. The pellet of claim 59 wherein the mold material includes an
epoxy.
66. The pellet of claim 59 wherein a length of the pellet body
transverse to the first and second end surfaces exceeds a widthwise
dimension of the first and second surfaces.
67. The pellet of claim 59 wherein the pellet body has a generally
right-cylindrical shape with a chamfered corer between the first
end surface and the side surface, the chamfered corner forming an
angle of approximately 45 degrees with both the first end surface
and the side surface.
68. A set of pellets for packaging microelectronic substrates in a
single mold, comprising: a first pellet formed from a first uncured
mold material and having a first length, a first radius transverse
to the first length, and a first volume of the first uncured mold
material less than or equal to pi times the first length times the
square of the first radius; and a second pellet formed from a
second uncured mold material having a composition the same as a
composition of the first uncured mold material, the second pellet
having a maximum body length approximately equal to the first
length and a maximum body cross-sectional dimension approximately
equal to twice the first radius, the second pellet further having a
second volume of the second uncured mold material less than first
volume of the first uncured mold material.
69. The set of pellets of claim 68 wherein at least one of the
first pellet and the second pellet has a cavity that forms a void
in the uncured mold material.
70. The set of pellets of claim 69 wherein the cavity is a first
cavity in the first end surface, the second end surface having a
second cavity.
71. The set of pellets of claim 69 wherein the cavity includes a
slot in the first end surface arranged transverse to the side
surface.
72. The set of pellets of claim 68 wherein a length of the first
pellet exceeds a widthwise dimension of the first pellet.
73. The set of pellets of claim 68 wherein the first pellet has at
least one cavity defining a first cavity volume and the second
pellet has at least one cavity defining a second cavity volume
greater than the first cavity volume.
74. The pellet of claim 68 wherein the pellet body has a generally
right-cylindrical shape with a chamfered corner between the first
end surface and the side surface, the chamfered corner forming an
angle of approximately 45 degrees with both the first end surface
and the side surface.
75. An apparatus for packaging a microelectronic substrate,
comprising: a mold body having a chamber with a first portion
configured to extend at least partially around the microelectronic
substrate and a second portion coupled to the first portion; and a
plunger positioned in the second portion of the chamber and
moveable within the second portion of the chamber in an axial
direction between a first position and a second position, the
plunger having a side wall aligned with the axial direction and an
end wall transverse to the axial direction, at least a portion of
the end wall extending axially away from the side wall.
76. The apparatus of claim 75 wherein the plunger is configured for
use with a pellet having a cylindrical side surface and two end
surfaces, each end surface having a cavity defining a cavity shape,
the end wall of the plunger being shaped to be received in the
cavity of the pellet.
77. The apparatus of claim 76 wherein the plunger has a spherical
end wall.
78. The apparatus of claim 76 wherein the end wall of the plunger
has a tab-shaped protrusion sized to be removably received in a
slot of the pellet.
79. The apparatus of claim 75 wherein the plunger is coupled to a
heat source.
80. The apparatus of claim 75, further comprising a pellet sized to
fit within the second portion of the chamber, the pellet having a
cavity sized and shaped to receive the portion of the plunger end
wall extending axially away from the plunger side wall.
81. An apparatus for packaging a microelectronic substrate, the
apparatus useable with a pellet of uncured thermoset material
having an end surface with a cavity, the apparatus comprising: a
mold body having a chamber with a first portion configured to
extend at least partially around the microelectronic substrate and
a second portion coupled to the first portion, the second portion
having a protrusion configured to be received in the cavity of the
pellet; and a plunger positioned in the second portion of the
chamber opposite the protrusion and moveable within the second
portion of the chamber in an axial direction between a first
position and a second position, the plunger having a side wall
aligned with the axial direction and an end wall transverse to the
axial direction and facing toward the protrusion.
82. The apparatus of claim 81 wherein the mold body is coupled to a
heat source.
83. The apparatus of claim 81 wherein the protrusion has a
spherical shape.
84. The apparatus of claim 81 wherein the protrusion includes a tab
sized to be removably received in the cavity of the pellet.
85. The apparatus of claim 81 wherein the pellet has a first
surface with a first cavity and a second surface with a second
cavity, further wherein the protrusion of the mold body is a first
protrusion configured to be removably received in the first cavity
and the plunger has a second protrusion configured to be removably
received in the second cavity.
