Method for joining electrical and mechanical components using laminated modular preforms

Abstract

A method of applying a sinterable film to a substrate during a surface mount technology (SMT) process includes providing a substrate; providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles (e.g., Ag, Ag alloy, Au, Au alloy, Cu, Cu alloy, Rd, Rd alloy, Ni, Ni alloy, Al, Al alloy, Ag coated Cu, Cu coated Ag) deposited on the first surface but not on the second surface; providing a pick and place machine with a placement head; picking up the preform via the second surface using the placement head of the pick and place machine; placing the preform in contact with the substrate using the pick and place machine, the contact being via the sinterable film; attaching the sinterable film to the substrate; and separating the support film from the sinterable film. The placement head may include a vacuum nozzle, and picking up the preform through the support film includes applying a vacuum to the second surface using the vacuum nozzle. Separating the support film from the sinterable film may be performed by moving the placement head of the pick and place machine away from the support film while maintaining the vacuum. The support film may be discarded from the pick and place machine by removing the vacuum. The support film may be used to manufacture additional preforms. The preform may be placed in contact with a cavity or recess in a substrate. The preform may be picked up from a holding carrier, preferably in the form of a waffle pack, carrier tape, or spool tape and reel station, using the placement head of the pick and place machine. The support film may include a polymer or polymer support film. The substrate may be selected from a direct bond copper (DBC) substrate, an active metal braze (AMB) substrate, a semiconductor surface in the form of a gate pad, a source pad, a drain pad, a collector pad, a silicon wafer substrate, a heat spreader, a metal connector, and a piezoelectric substrate. The preform may be square, rectangular, circular, and any polygonal shape that fits the approximate dimensions of the substrate.The metal particles have a longest dimension of 1-1000 nm, preferably 2-500 nm, more preferably 5-100 nm, even more preferably 10-60 nm. The metal particles may be capped with a capping agent, preferably selected from one or more of fatty acids, fatty amines and starches. The sinterable membrane may comprise non-metallic particles, which may be selected from one or more of carbon, silicon carbide, aluminum nitride, boron nitride and silicon dioxide, in coated or uncoated form. The metal particles may comprise silver particles and the sinterable membrane may be substantially free of copper, aluminum, glass, carbon and graphite particles. The sinterable membrane may be free of a silver foil layer. The sinterable membrane may comprise a binder, preferably having a softening point of 50-170°C, more preferably 70-120°C. The binder may comprise a resin and / or rosin, preferably hydrogenated rosin. The sinterable membrane may comprise a solvent, preferably selected from one or more of terpineol, butyl carbitol and isopropanol. The attachment of the sinterable film to the substrate is carried out at a temperature of 130-170°C and / or a pressure of 2-5 MPa and / or a time of 100-2000 ms, preferably 100-800 ms. A stack of sinterable films may be formed on a substrate by applying a first sinterable film to the substrate using the method described above and sequentially stacking one or more further sinterable films on the first sinterable film, each of the one or more further sinterable films being stacked by a similar method. The first sinterable film may be formed from the same material as the one or more further sinterable films or from a material having different mechanical and / or thermal properties than at least one of the one or more further sinterable films, and two further sinterable films may be stacked on the first sinterable film to form a stack having an inner sinterable film and two outer sinterable films, the inner sinterable film being formed from a material having different mechanical and / or thermal properties than the material forming the two outer sinterable films.The additive particles may be included between the first sinterable film and the further sinterable film and / or between the further sinterable films, the additive particles may include particles having a higher thermal conductivity than the first sinterable film and the material of the one or more further sinterable films, including, for example, diamond, and / or the additive particles include particles having a different Young's modulus than the material of the first sinterable film and the one or more further sinterable films. The die can be attached to the substrate by a method comprising applying a sinterable film to the substrate or forming a stack of sinterable films on the substrate using the above method, contacting the die with the sinterable film or stack of sinterable films, and sintering the sinterable film or stack of sinterable films to attach the die to the substrate. The width of the sinterable film may be smaller than the width of the die and the width of the substrate, and the die may be provided with an edge passivation and may contact the sinterable film such that the sinterable film does not contact the edge passivation. A method of attaching a clip, bond pad, or upper bridge structure to a die includes providing a die attached to a substrate, applying a sinterable film to the die, contacting the sinterable film with the clip, bond pad, or upper bridge structure, and sintering the sinterable film to attach the clip, bond pad, or upper bridge structure to the die, wherein applying the sinterable film to the die includes providing a preform including a support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface. The method includes providing a preform having a support film on a die, the support film having a sinterable film of metal particles laminated thereon, the support film having a sinterable film of metal particles laminated thereon, providing a pick and place machine with a placement head, picking up the preform via the second surface using the placement head of the pick and place machine, placing the preform in contact with the die using the pick and place machine, the contact being via the second surface, attaching the sinterable film to the die, and separating the sinterable film from the sinterable film, the sinterable film may comprise a stack of sinterable films. The bond pad may comprise a buffer layer between the sensitive top metal of the die and harsh interconnect methods such as copper wire or copper ribbon bonding that require high forces and ultrasonic energy.An upper bridge structure can result in a double-sided cooled module, where the drain and source connections of the die are sintered to the planar substrate to improve cooling potential and increase the volumetric density of the power module. Bridging contactors can also connect the die in the cavity of the substrate to the contacts of the substrate.

