Integrated circuit (IC) card having an IC module and reduced bond wire stress and method of forming

An integrated circuit (IC) module for an IC card includes a plurality of IC card contacts in side-by-side relation. A dielectric support layer is above the contact layer and has a plurality of openings and a first coefficient of thermal expansion (CTE). An IC die is above the dielectric support layer and includes a plurality of bond pads. A bond wire extends from a respective bond pad to a corresponding contact through an adjacent opening in the dielectric support layer. A respective body of fill material is within each opening and has a second CTE. A mold compound body is above the dielectric support layer, the bodies of fill material, and surrounding the IC die. The mold compound body has a third CTE. The first CTE is closer to the second CTE than to the third CTE.

FIELD OF THE INVENTION

The present invention relates to the field of integrated circuit (IC) cards, and more particularly, to an integrated circuit (IC) module for an IC card and having thermal matching of fill material at the contacts for reduced bond wire stress.

BACKGROUND OF THE INVENTION

An IC card is a pocket-sized card usually about the size of a normal credit card and having an embedded integrated circuit (IC) die. It is usually made from a flexible plastic. An IC module holds the IC die and the IC module is fixed on the surface of the IC card. The IC die includes a memory and the microprocessor and has electrical contacts that connect to a card reader when the IC card is inserted within the card reader. Bond wires connect the contacts with respective bond pads on the IC die. The IC module for an IC card usually includes eight metallic pads or contacts on its surface and each designed to international standards, including for example, VCC (power supply voltage), RST (used to reset the microprocessor of the IC card), CLK (clock signal), GND (ground), VPP (programming or write voltage), and I/O (serial input/output line). IC cards have random access memory (RAM) and read only memory (ROM) circuits, use a serial interface and receive power from external sources, e.g., the card reader. The RAM serves as a temporary storage for calculations and input/output communications while ROM includes the program memory and instructions for the chip operating system (COS), usually a “mask.”

When an IC card is inserted into the card reader, the metallic pads or contacts come into contact with the card reader and connect with metallic pins in the card reader, allowing the card and card reader to communicate. IC cards are reset when they are inserted into a card reader, causing the IC card to respond by sending an “answer-to-reset” (ATR) message, which informs the card reader to control communication and processing of a transaction.

The IC die is typically positioned above a dielectric support layer and includes a plurality of openings. The bond wires extend from a respective bond pad on the IC die to a corresponding contact through an adjacent opening in the dielectric support layer. The bond wire is connected by a “ball” bond on a bond pad and by a “stitch” bond, also known as a wedge bond, to a corresponding contact through an adjacent opening in the dielectric support layer. The stitch bond is usually a weld of the thin bond wire to a plated lead frame post or “finger” using an ultrasonic wire bonding process. It may include a compressed or ultrasonically bonded area of the wire to an underlying bonding surface.

A mold compound body is typically above the dielectric support layer and surrounds an IC die. The mold compound body is usually formed from a material that has a lower coefficient of thermal expansion (CTE), such as an epoxy with filler, as compared to the CTE of the dielectric support layer, which in one example, is formed from an E-glass material also known as a tape. The thermal mismatch created by the two substantially different CTE's may impart high stresses between the mold compound body above the dielectric support layer and the contacts formed at the contact layer causing delamination and a resultant pulling and failure of the bond wire stitch bond to the contact and additional stresses on the IC die.

SUMMARY OF THE INVENTION

An integrated circuit (IC) module for an IC card comprises a contact layer having a plurality of IC card contacts in side-by-side relation. A dielectric support layer is above the contact layer and has a plurality of openings therein. The dielectric support layer has a first coefficient of thermal expansion (CTE). An IC die is above the dielectric support layer and comprises a plurality of bond pads on an upper surface thereof. A plurality of bond wires are included, and each bond wire extends from a respective bond pad to a corresponding contact through an adjacent opening in the dielectric support layer. A respective body of fill material is within each opening in the dielectric support layer. Each body of fill material has a second CTE. A mold compound body is above the dielectric support layer, the bodies of fill material, and surrounding the IC die. The mold compound body has a third CTE. The first CTE is closer to the second CTE than to the third CTE.

The first CTE may be in a range of 60 to 200 PPM/° C. The second CTE may be in a range of 70 to 200 PPM/° C. The third CTE may be in a range of 3 to 50 PPM/° C.

In an embodiment, each body of fill material may fill the respective opening to a level flush with adjacent portions of the dielectric support layer. The dielectric support layer may have peripheral portions extending laterally outwardly from adjacent portions of the mold compound body. The dielectric support layer may comprise E-glass. The contact layer may comprise copper and the mold compound may comprise an epoxy. A first adhesive layer may be between the contact layer and the dielectric support layer, and a second adhesive layer may be between the dielectric support layer and the IC die.

