Patent Application
20160150594
The instant invention relates to microelectronics manufacturing and more particularly to electronic heaters useful in integrated circuit packaging and the thermocompression bonding of the electrical contacts between microelectronic components.
The microelectronics industry is constantly striving for further miniaturization of components to increase speed and functionality of electronic systems. This has led to the fabrication of highly complex integrated circuits (ICs) on chips of semiconductors such as silicon. In order to more effectively electrically connect these chips with printed circuit boards used in many small electronic systems such as smart phones, many processing techniques and apparatuses have been developed.
To improve fabrication yield, it is often desirable to replace a single larger IC chip with a plural number of smaller chips which can be interconnected to function equivalently to the larger chip. This in turn requires the denser packaging of the smaller chips into a single mountable package.
As shown in Tung, U.S. Pat. No. 6,681,982, incorporated herein by reference, a plurality of IC chips can be densely mounted upon a substrate silicon interposer structure which in turn can be mounted upon a larger scale package substrate such as a ball grid array (BGA) to form a microelectronic package mountable to a printed circuit board (PCB).
One common type of package using a silicon interposer between the package BGA and the individual chips is a so-called copper or solder bump or pillar-type package. As disclosed in Lin et at., U.S. Pat. No. 8,021,921, the high density and small geometries of the fine-pitch, micro bump electrical contact copper pillars on the chips requires highly precise and accurate alignment and heating during the bonding of the pillars to the contact pads on the interposer.
One way to form bonds between these types of chips and the silicon interposer structure is by using a thermocompression bonding technique known in the art.
Preferably, while the chip is being pressed on the interposer to help improve flatness during bonding, the temperature is rapidly ramped up to a temperature in which reflow of the conductive pillar material, such as copper tinned with AuSn solder for example, begins. The reflowing pillars each form a bond to their respective electrically conductive pads on the interposer. Simultaneously, as reflow begins, the mechanical resistance to compression by the chip and interposer reduces, whereupon the compressive force is removed, and the chip and interposer are slightly withdrawn from one another so that the pillars do not collapse. The temperature is then brought below the reflow temperature to freeze the pillars bonded to their pads on the interposer. Because of the small geometries involved and the large number of spaced apart pillars which should be briefly and simultaneously reflowed, maintaining adequately uniform temperatures across the entire area of contact between the interposer and chips is important and can be difficult to achieve.
Typically, heat is applied to the chip on its surface opposite the surface being bonded to the chips. The ideal heating profile 1 for many applications is shown in
Another problem with the above thermocompression bonding technique is that the heating profile cannot be controlled uniformly across the surface of the heater, leading to disuniform heating and non-simultaneous reflow of the pillars and thus inferior bonds.
For example, a single evenly spaced heater element run near the surface of a heater platform carrying the parts to be bonded will tend result in a hotter center region of the surface and a cooler edge region of the surface. In addition, such an element could tend create an initial, transient elevated temperature beyond the target reflow temperature during the intended plateau phase of the profile. In other words, it is difficult to obtain a flat, relatively constant temperature during the intended plateau phase of the profile.
Another problem involves precisely and accurately measuring the temperature of each portion of the surface area of the chip-to-interposer interface. Prior designs have employed thermocouples to measure the temperature. However, due to the highly dynamic, rapidly changing character of the ideal heating profile, thermocouple performance can be inadequate.
