Classifications

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  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/10—Bump connectors ; Manufacturing methods related thereto
  • H01L24/12—Structure, shape, material or disposition of the bump connectors prior to the connecting process
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  • H01L23/48—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor
  • H01L23/50—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor for integrated circuit devices, e.g. power bus, number of leads
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K1/00—Soldering, e.g. brazing, or unsoldering
  • B23K1/0008—Soldering, e.g. brazing, or unsoldering specially adapted for particular articles or work
  • B23K1/0016—Brazing of electronic components
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/02—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a press ; Diffusion bonding
  • B23K20/023—Thermo-compression bonding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
  • B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to soldering or welding
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  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/48—Manufacture or treatment of parts, e.g. containers, prior to assembly of the devices, using processes not provided for in a single one of the subgroups H01L21/06 - H01L21/326
  • H01L21/4814—Conductive parts
  • H01L21/4846—Leads on or in insulating or insulated substrates, e.g. metallisation
  • H01L21/486—Via connections through the substrate with or without pins
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  • H01L23/14—Mountings, e.g. non-detachable insulating substrates characterised by the material or its electrical properties
  • H01L23/145—Organic substrates, e.g. plastic
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  • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
  • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
  • H01L23/3733—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon having a heterogeneous or anisotropic structure, e.g. powder or fibres in a matrix, wire mesh, porous structures
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  • H01L23/492—Bases or plates or solder therefor
  • H01L23/4922—Bases or plates or solder therefor having a heterogeneous or anisotropic structure
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  • H01L23/498—Leads, i.e. metallisations or lead-frames on insulating substrates, e.g. chip carriers
  • H01L23/49827—Via connections through the substrates, e.g. pins going through the substrate, coaxial cables
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  • H01L23/498—Leads, i.e. metallisations or lead-frames on insulating substrates, e.g. chip carriers
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  • H01L24/86—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using tape automated bonding [TAB]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/36—Electric or electronic devices
  • B23K2101/40—Semiconductor devices
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  • H01L2224/056—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
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  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
  • H01L2924/151—Die mounting substrate
  • H01L2924/1517—Multilayer substrate
  • H01L2924/15172—Fan-out arrangement of the internal vias
  • H01L2924/15173—Fan-out arrangement of the internal vias in a single layer of the multilayer substrate
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/032—Organic insulating material consisting of one material
  • H05K1/0326—Organic insulating material consisting of one material containing O
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/032—Organic insulating material consisting of one material
  • H05K1/0333—Organic insulating material consisting of one material containing S
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/032—Organic insulating material consisting of one material
  • H05K1/0346—Organic insulating material consisting of one material containing N
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/0353—Organic insulating material consisting of two or more materials, e.g. two or more polymers, polymer + filler, + reinforcement
  • H05K1/036—Multilayers with layers of different types
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/01—Dielectrics
  • H05K2201/0104—Properties and characteristics in general
  • H05K2201/0116—Porous, e.g. foam
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/01—Dielectrics
  • H05K2201/0137—Materials
  • H05K2201/0154—Polyimide
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
  • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
  • H05K2201/10227—Other objects, e.g. metallic pieces
  • H05K2201/10378—Interposers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/10—Using electric, magnetic and electromagnetic fields; Using laser light
  • H05K2203/107—Using laser light
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/0011—Working of insulating substrates or insulating layers
  • H05K3/0017—Etching of the substrate by chemical or physical means
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/0011—Working of insulating substrates or insulating layers
  • H05K3/0017—Etching of the substrate by chemical or physical means
  • H05K3/0026—Etching of the substrate by chemical or physical means by laser ablation
  • H05K3/0032—Etching of the substrate by chemical or physical means by laser ablation of organic insulating material

Definitions

• This invention relates to new practical applications of uniaxially electrically conductive articles, and to special forms of such article for use therein.
• Porous polymer sheets in which selected areas of the interconnecting through-holes are masked and the unmasked through-holes are metal plated to provide electrically con ⁇ ductive spots surrounded by insulating areas, are known from Japanese Published Patent Application 80161306.