Yet another aspect is directed to a method for making an integrated circuit (IC) module for an IC card. The method may comprise forming a contact layer having a plurality of IC card contacts in side-by-side relation and forming above the contact layer a dielectric support layer having a plurality of openings therein, the dielectric support layer having a first coefficient of thermal expansion (CTE). The method may include positioning an IC die above the dielectric support layer and comprising a plurality of bond pads on an upper surface thereof. The method may further include coupling a plurality of bond wires to the IC card contacts, each bond wire extending from a respective bond pad to a corresponding contact through an adjacent opening in the dielectric support layer. The method may also include forming a respective body of fill material within each opening in the dielectric support layer, each body of fill material having a second CTE. The method may also include forming a mold compound body above the dielectric support layer, the bodies of fill material, and surrounding the IC die. The mold compound body has a third CTE. The first CTE may be closer to the second CTE than to the third CTE.

DETAILED DESCRIPTION

An IC card (or chip card)10is shown inFIG. 1and includes the IC card body12and an integrated circuit (IC) module14carried by the IC card body and having a plurality of IC card contacts16formed at a contact layer18as explained in greater detail below. In this example, the IC card10is a pocket-sized card about the size of a conventional credit card and includes an embedded integrated circuit die as part of the IC module14. The IC card body12is usually made from a flexible plastic material such as polyvinyl chloride, polyethylene terephthalate based polyester, acrylonitrile butadiene styrene (ABS), or polycarbonate. The IC card body12can also be formed from different card layers that are printed and laminated in a large press, followed by blanking or die cutting and then embedding the IC die.

The contact layer18of the IC module14is shown inFIG. 2where the plurality of IC card contacts16are formed in side-by-side relation. The IC card contacts16inFIG. 2also correspond to what is termed a IC card pinout as eight metallic pads and designed to international standards. For example, the VCC as contact C1is for the power supply voltage. Contact C2corresponds to the RST contact for the reset signal used to reset the microprocessor of the IC card and reset card communications. Contact C3is the CLK contact corresponding to the clock signal from which the data communications timing is derived. Contact C5corresponds to the ground (GND) as a reference voltage. Contact C6is VPP corresponding to the write voltage.

For example, the ISO/IEC 7816-3 standard designates a programming voltage and an input for a higher voltage to program persistent memories such as an EEPROM. Alternatively, the ISO/IEC 7816-3: 2006 standard designates SPU for either standard or proprietary use as an input and/or output. Contact C7corresponds to the I/O as the serial input/output line and typically an output as half-duplex. The remaining contacts C4and C8are auxiliary contacts as AUX1and AUX2and may be used for USB interfaces and other ancillary uses.

IC cards such as shown inFIGS. 1 and 2usually include a random access memory (RAM) and read only memory (ROM) and employ a serial interface. They receive power from external sources, e.g., the card reader, in most examples. The RAM serves as a temporary storage for calculations and input/output communications, while ROM includes the program memory and instructions for the chip operating system (COS) as a “mask” in most cases. Some IC cards may have 8-bit symmetric key (file based) EEPROM and 8, 16 and 32-bit public key encryption with a math coprocessor. The IC card operating system or chip operating system may include a fixed file structure or a dynamic application system with different encryption capabilities such as Symmetric Key or Asymmetric Key (public key). Some cards have up to eight kilobytes of RAM and 346 kilobytes of ROM with 256 kilobytes of programmable ROM and a 16-bit microprocessor. These values can vary depending on card design.

Usually the contact layer18forming the plurality of IC card contacts16as shown inFIG. 2has a contact area of about a square centimeter (0.16 square inches) as the eight gold-plated contact pads formed over the copper contact layer. The rectangular dimensions of the IC card10such as shown inFIG. 1are usually similar to those of a conventional credit card. For example, ID-1 of the ISO/IEO 7810 standard defines the IC card at about 85.60 by 53.98 millimeters (3.370 inches by 2.125 inches). Another popular size for the IC card10is ID-000, which is nominally about 25 by 15 millimeters (0.984 inches by 0.591 inches) and commonly used in SIM cards. Usually, IC cards are about 0.76 millimeters (0.030 inches) thick. These values can vary, of course, depending on IC card design requirements. Usually there is a tamper-resistant security system such as a secure cryptoprocessor and a secure file system.

When the IC card10is inserted into a card reader, the metallic pads, i.e., IC card contacts16come into contact with the card reader and connect with the metallic pins in the card reader, allowing the card and card reader to communicate. The IC card10is reset when it is inserted into the card reader, causing the IC card to respond by sending an “answer-to-reset” (ATR) message, which informs the card reader to control communication and processing of the transaction.