Desai, U.S. Pat. No. 4,799,983, incorporated herein by reference, teaches that a multilayer ceramic (MLC) technology can be used to form heater element traces in a ceramic substrate. In general, MLC technology involves mixing particles of high temperature-withstanding dielectric material such as alumina with an organic binder, which is then tape-cast, dried and separated into a number of flexible “green sheets”. Some of the sheets are screened and printed with metalization and other circuit patterns which, when stacked in alignment with other sheets, can form intricate three-dimensional electronic interconnects. The stacked sheets are laminated together at a predetermined temperature and pressure, and then slowly heated in a binder burn-off routine to about 400 degrees C. which vaporizes off a majority of the binder material. The resultant fragile baked out or debound part is then fired at an elevated temperature routine, typically reaching 1,600 degrees C. for alumina ceramic in a reducing atmosphere such as humidified hydrogen-nitrogen upon which any residual amount of the binder material vaporizes off while the remaining material fuses or sinters into a solid ceramic body having electrical circuitry coursing therethrough. Where alumina is generally used as the electrically insulating material, and refractory metals such as tungsten and molybdenum can be used for metallization. However, since tungsten oxidzizes readily in co-firing processes involving free oxygen, care must be taken to hermetically isolate tungsten traces. During sintering the body typically shrinks about 15 to 18% where alumina is the ceramic material.
Many potential problems are faced by a designer of a thermocompression bonding heater used for densely packed microelectronic packages. Areas of particular consideration include high operating temperatures, rapidly changing temperatures, high mechanical stresses induced by the compression forces which can exceed 300 Newtons per square inch, and the tendency for tungsten to rapidly oxidize in the presence of essentially any air when heated to such high temperatures. Increasing the mass of the heater helps ruggedness at the expense of rapid heating and cooling.
Another potential problem involves different dice having different masses and geometries. This often creates dice requiring far different heating requirements which in turn can lead to requiring many different heaters.
Another consideration involves the potential thermal expansion mismatches between the ceramic substrate and the metalization. The coefficient of thermal expansion (“CTE”) or simply the thermal expansion of a material is defined as the ratio of the change in length per degree Centigrade to the length at 25 degrees C. It is usually given as an average value over a range of temperatures.
One way of overcoming some of the above problems involves using Aluminum Nitride (hereinafter referred to as “AlN”) as the ceramic. The thermal expansion of tungsten and AN are similar at approximately 4.5 ppm/degree C. Further AN can readily form hermetic structures using MLC technology. For a MLC structure formed using AN as the ceramic, shrinkage during sintering is typically between 20 to 25%.
Another consideration involves the thermal conductivity of the materials in the heater and package components being thermocompression bonded. The thermal conductivity (“K” or “TC”) of a material is defined as the time rate of heat transfer through unit thickness, across unit area, for a unit difference in temperature or K=WL/AT where W=watts, L=thickness in meters, A=area in square meters, and T=temperature difference in degrees centigrade. A more highly thermally conductive structure will tend to spread heat increasing thermal uniformity on the part being bonded and reducing thermal stress within the heater/cooler allowing for increased ramp rates. Typically, to enhance uniformity across the area of the part being reflowed it is desirable to have higher TC near the part. Further, it is often desirable to have a lower TC between the heater and supportive structures in order to form a thermal break between the heater and those structures which may act as a heat sink.
The instant invention results from efforts to improve thermal control of a heater substrate used in thermocompression bonding of microelectronic components.
The primary and secondary objects of the invention are to provide an improved thermal control in a thermocompression bond forming heater substrate. These and other objects are achieved by a plural number of separately energizable heater element traces in a thermocompression bonding substrate.
The content of the original claims portion is incorporated herein by reference as summarizing features in one or more exemplary embodiments.
In some embodiments there is provided a solid state electrical heater apparatus for heating the surface of a part, said apparatus comprises: a part-contacting platform; said platform including a medial zone and a peripheral region laterally spaced a distance apart form said medial zone; a first heater element coursing along and being in thermal communication with said zone; a second heater element spaced apart from said first heater element; said second heater element coursing along and being in thermal communication with said region; and, wherein said first and second heater elements are separately energizable.
In some embodiments the apparatus further comprises: said first element coursing along both said zone and said region; and said second element coursing along both said zone and said region.
In some embodiments said first heater element disproportionately heats said zone more than said region over a given time frame; and, wherein said second heater element is adapted to provide proportionately greater heat flux to said region than said zone during a given energization period.
In some embodiments said first heater element comprises a first trace having a first circuitous pattern, and wherein said second heater element comprises a second trace having a second circuitous pattern.
