US20030209831A1 - Method and apparatus for packaging microelectronic substrates - Google Patents

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.

Description

TECHNICAL FIELD
• This invention relates to methods and apparatuses for packaging microelectronic substrates.[0001]
BACKGROUND OF THE INVENTION
• 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.[0002]
• In one conventional arrangement shown in FIG. 1, a mold or[0003]cull tool40 simultaneously encases a plurality ofmicroelectronic substrates30. Thecull tool40 can include anupper plate42 removably positioned on alower plate41 to define a plurality ofsubstrate chambers45, anupright pellet cylinder60, and a plurality ofchannels46 connecting thesubstrate chambers45 to thecylinder60. Anarrow gate44 is positioned between eachchannel46 and acorresponding substrate chamber45. Acylindrical pellet20 formed from an epoxy mold compound is positioned in thecylinder60, and aplunger50 moves downwardly within thecylinder60 to transfer heat and exert pressure against thepellet20. The heat and pressure from the plunger liquifies the mold compound of thepellet20. The liquified mold compound flows through thechannels46 and into thesubstrate chambers45 to surround themicroelectronic substrates30 and drive out air within thecull tool40 throughvents43.
• The mold compound in the[0004]substrate chambers45 forms a protective covering around eachmicroelectronic substrate30. The residual mold compound in thechannels46 and in the lower portion of thecylinder60 forms a “cull.” The cull has thin break points corresponding to the location of eachgate44. After theupper plate42 is separated from thelower plate41, the encapsulatedmicroelectronic substrates30 and the cull are removed from thetool40 as a unit. The encapsulatedmicroelectronic substrates30 are then separated from the cull at the break points.
• The mold compound that forms the[0005]pellet20 is typically a high temperature, humidity-resistant, thermoset epoxy. One drawback with this compound is that it can be brittle and accordingly the corners of thepellet20 can chip. One approach to addressing this drawback is to provide a shallow chamfer at thecorners21, 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 thecull tool40. Accordingly, thecull tool40 and theplunger50 can be heated to improve the heat transfer to thepellet20. Furthermore, thelower plate41 of thecull tool40 can include one ormore protrusions47 that can improve the flow of the mold compound within thecull tool40.
• 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[0006]pellet20 and, correspondingly, thechannels46 that define the shape and volume of the cull. For example, one conventional approach includes reducing the length and/or the diameter of thepellet20. 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 thepellets20 for axial insertion into thecylinder60 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
• 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.[0007]
• 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%.[0008]
• 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.[0009]
• 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.[0010]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a partially schematic cross-sectional view of a molding apparatus for encapsulating microelectronic substrates in accordance with the prior art.[0011]
• 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.[0012]
• 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.[0013]
• 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.[0014]
• FIG. 5 is a side cross-sectional view of a pellet having beveled corners in accordance with another embodiment of the invention.[0015]
• FIG. 6 is a side elevation view of a pellet having a hollow internal cavity in accordance with still another embodiment of the invention.[0016]
• FIG. 7 is a top isometric view of a pellet having a cavity extending therethrough in accordance with yet another embodiment of the invention.[0017]
• 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.[0018]
DETAILED DESCRIPTION
• 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.[0019]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.
• FIG. 2 is a partially schematic cross-sectional view of a portion of an[0020]apparatus110 for encapsulating amicroelectronic substrate130 in accordance with an embodiment of the invention. In one aspect of this embodiment, theapparatus110 includes a mold orcull tool140 configured to receive apellet120, with both thetool140 and thepellet120 configured to reduce the volume of waste pellet material when is compared to conventional arrangements. In one aspect of the invention, thetool140 includes anupper portion142 positioned above alower portion141. The upper andlower portions142 and141 have recesses which, when aligned as shown in FIG. 2, form aninternal chamber170 for encapsulating themicroelectronic substrate130. Themicroelectronic substrate130 can be a die, such as a DRAM die or a processor die, or alternatively, themicroelectronic substrate130 can include other electronic components.
• The[0021]internal chamber170 can include asubstrate portion145 that houses themicroelectronic substrate130, acylinder portion160 that houses thepellet120, and achannel portion146 connecting thecylinder portion160 to thesubstrate portion145. Thechamber170 can also include avent143 for exhausting air and/or other gases from thetool140 as thepellet120 fills thechannel portion146 and thesubstrate portion145. For purposes of illustration, onechannel portion146 and onesubstrate portion145 are shown in FIG. 2; however, thetool140 can includeadditional channel portions146 andsubstrate portions145 radiating outwardly from thecylinder portion160 so that asingle pellet120 can be used to encapsulate several (e.g., two-six, or even more)microelectronic substrates130.
