KR20010088292A - Flip chip devices with flexible conductive adhesive - Google Patents

Abstract

The electronic devices 10 and 100 of the present invention are one or more semiconductor chips 30 and 130 connected to the next level substrates 20 and 120 by a flip chip method using the flexible conductive adhesives 40 and 140 having low elastic modulus. ). The flexible conductive adhesive 40, 140 is used as the conductive bumps 40, 140 on the contact pads 24, 124 of the substrates 20, 120 or the contact pads 34, 134 of the semiconductor chips 30, 130. It is a flexible thermoplastic or thermoset resin supplied and filled with electrically conductive particles. Other electronic devices 44, 46, 144, 146, such as packaged components including resistors, capacitors, etc., are the same flexible conductive adhesive bumps 24, 124, 34 as used for semiconductor chips 30, 130. 134). The contact pads of the chips 30, 130 and the next level of substrates 20, 120 are surface stabilized with a metal coating 38 of the precious metal prior to connection to inhibit oxidation of the pads 37. The flexible insulating organic filler 150 may be one having a low modulus of elasticity that is substantially the same as that of the flexible conductive adhesives 40 and 140.

Description

FLIP CHIP DEVICES WITH FLEXIBLE CONDUCTIVE ADHESIVE

Since the invention of integrated circuits in the early 1960s, the use of integrated circuits has increased dramatically and has become indispensable for many electronic products that modern society must depend upon and become indispensable. There are many ways of packaging circuits and other semiconductor chips in functional form, but the practicality of the packaging method is greatly increased when the physical size of such a packaged electronic device is small and the device is inexpensive.

Typically, the connection of the semiconductor is made by pure gold or aluminum bond wires, which are attached to the bottom surface of the semiconductor chip from contact pads (i.e., the side of the chip on which the electronic circuit is formed) disposed around the top surface of the semiconductor chip. The lead frame, header or other package or substrate. Bond wire connection technology is perfected so that the cost of each bond wire connection is less than one cent (US $ 0.01). The electrical properties of thin bond wires that loop relatively short distances necessarily introduce unwanted inductance and capacitance into the connection, reducing bandwidth and operating speed of the electronic device. This limitation has become more important in recent years due to the development of high speed microprocessors and high frequency signal processing and communication devices.

One way to reduce this connection capacitance and inductance is to shorten the length of the connection path. One effective conventional method of realizing this is to flip the semiconductor chip (hence the name "flip chip") so that the contact pad is directly adjacent to the substrate forming a corresponding set of contact pads to which the contact pads of the semiconductor are directly coupled. will be. L.F. U.S. Patent No. 3,429,040, entitled "Method of Bonding Component Components to Substrate," describes a flip chip arrangement in which a semiconductor chip is attached to a substrate by solder bumps. The distance between the flip chip and the substrate has been reduced to approximately 50-100 μm (μm is also known as micron), thus enabling operation at significant high frequencies.

Semiconductor device connections of flip chip construction have evolved from the use of highly sophisticated metals and metallurgy to the use of less demanding and inexpensive solder bumps to form suitable high conduction bumps to be connected. Soldering and solder bump techniques and metallurgy are modified to known methods to accommodate variations in construction and deposition methods suitable for low and high temperature reflow solding of such connections. Inherent limitations in solder bump technology are evident when the semiconductor device is attached directly to the organic substrate depending on the difference in the coefficient of thermal expansion (CTE) of the material. For example, a semiconductor chip has a CTE of 3 ppm / ° C. while an FR-4 glass fiber substrate has a CTE of 17 ppm / ° C. Although flip chip connection was performed on an aluminum substrate with a CTE of only 7 ppm / ° C., the practical limit rises similarly if the size of the semiconductor chip is more than 5 mm at each edge. Soldering has an elastic modulus of approximately 700,000 kg / cm2 (0.0703 kg / cm2 equals 1 psi) and has a slight modulus of compliance with very slight compliance, so that if the temperature is affected periodically, fatigue failure).

US Pat. No. 4,113,981 to "Electrically Conductive Adhesives for Connecting Arrays of Conductors" by Fujita et al. Describes the basis of nonconductive adhesives filled with very little conductive particles that are allowed to conduct except for the compressed portion. Fujita et al. Normally contact non-conductive particles of non-conductive adhesive against the raised contacts of the device such that the raised contacts of the device are in electrical contact with the protruding contact pads of the substrate and the separation between the laterally adjacent contacts This contact agent will be described for attaching the protruding contact held by the insulating resin. In conventional semiconductor wafers, contact pads, which are generally formed of aluminum, are located below the final insulating inorganic surface stabilizer layer. One of the limitations of the Fujita patent is that the contact pads must extend over the insulating surface stabilizer or substrate. Thus, this additional preparation as part of a semiconductor wafer structure or as a separate process increases the cost of semiconductor devices and connections. Another limitation of Fujita's connection is that only a limited number of conduction paths can be formed at each conducting contact, so that electrical separation between only a few conductor particles makes the connection nonconductive and useless.

Equally, conductive adhesives have long been used to bond the back of the semiconductor die to the package before the die's contact pads are wire bonded to the package lead, and in hybrid circuits and printed wiring boards, semiconductor adhesives, chip resistors and chip capacitors have been used. It can be seen that it has been used in various ways to attach.