In some embodiments said second circuitous pattern comprises a first pair of adjacent runs spaced apart by said first shortest distance and a second pair of adjacent runs spaced apart by a second shortest distance, wherein said first and second shortest distances are different.
In some embodiments said second circuitous pattern comprises: a first run having a first smallest cross-sectional area; and, a second run having a second smallest cross-sectional area, wherein said first and second smallest cross-sectional areas are different.
In some embodiments said first and second heater traces are coplanar and laterally spaced apart and wherein said second trace surrounds said first trace.
In some embodiments said first heater element is energized according to a first operation routine, and wherein said second heater element is energized according to a second operation routine, wherein operation of said heater elements simultaneously according to said routines results in a temperature difference across said platform of no greater than plus or minus 3 percent.
In some embodiments said first heater element is energized according to a first operation routine, and wherein said second heater element is energized according to a second operation routine, wherein operation of said heater elements simultaneously according to said routines results in a temperature difference across said platform of no greater than plus or minus 2 percent.
In some embodiments said first operation routine comprises a first heater element ramp up phase followed by a first heater element plateau phase followed by a first heater element ramp down phase; wherein said second operation routine comprises a second heater element ramp up phase followed by a second heater element ramp down phase.
In some embodiments said second heater element ramp down phase begins before or during said first heater element plateau phase.
In some embodiments the apparatus further comprises: said first heater element being energized during a portion of said plateau phase at no more than a constant plateau power level; said second heater element operation routine comprising a second heater element maximum power level; and, said maximum power level being greater than said constant plateau power level.
In some embodiments said first trace has a substantially planar first geometry commensurately overlaying a substantially planar second geometry of said second trace.
In some embodiments the apparatus further comprises a RTD trace having a substantially planar geometry commensurately overlaying with said first geometry, interposed between said first heater trace and said surface.
In some embodiments the apparatus further comprises: a first grounding trace coursing along both of said region and said zone.
In some embodiments the apparatus further comprises: said heater being formed by a plurality of multilayer ceramic layers comprising: aluminum nitride; and, said traces comprising tungsten.
In some embodiments the apparatus further comprises: a first vacuum channel extending from said platform through a plurality of said layers.
In some embodiments the apparatus further comprises: a plurality of vacuum grooves emanating from said channel toward spaced apart regions of said platform.
In some embodiments the apparatus further comprises at least one conduit extending through a plurality of adjacently stratified ones of said layers, wherein said at least one conduit is adapted to carry a cooling fluid.
In some embodiments said cooling fluid comprises air.
In some embodiments the apparatus further comprises a network of cooling vias extending through a plurality of adjacently stratified ones of said layers, wherein said network is adapted to carry a cooling fluid comprising air.
In some embodiments said network comprises: a reservoir; a supply manifold leading from a source of cooling fluid to said reservoir; and, an exhaust manifold from said reservoir to an exhaust return.
In some embodiments said supply manifold comprises: a trunk portion; a plurality of branch portions emanating from said trunk portion; and, wherein each one of said branch portions includes a plurality of spaced apart feeder ducts leading between said one of said branch portions and said reservoir.
In some embodiments said second circuitous pattern comprises a plurality of interconnected, spaced apart runs wherein a spacing between adjacent runs progressively increases between said medial zone and said peripheral region.
In some embodiments said second circuitous pattern comprises a continuous flat spiral segment.
In some embodiments said second circuitous pattern comprises a continuous serpentine segment.
In some embodiments said continuous serpentine segment comprises: a set of parallel lines; and, perpendicular sections linking said lines.
In some embodiments the apparatus further comprises: said first circuitous pattern being topographically similar to the second circuitous pattern; wherein said first circuitous pattern has trace lines substantially perpendicular to the parallel lines of said second pattern; and, an electrically insulating layer between said patterns.