FIG. 3is a fragmentary sectional view of a conventional IC card10similar to that shown inFIGS. 1 and 2and showing the IC card body12and IC module14carried by the body. The IC module14includes the contact layer18described before that forms the plurality of IC card contacts16in side-by-side relation. The contact layer18is usually formed from copper, but other conductive materials may be used. Often, a thin gold foil layer is attached to the copper to form the outer surface of each IC card contact16.

A dielectric support layer20is formed above the contact layer18and includes a plurality of openings22as illustrated. These openings22are often referred to by those skilled in the art as wire bonding pots. An example of the wire bonding pots as openings22is shown inFIG. 5that illustrates six openings in this example for six contacts C1-C3and C5-C7without showing the auxiliary contacts C4and C8as shown inFIG. 2. The contact layer18is illustrated below the dielectric support layer20and a IC die24is positioned above the dielectric support layer. In this example, the dielectric support layer20is formed from E-glass, which is alumino-borosilicate glass with less than 1% to 2% w/w alkali oxides in many examples. It is considered an “E” type of glass because of its initial electrical application and is substantially alkali free although it may be somewhat susceptible to chloride ion attack. The E-glass does not melt, but softens. Because of the type of E-glass typically used with the IC module14, it has a coefficient of thermal expansion (CTE) as low as about 60 to as high as about 200 PPM/° C.

A first adhesive layer26such as an epoxy adhesive, as a non-limiting example, is between the contact layer18and the dielectric support layer20to adhere the contact layer18to the dielectric support layer. This dielectric support layer20is also referred to as a “tape” since it is often applied as a sheet, similar to a tape. The IC die24is above the dielectric support layer20and a second adhesive layer28, such as an epoxy layer, is between the dielectric support layer20and the IC die24and adheres the IC die to the dielectric support layer. The IC die24includes a plurality of bond pads30on an upper surface32as illustrated. The plurality of bond wires34are illustrated and each bond wire extends from a respective bond pad30to a corresponding IC card contact16through an adjacent opening22in the dielectric support layer20. Usually the bond wire34is connected by a “ball” bond36onto a respective bond pad30and by a “stitch” bond38, also known as the wedge bond, to a corresponding IC card contact16through the adjacent opening22in the dielectric support layer20. The stitch bond38is usually a weld of the thin bond wire to a plated lead frame post or “finger” using an ultrasonic wire bonding process and may include a compressed or ultrasonically bonded area of the wire to an underlying bonding surface.

The ball-bonding process typically includes a bonding wire made of gold, copper or palladium and usually from 15-50 um in diameter. The actual diameter will depend on the wire length, device power and wire loop height and other factors specific to the IC card design. The wire bonding process uses the ball-bonding process on the bond pads30located on the upper surface of the IC die24and requires first forming a ball on one end of the bond wire and then welding that formed ball to the bond pad30. The bond wire34is looped across the top of the IC die24and into the adjacent opening22in the dielectric support layer20. The stitch bonding process bonds the bond wire34to a corresponding IC card contact16. The stitch bond38usually has a particular width of stitch related to the diameter of the bond wire and, in one example, a typical minimum required area to bond the stitch measures about 90 by 90 um for a 15 um wire diameter, and 300 by 300 um for a 50 um wire diameter, and 150 by 150 um for a 25 um wire diameter.

As shown inFIG. 3, a mold compound body50is above the dielectric support layer20and surrounds the IC die24and forms the IC module14. Usually the mold compound body50is formed from an epoxy resin and may include a filler as a non-melting inorganic material and catalysts that accelerate the cure reaction. The final mold material may also include a pigment or colorant and include flame retardants, adhesion promoters, ion traps and stress relievers. Many of the epoxy mold compound bodies include fused silica. The various components, including fillers, are chosen to reduce the coefficient of thermal expansion (CTE) of the mold compound and minimize or reduce internal stresses. Increasing the filler loading, such as fused silica, usually reduces the CTE because the CTE of fused silica is about 10% of epoxy resin. Because increasing the filler content may degrade flow and modulus of the mold compound material, the epoxy may include formulators to maintain flow and modulus, for example, by lowering the polymer melt viscosity. The epoxy resin and filler content may be chosen based on the desired chip design, package design, mold process, test requirement, and formulators. Some of the mold compound bodies that form an encapsulant for the IC die are based on a reaction of epoxy cresol novolac with phenol novolac. Epoxies will wet many high-tension synthetic surfaces and form strong, stable bonds to metallic oxides. This type of mold compound body50adheres well not only to the IC die24, but also the dielectric support layer20formed from E-glass and the contact layer18formed from copper. The mold compound body50may have a coefficient of thermal expansion usually under about 50 PPM/° C., and thus, can range from as low as about 3 or 5 PPM/° C. to as high as about 50 PPM/° C. The dielectric support layer20usually has a much greater coefficient of thermal expansion than the mold compound body50and delamination may occur between the mold compound body and the IC card contact16in the openings22at the dielectric support layer. The stitch bond may weaken because of the thermal mismatch in the Z direction as shown by the vertical arrow A inFIG. 3that exists between the mold compound body50and the dielectric support layer20.