Description

[Technical Field]

[0001] The present invention generally relates to methods of applying sinterable films to substrates, forming stacks of sinterable films on substrates, attaching dies to substrates, attaching clips, bond pads, or upper bridge structures to dies and substrates, and methods of manufacturing electronic devices.

[0002] Sintered powders contain nano- or micron-sized metallic particles. They can be used to form sintered joints between electronic components by placing the sintered powder between the electronic components and then sintering the sintered powder. The use of sintered powders can enable the formation of joints at temperatures lower than the melting temperature of the powder and that of conventional high-temperature solders. Sintered silver electronic component attachment materials are innovative products that combine the unique physical properties of nanosilver powder with advanced chemical formulations, making it possible to join various electronic devices and create high thermal and electrical conductivity interfaces with extremely high functional reliability.

[0003] Applying sintering materials in paste form by printing methods is particularly challenging when they need to be applied to awkward locations, such as on complex circuit boards or elevated devices. Persistent problems, such as uneven print profiles, difficulty accessing the stencil in recessed locations, and stencil / substrate leakage, are common. In traditional printing methods, a metal stencil with a thickness ranging from 50 μm to 300 μm and openings in the form of a screen or blank, is used to create cavities on top of the target surface. The printing process involves using a specialized wiper to apply a volume of paste onto the metal stencil. The paste fills the openings, assuming its XY pattern and the height of the stencil thickness. After applying the paste, the stencil is removed, and the paste is dried in a specialized oven at temperatures ranging from 140°C to 170°C. The target components (in the form of power chips, temperature sensors, conductive / insulating spacers, etc.) are then placed on top and sintered by applying pressure (10-25 MPa), heat (210-270°C), and time (60-480 seconds). The printing technique is used to apply the paste on a flat surface and to create a cavity up to 15mm. 2 ~400mm 2 However, significant challenges exist when the paste needs to be applied to smaller or larger areas (due to printing artifacts), or when the paste needs to be applied in three dimensions, as the stencil physically interferes with the existing components. Printing onto the surface of the target component is also very difficult, requiring the use of three-dimensional stencils, which suffer from printing artifacts including large amounts of paste waste, leakage under the stencil, and uneven thickness of the printed paste.

[0004] The sintering powder can be applied in the form of a film or preform instead of a paste, allowing for better bond line control, access to otherwise inaccessible locations such as cavities, and a modular approach to building modules. The silver film can be applied or laminated to the backside of a die, wafer, or any other compatible electronic component.

