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.

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 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 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.