In some embodiments there is provided a thermocompression bonding apparatus comprises: a heater substrate; wherein said substrate comprises: a substantially planar part-carrying upper surface having a medial zone and a peripheral region laterally spaced a distance apart form said medial zone; and, a first heater element coursing under both of said region and said zone; a first cooling conduit coursing under both of said region and said zone; wherein said element comprises: a first trace having a first circuitous pattern having a first segment coursing along said zone and a second segment coursing along said region; wherein said first segment generates a first heat flux during an energization period, and wherein said second segment simultaneously generates a second heat flux during said energization period; wherein said second flux is greater than said first flux; whereby a unit area of said zone has a first temperature and a unit area of said region simultaneously has second temperature; wherein said first and second temperatures are within about 3 percent of one another.
In some embodiments there is provided a further comprises: said second segment has an electrical resistance per unit length of trace greater than said first segment.
In some embodiments the apparatus further comprises a network of cooling vias extending through a plurality of adjacently stratified ones of said layers, wherein said network is adapted to carry a cooling fluid comprising air.
In some embodiments said network comprises: a reservoir; a supply manifold leading from a source of cooling fluid to said reservoir; and, an exhaust manifold from said reservoir to a an exhaust return.
In some embodiments said supply manifold comprises: a trunk portion; a plurality of branch portions emanating from said trunk portion; and, wherein each one of said branch portions includes a plurality of spaced apart feeder ducts leading between said one of said branch portions and said reservoir.
In some embodiments the apparatus further comprises: a second heater element spaced apart for said first heater element.
In some embodiments the apparatus further comprises: said second heater element coursing under both of said region and said zone; and, wherein said first and second heater elements are separately energizable.
In some embodiments the apparatus further comprises: said first heater element comprising a first serpentine trace residing substantially within a first plane; said second heater element comprising a second serpentine trace residing substantially within a second plane; said first plane being parallely spaced apart from said second plane.
In some embodiments there is provided a method of controlling the temperature of a thermocompression bonding heater substrate, said method comprises: selecting a heater substrate comprising: a substantially planar operational surface comprising a medial zone and a peripheral region spaced a lateral distance apart from said medial zone; a first heater element trace coursing along said zone; a second heater element trace spaced apart for said first heater element trace; said second heater element trace coursing along said region; and, wherein said first and second traces are separately energizable; energizing said first trace according to a center-biased energization routine; simultaneously energizing said second trace according to a perimeter-biased energization routine; and, ceasing energizing one of said traces during a time when the other of said traces is being energized; whereby the simultaneous temperatures of said region and said zone are kept within about 3 percent of one another.
In some embodiments the method further comprises: said first trace coursing along both said zone and said region; and said second trace coursing along both said zone and said region.
In some embodiments the method further comprises: said center-biased energization routine having a plateau phase.
In some embodiments there is provided a thermocompression bonded structure comprises: an interposer; at least one integrated circuit chip; a plurality of spaced apart conductive metal pillars electrically interconnecting said at least one chip to said interposer; wherein each of said pillars has a geometry comprising a height dimension, a top end diametric dimension, and a medial diametric dimension potentially different from one another; wherein said height dimensions range between one percent of one another; wherein said top end diametric dimensions range between one percent of one another; and wherein said medial diametric dimensions range between one percent of one another.
In some embodiments there is provided a method for optimizing the powering routine for a TCB heater, said method comprises: selecting a sintered heater blank which can be machined to form an intended heater; first grinding, lapping and polishing a platform surface of said intended heater; cutting a demarcation of a pedestal into said surface; grinding away an amount of material surrounding said pedestal; modeling a preliminary heating routine from parameters associated with said die and said intended heater; performing a test run of said intended heater using said preliminary heating routine; and, adapting said preliminary heating routine into a final heating routine based on results of said performing.
The exemplary embodiment of the invention will be described by way of example in the field of the manufacture of a heatable and sensor-infused thermocompression bonding apparatus substrate. Thus, a thermocompression bonding substrate can be made primarily out of a ceramic material such as aluminum nitride (“AlN”) ceramic having a plurality of metallized heating element traces, thermal sensors in the form of so called “resistance temperature detector” (RTD) traces, electronic signal carrying and power interconnect traces, and grounded shielding traces using tungsten, and vias.