• Published EP-A-0213774 describes a superior form of uniaxially electrically conductive article comprising porous electrically insulating sheet material at least a selected portion of which has at least 25 substantially non- interconnected through-holes per square millimetre of its surface, at least a significant proportion of which through- holes individually contain electrically conductive material which provides an electrically conductive path between, and projects beyond at least one of, the main surfaces of the sheet material, each such conductive path being electrically separate from substantially all of the other such conductive paths.
• uniaxially electrically conduc ⁇ tive article for all aspects of the present invention are those supplied by Raychem Limited, for example as described in the aforementioned EP-A-0213774 or as described in copending British Patent Applications 8802567, 8802566, 8802568.
• the description of the present invention hereinafter will refer to uniaxially conductive sheets, it being understood, however, that the invention is not limited to the use of those specific preferred forms of uniaxially conductive article.
• Formation of the conductive article by laser drilling of through-holes in polymer sheets, especially by U.V. laser ablation (ablative photodecomposition) has advantages in producing a relatively low degree of taper in the holes com ⁇ pared with other perforating techniques such as etching with liquids or reactive gases.
• the lower taper permits closer pitch between through-holes. This is clearly advantageous, given that microcircuits are becoming progressively smaller and repeat njore densely patterned.
• Through-holes with taper (measured between the substantially straight inner surface of the hole and the axis of the hole) lessthan 10°, pre ⁇ ferably less than 8°, more preferably less than 6°, and especially less than 4° can advantageously be achieved by laser drilling of suitable polymer sheets, and may usefully be incorporated in all aspects of the invention described herein.
• One application according to this invention provides a method of making substantially permanent electrical connec ⁇ tions between connection sites on a first substrate and corresponding connection sites on a second substrate, comprising: (a) aligning the connection sites of first substrate face to face with the corresponding connection sites on the second substrate, (b) placing between the facing substrates a uniaxially electrically conductive article comprising electrically insulating sheet material with at least one through- hole aligned between each pair of facing connection sites, the through-holes being internally plated with electrically conductive material which provides an electrically conductive path between, and projects beyond, the main surfaces of the sheet material and including bonding material capable of bonding to the said connection site, and
• the electrically conductive material comprises a tube of the plated metal in each through-hole.
• the bonding material at least at one end of each through- hole, may be solder (e.g. held in a tube of plated metal), or may be gold, preferably plated to a thickness of at least 1.5, more preferably at least 2 micrometres.
• Gold espe ⁇ cially at thicknesses of 2 micrometres or more (e.g. 2.5,3, or 3.5 micrometres)
• the uniaxial sheet may be constructed with only one through-hole containing the electrically conductive material between pairs of facing connection sites, e.g. on a chip and a circuit board, in which case the size of the through-holes will preferably be chosen to suit the size of the connection sites. Alternatively, there may be two or more small through-holes independently containing the electrically con ⁇ ductive material between each pair of connection sites.
• the sheet may have substantially no other con ⁇ ductive through-holes, thus providing a single "one-to-one" pattern of conductive paths (one path or one group of paths for each pair of connection sites) as described in the aforementioned copending application; or the sheet may have two or more such "one-to-one” patterns interspersed with each other for selective use as also described in copending international application (RK360COM); or the sheet may have a multitude of conductive through-holes as described in the aforementioned EP-A-0213774 for random alignment between the facing pairs of connection sites; always provided that any conductive through-holes not acting between the facing pairs of connection sites do not inter ⁇ fere unacceptably with the operation of the resulting assembly of a first substrate (preferably a microcircuit chip) substantially permanently electrically connected to a second substrate by this method.
• a first substrate preferably a microcircuit chip
• Uniaxially conductive sheets can thus be used to bond chips (and other active devices, for example liquid crystal displays) permanently to circuit boards, chip carriers, or even to other chips.
• Known technology of this kind includes IBM's "flip chip”, in which method solder balls are formed on the chip's bond pads, the chip is flipped upside down and aligned with the tracks on a circuit board, and the solder is reflowed to make a joint.
