United States Patent [191
`Steffen
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,041,395
`Aug. 20, 1991
`
`[54] METHOD OF ENCAPSULATING AN
`INTEGRATED CIRCUIT USING A PUNCHED
`METAL GRID ATTACHED TO A
`PERFORATED DIELECTRIC STRIP
`Francis Steffen, Rousset, France
`[75] Inventor:
`[73] Assignee:
`SOS-Thomson Microelectronics S.A.,
`Gentilly, France
`[21] Appl. No.: 504,961
`[22] Filed:
`Apr. 5, 1990
`[30]
`Foreign Application Priority Data
`Apr. 7, 1989 [FR]
`France .............................. .. 89 04581
`
`[51] Int. Cl.5 ................... .. H01L 21/56; H01L 21/58;
`H01L 21/60
`[52] US. Cl. .................................. .. 437/206; 437/217;
`357/70; 357/72; 357/80
`[58]- Field of Search ............. .. 437/206, 207, 211, 217,
`437/219, 220, 224, 8, 209; 439/841, 827, 837,
`840, 68; 206/330; 264/272.l7; 357/70, 80;
`361/398, 401, 403, 404, 388, 406, 408, 421;
`428/571, 572; 228/1802
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,100,675 7/1978 Landsittel ........................... .. 29/841
`4,549,247 10/1985 Hoppe et a1. .
`.. 361/403
`4,674,175 6/1987 Stampfli ............................ .. 437/209
`
`FOREIGN PATENT DOCUMENTS
`
`0197438 10/1986 European Pat. Off. .
`0231937 2/ 1987 European Pat. Off. .
`55-68643 5/1980 Japan .................................... .. 437/8
`
`58-158953 9/1983 Japan .
`437/211
`59-16351 1/1984 Japan .......... ..
`437/211
`59-143336 8/1984 Japan
`437/211
`61-287125 12/1986 Japan
`62-92331 4/1987 Japan ................................. .. 437/211
`OTHER PUBLICATIONS
`IBM Technical Disclosure Bulletin, vol. 24, No. 2, 7-81
`. (29/840), “Flexible Tape Interconnection for Chips”, L.
`V. Avletta & R. Marks.
`Primary Examiner—-Olik Chaudhuri
`Assistant Examiner—David E. Graybill
`Attorney, Agent, or Firm-Roland Plottel
`[57]
`ABSTRACT
`The disclosure concerns the encapsulation of integrated
`circuit chips, notably with a view to their being incor
`porated in a chip card. The encapsulation method com
`prises the formation of a pre-punched metallic conduc
`tive grid, the formation of a strip of pre-perforated
`plastic material, the transfer of a strip to the grid, the
`positioning of an integrated circuit chip in a perforation
`of the strip, and the formation of electrical connections
`between the chip and zones of the grid located in perfo
`rations of the strip. The perforations of the strip and the
`punched slots of the grid are arranged so that the strip
`covers and blocks all the interstices between conductors
`of the grid in the useful region corresponding to a mod
`ule to be made. When a protecting resin is laid, it is
`confined and does not leak through the interstices of the
`grid. A plastic or metal ring de?nes the heightwisc
`dimension of the micromodule.
`
`11 Claims, 2 Drawing Sheets
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`5,041,395
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`strate of plastic material and metal formed by the trans
`fer (by bonding or hot transfer) of a pre-perforated
`dielectric screen to a pre-punched metal grid. In one
`example, this dielectric screen is a strip of plastic mate
`rial. In another example, this screen is a molded,
`punched or machined preform.
`The method more particularly comprises the follow
`ing operations:
`V
`preparation of a grid of connection conductors by the
`punching of a metal strip;
`preparation of a dielectric screen perforated at cer
`.tain places;
`transfer of the dielectric screen to the grid, by bond
`ing or hot transfer, the transfer being such that zones of
`the metal grid are facing perforations of the screen;
`positioning of a integrated circuit chip on an exposed
`zone of the metal grid, through a perforation in the
`screen;
`soldering of conducting connections between the
`chip and exposed zones of the metal grid;
`protection of the chip and connections by a dielectric
`or antistatic protecting material covering the chip and
`the connections in the perforations of the screen.