• The portions of the[0022]internal chamber170 that fill with waste pellet material (i.e., the pellet material that extends from thecylinder portion160 to the substrate portion145) define the cull volume as discussed above. These portions of theinternal chamber170 have a volume less than that of conventional chambers configured to encapsulate the same number and type ofmicroelectronic substrates130. For example, thechannel portions146 can be smaller than the channels of conventional molds. Furthermore, theupper portion142 of thetool140 can include aprotrusion147 aligned with acentral portion148 of thechamber170. Theprotrusion147 can further reduce the volume of thechamber170.
• The volume of the[0023]pellet120 is also less than the volume of conventional pellets; however, the maximum external dimensions of thepellet120 are approximately identical to those of conventional pellets configured to encapsulate the same number and type ofmicroelectronic substrates130. For example, the overall length L and diameter D of thepellet120 are identical to or nearly identical to the length and diameter, respectively, of a conventional pellet used for the same application. Accordingly, thepellet120 can be used with conventional pellet handling and sorting machines without changing the design, configuration or settings of the conventional machines. In one embodiment, thepellet120 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, thepellet120 can have other dimensions so long as the length L exceeds the diameter D by an amount sufficient to allow thepellet120 to be used with conventional pellet handling machines that properly orient thepellets120 in thechamber160 by distinguishing the length L from the diameter D.
• In one embodiment, the volume of the[0024]pellet120 is less than that of conventional pellets having the same maximum external length and diameter because the external surfaces of thepellet120 include one or more cavities. For example, thepellet120 can include acylindrical side surface125 positioned between two circular end surfaces124, and eachend surface124 can include acavity122. In one aspect of this embodiment, thecavities122 reduce the volume of the mold compound forming thepellet120 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 πR²L, where R (radius)=½D. Alternatively, thepellet120 can have a greater than 20% volume reduction when compared to conventional pellets. In another aspect of this embodiment, thecavities122 can be defined by a hemispherical or partiallyhemispherical cavity wall123. Alternatively, thecavities122 can have other shapes that reduce the volume of thepellet120 without reducing the overall external dimensions of thepellet120, as will be described in greater detail below with reference to FIGS.3-8.
• The[0025]pellet120 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, thepellet120 can have other formulations suitable for encapsulating themicroelectronic substrates130.
• In all the foregoing embodiments described with reference to FIG. 2, the[0026]pellet120 is sized to fit within thecylinder160 of thecull tool140 and above aplunger150. Theplunger150 is axially movable within thecylinder160 between a first position (shown in FIG. 2) to receive thepellet120 and a second position with theplunger150 moved axially upwardly to compress thepellet120. Accordingly, theplunger150 can force the mold compound forming thepellet120 into thechannel portion146 and thesubstrate portion145 of thechamber170.
• In one aspect of this embodiment, the[0027]plunger150, the walls of thecylinder160, and/or the other surfaces of thecull tool140 that define thechamber170 are heated to liquefy thepellet120. In still a further aspect of this embodiment, theplunger150 can include aside wall151 adjacent the walls of thecylinder160, anend wall152 transverse to theside wall151 and aprotrusion153 that extends axially away from theend wall152 and the corner between theend wall152 and theside wall151. Theprotrusion153 can have a width less than or equal to the width of theend wall152. In still a further aspect of this embodiment, theprotrusion153 is sized to fit within thecavity122 at the end of thepellet120. Accordingly, when theplunger150 is heated, theprotrusion153 can increase the rate of heat transfer to the pellet120 (relative to a conventional plunger having a flat end surface) because more surface area of theplunger150 contacts thepellet120. Similarly, when theupper portion142 of thecull tool140 is heated, theprotrusion147 can increase the heat transferred to thepellet120 by engaging thewalls123 ofcavity122 at the opposite end of thepellet120.
• In operation, the[0028]microelectronic substrate130 is positioned in thesubstrate portion145 of thechamber170 and thepellet120 is positioned in thecylinder portion160. Theplunger150 and/or the surfaces defining thechamber170 are heated, and theplunger150 is moved upwardly to compress and liquify thepellet120. The plunger accordingly forces theliquified pellet120 through thechannel portion146 and into thesubstrate portion145 around themicroelectronic substrate130. The encapsulatedmicroelectronic substrate130 and the cull (which occupies thechannel146 and thecentral portion148 of the chamber170) are removed as a unit, and then the encapsulatedmicroelectronic substrate130 is separated from the cull, in a manner generally similar to that discussed above.