86. The apparatus of claim 81, further comprising a pellet sized to
fit within the second portion of the chamber, the pellet having a
cavity sized and shaped to receive the protrusion of the mold body.
Description
TECHNICAL FIELD
[0001] This invention relates to methods and apparatuses for
packaging microelectronic substrates.
BACKGROUND OF THE INVENTION
[0002] Packaged microelectronic devices, such as memory chips and
microprocessor chips, typically include a microelectronic substrate
die encased in an epoxy protective covering. The die includes
functional features, such as memory cells, processor circuits, and
interconnecting circuitry. The die also typically includes bond
pads electrically coupled to the functional features. The bond pads
are coupled to pins or other types of terminals that extend outside
the protective covering for connecting to buses, circuits and/or
other microelectronic devices.
[0003] In one conventional arrangement shown in FIG. 1, a mold or
cull tool 40 simultaneously encases a plurality of microelectronic
substrates 30. The cull tool 40 can include an upper plate 42
removably positioned on a lower plate 41 to define a plurality of
substrate chambers 45, an upright pellet cylinder 60, and a
plurality of channels 46 connecting the substrate chambers 45 to
the cylinder 60. A narrow gate 44 is positioned between each
channel 46 and a corresponding substrate chamber 45. A cylindrical
pellet 20 formed from an epoxy mold compound is positioned in the
cylinder 60, and a plunger 50 moves downwardly within the cylinder
60 to transfer heat and exert pressure against the pellet 20. The
heat and pressure from the plunger liquifies the mold compound of
the pellet 20. The liquified mold compound flows through the
channels 46 and into the substrate chambers 45 to surround the
microelectronic substrates 30 and drive out air within the cull
tool 40 through vents 43.
[0004] The mold compound in the substrate chambers 45 forms a
protective covering around each microelectronic substrate 30. The
residual mold compound in the channels 46 and in the lower portion
of the cylinder 60 forms a "cull." The cull has thin break points
corresponding to the location of each gate 44. After the upper
plate 42 is separated from the lower plate 41, the encapsulated
microelectronic substrates 30 and the cull are removed from the
tool 40 as a unit. The encapsulated microelectronic substrates 30
are then separated from the cull at the break points.
[0005] The mold compound that forms the pellet 20 is typically a
high temperature, humidity-resistant, thermoset epoxy. One drawback
with this compound is that it can be brittle and accordingly the
comers of the pellet 20 can chip. One approach to addressing this
drawback is to provide a shallow chamfer at the corners 21, as
shown in FIG. 1. Another drawback with this compound is that it
must be elevated to a relatively high temperature before it will
flow through the cull tool 40. Accordingly, the cull tool 40 and
the plunger 50 can be heated to improve the heat transfer to the
pellet 20. Furthermore, the lower plate 41 of the cull tool 40 can
include one or more protrusions 47 that can improve the flow of the
mold compound within the cull tool 40.
[0006] Still another drawback with the molding process discussed
above is that the cull cannot be easily recycled because it is
formed from a thermoset material that does not "re-liquify" upon
re-heating. Accordingly, the cull is waste material that must be
discarded, which increases the materials cost of producing the
packaged microelectronic devices. One approach to address this
drawback is to reduce the volume of the pellet 20 and,
correspondingly, the channels 46 that define the shape and volume
of the cull. For example, one conventional approach includes
reducing the length and/or the diameter of the pellet 20. However,
such pellets are not compatible with existing handling machines.
For example, if the pellet length is decreased substantially, the
length and diameter of the pellet will be approximately equal. The
sorting and handling machines (not shown) that orient the pellets
20 for axial insertion into the cylinder 60 cannot properly orient
the shorter pellets because the machines cannot distinguish between
the length and diameter of the pellet. Furthermore, the handling
machines are typically calibrated to reject undersized pellets on
the basis of pellet length and accordingly would likely reject all
or none of the reduced-length pellets.
SUMMARY OF THE INVENTION
[0007] The present invention is directed toward methods and
apparatuses for packaging microelectronic substrates. A method in
accordance with one aspect of the invention includes forming a
pellet of uncured thermoset mold compound to have a first end
surface, a second end surface opposite the first end surface, and
an intermediate surface between the first and second end surfaces.