`Preferably, the slots of the grid and the perforations
`of the strip are such that the grid fully blocks all the
`perforations of the strip, at least in the useful zone of the
`contacts of the encapsulated module thus made.
`The “hot transfer” of the dielectric screen to the grid
`implies an operation by which the dielectric screen is
`unrolled in a strip and applied against the grid at a tem
`perature at which the strip gets softened. The strip
`adheres to the grid during the cooling. In this case, it is
`preferably seen to it that the grid has rough features and
`slots that contribute to catching the strip. These rough
`features are for example, punching burrs that have not
`been removed, projecting snugs on the grid, holes etc.
`The strip of plastic material may be formed by a ?at
`tape. In this case, it is preferably provided that, before a
`protective material is deposited, or even before the chip
`is positioned, the zone comprising the chip and its con
`nections is surrounded by a protective ring with a
`height that is as small as possible but enough to go
`beyond the height of the chip and of the connections
`(especially if these connections are soldered wires). This
`ring is used to form a cavity into which the protective
`material is poured. It may be a metal ring.
`The strip of plastic material may also be formed by a
`flat tape having ring-shaped protuberances from place
`to place. Instead of being transferred to the strip at a
`later stage, the ring may be formed at the same time as
`the strip, for example by molding or machining.
`The protective material may be a thermoplastic resin
`(of the polyurethane type) or thermosetting resin (of the
`silicone type). It is an insulator in principle, but may
`preferably be an imperfect dielectric (to achieve a resis
`tance of the order of 10 to 10000 megohms). This ena
`bles the flow of the electrostatic charges through the
`connection wires.
`When the protective resin is laid, it does not leak
`through the interstices of the punched grid for, prefera
`bly, care has been taken to see to it that these interstices
`are all blocked by the strip of plastic material, at least in
`the useful parts.
`Thus a micromodule is made having, firstly, an insu~
`lating material (plastic) which is the perforated strip
`transferred by bonding or by hot transfer to the
`punched grid of conductors and, secondly, preferably a
`
`65
`
`METHOD OF ENCAPSULATING AN
`INTEGRATED CIRCUIT USING A PUNCHED
`METAL GRID ATTACHED TO A PERFORATED
`DIELECTRIC STRIP
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The invention concerns the encapsulation of inte- 10
`grated circuit chips, notably with a view to incorporat
`ing them in a portable support.
`2. Description of the Prior Art
`The following is the usual technique for encapsulat
`ing integrated circuits designed to be incorporated, for
`example, into a chip card:
`the chip is transferred either to a grid of metallic
`conductors or to a grid-patterned epoxy glass type of
`dielectric support bearing photo-etched printed con
`ductors. These conductors have, ?rstly, a contact zone
`to which the rear face of a chip is soldered and, se
`condly, contact zones to which wires, made of gold or
`aluminium for example, are soldered, these wires being
`also soldered to output contacts of the chip. These con
`ductors moreover form external connection terminals
`25
`of the integrated circuit after encapsulation. The
`contact zones may also be soldered directly to the chip
`(by the so-called TAB technique);
`the chip and its wires are partially or totally covered
`with a protection against mechanical and chemical ag
`gression; this protection may be provided by an epoxy
`resin or a silicone resin;
`the strip carrying the chips protected by the resin is
`punched out into individual micromodules;
`the micromodule is bonded in a surface cavity made
`in a portable support made of plastic material, in such a
`way that the connection conductors remain accessible
`at the surface.
`The plastic support may be made by injection mold
`ing (the plastic material is then, for example, ABS
`resin). It may also be made by machining. It may be
`made by rolling pre-punched sheets of plastic material
`(the punched slots are used notably to make the cavity
`house of the micromodule); in this case, the plastic ma
`terial may be polyvinyl chloride.