• This method has the advantage of having a very small "footprint” (no larger than the chip itself) , but a major drawback of "flip chip” is the tendency of the solder bonds to shear on thermal cycling. This is because the chip (made of silicon) often has a different thermal expansion coefficient from the substrate it is attached to (a glass-epoxy board, for example) . Thus the two components expand and contract by different amounts, and failure occurs.
• Flip chip is also unpopular because a further pro- ⁇ essing step is required to place solder bumps on IC bonding pads.
• Figure FCl illustrates a solder-bumped chip in a known "flip chip” assembly.
• Figure FC2 shows an assembly of a "flip chip" prior to bonding to a uniaxially conductive article according to the present invention.
• Figure FC3 illustrates the Fig. FC2 uniaxially conduc ⁇ tive article bonded by ther ocompression to the "flip chip", before bonding to a hybrid circuit board or multichip module.
• Figure FC4 shows the Fig.FC3 assembly after bonding by solder reflow to the hybrid board or module.
• Figure FC5 illustrates an assembly ready for ther ⁇ mocompression bonding of the projecting plated tubular metal uniaxial conductors to an unbumped integrated circuit chip cfccording to the present invention.
• Figure FC6 shows the Fig. FC5 assembly being bonded by thermocompression.
• the uniaxial sheets act as stand-offs, tending to reduce the shear stress at the bond interfaces, and calcula ⁇ tions suggest that significant increases in working lifetime over solder bumps may be achievable.
• the invention accordingly includes a uniaxially electrically conductive article comprising electrically insulating sheet material with through-holes individually containing electrically conductive material which provides an electrically conductive path between the main surfaces of the sheet material, the surface of the electrically conduc ⁇ tive material which is exposed to contact comprising at least 2 micrometres thickness of gold.
• the gold is plated on at least part of a tubular formation of another metal plated in the through- holes, which through-holes are preferably not more than 200 micrometres in diameter.
• Gold plating techniques are described, for example, in "Gold Plating Technology" by F.H. Reid & W. Goldie, Electrochemical Publications Limited (1974).
• electroless methods in which gold is deposited onto copper or nickel electro- lessly deposited layers without depositing on the polymer sheet, but other methods, for example thick-film deposition from pastes introduced into the through-holes, may be used if acceptable results are produced.
• the polymer sheet material will be selected to withstand the chosen metal- deposition techniques.
• an anisotropi- cally (preferably substantially uniaxially) electrically conductive article comprising electrically insulating sheet material and electrically conductive material providing electrically separate conductive paths within (preferably close-fitting within holes in) the sheet material between the opposed main surface regions thereof, wherein Case (a) the conductive material at one end of the said paths (preferably projecting beyond one of the sheet surface regions) is bondable by thermocompression, and the conduc ⁇ tive material (which may be the same or different) at the other end of the said paths is bondable by solder, and/or Case (b) the conductive material at one end of the said paths is bondable at a temperature lower than the minimum bonding temperature of the conductive material at the other end of the said paths.
• solder examples include low-melting-point metals and alloys which can be used in ways similar to commercially available solders.
• the articles in question may conduct electricity in more than one plane, for example by way of conductive paths running parallel to the sheet surfaces either within or on the sheet in addition to those extending from one surface region to the other within the sheet.
• conductive paths running parallel to the sheet surfaces either within or on the sheet in addition to those extending from one surface region to the other within the sheet.
• the article it is often most useful for the article to be substantially uniaxially conductive with the conductive paths extending within the sheet material substantially only from one surface region to the other, preferably substantially straight and normal to the sheet surfaces, although non-linear paths and/or other angles to the sheet surfaces are possible.
• the sheet material it is usually convenient for the sheet material to have through-holes lined with the conductive material, and the conductive material in each through-hole is preferably electrically separate from that in the other through-holes.
• the through-holes may be internally plated with a tubular formation of metal to provide at least part of the conduc ⁇ tive paths, for example by the plating methods described in the aforementioned European, British and International patent applications.
• ther ocompression-bondable material of case (a) above comprises gold metal and the solder-bondable material may comprise gold or may comprise at least one other metal.