The method further includes forming at least one cavity in the
pellet and at least partially enclosing the microelectronic
substrates by pressurizing the pellet and flowing the pellet around
the microelectronic substrate.
[0008] A method in accordance with another aspect of the invention
includes forming a pellet suitable for use with a pellet-handling
apparatus configured to handle cylindrical pellets having a
selected length, a selected radius less than the selected length,
and a selected volume approximately equal to pi times the selected
length times the square of the selected radius. The method includes
forming a pellet material into a pellet body having a first end
surface, a second end surface opposite the first end surface, and
an intermediate surface between the end surfaces. The pellet body
has a maximum length approximately equal to the selected length, a
maximum cross-sectional dimension approximately equal to twice the
selected radius, and a volume less than the selected volume by at
least about 5%.
[0009] The invention is also directed to a pellet for packaging at
least one microelectronic substrate. The pellet can include a
pellet body formed from an uncured thermoset mold material. The
pellet body has a first end surface, a second end surface facing
opposite the first end surface, and an intermediate surface between
the first and second end surfaces. The first end surface, the
second end surface and the intermediate surface define an internal
volume, and at least one of the surfaces and/or the internal volume
has at least one cavity. In one aspect of this invention, the
cavity has a generally spherical shape. In another aspect of this
invention, the cavity can include a slot in the first end surface
arranged transverse to the side surface. In still another aspect of
this invention, the pellet body can have a generally
right-cylindrical shape with a chamfered corner forming angles of
approximately 45 degrees between the first end surface and the side
surface.
[0010] The invention is also directed to an apparatus for packaging
a microelectronic substrate. The apparatus can include a mold body
having a chamber with a first portion configured to extend at least
partially around the microelectronic substrate and a second portion
coupled to the first portion. A plunger is positioned in the second
portion of the chamber and is moveable within the second portion of
the chamber in an axial direction. The plunger has a side wall
aligned with the axial direction and an end wall transverse to the
axial direction. At least a portion of the end wall extends axially
away from the side wall. In one aspect of this embodiment, the
plunger is configured for use with a pellet having a cylindrical
side surface and two end surfaces. Each end surface can have a
cavity defining a cavity shape, and the end wall of the plunger can
be shaped to be received in the cavity of the pellet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a partially schematic cross-sectional view of a
molding apparatus for encapsulating microelectronic substrates in
accordance with the prior art.
[0012] FIG. 2 is a partially schematic cross-sectional view of a
molding apparatus and pellet for encapsulating microelectronic
substrates in accordance with an embodiment of the invention.
[0013] FIG. 3 is a top isometric view of a pellet having a slotted
end surface for encapsulating a microelectronic substrate in
accordance with another embodiment of the invention.
[0014] FIG. 4 is a side cross-sectional view of a pellet having an
end surface with conical indentations in accordance with still
another embodiment of the invention.
[0015] FIG. 5 is a side cross-sectional view of a pellet having
beveled corners in accordance with another embodiment of the
invention.
[0016] FIG. 6 is a side elevation view of a pellet having a hollow
internal cavity in accordance with still another embodiment of the
invention.
[0017] FIG. 7 is a top isometric view of a pellet having a cavity
extending therethrough in accordance with yet another embodiment of
the invention.
[0018] FIG. 8 is a top isometric view of a pellet having a side
surface with a plurality of cavities in accordance with still
another embodiment of the invention.
DETAILED DESCRIPTION
[0019] The present disclosure describes methods and apparatuses for
encapsulating microelectronic substrates. Many specific details of
certain embodiments of the invention are set forth in the following
description and in FIGS. 2-8 to provide a thorough understanding of
these embodiments. One skilled in the art, however, will understand
that the present invention may have additional embodiments, or that
the invention may be practiced without several of the details
described below.
[0020] FIG. 2 is a partially schematic cross-sectional view of a
portion of an apparatus 110 for encapsulating a microelectronic
substrate 130 in accordance with an embodiment of the invention. In
one aspect of this embodiment, the apparatus 110 includes a mold or
cull tool 140 configured to receive a pellet 120, with both the
tool 140 and the pellet 120 configured to reduce the volume of
waste pellet material when compared to conventional arrangements.