The initial use of conductive adhesives for flip chip bonding was submitted by Scharf et al. To the 1967 Proceedings of IEEE Electronic Component Conference (pp. 269-275). Conductive adhesive bumps are stenciled on a substrate with an array of 16 bond pads for each semiconductor die bonded. Scharf et al focus on how to produce good stencils that print precise bumps and explain some of the advantages of using conductive adhesives such as low temperature adhesion and low cost. Next, U.S. Patent No. 4,442,966 to P.Jourdain et al. Entitled "Method of Making Multiple Electrical Connections Simultaneously Between Two Electronic Devices" describes a stencil method of depositing conductive adhesive bumps on contact pads and pressure and heat. The use of a conductive paste for adhering the aluminum pads on the semiconductor to the substrate by the method applied to the substrate during assembly of the semiconductor will be described.

The use of such conductive epoxy adhesives to bond semiconductor chips and applications for such adhesives are described in K.Gilleo's "Direct Chip Connections Using Polymer Adhesion" (pp. 37) at the 39th Electronic Component Conference in May 1989 and US patents. Several papers have been reported. The limitation of the strong conductive adhesive is similar to the limitation of the solder bump method, i.e. the limitation that the connection breaks under temperature cycling. As a result, the adhesive bonds in reported applications use steel adhesives with modulus of elasticity of 70,000 kg / cm 2 (1,000,000 psi) or more, have very small compliance, and peel or fatigue fracture with repeated temperature effects.

Thus, the main problem of directing the chip to the component or to the board connection is the internal pressure rising from the difference between the coefficient of thermal expansion of silicon of the semiconductor chip and the coefficient of thermal expansion of the next level board, i.e., the substrate on which the semiconductor chip is attached. Conventional conductive adhesive and solder bump techniques are limited by this high pressure related breakdown and exacerbated by extreme temperature differences and large chips, which is a trend of modern electronic technology.

This application is directed to US Provisional Application No. 60 / 082,885, filed April 24, 1998, US Provisional Application No. 60 / 092,147, filed July 9, 1998, US application, filed October 5, 1998. No. 09 / 166,633, US Provisional Application No. 60 / 083,326, filed April 28, 1998, and US Application No. 09 / 276,259, filed March 25, 1999.

The present invention relates to an electronic device, in particular an electronic device comprising a semiconductor chip bonded thereon.

1 is a cross-sectional view of an embodiment of an electronic device including a flip chip semiconductor device according to the present invention.

2 is a graph showing the modulus of elasticity of various adhesives as a function of temperature.

3 is a plan view of a semiconductor device used in the embodiment of FIG.

4 and 5 are cross-sectional views of the semiconductor device of FIG. 3 before and after application of the flexible conductive adhesive.

6 is a cross-sectional view of another embodiment of an electronic device including the flip chip semiconductor device according to the present invention.

7 is a plan view of a semiconductor device used in the embodiment of FIG.

8 is a cross-sectional view of the semiconductor device of FIG. 7 after application of the flexible conductive adhesive and the flexible underfill.

9 and 10 are cross-sectional views of another embodiment of the semiconductor device shown in FIGS. 4 and 7 after application of the flexible conductive adhesive.

A common solution to this pressure problem is to use epoxy underfill in a region that does not include conductive adhesive connections to widen the pressure range. In many cases, the inherent underfill increases the number of thermal cycles and depending on the size and temperature effects of the semiconductor die, this connection can remain by a factor of 6 to 8, but devastating shear stress The inherent problem of balancing the beneficial compressive forces of high-strength underfills, which limits the cyclic strain reached with respect to), is that they peel or break the bond or partial residue. Increasing the semiconductor die size all increases the shear stress, and therefore the reliability of the assembled flip chip under heat cycle has to be reassessed in a particular region of each temperature. Similarly, when the influence of extreme heat extends to low or high temperatures, additional shear stresses adversely affect the reliability of the assembled flip chip and also require expensive reevaluation tests. Suitable high modulus underfills increase the performance of flip chip devices to withstand the pressures of heat, but nevertheless differ between the size of the available semiconductor devices and the coefficients of thermal expansion of the expansion of the semiconductor chip and the coefficient of thermal expansion of the next level substrate. Are limited. In addition, the cost of incorporating such steel adhesive underfills is relatively expensive and high strength adhesive underfills (if at least possible) are very difficult to repair and rework to add to the cost of many flip chip integration devices.

Another possible solution to this technical problem is to design the next level board, ie the substrate, to have the same coefficient of thermal expansion, for example the CTE of a semiconductor chip of approximately 3 ppm / ° C. This technique method has been used successfully by some methods, but is not widely used because of the undesired high cost of developing and manufacturing such substrates and creating the underlying tissue structures required to provide these new technologies. A more serious problem is the fact that the lowest cost common electronic substrates are glass fiber laminates such as FR-4 with epoxy resins commonly used in printed wiring circuit boards and having a CTE of 17 ppm / ° C. Conventional commercial electronic equipment most commonly uses FR-4 printed circuit boards. Thus, additional intermediate substrates are required at additional cost or special substrate materials are required to replace FR-4.

Accordingly, there is a need for chip size packaging and direct chip attachment on a functional circuit board that accommodates the coefficient of thermal expansion difference between silicon of a semiconductor chip and silicon of a next level board.

To this end, the present invention includes a semiconductor chip having contact pads surface stabilized by a noble metal, which is connected in a flip chip method to a substrate having a corresponding contact pad surface stabilized by a noble metal. The connection between the corresponding contact pad on the semiconductor chip and the corresponding contact pad on the substrate is carried out using a flexible conductive adhesive having a low modulus of elasticity.

Detailed description of the preferred embodiment of the present invention will be more readily understood with reference to the drawings.

It is to be understood that the specific embodiments of the invention described herein are shown by way of example and not limitation, the principles and characteristics of which may be used in various embodiments without departing from the spirit and scope of the invention.