• the conductive paths comprise at least one metal which is not thermocompression-bondable carrying at least two micrometres thickness of the gold metal at the thermocompression- bondable end.
• the conductive material may carry solder (applied by known methods) for bonding the solder-bondable ends of the path, but it may be preferable in many practical applications to effect the solder bonding by reflow of solder carried by the substrate to which the article is to be solder-bonded, for example a solder-bumped microchip or inter-connect device.
• solder-bondable conductive material projects beyond the other sheet surface region; while in other forms the solder-bondable conductive material ends in a recess below the level of the sheet surface in the sense that it ends sufficiently far below the surface to avoid making electri ⁇ cal contact with an electrically conductive member when a surface of that member which is wider than the recess is brought into contact with the sheet surface so as to lie across the recess.
• bonding may be effected by flow of solder into the recesses to contact the conductive material therein, for example from solder-bumped chips of interconnect devices.
• An article according to the invention may be designed for making electrical connections to a predetermined pattern of connection sites on a first substrate when arranged in face-to-face alignment with a corresponding pattern of con ⁇ nection sites on a second substrate, the article having a pattern of the said conductive paths corresponding to the said patterns of connection sites to make electrical connec ⁇ tions between facing pairs of the connection sites when the sheet material in use is arranged between the substrates with the conductive material at the respective ends of each path in contact with its corresponding pair of connection sites.
• an article could be designed at least a portion of which has at least 25 of the conductive paths per square millimetre of the sheet surface.
• Such an article especially at higher path densities per square millimetre, could be used to provide microelectronic connec ⁇ tions in the manner described in the aforementioned European application, i.e. without the pattern of conductive paths having to correspond accurately with the connection sites on other substrates.
• some (more pre ⁇ ferably substantially all) of the conductive paths are not more than 200 micrometres in diameter.
• This aspect of the invention includes an assembly wherein an article of the kind (a) hereinbefore described has the thermocompression-bondable ends of at least some of the conductive paths thermocompression-bonded to connection sites on an integrated circuit semiconductor device. .
• Such an assembly may be useful in manufacturing a further assembly or device in which the said article has the solder- bondable ends of at least some of the conductive paths solder bonded to microelectronic interconnect circuitry.
• thermocompression-bondable ends of at least some of the conductive paths thermocompression-bonded to micro electronic interconnect circuitry which could be use ⁇ ful in manufacturing an alternative further assembly or device wherein the said article has the solder-bondable ends of at least some of the conductive paths solder bonded to connection sites on an integrated circuit semiconductor device.
• the integrated circuit devices referred to could for example be silicon or gallium arsenide microchips for "flip chip" mounting in an interconnect circuitry package.
• the interconnect circuitry could for example be a fan-out circuit board, multi-chip module, or another microchip, for example a "mirror" chip as described in the aforementioned British Application 8802565.
• thermocompression-bonds are relatively permanent, while the solder-bonded ends of the conductive paths can be rela ⁇ tively easily disconnected to permit replacement of defec ⁇ tive components without destroying the whole assembly.
• the anisotropically (preferably uniaxially) conductive articles according to this aspect of the invention may be fabricated using any of the structures and/or methods and/or materials described in any of the ⁇ aforementioned European, British and International applications, with the thermocompression-bondable material (and the solder if pre ⁇ sent) being applied during or after the other fabrication steps.
• the following description will refer to gold, this being the preferred thermocompression-bondable material, although other materials can be used, for example copper, aluminium, or indium, with suitable bonding sites.
• Figure 7GS shows schematically a uniaxially conductive sheet according to the invention and an integrated circuit microchip to be bonded thereto;
• Figure 8GS shows the sheet and chip of Figure 1 after bonding
• Figure 9GS shows schematically the inverted assembly of sheet and chip bonded to a fanout circuit board
• Figure 10GS shows schematic enlargements of two forms of plated through-holes capable of providing the conductive paths through the sheet of Figures 7GS to 9GS.