The substrate is manufactured using a multi-layer ceramic (“MLC”) process including the steps of tape casting, blanking, screening, metalization, stacking, laminating, debinding, sintering, flatfiring, lapping, polishing, grinding plating, and brazing for example.
Referring now to drawing, there is shown in
For example, the part 13 contacting the heater 11 can be an integrated circuit die having an array of electrically conductive bumps 17 oriented to electrically interconnect with a corresponding array of bumps 18 on the exposed surface of another part 14 such as an interposer for use in a microelectronic semiconductor integrated circuit package. It is important to note that the part or parts being heated by the heater can, for example be an integrated circuit die, an interposer, or electronic package or subsubstate, an electronic device such as a transistor, or other electronic structures having spaced apart electrically conductive structures such as copper pillars, tinned copper pillars, solder balls or bumps, or electrical contact pads.
A pressure plate 19 is oriented to carry the heater 11 which includes an number of electrical traces 9 within an electrically insulating ceramic body 10. The die 13 can be vacuum carried upon the substantially flat undersurface platform 15 of the heater by way of a vacuum channel 16 coursing through the heater and pressure plate and terminating at the platform surface in a number of vacuum grooves 7. The platform can be shaped in the form of a pedestal 8 to reduce the mass of the heater and have a smooth surface area shaped to closely conform with the shape of the die surface contacting it. The interposer 14 is supported upon a support plate 12. During bonding the two plates are alignedly pressed together. For many common applications the support plate 12 can be warmed to about 80 degrees centigrade.
During bonding the heater 11 is heated, and the support plate 12 and pressure plate 19 are brought together under a force sufficient for thermocompression bonding to occur between the die and interposer where the interfacing bumps contact one another. During bonding the heater is energized to rapidly heat the bumps to the reflow temperature whereupon the force resisting compression reduces slightly. Upon detecting a reflow condition the compressing force is terminated and the plates drawn slightly apart to help avoid the reflowed bumps from mushrooming out, and bringing adjacent bumps too close together, possibly resulting in unwanted electrical shorts. The heater is denergized and the flowed material is allowed to cool and resolidify as spaced apart columns or pillars as shown for example in
Referring primarily now to
A first interface layer 21 forms the platform surface 15 of the heater which interfaces with the substantially flat backing surface of the die or dice during bonding. The interface layer thus can form the substantially planar operational surface of the heater. The interface layer also hermetically seals the internal metalization of the heater from the outside environment. A number of intermediate layers 22 can separate the interface layer from the rest of the heater body and add thickness to the body for structural integrity purposes, to enhance hermeticity, and to improve electrical isolation. (For clarity, the intermediate layers are not shown in
Parallely spaced apart from the interface layer 21 is a temperature sensor layer 23 including a serpentine RTD trace 24 electrically connected across the layers of the heater through metallized vias to RTD contact lands 25. An intermediate electrically insulating layer 26 can separate the RTD layer from a grounded shielding layer 27 having an interconnected grid of traces 28 electrically connected across the layers of the heater to a grounding contact land 29. The shielding layer helps reduce electromagnetic radiation from reaching the RTD traces to induce noise.
Another intermediate electrically insulating layer 30 can separate the shielding layer 27 from a first heater element layer 31 which includes a serpentine first heater element trace 32 which electrically interconnects across the layers of the heater to first heater trace contact lands 33. Another intermediate electrically insulating layer 35 can separate the first heater element layer 31 from a second heater element layer 37 which includes a serpentine second heater element trace 38 which electrically interconnects across the layers of the heater to second heater trace contact lands 39. One or more intermediate layers 41 can seal the second heater element layer within the heater and provide additional structural integrity to the heater body. A number of electrical lines 40 electrically connect the contact lands of the heater with outboard electronics. Further it is understood that each of the heater elements can be separately energized.