In general, the present invention relates to the connection between a substrate and an electronic device mounted on the substrate, such as a flip chip including a semiconductor device, a resistor, a capacitor, and other components, the thermal expansion coefficient (CTE), fatigue breakdown, and delamination breakdown of the electronic device. To an electronic device in which a flexible conductive adhesive having a low modulus of elasticity is formed to exhibit actual compliance to accommodate a difference in the coefficient of thermal expansion (CTE) of the substrate reaching 60 ppm / ° C., which does not require a high value of underfill. It is about. If any underfill is accommodated by improving electrical separation and reducing the movement of any metal used as a conductor, such underfill will have the same or lower low modulus and flexibility as that of the flexible conductive adhesive.

The electronic device 10 of FIG. 1 includes an insulating plate 20 on which a plurality of electronic devices such as a semiconductor chip 30, a chip resistor 44, and a chip capacitor 46 are disposed. In this embodiment there is no insulation underfill between the devices 30, 44, 46 and the substrate 20. The semiconductor chip 30 includes a plurality of contact pads 34 that form an electrical connection between an electronic circuit included in the semiconductor chip 30 and an external electronic device on the first surface 32 of the substrate die. Similarly, each of the resistor 44 and the capacitor 46 may pass through the substrate 20 and the resistive and capacitive circuit elements included in the chip resistor 44 and the chip capacitor 46, respectively, on their respective first surfaces. And a plurality of contact pads that form an electrical connection between the external electronic devices.

The substrate 20 includes a printed wiring conductor 22 that forms the conductor of the electronic circuit in a conventional manner on the first surface of the substrate. The plurality of contact pads 24 are conductors of the substrate 20 at positions corresponding to the respective positions of the corresponding adhesive pads 34, 45, 47 of the electronic devices 30, 44, 46 for mounting on the substrate. It is formed on (22). In addition, the arrangement, size, and position of the contact pads 24 of the substrate 20 correspond to the arrangement, size, and position of the contact pads 34 of the semiconductor device 30. The substrate 20 is made of a laminate such as FR-4 glass fiber or BT material, coated aluminum or alumina, ceramic or other suitable insulating material, and the conductor 22 on the substrate is made of metal such as copper, aluminum, gold or silver. Or by conductive inks formed by known techniques such as thin film or thick film mounting. If the contact pad is not composed of a non-oxidizing material such as a noble metal, the contact must be surface stabilized with a noble metal coating or alloy for electrical contact with constant long term stability and integrity, even for devices attached to the substrate. to be.

Electronic devices 30, 44, 46 are disposed on respective first surfaces proximate the first surface of the substrate 20 so that the contact pads of each electronic device 30, 44, 46 may be flipped over the substrate 20 by a flip chip method. Adjacent to each corresponding contact pad 24 on. Electronic devices 30, 44, 46 provide mechanical attachment of each device 30, 44, 46 to substrate 20 and correspond to respective contact pads 34, 45, 46 and substrate 20. And are attached to the substrate 20 by a plurality of flexible conductive adhesive bumps 40 that provide low impedance, typically 0.1 ohm or smaller electrical connection between the correspondingly positioned portions.

Conductive adhesive 40 requires "flexibility" which means it has a low modulus of elasticity. There is a need for conductive adhesives having modulus of elasticity of up to approximately 35,000 kg / cm 2 (approximately 500,000 psi) as filled composites. Adhesives or mixed or interpolymers, which may include thermoplastic resins or thermosetting resins, become conductive by the inclusion of fine particles of conductive material and increase the modulus of elasticity to the extent of the knit resin. Suitable flexible conductive adhesives are type LTP8150 liquid flexible thermoplastic conductive adhesive, type ESS8450 (silver filler), ESS8456 (silver-palladium alloy filler), ESS8457 (gold plated copper filler), ESS8458 (gold powder filler) and ESS8459 (gold plated nickel filler) ) Adhesive paste and type PSS8156 (silver-palladium alloy filler), PSS8157 (gold plated copper filler), PSS8158 (gold powder filler) and PSS8159 (gold plated nickel filler) flexible paste adhesive based on flexible epoxy The ones are commercially available from AI Technology, Inc. of Princeton, NJ. Such flexible conductive adhesives have a glass transition temperature of approximately -55 ° C to -60 ° C, and thus have an elastic modulus of approximately 35,000 kg / cm 2 (about 500,000 psi) at low temperature as shown in FIG. 2. Type PSS8150 flexible conductive adhesives comprise thermoplastic resins having a glass transition temperature of -20 ° C. or less and expanding at least 30% of their size prior to breakdown. Type ESS8450 flexible conductive adhesives comprise a modified thermosetting epoxy resin having a glass transition temperature of 0 ° C. or less and expanding at least 30% of its length before failure. Thermoplastic resins having a melt flow temperature of 300 ° C. or less are preferred.

2 is a graph of the function of temperature (in ° C.) and the modulus of elasticity (in psi) for various conductive adhesives. Conventional adhesives such as solders and epoxies exhibit modulus of elasticity in excess of approximately 70,000 kg / cm 2 (approximately 1,000,000 psi) for most temperature ranges in which semiconductor devices typically operate. Typical operating temperatures specified for semiconductor devices range from -55 ° C to + 150 ° C for devices requiring applications such as automotive, aerospace, and military applications, and for devices requiring less applications such as home entertainment and consumer electronics applications. In this case, there will be a smaller temperature range than specified.