`Several problems are encountered in these techniques
`45
`for assembling the module in its insertion support. A
`first problem is the risk that the resin protecting the chip
`might flow between the conductors when it is depos
`ited. The overflow hinders the operations for assem
`bling the module on its support. A second problem, in
`the case of a card, is the obligation to assemble the
`micromodule by bonding. The reliability of this mode
`of transfer is not ideal in view of the difference between
`the materials forming the card and those forming the
`micromodule. A third problem is the inde?nite repro
`duction of the external dimensions of the micromodule
`which has to fit into a cavity with given dimensions
`(preferably very shallow) of the chip card.
`_
`The invention is aimed at improving the reliability of
`assembly, achieving reproducibility of the dimensions
`of the micromodule and reducing its height while, at the
`same time, preserving a fabrication method that is easy
`to implement.
`
`SUMMARY 0F THE INVENTION
`According to the invention, there is proposed a
`method for the encapsulation of an integrated circuit
`consisting essentially, starting from a composite sub
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`BRIEF DESCRIPTION OF THE DRAWINGS
`Other features and advantages of the invention will
`appear from the following detailed description, made
`with reference to the appended ?gures, wherein:
`FIG. 1 shows a top view and a sectional view of a
`punched metal grid used in the invention;
`FIG. 2 shows a top view and a sectional view of a
`strip of pre-perforated dielectric screens used according
`to the invention.
`FIG. 3 shows a sectional view of the strip transferred
`by bonding or hot transfer to the grid;
`FIG. 4 shows an integrated circuit chip positioned
`and connected to the grid;
`FIG. 5 shows the positioning of a ring and of a pro
`tective resin; the ring may even preferably be positioned
`before the chip;
`F IG._6 shows an alternative embodiment wherein the
`protecting ring is integrated into the strip and not trans
`ferred to it.
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`5
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`5,041,395
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`protective material (resin) to complete the protection of
`Furthermore, a perforated plastic strip of dielectric
`the chip against chemical and mechanical aggression.
`screens 20, in the form of an essentially plane tape form
`The perforations of the strip overlap conductive zones
`is made (FIG. 2). Perforations are made, for example by
`of the punched grid without overlapping interstices
`stamping in this strip, at carefully chosen places. In
`between these zones. An integrated circuit chip is
`principle, these perforations include a central hole 22
`placed in a perforation of the strip and is electrically
`(to house an integrated circuit chip) and peripheral
`connected to conductive zones located in other perfora
`holes 24 (for access to the connection terminals).
`tions of the strip.
`The positions of the central hole 22 and the central
`For incorporation in a card, it is preferably provided
`zone 12 correspond to each other in such a way that,
`when the plastic strip is transferred to the metal grid,
`that the material of the transferred plastic screen is
`compatible with the plastic material of the card (polyvi
`the central hole 22 comes on top of the central zone 12,
`nyl chloride for example), and it is thus possible to place
`‘preferably without coming on top of an interstice 16 of
`the punched grid. The central hole 22 is therefore
`the micromodule directly in a cavity formed in the card,
`the strip of plastic material of the micromodule being
`smaller than the zone 12 and will be placed inside this
`directly in contact with the plastic material of the card.
`zone.
`Similarly, the positions of the peripheral holes corre
`The mounting is done by bonding or ultrasonic solder
`spond to the positions of the peripheral conductive
`ing for example. This was dif?cult to carry out in the
`zones in such a way that, when the strip 20 is transferred
`prior art with materials on the card and on the micro
`module that had little compatibility with each other
`to the grid 10, each peripheral hole 24 faces an end of a
`respective conductive zone 14. Here again, preferably,
`the holes do not overlap interstices 16 between conduc
`tive zones.
`Starting from the pre-punched grid and the pre-per
`forated strip, an operation is conducted for transferring
`the strip to the grid, in keeping to the relative positions
`indicated above. In principle, therefore, the plastic strip
`will block all the interstices between conductive zones
`of the grid.