It is understood that each heater element can be formed by a continuous serpentine trace lamellarly spaced apart or separated from the other heater element trace by intermediate layers. Further, each trace can run in a pattern having a number of successive switchback spaced apart curves or runs 43,44 to form successive loops which course beneath and supply heat to the platform of the heater. Further, a pattern of parallely spaced apart straight line segments of one element trace 32 can be oriented orthogonally to the pattern of parallely spaced apart straight line segments of the other element trace 38 in order to reduce magnetic induction between physically proximal traces, primarily from the heater traces to the RTD trace, and to more uniformly distribute heat across the heater platform. In this embodiment both heater traces have heater trace runs that have straight line segments that are substantially uniformly spaced apart. A vacuum channel 16 can be formed through the layers and terminate in one or more openings on the platform 15.
Further, the platform 15 of the heater can be characterized as having surface locations including a medial zone 46 and a peripheral region 47 located adjacent to, or peripherally spaced a distance apart from, the medial zone. Both the first heater element trace 32 and the second heater element trace 38 course beneath both the zone and the region locations. In this way, a trace can be said to be in thermal communication with the zone or region when the temperature of the region is determined to a significant extent by the proximity of part of the trace. Another way of characterizing the state of the trace being in “thermal communication” with a location on the platform can be by way of the top plan view projection or footprint of the trace upon the platform surface as shown for example in
Referring now to
The first element trace 51 has a trace pattern formed by a single serpentine trace running between a pair of powering contact pads 52 forming a plurality of adjacently spaced apart heating element runs 53 and having straight line segments 56 having substantially uniform spacing S1, and running under both a medial zone 54 and a peripheral region 55 locations of the heater platform. In other words, the spacing between the straight line segments of an adjacent pair of loops running below the medial zone is substantially the same as the spacing between an adjacent pair of straight line segments of loops running below the peripheral region. It is further shown that the pattern of curves can be in the form of a set of substantially uniformly spaced apart parallel lines 56 and perpendicular arcuate sections 57 linking the lines. Operating a trace having this geometry results in a center-biased heating profile.
A second substantially planar heater element trace 61 can have a trace pattern formed by a single serpentine trace running between a pair of powering contact pads 64. The pattern can have a set of adjacently spaced-apart heating element curves 62 laid in a progressively denser formation between the medial zone 54 and the peripheral region 55. In other words, the spacing S2 between an adjacent pair of straight line segments of loops located within the medial zone is greater than the spacing S3 between an adjacent pair of straight line segments of loops located within the peripheral region. It is further shown that the pattern of curves can be in the form of a set of parallel lines 65 and substantially perpendicular arcuate sections 66 linking the lines. Therefore, it can be said that the second heater element trace pattern can have substantially non-uniform spacing between parallely spaced apart line segments. Operating a trace having this geometry results in a perimeter-biased heating profile.
By having non-uniform spacing, the second trace can generate heat flux through one area 54 of the trace footprint that is different from the heat flux through a different area 55 of the trace footprint. In other words, by running the pattern of trace lines more closely together the heat flux in the peripheral region can be increased, while the heat flux through the medial zone can be reduced over the fluxes expected by uniformly spaced apart trace patterns.
Further, it can be clearly understood that the set of uniformly spaced apart parallel line segments of a first heater element trace pattern can be run in a first orientation and the trace pattern of the second heater element can be selected to have parallely spaced apart parallel line segments which run at second orientation forming an angle A relative to the first orientation. That angle can be selected to be approximately 90 degrees so that the parallel line segments of one trace are substantially perpendicular to the lines of the other trace. In this way, the combined heat flux generated by the two heaters can be better dispersed and currents in one trace are less likely to magnetically induce unwanted currents in the other heater or RTD traces.
Thus it shall be understood that the two superimposed heater traces can be adapted to have a substantially commensurate footprint existing beneath the medial zone 54 and the peripheral region 55. The medial zone can be referred to as the “center” part of the footprint, and the peripheral region as the “edge” part of the footprint.