[0005] U.S. Patent No. 10,710,336 (B2) describes the use of sintered membranes made of nano-sintered material reinforced with either particles or intermediate foil to produce freestanding preforms that can be used for attaching electronic devices. After sintering, the reinforcing particles or intermediate foil remain in the sintered joint, making a pure nano-silver sintered joint impossible and thereby potentially adversely affecting the properties of the sintered joint. Both the reinforcing particles and the silver foil increase the cost of the membrane through additional materials and processing steps. Freestanding membranes are typically damaged when handled by conventional pick-and-place machines.

[0006] Sintered films are also described in U.S. Patent Application Publication No. 2012 / 0114927(A1). This publication also describes methods for transferring sintered films to dies or substrates. In one of these methods (known in the art as "Die Transfer Film" or DTF), a sinterable material in the form of a film is placed on top of a rubberized holder in an automated pick-and-place workspace, ready for processing. The prepared film and rubberized holder assembly are referred to as the film station. During processing, a target component (in the form of a power chip, temperature sensor, conductive / insulating spacer, etc.) is picked up from the holding station by a pick-and-place bonding head and transferred onto the prepared film. The target component is then pressed onto the film using pressures ranging from 2 to 5 MPa, temperatures ranging from 130 to 170°C, and times ranging from 100 to 500 ms. Under these pressing conditions, a sinterable film is laminated onto the bottom surface of the target component. Following the lamination process, the target component is lifted from the film station and transferred onto the target surface, where it is pressed onto the target surface using pressures ranging from 3 to 5 MPa, temperatures ranging from 130 to 170°C, and times ranging from 200 to 800 ms. After the pressing process, the target component is attached to the target surface with sufficient loose attachment strength to transport the unfinished power module to the sintering step. Sintering is then carried out by applying pressure (10 to 25 MPa), heat (210 to 270°C), and time (60 to 480 seconds) to obtain a fully sintered joint. While die-transferred film technology is well suited to laminating the bottom of a target component with a highly uniform sinterable material, it is limited to processes where lamination is achieved on the bottom of a separate sinterable component. Applying the die-transferred film concept to laminating on top of a target component or to placing a film-based sinterable material on specific regions of the target surface is essentially impossible.

[0007] The present invention aims to solve at least some of the problems associated with the prior art or to provide a commercially acceptable alternative.

[0008] In a first aspect, the present invention provides a method of applying a sinterable film to a substrate during a surface mount technology (SMT) process, the method comprising: Providing a substrate; providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using a placement head of a pick and place machine; placing the preform in contact with a substrate using a pick and place machine, the contact being via the sinterable film; attaching the sinterable film to a substrate; and separating the support membrane from the sinterable membrane.

[0009] The present invention will now be further described. In the following sections, different aspects of the present invention are defined in more detail. Each aspect so defined can be combined with any one or more other aspects, unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other one or more features indicated as being preferred or advantageous.

[0010] Surprisingly, in contrast to printing methods, the method of the present invention allows for the production of e.g. 2 ~100mm 2 The method of the present invention allows for a very uniform and homogeneous application of sinterable material onto target surfaces ranging in size from 100 to 2000 mm. The method of the present invention can also allow for the sinterable material to be applied completely dry, i.e., without the presence of solvents, which means that no separate drying step is required.

[0011] Advantageously, in contrast to the DTF method, the method of the present invention allows the sinterable material to be applied to hard-to-reach locations, such as within recesses in a substrate or on top of a die or clip already attached to the substrate. The sinterable material may also be applied in any desired shape and size that does not have to conform to the shape and size of the surface to which it is applied.

[0012] In conventional surface mount technology (SMT) methods, components are typically laminated with a sinterable film and then placed on a substrate. In the present invention, the lamination process is separated from the component handling process. Since not all components can be laminated, the present invention therefore allows for sinterable films to be placed where specifically needed.

[0013] The present invention may allow for the sequential application of multiple sinterable films to the same portion of a substrate, which allows for control of the thickness of the final sinterable film.

[0014] The method can achieve attachment of the sinterable film without the use of adhesives.