As illustrated, the dielectric support layer20has peripheral portions52that extend laterally outward from adjacent portions of the mold compound body50. These portions52help position and support the IC module14in a IC card module receive area54formed in the IC card body12as shown, for example, inFIG. 5. To help retain the IC module14relative to the IC card body12, a hot melt adhesive56may be positioned between the peripheral portions52extending laterally outward from adjacent portions of the mold compound body50and the IC card body12. Other materials can be used, but hot melt adhesives have been found advantageous.

To alleviate the stresses between the mold compound body and the IC card contacts formed at the contact layer, a respective body of fill material is within each opening in a dielectric support layer, in accordance with a non-limiting example, to aid in relieving these stresses as illustrated inFIG. 4. It fills a respective opening to a level flush with adjacent portions of the dielectric support layer. For purposes of description, the IC card illustrated inFIG. 4is given reference numerals in the 100 series with those common elements having the same 100 series as in a lower numeral series as referenced inFIG. 3.

As illustrated inFIG. 4, in accordance with a non-limiting example for the fill material, the IC card110includes the IC card body112and the IC module114carried thereby and including the contacts116and contact layer118and dielectric support layer120with the openings122forming what is termed the wire bonding pots. The IC die124is above the dielectric support layer120and includes the plurality of IC bond pads130on the upper surface132thereof with the bond wires134extending from a respective bond pad to a corresponding IC card contact116through an adjacent opening122in the dielectric support layer120. The respective body of fill material is illustrated at160within each opening122in the dielectric support layer120. Each body of fill material160has a second CTE of about 70 to about 200. This CTE is similar or closer to the first CTE of the dielectric support layer120(having a CTE of about 60 to 200 PPM/° C.) than the third CTE of the mold compound body150, which is usually much lower (e.g., 3 to 50 PPM/° C.) as explained above. The mold compound body150is above the dielectric support layer120and the body of fill material160and surrounds the IC die124and this mold compound body150has a third CTE. The first CTE is closer to the second CTE than the third CTE. Also included are the first adhesive layer126and second adhesive layer128and hot melt adhesive156between the peripheral portions152extending laterally outward from adjacent portions of the mold compound body150and the IC card body122.

The respective bodies of fill material160within each opening122in the dielectric support layer120could be formed from an adhesive that has a different filler to create a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the dielectric support layer and could have a similar range. For example, it could range from about 70 to about 200. As a result, the stress at the contacts116is lower while also reducing die stress since the bond wires134may not be pulled permitting greater stability in the IC module114and also relative to the IC card110.

FIG. 5is a perspective view of a portion ofFIG. 3showing the contact layer18and dielectric support layer20and illustrating the plurality of openings22in the dielectric support layer that form the wire bonding pots and form the interface between the mold compound body50and the contact layer18in the example ofFIG. 3, where there is no fill material within each opening and only a mold compound body.

FIGS. 6 and 7illustrate simulation results with the results shown inFIG. 6corresponding to when the mold compound body50is encapsulating the IC die24and extends into the dielectric support layer openings22forming the wire bonding pots as in the prior art. These results show the high peel stress of 16.5 MPa on the peripheral edges of the IC card contacts16in the contact layer18.FIG. 7shows the simulation results when the body of fill material160extends within each opening122as inFIG. 4, in accordance with the present invention, and showing the reduced stress of only 4.6 MPa with the use of the fill material in the openings instead of the mold compound body. For purposes of illustration, the different stresses are labeled A from the lowest of −4.153 up to the highest of I of 16.475 MPa and shows the regions of stress.

Another aspect relative to a IC card that may comprise a IC card body and the IC card integrated circuit (IC) module carried thereby. Yet another aspect is directed to a method for making an integrated circuit (IC) module for a IC card. The method may comprise forming a contact layer having a plurality of IC card contacts in side-by-side relation and forming above the contact layer a dielectric support layer having a plurality of openings therein, the dielectric support layer having a first coefficient of thermal expansion (CTE). The method may include positioning an IC die above the dielectric support layer and comprising a plurality of bond pads on an upper surface thereof. The method may further include coupling a plurality of bond wires to the IC card contacts, each bond wire extending from a respective bond pad to a corresponding contact through an adjacent opening in the dielectric support layer. The method may also include forming a respective body of fill material within each opening in the dielectric support layer, each body of fill material having a second CTE. The method may also include forming a mold compound body above the dielectric support layer, the bodies of fill material, and surrounding the IC. The mold compound body has a third CTE. The first CTE may be closer to the second CTE than to the third CTE.