As shown in
The cooling stack 71 is formed by a number of successive layers starting with an interface layer 81 which separates the nearest heater trace layer 77 from a reservoir layer 82 having an enlarged heat transfer reservoir 83 for carrying a flow of fluid coolant such as air. Cool air is supplied to the reservoir through a supply manifold 84 connected to a cool air supply source line 85 while heated air is withdrawn from the reservoir through an exhaust manifold 86 connected to an exhaust return line 87. Both the supply and exhaust manifolds are formed by a number of stacked layers having interconnected vias formed therein.
Specifically, both the cool fluid supply manifold 84 and the warm fluid exhaust manifold 86 can be formed by similar via structures in the successive layers. Thus the supply and exhaust lines, the manifolds and the reservoir form a network of cooling vias extending through a plurality of adjacently stratified layers. The cool air supply manifold 84 can include a trunk portion 191 from which a number of branch portions 192 emanate. Each one of the branch portions includes a plurality of spaced apart feeder ducts 193 leading between the branch portion and said reservoir. The exhaust manifold has a similar form, however since it is carrying fluid at a higher temperature, the size of the ducts, branches and trunk can be enlarged. In this way the supply ducts can form a uniformly spaced apart grid which can supply cooling fluid to the reservoir in a highly dispersed way. Similarly, the exhaust ducts remove warmed fluid in a similarly dispersed way. This results in more uniformly rapid cooling than less dispersed supplies and exhausts.
It shall be understood that the above network of vias can have their geometry adjusted to adjust the flow of fluid to regions of the reservoir requiring more rapid cooling.
Referring now to
Specifically,
Referring now to
The resultant average temperature on the platform as detected by the RTD trace shows a profile 94 very close to ideal. Further, it can be seen that the maximum powering 93 of the first, perimeter biased heater occurs just prior to the onset 94b of the intended plateau phase of the average temperature on the platform. Further, the maximum temperature differential 95 at any given time across the entire area of the platform, in this example, is no greater than about 10 degrees centigrade, and as graphed more clearly in
The result is a thermally uniform heater platform which is substantially isothermal across its active surface area platform. In other words, the platform provides substantially uniform temperatures across its active surface area for heating a carried chip during thermocompression bonding. In this context, substantially uniform temperatures will depend on the application of the heater. However for most TCB applications a temperature differential of no more than about 10 degrees centigrade which is about 3 percent difference, either plus or minus, can be said to be substantially uniform.
A further advantage of the above heater is that the power routines of the plural heater traces can be adjusted according to the parts being bonded. In other words, for smaller, low-mass parts the powering routine can be adjusted lower, whereas for larger, higher mass parts the power routines can be adjusted higher.
It is important to recognize that the powering routines can be easily adjusted to obtain vastly different heating profiles. Various adjustable powering routine parameters can include: shifting the entire curves in time; steepening or shallowing the ramp-up phases; raising, lowering, extending or shortening any plateau phases; and, steepening or shallowing the ramp-down phases.
Referring now to
The two elements are also selected 102 so that operation of the first element will result in specific portions of the active area receiving less heat than ideal during the heating profile. The second element is selected to provide additional heat to those specific portions at specific times. In other words, the thermal flux generated by one of the elements will be deficient at some time and place on the surface. The other element can be selected and energized to provide additional flux at one or more of the deficient locations.
Thus each of the two heaters can be used differently. The first heater can be used as a center-biased heating element which has a substantially uniformly spaced trace pattern and is intended to be energized according to a center-bias routine. The second heater element can have a non-uniformly spaced trace pattern and can be used as a perimeter-biased heating element which can be energized preimeter-bias so as to overcome deficiencies in the spacial and temporal uniformity of the heating created by the uniformly spaced heater element.
During bonding, both elements are energized 103 to initiate the ramp up of the profile. This will tend to heat the center part of the active area of the platform more than the edges. In order to address this potential disuniformity, the transient heater is energized more forcefully just prior to the anticipated shortfall in heat expected by the first heater. This is because measured heat lags the energy input to the elements.