• One feature of an embodiment of the[0029]apparatus110 and the method described above with reference to FIG. 2 is that thepellet120 has the same maximum length and width as a conventional pellet to be compatible with existing pellet handling machines, but thepellet120 has a reduced volume. Accordingly, the culls formed from thepellet120 have a lower volume than conventional culls to reduce the cost of the pellets and the waste material left over after encapsulating themicroelectronic substrates130 with the pellets.
• Another feature of an embodiment of the[0030]apparatus110 and method described above with reference to FIG. 2 is that the size of thecavities122 can be selected to match the size of theinternal chamber170 and/or the size of themicroelectronic substrate130. For example,pellets120 having relativelylarge cavities122 can be used withcull tools140 having relatively smallinternal volumes170, andpellets120 having relatively small cavities122 (or no cavities) can be used withcull tools140 having relatively largeinternal volumes170. Similarly,pellets120 having relativelylarge cavities122 can be used to encapsulate relatively largemicroelectronic substrates130 andpellets120 having relatively small cavities122 (or no cavities) can be used to encapsulate relatively smallmicroelectronic substrates130. Accordingly,pellets120 having the same overall external dimensions can be used withdifferent cull tools140 to encapsulate differentmicroelectronic substrates130 without requiring different pellet handling equipment.
• FIGS.[0031]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 apellet220 having a generallycylindrical side surface225, circular end surfaces224, and aslot222 in eachend surface224. Eachend surface224 can include asingle slot222, or alternatively, eachend surface224 can include a plurality ofslots222. In either embodiment, thepellet220 can be used in conjunction with an apparatus generally similar to theapparatus110 shown in FIG. 2, but having tab-shaped protrusions that match the shape of theslots222 instead of thehemispherical protrusions147 and153 shown in FIG. 2. Accordingly, the rate of heat transfer to thepellet220 can be increased when compared to conventional devices in a manner generally similar to that described above with reference to FIG. 2.
• Referring now to FIGS. 2 and 3, the[0032]pellet220 can be compressed with aplunger150 having aflat end wall152 and acull tool140 having a flatcentral portion148 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 thecavities222 by reducing the volume of thechannels146 and/or other portions of thecull tool140. Accordingly, theslots222 inpellet220 may have certain advantages over thespherical cavities122 in thepellet120 described above with reference to FIG. 2. For example, when theplunger150 has aflat end wall152, theslot222 will not entrap air as theplunger150 engages thepellet220. Instead, air in theslot222 will tend to flow laterally around theside surface225 of thepellet220 as theplunger150 compresses thepellet220.
• FIG. 4 is a side cross-sectional view of a[0033]pellet320 having frustro-conical cavities322 eachend surface324. FIG. 5 is a side cross-sectional view of acylindrical pellet420 having aside surface425, end surfaces424 and a chamfered orbeveled corner421 at the intersection between theside surface425 and eachend surface424. In one aspect of this embodiment, the chamferedcorner421 can form an angle of approximately 45 degrees with theside surface425 and each of the end surfaces424. In alternate embodiments the chamferedcorner421 can form other angles with theside surface425 and endsurfaces424, so long as thepellet420 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.
• FIG. 6 is a side elevation view of a[0034]pellet520 having aside surface525 and endsurfaces524 that completely enclose aninternal cavity522. Alternatively, theside surface525 and/or the end surfaces524 can have one or more apertures that extend into thecavity522 to provide a vent. An advantage of this alternate arrangement is that the apertures can reduce the likelihood for entrapping air as thepellet520 is compressed by the plunger150 (FIG. 2).
• FIG. 7 is a top isometric view of a[0035]pellet620 having aside surface625, opposite-facing end surfaces624, and acavity622 extending entirely through thepellet620 from oneend surface624 to the other. FIG. 8 is a top isometric view of apellet720 having round end surfaces724 and acylindrical side surface725 with a plurality ofcavities722. In one aspect of this embodiment, thecavities722 extend part-way into theside surface725. Alternatively, thecavities722 can extend entirely through theside surface725.
• In each of the foregoing embodiments discussed above with reference to FIGS.[0036]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 theplunger150 and/or theupper plate142 and/or by reducing the volume of thechannels146 extending between thecylinder160 and thesubstrate portion145. Accordingly, reducing the volume of the pellet will not result in the mold material failing to fill thesubstrate portion145 of thecavity170, which could result in incomplete encapsulation of themicroelectronic substrate130.
• 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.[0037]