The flexible conductive adhesive used in the present invention exhibits about 35,000 kg / cm 2 (about 500,000 psi) or less modulus at least about 50% of the specified operating temperature range for the semiconductor device to operate. Good adhesives exhibit an elastic modulus of less than approximately 7,000 kg / cm 2 (approximately 100,000 psi) for this temperature region as shown by type ESS8459 and less than approximately 3,500 kg / cm 2 (approximately 50,000 psi) as shown with type PSS8159. And these two types are semiconductor adhesives having glass transition temperatures of approximately -55 ° C to -60 ° C.

Conductive fillers suitable for flexible conductive adhesives included in the aforementioned various flexible conductive adhesives available from AI Technology, Inc. are silver, gold, palladium or platinum particles [flake, sphere or powder] silver-palladium alloy Particles and gold plated copper or nickel particles. Although high proportions of palladium are more resistant to silver migration and their fillers are very expensive in many applications, silver-palladium alloy powder fillers are most likely for silver migration when the optimum ratio of palladium is in the region of at least approximately 10% to 30%. Become resistant. Other alloys of precious metals are also suitable. Flexible conductive adhesive connections according to the present invention may exhibit a contact resistance of 0.1 ohm or smaller.

In addition, one preferred flexible conductive adhesive includes a conductive filler comprising copper flakes of gold plating and palladium plating. Other preferred flexible conductive adhesives include conductive fillers comprising nickel flakes of gold plating and palladium plating. Other non-noble metal and other non-noble metal alloy cores such as aluminum can also be effectively used for precious metal plating. Core materials and plating materials are selected based on cost and ease of plating. Other flexible conductive adhesives have a volume electrical resistivity of 0.00009 ohm-cm or less and consist of silver particles specially prepared to allow high current to flow through a particular connection, ie to have a high current density at the connection. The conductive filler is not particularly limited to the fillers described above, but the filler particles must be at least surface stabilized by resist oxidation by coating or plating of a noble metal whose core particles are not composed of a noble metal.

For gold, palladium and platinum coated metal flakes and powders, the precious metal coating is approximately 5 wt. Must be at least% If the precious metal coating exceeds approximately 50% of the total weight of the filler, the cost effectiveness of using the coating metal is lost. Gold content in the region of approximately 5% to 30% by weight is effective for saturated electrical performance and cost effectiveness.

Thus, the coating described above is a low cost flexible conductive adhesive connection because it has a low elastic modulus that is elastic and therefore not susceptible to reduced pressure due to the inherent CTE difference between the substrate 20 and the substrate 32. Embodiments of the above-described electronic devices include 100 cycles for a temperature range of -55 ° C to + 150 ° C and a temperature of between -65 ° C and + 150 ° C with a 10 minute stay time at each temperature and a transition of 10 seconds between temperatures. 12 millimeters of semiconductor device every 12 mm without underfill, which shows unmeasurable degradation of bond strength and contact resistance after 50 cycles of thermal shock. The superiority of the aforementioned electronic device using a flexible conductive adhesive to connect a semiconductor chip to a substrate can be easily evaluated by comparing published heat cycle data. A recent study by Rosner et al. At the Proceedings of Electronic Component and Technology Conference (pp.578-581) in May 1996, "Flip Chip Adhesion Using Isotropic Conductive Adhesives," May 1996 Electronic Components and Technology Conference (pp.524). "Flip Chip Organics Packaging Materials and Machines" by Wu et al. And Gamota et al., "Advanced Capsule Material Systems for Flip Chips" by Advancing Microelectronics (pp. 22-24), July / August 1997. Reliability and improvement of contact resistance as a function of heat cycle for bump attachment and strong conductive adhesive attachment have been reported. Samples of solder bumps and steel conductive adhesive connections without underfill fail within 100 cycles if they have a thermal cycle for a suitable region of -25 ° C to + 125 ° C.

One method of configuring an electronic device of the portion shown and described with reference to FIG. 1 will be understood with reference to FIGS. 3, 4, and 5. In FIG. 3, the top view of the semiconductor substrate 32 includes a plurality of contact pads or adhesive pads 34 on the top surface of the substrate. The contact pads 34 may be around the substrate 32 or inside or within the substrate 32, depending on the convenience of the designer of the semiconductor device 30. Areas of the substrate 32 that do not include contact pads 34 are surface stabilized with inorganic nitrides such as silicon nitride or other insulating coatings, and do not accept flexible conductive adhesives. Bumps 40 of the flexible conductive adhesive are provided on each of the plurality of contact pads 34 as described below. If ease of use and lowest cost are desired, the bumps of the flexible conductive adhesive may be wafer level on all the substrates 32 formed on the semiconductor before the wafers are evaluated and the individual substrate dies are separated, even if the contact is provided on the individual substrates 32. It is preferred to be supplied with.

4 is a cross-sectional view of the semiconductor device of FIG. 3 obtained by cutting lines 3 to 3. The contact pad 34 includes an aluminum pad 37 deposited on the semiconductor substrate 32 at a position at which electrical contact occurs for an electrical function of a circuit (not shown) formed on the semiconductor substrate, and the aluminum pad 37 ) Is preferably surface stabilized by a deposited metal layer 38 of non-oxide metal in order of nickel and gold or other precious metals such as gold, silver, platinum, palladium or alloys thereof. Nickel and chromium can also be used as non-oxidizing surface stabilizers. The contact pads 24 of the substrate 20 are also surface stabilized with non-oxides. Surface stabilization is common in semiconductor manufacturing but is unnecessary, so that the thickness of the inorganic surface stabilization layer 36 is thicker than the thickness of the contact pad 34.