`The transfer can be done by simple bonding: the
`perforated plastic strip and the punched grid tape are
`unrolled simultaneously, in interposing a ?ne layer of
`bonder between both of them and pressing the strip
`against the grid. The transfer can be done also by hot
`transfer by simply pressing the strip against the grid at
`a temperature where the material forming the strip is
`softened (for example, a temperature of 150 to 200 de
`grees Celsius depending on the plastic material used).
`This hot pressing enables the strip to catch on to the
`grid ef?ciently during the cooling stage.
`The catching-on process is helped along if the surface
`of the grid has rough features (punching burrs, folds of
`snugs projecting in a direction perpendicular to the grid
`tape surface, or in an oblique direction, etc.).
`FIG. 3 shows the grid and the strip superimposed, in
`a sectional view on an enlarged scale (but an arbitrary
`one: the relative thicknesses of the layers and widths
`shown are not signi?cant).
`It can be ascertained, in FIG. 3, that it has been seen
`to it that the central hole 22 is placed on top of the
`central zone 12, without going beyond this zone. And
`the holes 24 are placed on top of ends of conductive
`zones 14, without going beyond, on the top of the inter
`stices 16.
`The interstices of the grid are therefore all blocked, in
`any case in the useful region of the micromodule.
`A chip 26 is then positioned on the composite metal/
`plastic tape thus formed (FIG. 4).
`In the example shown, the chip 26 is bonded or
`soldered by its rear face to the central conductive zone
`12, inside the hole 22. It is connected to the peripheral
`conductive zones 14 by connecting wires 28 (gold or
`aluminium wires for example). These wires are soldered
`?rstly to contacts of the chip and, secondly, to the con
`ductive zones 14 inside holes 24 of the plastic strip 20.
`The surfaces of the punched metal grid of the rear
`side, namely the side not covered by the strip 20, will be
`the contact surfaces providing access to the integrated
`
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
`The method according to the invention shall now be
`described in detail with reference to the ?gures. The
`method starts with a pre-punched metal grid 10 in FIG.
`1 de?ning the future electrical connection terminals of
`the micromodule to be fabricated. In practice, what is
`made is not an isolated grid for a single micromodule
`but a grid in a continuous strip. The micromodules will
`be made serially on this strip. They will be separated
`from one another only at the end of the fabrication
`process or even, in the case of micromodules designed
`for chip cards, only at the time of insertion into cards.
`The metal grid is formed by mechanical punching. It
`has a thickness of about some tenths of millimeters. It is
`therefore relatively strong. It may be made of iron
`nickel or copper for example or, again, of pure nickel. It
`may be coated with gold or silver on the rear face, and
`on the front face at the position where connections with
`a chip will be soldered.
`In principle, the grid has a conductive central zone 12
`to receive an integrated circuit chip, and peripheral
`conductive zones 14 surrounding this central zone. The
`zones are separated from one another by interstices 16
`65
`formed by the punching operation. These interstices
`can be seen in the top view and the sectional view of
`FIG. 1.
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`should be a very reliable fabrication process, and this is
`circuit from the exterior, notably when the micromod
`what the invention provides.
`ule is incorporated in a chip card.
`A protecting ring 30 is placed around the chip 26 and
`What is claimed is:
`connecting wires 28 (FIG. 5). This ring is preferably
`1. A method for the encapsulation of an integrated
`circuit, comprising formation of a prepunched metal
`metallic (but it could be made of plastic); it may be
`conductive grid, formation of a strip of preperforated
`bonded or hot-transferred to the plastic strip 20. In this
`case, the ring is preferably transferred before the chip is
`dielectric screen, transfer of the strip to the grid, posi
`positioned. The ring surrounds the central and periph
`tioning of an integrated circuit chip in a perforation of
`eral perforations formed in the strip 20 and correspond
`the strip, and formation of electrical connections be
`ing to a determined micromodule. It may be supposed
`tween the chip and zones of the grid located in perfora
`that a micromodule will include several chips which
`tions of the strip.