• the electrically insulating polyimide sheet 10 of an article according to the present invention carries electrically conductive plated nickel-on- copper tubes 12 (greatly enlarged for clarity) which provide the conductive paths projecting from both surfaces of the sheet.
• the upper ends (as illustrated) of the copper tubes are the plated solder-bondable nickel, while the lower ends are overplated with thermocompression-bondable gold to a thickness of 3 micrometres.
• the gold-plated ends of the tubes 12 are aligned for bonding to aluminium bonding sites (not shown) on an integrated circuit microchip 14.
• Figures 10AGS and 10BGS respectively show in enlarged schematic cross-section one of the through-holes in the sheet 10 which has been plated with copper and then with nickel to form a tapered tube 20 of metal. Surface layers have been removed from the sheet after the plating to leave the tapered metal tubes 20 projecting from both sheet sur ⁇ faces, as described in the aforementioned European, British and International applications.
• the holes, and therefore the plated metal tubes are usually somewhat tapered, as shown.
• Thermocompression-bondable gold layer 22 illustrated in Figure 10AGS has been plated on the wider end of the tapered tube 20, while Figure 10BGS illustrates the alternative plating of the gold 22 on the narrower end of the tapered tube 20.
• the gold plating 22 need not extend as far into the tube 20 as illustrated.
• the tube 20 could carry solder at its other (not gold-plated) end, which solder could partially fill the tube 20.
• the temperatures used for thermocompression bonding the gold- plated end would not prematurely melt the chosen solder.
• thermocompression-bondable material or solder
• this is easily achieved for example, by masking all the other side of the sheet with a suitable resist, electro- lessly plating the material, e.g. gold (or melt coating the solder) on the exposed ends of suitable metal e.g. copper- nickel passing through the sheet, then removing the resist to expose the unplated (or unsoldered) ends of the paths.
• the unplated (unsoldered) ends may then be similarly pro ⁇ vided with an appropriate bonding material, preferably a solder having a lower melt temperature than the material applied to the first ends, which may be thermocompression- bondable in the aforesaid case (a), or another solder in case (b) .
• an appropriate bonding material preferably a solder having a lower melt temperature than the material applied to the first ends, which may be thermocompression- bondable in the aforesaid case (a), or another solder in case (b) .
• This aspect of the invention includes a method of making electrical connections wherein an anisotropically electrically conductive article according to the aforesaid case (a) is thermocompression bonded to electrical conduc ⁇ tors at one end of the said paths, and is solder bonded to electrical conductors at the other end of the said paths, or wherein an anisotropically electrically conductive article according to the aforesaid case (b) is solder bonded to electrical conductors at one end of the said paths by solder having a first minimum bonding temperature, and is solder bonded to electrical conductors at the other end of the said paths at a temperature below the said first minimum bonding temperature by solder having a second minimum bonding tem ⁇ perature which is lower than the first minimum bonding tem ⁇ perature.
• the higher-temperature bonding material will be able to survive the exposure to lower temperatures involved in bonding the lower temperature ends.
• Thermocompression bonding is preferably conducted at signi ⁇ ficantly higher temperatures than solder-bonding.
• thermode was brought into contact with the uniaxially conducting material, the thermode temperature raised to 350 Celsius during the appli ⁇ cation of pressure for approximately 2 seconds in order to form a thermocompression bond. At this stage the integrated circuit was bonded to the sheet of uniaxially conducting material.
• the sub-assembly was then 'flipped' so as to bring the side of the uniaxially conducting material not yet used for bonding into contact and alignment with a circuit board.
• the tracks on the circuit board had previously been solder tipped with an 80% gold - 20% tin solder which forms a good solder bond to gold metallisations.
• the stage on which the circuit board was held was heated so as to raise the temperature of the solder above its melting point i.e. greater than 280 Celsius. Once cooled, a strong solder bond had been achieved between the uniaxially conductive material and the circuit board.
• the result of these two bonding stages is an integrated circuit bonded to a circuit board via a sheet of uniaxially conducting material.