In FIG. 5, a plurality of flexible conductive adhesive bumps 40 are deposited on the plurality of contact pads 34. The flexible conductive adhesive bumps 40 are formed on the nickel-gold surface stabilization layer 38 of the contact pads 34. It is prepared by depositing a flexible thermoplastic conductive adhesive, such as the liquid thermoplastic conductive adhesive LTP8150 sold commercially. The ratio of resin to silver filler produces a deposited volume resistance of approximately 0.00015 ohm-cm between approximately 100: 100 and 100: 600. The mixture viscosity of silver flakes and liquid thermoplastic adhesive is adjusted to approximately 200,000 cp measured at 0.5 rpm from Brookfield Company of Stoughton, Mass., With an ester alcohol solvent such as commercially sold by Eastman Kodak Chemicals under the trade name Texanol.

The flexible conductive adhesive for forming the bump 40 may be deposited using standard stainless steel stencils or screen areas with ink having 75 mm or larger bump area printing, contact deposition, preform stacks or other suitable deposition means. . The bumps can be round or rectangular. The size and shape of the bumps is not important for most applications, but the area (diameter) of the bump 40 is at least as large as the area (diameter) of the contact pad 34 so that the smallest possible when assembled into the final device 10 is possible. It should show contact resistance. The liquid thermoplastic paste is allowed to dry at 60-80 ° C. for 30-60 minutes for deposition with a wet thickness of 75-125 μm. The crystal height of the dried adhesive bumps 40 is usually about 50-60% of the wet thickness, and the bumps are constant at a diameter close to 98% and a bump height close to 90%. The altitude of the dried bumps is usually 50-100 μm. If the semiconductor chip 30 is in wafer form after the aluminum adhesive pad 37 is surface stabilized in the nickel-gold layer 38 to prevent oxidation, the flexible conductive adhesive bump 40 is preferably deposited. The wafer with the dried conductive bumps 40 may be further exposed to 200 ° C. for 1 to 5 seconds to utilize the adhesion of the adhesive bumps 40 to the contact pads 34. The prepared wafers are then placed on individual substrate dies that accumulate at ambient temperature before subsequent assembly into the electronic device.

The prepared semiconductor device 30 with the bumps of the flexible conductive adhesive as shown in FIG. 5 is the next level board, ie, the substrate 20, to form the electronic device 10 shown in FIG. 1 as described below. Is assembled on. Since the semiconductor device 30 is aligned on the substrate 20, the contact pads 24 and 34 of the substrate 20 and the semiconductor device 30 are aligned. If the device 30 and the substrate 20 are pressed together and the temperature is in the region of 195-215 ° C. and the placement pressure is approximately 0.7 kg / cm 2 (approximately 10 psi), the flexible adhesive bumps 40 are associated with each contact pad. Are glued together immediately. For superior efficiency, the substrate 20 is preheated to a temperature of approximately 150 to 200 degrees Celsius while the chuck that picks up the semiconductor chip 30 is preheated to approximately 220 to 280 degrees Celsius. An electronic device 10 assembled as described above, including a semiconductor die 30 having an edge area of at least 10 mm bonded to an aluminum substrate 20, has at least 1000 thermal cycles between -65 ° C. and 150 ° C. And withstands more than 50 thermal shocks between -65 ° C and 150 ° C without measurable change in contact resistance. In addition, exposure to 85 ° C. at 85% relative humidity (RH) for 168 hours does not produce measurable degradation of electrical contact resistance, and exposure to 100 ° C. at 100% RH for 200 hours is also required for substrate 20. There was no measurable deterioration in the shear adhesive strength of the die 30 to. Thick films and thin film gold adhesive pads on the alumina substrate are prevented from saturation.

The tools and temperatures used in the assembly methods described above are compatible with those used for placement and attachment of traditional flip chip devices with solder bumps by reflow soldering. In both cases, the contact pads of the flip chip device are aligned with the contact pads corresponding to the substrate, and then pressed together at a temperature below 300 ° C. and a pressure of 0.7 kg / cm 2 (10 psi) or less, and the adhesion is approximately 10 Complete in seconds

Although the above-described embodiments described in connection with FIGS. 1-5 did not require and do not require underfilling, the use of an underfill with suitable flow characteristics may be desirable in some applications. The underfill is an insulating adhesive material located in the space between the conducting connections between the substrate and the mounted device, such as a flip chip device. In order to preserve the mechanical flexibility and the internal low pressure characterizing the connection bonding according to the invention, a suitable underfill material is a nonconductive flexible adhesive which is actually used for conducting connections between the semiconductor device and the substrate. It has the same or lower modulus of elasticity as the flexible conductive adhesive used, i.e. less than about 35,000 kg / cm 2 (about 50,000 psi).

The electronic device 100 of FIG. 6 includes an insulating substrate 120 that aligns and mounts a plurality of electronic devices such as the semiconductor chip 130, the chip resistor 144, and the chip capacitor 146 thereon. The semiconductor chip 130 includes a plurality of contact pads 134 electrically connecting an electronic circuit included in the semiconductor chip 130 and an external electronic device on the first surface of the substrate 132. Similarly, each of resistor 144 and capacitor 146 pass through substrate 120 and resistive and capacitive circuit elements included in chip resistor 144 and chip capacitor 146, respectively, on a respective first surface. It includes a plurality of contact pads for electrically connecting between external electronic elements.