In one aspect of the invention, the tool 140 includes an upper
portion 142 positioned above a lower portion 141. The upper and
lower portions 142 and 141 have recesses which, when aligned as
shown in FIG. 2, form an internal chamber 170 for encapsulating the
microelectronic substrate 130. The microelectronic substrate 130
can be a die, such as a DRAM die or a processor die, or
alternatively, the microelectronic substrate 130 can include other
electronic components.
[0021] The internal chamber 170 can include a substrate portion 145
that houses the microelectronic substrate 130, a cylinder portion
160 that houses the pellet 120, and a channel portion 146
connecting the cylinder portion 160 to the substrate portion 145.
The chamber 170 can also include a vent 143 for exhausting air
and/or other gases from the tool 140 as the pellet 120 fills the
channel portion 146 and the substrate portion 145. For purposes of
illustration, one channel portion 146 and one substrate portion 145
are shown in FIG. 2; however, the tool 140 can include additional
channel portions 146 and substrate portions 145 radiating outwardly
from the cylinder portion 160 so that a single pellet 120 can be
used to encapsulate several (e.g., two-six, or even more)
microelectronic substrates 130.
[0022] The portions of the internal chamber 170 that fill with
waste pellet material (i.e., the pellet material that extends from
the cylinder portion 160 to the substrate portion 145) define the
cull volume as discussed above. These portions of the internal
chamber 170 have a volume less than that of conventional chambers
configured to encapsulate the same number and type of
microelectronic substrates 130. For example, the channel portions
146 can be smaller than the channels of conventional molds.
Furthermore, the upper portion 142 of the tool 140 can include a
protrusion 147 aligned with a central portion 148 of the chamber
170. The protrusion 147 can further reduce the volume of the
chamber 170.
[0023] The volume of the pellet 120 is also less than the volume of
conventional pellets; however, the maximum external dimensions of
the pellet 120 are approximately identical to those of conventional
pellets configured to encapsulate the same number and type of
microelectronic substrates 130. For example, the overall length L
and diameter D of the pellet 120 are identical to or nearly
identical to the length and diameter, respectively, of a
conventional pellet used for the same application. Accordingly, the
pellet 120 can be used with conventional pellet handling and
sorting machines without changing the design, configuration or
settings of the conventional machines. In one embodiment, the
pellet 120 can have an overall diameter D of approximately 13
millimeters to 16 millimeters and an overall length L greater than
the diameter D. For example, when the diameter D is about 13
millimeters, the length L can be about 17 millimeters. In other
embodiments, the pellet 120 can have other dimensions so long as
the length L exceeds the diameter D by an amount sufficient to
allow the pellet 120 to be used with conventional pellet handling
machines that properly orient the pellets 120 in the chamber 160 by
distinguishing the length L from the diameter D.
[0024] In one embodiment, the volume of the pellet 120 is less than
that of conventional pellets having the same maximum external
length and diameter because the external surfaces of the pellet 120
include one or more cavities. For example, the pellet 120 can
include a cylindrical side surface 125 positioned between two
circular end surfaces 124, and each end surface 124 can include a
cavity 122. In one aspect of this embodiment, the cavities 122
reduce the volume of the mold compound forming the pellet 120 by
from about 5% to about 20% when compared to a conventional pellet
with the same maximum external dimensions for the length and width.
Conventional pellets have a volume of approximately .pi. R.sup.2 L,
where R (radius)=1/2 D. Alternatively, the pellet 120 can have a
greater than 20% volume reduction when compared to conventional
pellets. In another aspect of this embodiment, the cavities 122 can
be defined by a hemispherical or partially hemispherical cavity
wall 123. Alternatively, the cavities 122 can have other shapes
that reduce the volume of the pellet 120 without reducing the
overall external dimensions of the pellet 120, as will be described
in greater detail below with reference to FIGS. 3-8.
[0025] The pellet 120 can be formed from a mold compound that
includes a high temperature, humidity resistant thermoset material,
such as an epoxy resin. The epoxy resin can have a variety of
suitable formulations and can include biphenyl compounds, di-cyclo
pentadiene compounds, ortho-cresole novolak compounds and/or
multifunctional compounds, all of which are available from Nitto
Denko Co. of Fremont, Calif. In other embodiments, the pellet 120
can have other formulations suitable for encapsulating the
microelectronic substrates 130.