• a preferred polymer material for this and the other aspects of the invention is a polyimide capable of retaining at least 50%, preferably at least 75%, more preferably at least 85%, of its original elongation after immersion in water of pHlO at 100°C for 4 days according to ASTM D882. It will be readily understood that a sufficiently fully cyclised polyimide having less than 15%, preferably less than 10%, more preferably less than 5%, and if possible substantially no open imide rings or uncyclised amic acid groupings may be better able to survive hot alkaline metal plating baths, which attack incompletely cyclised polyimides such as Kapton (TM) .
• TM Kapton
• Preferred materials include polyimides derived from polymerisation of 4,4'-biphenyl dianhydride and (4,4'-diaminobiphenyl, or 4,4'-diaminobiphenyl ether, or phenylenediamine) .
• UPILEX polyimide
• Ube/ICI trademark of Ube/ICI
• UPILEX R is believed to be a relatively completed cyclised polymer having a repeat unit derived from biphenyl dianhydride and diaminodiphenylether
• UPILEX S which is believed to have a repeat unit derived from the same anhydride anod phenylene diamine, viz
• the polyimide of the 4,4'-diaminobiphenyl has thermal expansion/contraction characteristics which may render it particularly suitable for use with microcircuit chips and circuit boards.
• the diameter and distribution of the through-holes will preferably be such that the through-holes occupy from 3 to 35 per cent, more preferably 10 to 20 per cent, of the sheet surface area.
• Through-holes of less than 500, preferably less than 200, e.g 5 to 150, micrometres diameter are pre ⁇ ferred.
• a sheet with at least 25 through-holes per square millimetre having plated electrically conductive material (metal) within (preferably substantially only within) the through-holes is especially useful, the through-holes thus providing high density electrically conductive paths between the sheet surfaces, each such path being electrically separate from substantially all the other paths.
• While a "significant proportion" of the through-holes in the selected areas may contain the conductive material, it is preferred that a majority (more than 50%) do so. Proportions of at least 70%, or better still at least 85% are preferred, and in many cases, substantially all of the through-holes will contain the conductive material.
• the through-holes, whether containing the conductive material or not, may be confined to selected areas of the sheet.
• the through-holes in "one-to-one” or in “multitudinous” uniaxial sheets may for example be 1 to 200 micrometres in diameter, and it is also preferable in some cases that the conductive material project beyond both main surfaces of the sheet material, the projections from either surface pre ⁇ ferably being, for example, 0.2 to 100 micrometres in height, preferably 0.5 to 30 micrometres.
• the insulating sheet material will preferably be a flexible polymeric material, and the number of through-holes per square millimetre of the sheet material (whether flexible polymeric or not) may be as high as 10000, but will preferably be in the range from 25 to 2000, more preferably 50 to" ⁇ L000.
• the through-holes will preferably have a tor ⁇ tuosity factor (mean path length/sheet thickness) less than 3, preferably less than 1.2; and will preferably have an aspect ratio (length/diameter) of at least 2.5.
• the "electrically conductive" paths between the sheet surfaces may give the sheet an average electrical conductivity in the thickness direction within the 'semicon- ductive range, it is preferable to achieve generally metallic levels of conductivity e.g. at least 1000 Siemens per centimetre, preferably at least 5000 Siements, espe ⁇ cially at least 10000 Siemens per centimetre.
• the preferred conductive materials are metals, preferably plated, espe ⁇ cially electrolessly plated, on the interior surface of the through-holes. Any suitably applicable metals may be used, for example Ni, Cu, Ag, Au, Co, Pd, Pd-Ni, Sn, Pb, Pb-Sn, In.
• At least a selected por ⁇ tion of the sheet has a plurality (at least 4, preferably at least 8, more preferably 25 to 1000) of substantially non- interconnected through-holes per square millimetre of its surface, at least a significant proportion of which through- holes individually contain a tubular formation of electri ⁇ cally conductive material projecting beyond at least one of the sheet surfaces.
• This and other forms of the invention could be used to provide relatively large "posts" of solder or other fusible metals eg. indium supported by the tubular formation, for use in making connections to microcircuits.