Substrate 120 includes a printed wiring conductor 122 that forms a conductor of an electronic circuit on a first surface in a conventional manner. The plurality of contact pads 124 correspond to the conductors of the substrate 120 at positions corresponding to the positions of the adhesive pads 134, 145, 147 corresponding to the respective electronic devices 130, 144, 146 mounted on the substrate. 122). In addition, the alignment, size, and positioning of the contact pads 124 of the substrate 120 coincide with the alignment, size, and positioning of the contact pads 134 of the semiconductor device 130. Substrate 120 is made of a laminate such as FR-4 glass fiber or BT material or alumina, ceramic or other suitable insulating material, and conductor 122 is formed of a metal such as copper, aluminum, gold or silver, or a thin film or It may be formed by a conductive ink formed by a known technique such as deposition of a thick film. If the contact pad is not a non-oxidizing material such as a noble metal, the contact must be surface stabilized with a noble metal coating or alloy that has a certain long term stability and integrity to electrical contact, even for devices attached to a substrate.

Electronic devices 130, 144, and 146 are located on respective first surfaces proximate the first surface of substrate 120, so that each contact pad of electronic devices 130, 144, and 146 is respectively on substrate 120. Close to the corresponding contact pad 124. The electronic devices 130, 144, and 146 are attached to the substrate 120 by a plurality of flexible conductive adhesive bumps 140, and the plurality of flexible conductive adhesive bumps 140 are each attached to the substrate 120. 130, 144, 146 are mechanically attached and provide a low impedance electrical connection between each of the contact pads 134, 145, 146 and the correspondingly located portion on the substrate 120. The insulating flexible filler 150 actually fills the gap or space between the device 130, 144, 146 and the substrate 120 that is not filled by the flexible conductive adhesive 140 of the embodiment of FIG. 5.

The conductive adhesive 140 and the insulating adhesive 150 need to be "flexible" meaning that each has an elastic modulus of approximately 35,000 kg / cm 2 (approximately 500,000 psi) or less. Suitable flexible conductive adhesives commercially available from AI Technology, Inc. of Princeton, NJ, are identified in connection with the embodiment of FIG. Non-conductive or insulating resins, which can be thermoplastic or thermoset resins, can be selected from flexible underfills or encapsulating materials such as MEE7650-5 epoxy based capsular materials available from AI Technology, Inc., which are 1050 kg / cm 2 Elastic modulus of 15,000 psi or less and a glass transition temperature of -20 ° C or less. In addition to the increase in the adhesive strength between the components 130, 144, 146 and the substrate 120, which may occur in high humidity conditions, this flexible insulating underfill also includes contact pads of the components 130, 144, 146. Silver movement between the contact pads of the substrate 120 is prevented.

One method of configuring an electronic device of the type shown and described with reference to FIG. 6 will be understood with reference to FIGS. 7 and 8. In FIG. 7, the semiconductor substrate 132 of the plan view includes a plurality of contact pads or adhesive pads 134 on an upper surface thereof. The area of the substrate 132 that does not include the contact pads 134 is surface stabilized with an inorganic nitride, such as silicon nitride or other insulating coating, and will accommodate the flexible nonconductive adhesive 150. The flexible conductive adhesive bumps 140 are supplied for each of the plurality of contact pads 134 and the pattern of the insulating flexible adhesive 150 is supplied to the spaces between the flexible conductive adhesive bumps described below. If ease of use and low cost are desired, the flexible conductive adhesive bump 140 and non-conductive flexible adhesive 150 patterns, even though the adhesive is supplied to the individual substrates 132, may be used before the wafer is recorded and the individual substrate dies are separated. All substrate dies 132 formed thereon are supplied at the wafer level. The insulating flexible adhesive 150 does not completely fill the spaces between the contact pads 34 so that the flexible adhesives 140 and 150 flow and fill the space while adhering the semiconductor device 130 to the substrate 120. More preferably not.

8 is a cross-sectional view of the semiconductor device 130 of FIG. 7 obtained by cutting lines 7 to 7. The contact pad 134 includes an aluminum pad 137 deposited on the semiconductor substrate 132 at a location of electrical contact made for the electrical function of a circuit (not shown) formed on the substrate. The aluminum pad 137 is in the order of non-oxide metal, preferably nickel and gold or nickel and palladium layers, or on deposited metal layers 138 of other precious metals such as gold, silver, platinum, palladium or alloys thereof. Surface is stabilized by In the embodiment of FIG. 8, the thickness of the inorganic surface stabilization pad 136 is actually equal to the thickness of the contact pad 134.

A plurality of flexible conductive adhesive bumps 140 are deposited on the plurality of contact pads 134. As discussed above in connection with the embodiment of FIG. 1, the flexible conductive adhesive bump 140 is commercially sold by AI Technology, Inc. on the nickel-gold surface stabilizer layer 138 of the contact pad 134. It is made by depositing with a flexible thermoplastic conductive adhesive such as liquid thermoplastic conductive adhesive LTP8150. In addition, although the size and shape of the bumps are not critical for most applications, the size of the bumps 140 is at least larger than the contact pads 134 so that they exhibit the lowest possible contact resistance when assembled into the final device 100.

Similarly, the insulating flexible adhesive 150 fills the space between the bumps 140 or does not completely fill the space so that the flexible conductive adhesive 140 when the semiconductor device 130 is assembled on the substrate 120. And flexible flow of insulating adhesive 150 is enabled. The patterns of the flexible conductive adhesive bump 140 and the flexible insulating adhesive 150 are surface-stabilized with the nickel and gold layers 38 or other precious metals to prevent the aluminum adhesive pads 137 from being oxidized, and then the semiconductor chip ( 30) to be deposited when in wafer form. The prepared wafers are then placed on individual substrate dies accumulated at ambient temperature before being assembled into the next electronic device. The deposition of the flexible conductive adhesive and the pattern of the flexible insulating adhesive 150 to form the bump 140 may be performed using standard stainless steel stencils or screens or inkjet printing, contact deposition, preform laminates or other suitable deposition. It can be executed by the method.