[0026] In all the foregoing embodiments described with reference to
FIG. 2, the pellet 120 is sized to fit within the cylinder 160 of
the cull tool 140 and above a plunger 150. The plunger 150 is
axially movable within the cylinder 160 between a first position
(shown in FIG. 2) to receive the pellet 120 and a second position
with the plunger 150 moved axially upwardly to compress the pellet
120. Accordingly, the plunger 150 can force the mold compound
forming the pellet 120 into the channel portion 146 and the
substrate portion 145 of the chamber 170.
[0027] In one aspect of this embodiment, the plunger 150, the walls
of the cylinder 160, and/or the other surfaces of the cull tool 140
that define the chamber 170 are heated to liquefy the pellet 120.
In still a further aspect of this embodiment, the plunger 150 can
include a side wall 151 adjacent the walls of the cylinder 160, an
end wall 152 transverse to the side wall 151 and a protrusion 153
that extends axially away from the end wall 152 and the corner
between the end wall 152 and the side wall 151. The protrusion 153
can have a width less than or equal to the width of the end wall
152. In still a further aspect of this embodiment, the protrusion
153 is sized to fit within the cavity 122 at the end of the pellet
120. Accordingly, when the plunger 150 is heated, the protrusion
153 can increase the rate of heat transfer to the pellet 120
(relative to a conventional plunger having a flat end surface)
because more surface area of the plunger 150 contacts the pellet
120. Similarly, when the upper portion 142 of the cull tool 140 is
heated, the protrusion 147 can increase the heat transferred to the
pellet 120 by engaging the walls 123 of cavity 122 at the opposite
end of the pellet 120.
[0028] In operation, the microelectronic substrate 130 is
positioned in the substrate portion 145 of the chamber 170 and the
pellet 120 is positioned in the cylinder portion 160. The plunger
150 and/or the surfaces defining the chamber 170 are heated, and
the plunger 150 is moved upwardly to compress and liquify the
pellet 120. The plunger accordingly forces the liquified pellet 120
through the channel portion 146 and into the substrate portion 145
around the microelectronic substrate 130. The encapsulated
microelectronic substrate 130 and the cull (which occupies the
channel 146 and the central portion 148 of the chamber 170) are
removed as a unit, and then the encapsulated microelectronic
substrate 130 is separated from the cull, in a manner generally
similar to that discussed above.
[0029] One feature of an embodiment of the apparatus 110 and the
method described above with reference to FIG. 2 is that the pellet
120 has the same maximum length and width as a conventional pellet
to be compatible with existing pellet handling machines, but the
pellet 120 has a reduced volume. Accordingly, the culls formed from
the pellet 120 have a lower volume than conventional culls to
reduce the cost of the pellets and the waste material left over
after encapsulating the microelectronic substrates 130 with the
pellets.
[0030] Another feature of an embodiment of the apparatus 110 and
method described above with reference to FIG. 2 is that the size of
the cavities 122 can be selected to match the size of the internal
chamber 170 and/or the size of the microelectronic substrate 130.
For example, pellets 120 having relatively large cavities 122 can
be used with cull tools 140 having relatively small internal
volumes 170, and pellets 120 having relatively small cavities 122
(or no cavities) can be used with cull tools 140 having relatively
large internal volumes 170. Similarly, pellets 120 having
relatively large cavities 122 can be used to encapsulate relatively
large microelectronic substrates 130 and pellets 120 having
relatively small cavities 122 (or no cavities) can be used to
encapsulate relatively small microelectronic substrates 130.
Accordingly, pellets 120 having the same overall external
dimensions can be used with different cull tools 140 to encapsulate
different microelectronic substrates 130 without requiring
different pellet handling equipment.
[0031] FIGS. 3-8 depict other pellets having the same overall
external dimensions as conventional pellets (but reduced volumes)
in accordance with alternate embodiments of the invention. For
example, FIG. 3 is a top isometric view of a pellet 220 having a
generally cylindrical side surface 225, circular end surfaces 224,
and a slot 222 in each end surface 224. Each end surface 224 can
include a single slot 222, or alternatively, each end surface 224
can include a plurality of slots 222. In either embodiment, the
pellet 220 can be used in conjunction with an apparatus generally
similar to the apparatus 110 shown in FIG. 2, but having tab-shaped
protrusions that match the shape of the slots 222 instead of the
hemispherical protrusions 147 and 153 shown in FIG. 2. Accordingly,
the rate of heat transfer to the pellet 220 can be increased when
compared to conventional devices in a manner generally similar to
that described above with reference to FIG. 2.