Claims (86)

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 ofclaim 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 ofclaim 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 ofclaim 1, further comprising forming the cavity to extend entirely through the pellet.

5. The method ofclaim 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 ofclaim 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 ofclaim 1, further comprising selecting the mold material to include an epoxy.

8. The method ofclaim 1, further comprising forming the cavity to have a generally hemispherical shape.

9. The method ofclaim 1, further comprising forming the cavity to have a generally cylindrical shape.

10. The method ofclaim 1, further comprising forming the cavity to include a slot in the first end surface arranged transverse to the side surface.

11. The method ofclaim 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 ofclaim 1, further comprising selecting the mold material to include biphenyl, di-cyclo pentadiene, ortho-cresole novolak and/or a multifunctional material.

13. The method ofclaim 1, further comprising selecting the microelectronic substrate to include a DRAM device.

14. The method ofclaim 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 ofclaim 15, further forming a cavity in the pellet body.

17. The method ofclaim 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 ofclaim 16, further comprising forming the cavity to extend entirely through the pellet.

19. The method ofclaim 16, further comprising forming the cavity to have a generally hemispherical shape.

20. The method ofclaim 16, further comprising forming the cavity to include a slot in the first end surface arranged transverse to the side surface.

21. The method ofclaim 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 ofclaim 15, further comprising selecting the mold material to include biphenyl, di-cyclo pentadiene, ortho-cresole novolak and/or a multifunctional material.

23. The method ofclaim 15, further comprising chamfering an edge between the first end surface and the intermediate surface.

24. The method ofclaim 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 ofclaim 25, further comprising heating walls of the cavity by heating the plunger.

27. The method ofclaim 25, further comprising receiving a protrusion of the packaging chamber in the cavity of the pellet.

28. The method ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 32 wherein the cavity is a first cavity in the first end surface, the second end surface having a second cavity.

34. The pellet ofclaim 32 wherein the cavity extends entirely through the pellet body.

35. The pellet ofclaim 32 wherein the cavity is completely enclosed within the internal volume.

36. The pellet ofclaim 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 ofclaim 32 wherein the pellet body is sized to form from two to six packaged microelectronic devices.

38. The pellet ofclaim 32 wherein the mold material includes an epoxy.

39. The pellet ofclaim 32 wherein the first and second end surfaces are generally circular and the intermediate surface is generally cylindrical.

40. The pellet ofclaim 32 wherein the cavity has a generally hemispherical shape.

41. The pellet ofclaim 32 wherein the cavity has a generally cylindrical shape.

42. The pellet ofclaim 32 wherein the cavity includes a slot in the first end surface arranged transverse to the side surface.

43. The pellet ofclaim 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 ofclaim 32 wherein the thermoset mold material includes biphenyl, di-cyclo pentadiene, ortho-cresole novolak and/or a multifunctional material.

45. The pellet ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 47 wherein the mold material includes an epoxy.

50. The pellet ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 53 wherein the mold compound includes an epoxy.

56. The pellet ofclaim 53 wherein the first and second end surfaces are generally circular and the intermediate surface is generally cylindrical.

57. The pellet ofclaim 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 ofclaim 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 ofclaim 59 wherein the pellet body has a cavity that forms a void in the uncured mold material.

61. The pellet ofclaim 60 wherein the cavity is a first cavity in the first end surface, the second end surface having a second cavity.

62. The pellet ofclaim 60 wherein the cavity extends entirely through the pellet body.

63. The pellet ofclaim 60 wherein the cavity is completely enclosed within the internal volume.

64. The pellet ofclaim 60 wherein the cavity includes a slot in the first end surface arranged transverse to the side surface.

65. The pellet ofclaim 59 wherein the mold material includes an epoxy.

66. The pellet ofclaim 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 ofclaim 59 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.

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 ofclaim 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 ofclaim 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 ofclaim 69 wherein the cavity includes a slot in the first end surface arranged transverse to the side surface.

72. The set of pellets ofclaim 68 wherein a length of the first pellet exceeds a widthwise dimension of the first pellet.

73. The set of pellets ofclaim 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 ofclaim 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 ofclaim 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 ofclaim 76 wherein the plunger has a spherical end wall.

78. The apparatus ofclaim 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 ofclaim 75 wherein the plunger is coupled to a heat source.

80. The apparatus ofclaim 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 ofclaim 81 wherein the mold body is coupled to a heat source.

83. The apparatus ofclaim 81 wherein the protrusion has a spherical shape.

84. The apparatus ofclaim 81 wherein the protrusion includes a tab sized to be removably received in the cavity of the pellet.

85. The apparatus ofclaim 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 ofclaim 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.

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