• Gold filling material could also be used to make such "permanent" electricial connections, instead of, or in addition to, plated gold.
• this tubular formation comprises a first portion of electrically conductive material on the interior through-hole surface, and a second portion of electrically conductive material, on at least one of the end surfaces of the first portion, at least the parts of the second portion on one or both of the end surfaces of the first portion pro ⁇ jecting beyond the sheet surface(s).
• the first portion of electrically conductive material on the through- hole surface is tubular and the second portion of electri ⁇ cally conductive material is on the interior surface as well as the end surface(s) of the first portion.
• the first portion is preferably metal and is preferably plated, espe ⁇ cially electrolessly plated, on the interior through-hole surface, and the second portion is preferably metal plated, especially electrolessly plated, on the first portion.
• the first and second portions respectively may comprise dif ⁇ ferent electrically conductive materials, and the second portion may fill the tubular first portion or may itself be tubular, in which case it may be filled with further electrically conductive or insulating material. Where the metal-lined through-holes are filled with another metal, this will preferably be a solder, a low-melting-point metal, a fusible alloy, or a plated metal. Either the tubular metal lining, or the metal fillings, or both, may project beyond the sheet surface(s), and the other criteria men ⁇ tioned above may apply as appropriate.
• electrically insulating material may be removed from one or both surfaces of the sheet material to expose portions of the electrically conductive material ori ⁇ ginally within the through-holes, thus producing or increasing the desire projections of the conductive material beyond the sheet surface(s).
• This may be done by any con ⁇ venient means, for example by dissolving away a surface layer of the sheet material, as described in the aforemen ⁇ tioned EP-A-0213774, for which purpose a sheet having sur ⁇ face layers of materials more readily soluble in a selected solvent than the underlying layers may be used, especially the sheets described in copending International application (RK362COM).
• the invention also provides a strip of electrically insulating material carrying two or more arrays of the through-holes containing electrically conductive material as hereinbefore described, the strip preferably being adapted for feeding to suitable processing equipment (e.g. for chip testing, permanent bonding, or heat-sink applications as hereinbefore described) by mechanical, preferably automatic, feed means.
• suitable processing equipment e.g. for chip testing, permanent bonding, or heat-sink applications as hereinbefore described
• Figure 11PB illustrates schematically permanent attach ⁇ ment of a microchip to associated circuitry by bonding to a uniaxially conductive sheet
• Figure 12PB shows schematically a magnified portion of a uniaxially conductive sheet suitable for permanent bonding as shown in Fig.llPB;
• Figure 13PB shows schematically a permanent bond formed by one of the plated through-holes as shown in Fig.l2PB.
• thermocompression- bonding was used to fabricate a three layer structure comprising (a) a silicon chip, with bonding sites a' metallised with aluminium - 1% silicon, (b) a sheet of uniaxially conducting material, the through-holes b 1 of which have been plated with 5 um copper, 1 um nickel, 2 um gold, (c) a silicon substrate, metallised with aluminium -1% silicon conductive tracks c'.
• Two types of uniaxially con ⁇ ducting sheets were evaluated, the first consisting of an area with 35 micrometre diameter tubes in a multi-tube array (not shown) , the second consisting of an area containing a small number of specially-positioned 35 micrometre diameter tubes as shown corresponding to the positions of the bonding sites a 1 and conductive tracks c'. Bonding conditions for each case were similar, and typically used a thermode tem ⁇ perature of 350-500°C and bonding forces from 80-200N, with a duration of 2-4s. Thermocompression-bonds as illustrated in Figure 13PB were obtained using this method.
• Figure 12PB comprising an electrolessly plated layer of copper, overlaid with nickel and then with gold as aforesaid, the polyamide surface layers originally present on the sheet during the copper plating process having been removed prior to the nickel and gold plating to produce the sheet b shown in Fig. 12PB with the metal tubes protruding from it.
• Figure. 13PB the structure of Figure. 12PB has been thermocompression-bonded to the chip a and substrate c as aforesaid.
• the uniaxial conductor can advantageously be used as a permanent bonding medium in conjunction with TAB (tape auto ⁇ mated bonding).