[0032] Referring now to FIGS. 2 and 3, the pellet 220 can be
compressed with a plunger 150 having a flat end wall 152 and a cull
tool 140 having a flat central portion 148 opposite the end wall in
an alternate embodiment. In this alternate embodiment, the volume
of the cull can be reduced by an amount equal to the volume of the
cavities 222 by reducing the volume of the channels 146 and/or
other portions of the cull tool 140. Accordingly, the slots 222 in
pellet 220 may have certain advantages over the spherical cavities
122 in the pellet 120 described above with reference to FIG. 2. For
example, when the plunger 150 has a flat end wall 152, the slot 222
will not entrap air as the plunger 150 engages the pellet 220.
Instead, air in the slot 222 will tend to flow laterally around the
side surface 225 of the pellet 220 as the plunger 150 compresses
the pellet 220.
[0033] FIG. 4 is a side cross-sectional view of a pellet 320 having
frustro-conical cavities 322 each end surface 324. FIG. 5 is a side
cross-sectional view of a cylindrical pellet 420 having a side
surface 425, end surfaces 424 and a chamfered or beveled corner 421
at the intersection between the side surface 425 and each end
surface 424. In one aspect of this embodiment, the chamfered corner
421 can form an angle of approximately 45 degrees with the side
surface 425 and each of the end surfaces 424. In alternate
embodiments the chamfered corner 421 can form other angles with the
side surface 425 and end surfaces 424, so long as the pellet 420
has a reduced volume of at least 5% (and between 5% and 20%, in one
embodiment) when compared to a conventional pellet having the same
maximum length and width.
[0034] FIG. 6 is a side elevation view of a pellet 520 having a
side surface 525 and end surfaces 524 that completely enclose an
internal cavity 522. Alternatively, the side surface 525 and/or the
end surfaces 524 can have one or more apertures that extend into
the cavity 522 to provide a vent. An advantage of this alternate
arrangement is that the apertures can reduce the likelihood for
entrapping air as the pellet 520 is compressed by the plunger 150
(FIG. 2).
[0035] FIG. 7 is a top isometric view of a pellet 620 having a side
surface 625, opposite-facing end surfaces 624, and a cavity 622
extending entirely through the pellet 620 from one end surface 624
to the other. FIG. 8 is a top isometric view of a pellet 720 having
round end surfaces 724 and a cylindrical side surface 725 with a
plurality of cavities 722. In one aspect of this embodiment, the
cavities 722 extend part-way into the side surface 725.
Alternatively, the cavities 722 can extend entirely through the
side surface 725.
[0036] In each of the foregoing embodiments discussed above with
reference to FIGS. 2-8, the pellets have the same overall external
dimensions as conventional pellets, but are formed from a volume of
mold compound that is less than the volume used for conventional
pellets having the same maximum length and width. In one aspect of
these foregoing embodiments, the volume is at least 5% less than
the volume of the conventional pellets. In another aspect of these
foregoing embodiments, the density of the mold compound used to
form the pellets is approximately the same as the mold compound
density of the corresponding conventional pellets. Alternatively,
the mold compound density can be increased or decreased. In any of
the foregoing embodiments, the volume occupied by the cull is
reduced by an amount approximately equal to the volume of the
cavity or other volume-reducing feature of the pellet, for example
by providing protrusions in the plunger 150 and/or the upper plate
142 and/or by reducing the volume of the channels 146 extending
between the cylinder 160 and the substrate portion 145.
Accordingly, reducing the volume of the pellet will not result in
the mold material failing to fill the substrate portion 145 of the
cavity 170, which could result in incomplete encapsulation of the
microelectronic substrate 130.
[0037] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention. For
example, the cavities and other volume-reducing features described
individually with respect to a particular embodiment can be
combined in other embodiments. Accordingly, the invention is not
limited except as by the appended claims.
* * * * *