`2. A method for the encapsulation of an integrated
`may or may not be connected to one another, in which
`case the ring will surround all the chips and the con
`circuit, comprising formation of a prepunched metal
`necting wires corresponding to this micromodule. Tak
`conductive grid, formation of a strip of preperforated
`ing into account the thickness of the strip 20, the height
`dielectric screen, transfer of the strip to the grid, posi
`of the ring is chosen so that the upper edge of the ring
`tioning of an integrated circuit chip in a perforation of
`goes beyond the height of the chip and the wires.
`the strip, and formation of electrical connections be
`The ring and the composite plastic/metal tape then
`tween the chip and zones of the grid located in perfora
`de?ne a cavity for the protection of the chip and the
`tions of the strip, and wherein the perforations of the
`wires. This cavity is ?lled with at protecting material 32
`strip and punched slots of the grid are such that the strip
`(for example, a thermoplastic resin such as polyurethane
`covers and blocks all interstices between conductors of
`or a thermosetting resin such as silicone resin). The
`the grid in a region in which a chip may be placed.
`protecting material completely coats the chip and the
`3. A method according to claim 1, comprising a step
`wires. Its volume is de?ned laterally by the protecting
`for setting up of protection by a protecting material
`ring. Heightwise, the material preferably ?lls the ring
`covering the chip and the connections in the perfora
`completely. If it goes beyond the ring during the ?lling
`tions of the strip.
`process, it can subsequently be levelled down.
`4. A method according to claim 3, comprising a step
`Since it has been seen to it that all the perforations of
`for positioning, on the strip, of a protecting ring sur
`the plastic strip 20 are completely blocked with portions
`rounding the chip and its connections, this ring being
`of conductive grid 10, the resin, even if it is very fluid,
`?lled with protecting insulator material after it has been
`does not leak through the interstices 16 between the
`positioned.
`conductive zones of the grid.
`5. A method according to claim 3, wherein, the strip
`FIG. 6 shows an alternative embodiment which is
`has a ring-shaped protuberance surrounding the space
`distinguished from the preceding one in that the pro
`reserved for the chip and its connections, and wherein
`tecting ring is not a ring transferred to the strip 20 but a
`this ring is ?lled with a protecting material after the
`molded or machined, integral part of the strip 20. This
`chip and its connections have been positioned.
`part 34 forms projections from place to place (at the
`6. A method according to any of the claims 3 to 5 or
`position of each micromodule) on the plane tape form
`11 to 13 wherein the protecting material is a thermo
`ing the strip 20.
`plastic or thermosetting resin.
`The rear face of the grid is totally bared, i.e. not
`7. A method according to claim 6, wherein the pro
`coated with insulating material. The rear face of the
`tecting material is an imperfect dielectric to enable the
`grid will remain directly accessible for an electrical
`outflow of electrostatic charges.
`contact between the conductors and contacts of a chip
`8. A method according to claim 1 or claim 2, wherein
`card reader.
`the strip is transferred to the screen by bonding or hot
`Thus, a composite metal/plastic tape is made, bear
`transfer.
`ing, from place to place, chips protected by a ring and
`9. A method according to claim 2, comprising a step
`an insulating protective material. Thus, a roll of micro
`for setting up of protections by a protecting material
`modules in strip form is formed. The strip will be
`covering the chip and the connections in the perfora
`punched into individual micromodules only at the end
`tions of the strip.
`of fabrication of the micromodules, or even only at the
`10. A method according to claim 9, comprising a step
`time of insertion into cards.
`for positioning, on the strip of a protecting ring sur~
`The precision obtained in the dimensions of the mi
`rounding the chip and its connections, this ring being
`cromodule is very high and reproducible from one
`?lled with protecting insulator material after it has been
`micromodule to another. Therefore, there will be no
`positioned.
`trouble, as in the past, because of problems of impreci
`11. A method according to claim 11, wherein, the
`sion of the dimensions, both heightwise and in width, of
`strip has a ring-shaped protuberance surrounding the
`the drop of protective resin.
`space reserved for the chip and its connections, and
`The height of the ring 30 can be reduced to the strict
`wherein this ring is ?lled with a protecting material
`minimum since it is very well controlled. It is important
`after the chip and its connections have been positioned.
`for a chip card that the micromodule should have as
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