Flexible insulating adhesives used as underfills, such as good flexible conductive adhesives, can accumulate at ambient temperature for extended periods after deposition and drying and before final assembly bonding. Examples of suitable materials are LTP7150 of liquid thermoplastic paste type and LESP7450 of liquid epoxy type available from AI Technology, Inc. LTP7150 is deposited to form a solid film by treatment at 60-80 ° C. for 30-60 minutes. It is a thermoplastic paste that can be conditioned. LESP7450 is an epoxy paste that can be deposited and B-stated to form a solid film by treatment at 60-80 ° C. for 30-60 minutes. This modified B-state flexible adhesive has a molecular structure in the form of a knit resin, so that the overall glass transition temperature is below -55 ° C. The two B-state flexible insulating adhesives have a higher flow index and lower modulus than the flexible conductive adhesive bumps. This is more protected at the edge of the device when the insulating adhesive fills the space adjacent the edge of the device. Mechanical testing at high accelerated vapor and temperature exposure conditions showed up to 20% variation in adhesion strength and no delamination of the adhesion. Thermal cycling of -65 ° C. to 150 ° C. during the 2000 cycles of the assembled electronic device using an adhesive that adheres a large silicon semiconductor die (16 mm edge region) to an aluminum substrate having a CTE of 20 ppm / ° C. or higher, resulting in delamination of adhesion. And the decrease in adhesive strength cannot be measured.

The prepared semiconductor device 130 having a pattern of the flexible conductive adhesive bump 140 and the insulating flexible adhesive 150 as shown in FIG. 8 may be configured to use the electronic device 100 as shown in FIG. 6 as follows. It is assembled on the next level board, ie substrate 120, to form. Since the semiconductor device 130 is aligned with respect to the substrate 120, the contact pads 124 and 134 of the substrate 120 and the semiconductor device 130 are aligned. If the device 130 and the substrate 120 are pressed together and the temperature is in the region of 195-215 ° C. and the placement pressure is approximately 10 psi, then the flexible adhesive bump 140 immediately moves the respective contact pads 124, 134 together. Glue. In a similar manner, the insulating flexible adhesive 150 adheres to the area between the contact pads 124 of the substrate 120 to the corresponding area between the contact pads 134 of the semiconductor device 130. For superior efficiency, the substrate 120 is preheated to a temperature of approximately 150-200 ° C. while the chuck picking up semiconductor chip 130 is preheated to approximately 220-280 ° C. Thus, the electronic device 100 assembled as described above, including the semiconductor die 130 having an edge area of 10 mm or more bonded on the alumina substrate 120, has a thickness of 1000 between -65 ° C and + 150 ° C. It has been shown to withstand over 50 thermal shocks between -65 ° C and + 150 ° C without thermal cycling abnormalities and without measurable change in contact resistance. Exposure to 85 ° C. at 85% relative humidity (RH) for 168 hours does not result in measurable deterioration of electrical contact resistance, and exposure to 100 ° C. at 100% RH for 200 hours does not affect die There is no measurable degradation in the shear adhesive strength of 130. Thick films and thin film gold adhesive pads on the alumina substrate are prevented from saturation.

The assembly process is similar to the one in which a flexible epoxy adhesive is used. The placement chuck is contained at a low temperature of 150-175 ° C. and the die placed on the next level board substrate is allowed to be processed for an additional 5 minutes at 150-175 ° C. without pressure or other manipulation before assembly. If a thermoplastic based flexible adhesive is used, the temperature of the placement chuck (and maintaining the temperature of the die) and the substrate should be maintained at a temperature of several degrees above the temperature at which the flexible adhesive conductive bumps and insulating conductive underfill can flow.

In most applications, contact pads 34 and adhesive bumps 40 may be the same size. In some cases, however, because of the relatively small number of contact pads, the overall area of adhesion becomes relatively small, while the contact pads contain the pitch of the contact pads (i.e., intermediate to intermediate positions between adjacent contact pads). It may have the advantage of having a conductive bump that actually grows in relation to the area of. Increasing the area of the flexible conductive bumps increases the mechanical strength of the adhesion between the semiconductor device 30 and the substrate 20, reduces the overall electrical resistance and increases the current carrying capacity of the flexible conductive connections.

The total area of the contact pads 34 is actually approximately 33% or less of the total area of the semiconductor device 30, and the adhesive area is sufficient to supply a suitable adhesive strength without reinforcement. In the embodiment of FIG. 9, the flexible conductive adhesive bump 240 on the semiconductor device 30 intentionally grows to actually cover more than the area of the individual adhesive pads 34. The larger conductive adhesive bumps 240 are used while including the recommended minimum space between dense pads of 50 μm or more, and the “overhang” of the conductive bumps 240 increases the total adhesive area by approximately 50% or more, Only a flexible conductive adhesive is used without the need for a filler layer to increase adhesion integrity.

In addition, when the number of contact pads 34 and the pitch of the contact pads are small, it is desirable to actually reduce the area of the flexible conductive bumps while maintaining the pitch. This reduction in the area of the conductive bumps allows to reduce neighbor bridging between adjacent connections during the bonding process. Reduction of the area of flexible connection is particularly useful where insulation underfill is not used.

For example, if the contact pads 34 are closer together than approximately 100 μm, capacitive bumps 340 are used that have an area smaller than the area of the contact pads 34. In FIG. 10, the capacitive bump 340 is actually in a smaller area than the adhesive pad 34 of the semiconductor device 30. This method is more suitable for low current density connections, and higher connection resistance can be tolerated by electronic circuits in which the substrate 20 and the semiconductor device 30 form part.