• TAB is known as a method of achieving electrical connection between a bare chip and a substrate such as a hybrid board, printed circuit board, chip carrier or other package.
• a polymer tape Al having edge sprocket holes A2 for feeding the tape in automated bonding equipment carries a series of arrays (one shown) of conductive tracks A3 arranged in a pattern suitable for bonding their inner ends A4 to the bonding sites of a microchip (not shown) .
• the tape Al is cut away under the ends A4 of the tracks so that the ends project as unsupported "fingers" over the cut-away space A5. Bonding is effected by bending the fingers into the space A5 to make contact with the chip positioned against the opposite side of the tape from that carrying the tracks. This is followed by bonding by known techniques which often require the chip bonding sites to be "bumped" with bonding material, e.g. solder.
• the present invention can avoid such disadvantageous "bumping" processes.
• the invention provides a method of making electrical connections between an array of connection sites on an integrated circuit microelectronic device and electrical conductors carried on a film or tape support material with an array of unsupported end portions of the conductors pro ⁇ jecting beyond an edge of the support material wherein: (a) the said end portions of the conductors are respec ⁇ tively aligned with the said connection sites to which connections are to be made,
• an anisotropically (preferably uniaxially) electrically conductive article comprising electrically insulating sheet material with through-holes containing electri ⁇ cally conductive material which provides an electri ⁇ cally conductive path from one of the main surface regions of the sheet material to the other is posi ⁇ tioned with the respective ends of at least one such path aligned between each connection site and the con ⁇ ductor end portion aligned therewith, and
• the uniaxially conductive article for use with TAB articles according to the present invention maybe in any appropriate form among those described in the aforemeni ⁇ oned copending Applications or in European Published Application EP-A-0213774, the disclosures of all of which are incor ⁇ porated herein by reference.
• the uniaxially conductive articles may be made using any of the methods and/or materials disclosed in those copending or published applica ⁇ tions.
• the invention includes the use of a TAB article or process with any novel sub-set or sub-combination of the aforesaid forms, methods of materials.
• FIG 15 TAB shows two plated metal tubes projecting from a uniaxially conducting article made by the aforesaid methods aligned with the ends of conductive tracks by a TAB device.
• Figure 16 TAB illustrates thermocompression (TO bonding of the outer track ends of a TAB device using multi- tube uniaxially conductive articles as described in the aforementioned EP-A-0213774; and
• TAB shows a TAB production line bonding TAB tracks to a series of unbumped integrated circuit chips.
• Figure 18 illustrates connections made by fusible metal (e.g. solder, gold, indium) columns presented in a uniaxially conductive article from which the polymeric carrier sheet (dotted lines in inset) has been removed, e.g. by a suitable solvent after bonding of the columns.
• fusible metal e.g. solder, gold, indium
• Such columns could be used in devices embodying various aspects of the present invention, and may be especially useful in high-density arrays of interconnections, for example a closely-packed array of "III" interconnections, having one such column for each pair of opposed bonding sites.
• the columns are made, for example, by filling the initial plated metal tubes with molten metal, and allowing the molten metal to solidify.
• the thin tubular plating but may remain as a surface layer theron. Solid columns of other metals may be similarly made, and the filling metal may be the same as or different from the plating metal.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Ceramic Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Non-Insulated Conductors (AREA)
• Wire Bonding (AREA)
• Adhesive Tapes (AREA)

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• 1989
  • 1989-02-03 JP JP1502204A patent/JP2758053B2/ja not_active Expired - Fee Related
  • 1989-02-03 WO PCT/GB1989/000111 patent/WO1989007339A1/en not_active Application Discontinuation
  • 1989-02-03 KR KR1019890701828A patent/KR900701042A/ko not_active Application Discontinuation
  • 1989-02-03 EP EP89902401A patent/EP0440615A1/de active Pending
  • 1989-02-03 EP EP89301107A patent/EP0329314A1/de not_active Ceased
  • 1989-02-06 CA CA000590179A patent/CA1321659C/en not_active Expired - Fee Related

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