[0015] In contrast to the sinterable membranes of U.S. Pat. No. 1,071,0336 (B2), the sinterable membranes of the present invention preferably are substantially free (more preferably completely free) of support particles (e.g., non-metallic particles such as graphite, carbon, or glass), i.e., solid particles other than metal particles. Such support particles are not necessary in the sinterable membranes of the present invention, both from the standpoint of the support membrane and from the standpoint of the fact that the membrane does not need to be self-supporting. Furthermore, such support particles may adversely affect the properties of the final sintered joint and / or increase the cost of the sinterable membrane. In contrast to the sinterable membranes of U.S. Pat. No. 1,071,0336 (B2), the sinterable membranes of the present invention preferably do not include a silver foil layer. Such a silver foil layer is not necessary from the standpoint of the support membrane. Furthermore, it does not need to be self-supporting due to the way the pick-and-place machine handles the sinterable membrane. Such a silver layer may increase the cost of the sinterable membrane.

[0016] As used herein, the term "surface mount technology (SMT) process" may encompass a process in which electrical components are mounted directly onto the surface of a printed circuit board (PCB).

[0017] As used herein, the term "preform" can encompass a prefabricated shape of sinterable particles specifically designed for the application for which it is to be used. The support film of the preform has first and second surfaces. The first and second surfaces are the major, or largest, surfaces of the film. The support film is laminated with a sinterable film of metal particles on the first surface. Typically, the sinterable film of metal particles covers the entire first surface.

[0018] The metal particles of the sinterable film may be in the form of, for example, spheres, rods and / or plates.

[0019] Providing a preform may include laser cutting to ensure the preform is the desired size and shape. For example, a large support film may be provided having a film of sinterable particles on a first surface thereof but not on a second surface thereof. Continuous wave or short pulse ablative laser cutting can then be used to cut the large support film into one or more preforms of the desired size and shape. Laser cutting allows the preforms to be prepared with a high degree of precision and negligible edge damage.

[0020] The term "pick-and-place machine" is understood by those skilled in the art and may encompass robotic machines used to place surface-mount devices (SMDs) on printed circuit boards (PCBs). Commercially available examples of suitable pick-and-place machines include the Datacon EVO 2200, Infotech Die Bonder, and ASM ForceVector. Pick-and-place machines include a placement head (also known as a bonding head or pickup head). The placement head is used to pick up and position the preform, attach the sinterable film to the substrate, and separate the support film from the sinterable film. The placement head typically includes vacuum functionality. Such functionality may be used to pick up the preform. The placement head may also include gas purging functionality. The placement head may also include heating functionality. Such heating functionality may be used to heat the preform, facilitating film adhesion and separation of the support film from the sinterable film.

[0021] The method includes using a placement head of a pick-and-place machine to pick up the preform via the second surface. In other words, during pickup, the placement head contacts only the second surface of the preform, and not the first surface of the preform or the sinterable film. As a result, damage to the sinterable film during pick-up and placement can be avoided. This can avoid the formation of a compromised joint, such as a joint between the die and the substrate that exhibits unfavorable thermal, electrical, and / or mechanical properties, when the sintered film is sintered during the SMT process.

[0022] The method includes attaching the sinterable film to a substrate. Attachment is typically achieved by application of heat and / or pressure. Attachment typically occurs by slight infusion of metal particles into the substrate.

[0023] The method includes separating the support film from the sinterable film. The support film can then be discarded. Alternatively, the support film may be used to manufacture additional preforms. Separation can occur, for example, due to evaporation of organic compounds (e.g., binders) contained in the sinterable film, which push the support film away from the sinterable film.

[0024] Preferably, the placement head includes a vacuum nozzle, and picking up the preform through the support film includes applying a vacuum to the second surface using the vacuum nozzle. The vacuum may be particularly suitable for picking up sinterable films, and when applied to the second surface, i.e., the uncoated surface, damage to the sinterable film can be avoided. By picking up the preform through the second surface, metal particles from the sintered film are not sucked into the pick-and-place machine and ultimately into the vacuum pump.