Just prior to the plateau phase of the ideal temperature profile, the perimeter-biased routine reaches a maximum and then begins decreasing 104. The ramp down phase of the perimeter-biased heater can also occur during the plateau phase of the center-biased heater.
At the end of the plateau phase, both elements are de-energized 105 allowing the area to cool. Alternately, active cooling can reduce the temperature this time.
The above process can result in a bonded die having more uniformly reflowed pillars than can be expected of many prior processes. The specifics of that greater uniformity can be characterized as follows.
In one embodiment the two heater traces are superimposed, one over the other so that each heater can supply heat to the same parts of the substantially planar operational surface carrying the component being thermocompression bonded thereon. In other words, a first heater element can fully heat the area necessary to heat the component being bonded and the second heater element can similarly fully heat the same area necessary to heat the component being bonded.
Referring now to
An adjacent pillar 124 nearest to the first pillar 122 is located a pillar spacing S apart. This is the shortest distance between adjacent pillars on a single chip.
Each pillar has a geometry that can be characterized as having a chip terminal end 131 and an opposite interposer terminal end 132 separated by a pillar height H. Both ends tend to have a similar diameter Pe. A medial part of the pillar has the narrowest pillar diameter Pm of the pillar.
Uniformity can be characterized where the maximum difference between the narrowest diameters Pm of all the pillars associated with a chip is less than 1%.
Referring now to
In this way, the heat flux generated by the combined pair of transient traces can have two dimensional heat flux variation as shown in the isobar of
The perimeter-biased heater traces 140,145 can have non-uniform spacing between the centers of parallely spaced apart line segments. For example, a first pair of adjacent spaced apart line segments can have a spacing S4 which is different from the spacing S5 between another adjacent pair.
Further, the smallest cross-sectional geometry area of the trace run can be non-uniform with respect to different segments of the same trace. The smallest cross-sectional geometric area of a trace at a given segment location is typically found by taking the cross-section plane perpendicular to tangent line of the trace curve at that point. Conveniently, the smallest cross-sectional area of a trace run can be changed by changing the width of the trace at various locations. In other words, the width W1 of the trace segment 163 is larger than the width W2 of the trace segment 164, resulting in a smallest cross-sectional area of trace segment 163 being larger than the smallest cross-sectional area of trace segment 164. By changing the width of the trace, the electrical resistance of the trace can be changed at various segments resulting in greater heat flux per length of trace along that segment at that location. In other words, the heat flux over a given length of trace can be adjusted by reducing or increasing the uniform width of the trace along that given length. In other words, the present apparatus allows for adjustment of the so-called number of “squares” or per unit length resistance of a given segment of trace.
Referring now to
The resultant average temperature on the platform as detected by the RTD trace shows a profile 194 very close to ideal. Further, it can be seen that the maximum powering 193 of the first, perimeter biased heater occurs just prior to the onset of the intended plateau phase 194a of the average temperature on the platform. Further, the maximum temperature differential 195 at any given time across the entire area of the platform, in this example, is no greater than about 6 degrees centigrade, and as graphed more clearly in
Although the above embodiments utilize the stacking of substantially planar layers of green tape, the topographically similar layers can have three-dimensional shapes such as nested curves, saddles, coaxial cylinders, or co-centric spheres for example. In this way, by using coaxial, radially adjacent cylindrical layers, cylindrical, highly controllable heaters can be formed.
Referring now to
The heater/cooler can be adapted to a particular die size or type by simply machining a standard sintered body differently. For example, as shown in
Next, as shown in
As shown in
In this way, pedestals of widely different areas and even shapes can be formed into standard sintered heater bodies. This can significantly reduce manufacturing costs associated with TCB of different sized dice.
While the preferred embodiment of the invention has been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.
This application is a continuation of U.S. patent application Ser. No. 14/192,787, filed 27 Feb. 2014, incorporated herein by reference, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/843,302 filed 5 Jul. 2013 incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/045483 | 7/3/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61843302 | Jul 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14192787 | Feb 2014 | US |
| Child | 14902973 | US |