While the invention has been described with respect to the foregoing embodiments, it will be apparent to those skilled in the art that variations within the scope and spirit of the invention as defined in the following claims will be apparent. For example, the substrate 20 circuit board material is different from ceramic alumina having a CTE of 7 ppm / ° C. In fact, most commercial applications use FR-4, BT and other organic substrate materials with much higher CTEs, resulting in mismatches between silicon flip chips with CTEs with a CTE of 3 ppm / ° C and substrates of alumina. Increase from CTE of ppm / ° C. to CTE of 17 ppm / ° C. of FR-4. At higher CTE mismatches, such as CTEs above 10 ppm / ° C., thermal cycling and thermal shock can cause failures due to delamination or destruction of the connections. Using LTP8150 and ESS8450, a flexible conductive adhesive type available from AI Technology, Inc., with a CTE mismatch of 3 or 25 ppm / ° C, including silicon devices with edge areas as large as 16 mm bonded to an aluminum substrate. In the assembled electronic device 10 according to the present invention, a heat cycle of -65 ° C to 150 ° C for more than 2000 cycles cannot detect peeling and change in adhesive strength. Similar tests were formed on electronic devices using FR-4 substrates and no delamination or change in adhesive strength was detected.

In addition, flexible adhesives using other flexible conductive adhesive materials and other conductive fillers having the same or similar molecular flexibility, adhesion, and capacities as type LTP8150 of AI Technology may be substituted. Other suitable deposition methods, such as stenciling, screening, masking, ink jet printing, contact deposition, preform stacks, needle disassembly, and others, may include conductive adhesive bumps 40, 140, 240 on contact pads of semiconductor device 30. Or to deposit other electronic components 44, 46 or deposit conductive adhesive bumps 40, 140, 240 on contact pads of the substrate 20.

While the above embodiment has a flexible conductive adhesive bump and a flexible insulating adhesive pattern deposited on a semiconductor die, the flexible conductive adhesive bump and the flexible insulating adhesive pattern can be deposited on a substrate. In addition, the pattern of flexible insulating adhesive may be deposited on one of the semiconductor devices or substrates, and the flexible conductive adhesive bumps may be deposited on the other. In addition, the flexible insulating adhesive is thermally capacitive but loaded with a cathodic filler. Some suitable such adhesives include types LESP7455, LESP7555, LTP7555 and LTP7095 available from AI Technology, Inc.

Although the above embodiment shows a single flip chip attachment, it is clear that multiple semiconductor chips can be mounted on the same device substrate using the method described herein. Bare (ie, uncoated) flip chip semiconductor devices and other electronic devices, packaged semiconductor devices, and electronic devices may be attached on the same circuit board using the capacitive bumps and methods described herein.

Claims (9)

In the electronic device (10, 100), At least one semiconductor device (30, 130) having a plurality of contact pads (34, 134) on the first surface; A substrate 20, 120 having a plurality of contact pads 24, 124 on a first surface, wherein the contact pads 24, 124 of the substrate 20, 120 are the semiconductor devices 30, 130. Are arranged in a pattern corresponding to the contact pads (34, 134) on the substrate, and the semiconductor devices (30, 130) and the substrates (20, 120) are disposed close to each other on their respective first surfaces; Disposed between one of the contact pads 34, 134 of the semiconductor devices 30, 130 and one of the contact pads 24, 124 of the substrates 20, 120, wherein the connection is 35,000 kg / cm 2 or less. And a plurality of flexible conductive adhesives (40, 140) having a modulus of elasticity. The electronic device of claim 1 wherein the flexible conductive adhesive (40, 140) has an elastic modulus of 7,000 kg / cm 2 or less. The electronic device according to claim 2, wherein the elastic modulus is maintained at 50% or more of the temperature range in which the electronic device (10, 100) is designated to operate. The method of claim 1, wherein the flexible conductive adhesive (40, 140) comprises an organic resin selected from the group consisting of thermoplastics, crosslinkable thermosetting materials, mixtures, interpolymers having a melt flow temperature of 300 ° C or less. A substantial portion of the molecular structure of the resin is an electronic device having a glass transition temperature of 0 ° C. or less, such as a knit resin. 38. The flexible conductive adhesive (40, 140) of claim 37 is substantially smaller than any contact pads (24, 124, 34, 134) of the semiconductor device (30, 130) and the substrate (20, 120). Conductive particles comprising (a) a metal selected from the group consisting of silver, gold, palladium, platinum and alloys thereof, and (b) a metal selected from the group consisting of silver, gold, palladium, platinum and alloys thereof An electronic device comprising at least one of the non-noble metal core plated with. The electronic device of claim 5, wherein the alloy is a silver-palladium alloy having at least 10 wt% palladium. The electronic device of claim 5, wherein the plated non-noble metal core does not contain 5 wt% or less of gold, palladium, platinum, and alloys thereof. The method of claim 1, wherein the flexible conductive adhesive 40, 140 is deposited on the adhesive pads 24, 124, 34, 134 of one of the semiconductor devices 30, 130 and the substrate 20, 120. And while maintaining the pitch between the adhesive pads 24, 124, 34, 134, the flexible conductive adhesives 40, 140 deposited on the at least some adhesive pads 24, 124, 34, 134 are ( a) actually having an area larger than the area of the adhesive pads 24, 124, 34, 134, and (b) an area that is actually smaller than the area of the adhesive pads 24, 124, 34, 134. An electronic device. A region of the semiconductor device (30, 130) that is not connected to the substrate (20, 120) having the flexible conductive adhesive (40, 140) is formed by the flexible conductive adhesive (40, 140). The electronic device is at least partially filled by a flexible insulating adhesive (150) having a modulus of elasticity less than the area.