[0025] Separating the support film from the sinterable film is preferably done by moving the placement head of the pick and place machine away from the support film while maintaining the vacuum.

[0026] Preferably, the method further comprises discarding the support film from the pick and place machine by removing the vacuum.

[0027] In a preferred embodiment, the vacuum nozzle is capable of supplying a purge gas, the vacuum nozzle simultaneously removing the vacuum and supplying the purge gas.

[0028] Placing the preform in contact with the substrate preferably includes placing the preform in contact with a cavity or recess in the substrate. In contrast to conventional methods, the method of the present invention is capable of placing the preform in such hard-to-reach locations. Thus, in contrast to conventional methods, the method of the present invention can be used to manufacture more complex devices and / or to manufacture such devices more easily.

[0029] Picking up the preforms through the support film using the placement head of the pick and place machine preferably includes picking up the preforms from a holding carrier, more preferably in the form of a waffle pack, carrier tape, or spool tape and reel station.

[0030] In a preferred embodiment, the method comprises: providing a further preform including a further support film, the further support film having a first surface and a second surface opposite the first surface, the further support film having a further sinterable film of metal particles deposited on the first surface but not on the second surface; picking up the preform via the second surface of the further support film using a placement head of the pick and place machine; placing the preform in contact with the sinterable film using a pick and place machine, the contact being via a further sinterable film; attaching a further sinterable film to the sinterable film; and separating the further support film from the further sinterable film.

[0031] This can increase the thickness of the sinterable film and the sintered joint formed using the further sinterable film.

[0032] The support film preferably comprises a polymer, or the support film comprises a polymer support film. Polymers may be particularly suitable for supporting sinterable films and may be particularly suitable for being handled by pick-and-place machines.

[0033] The substrate is preferably selected from Direct Bonded Copper (DBC) substrates, Active Metal Brazed (AMB) substrates, semiconductor surfaces in the form of gate, source, drain, and collector pads, silicon wafer substrates, heat spreaders, metal connectors, and piezoelectric substrates. Such substrates may contain hard-to-reach locations, such as recesses. As mentioned above, the method of the present invention is capable of applying sinterable films to such locations.

[0034] The preform preferably has a longest dimension of 0.5 mm to 40 mm. If the preform is in the shape of a disk, the longest dimension is the diameter of the disk.

[0035] Preforms are preferably square, rectangular, circular, and any polygonal shape that matches the approximate dimensions of the target substrate.

[0036] The thickness of the support film is preferably 40 to 80 μm. If the thickness is smaller, the support film may break when handled by a pick-and-place machine. If the thickness is larger, the cost of the support film may increase.

[0037] The thickness of the sinterable film is preferably 30 to 120 μm. Sintered joints formed from sinterable films with thicknesses less than 30 μm may exhibit unfavorable mechanical and / or thermal properties. Thicknesses greater than 120 μm may disadvantageously increase the size of the final device and may increase the cost of the sinterable film.

[0038] The metal particles are preferably selected from one or more of silver, silver alloys, gold, gold alloys, copper, copper alloys, palladium, palladium alloys, nickel, nickel alloys, aluminum and aluminum alloys, silver-coated copper, copper-coated silver, and more preferably silver. Such metals are particularly suitable for use as sinterable particles in view of their favorable thermal, electrical, and mechanical properties.

[0039] The metal particles preferably have a longest dimension of 1 to 1000 nm, preferably 2 to 500 nm, more preferably 5 to 100 nm, and even more preferably 10 to 60 nm. If the particles are in the form of a sphere, the longest dimension is the diameter of the sphere. The longest dimension can be determined using laser diffraction methods. Smaller particles can be more difficult to handle. Larger particles may require higher sintering temperatures and / or pressures and / or times.

[0040] The sinterable film preferably contains 30-95 wt. % metal particles. Lower amounts may mean that sintered joints formed from the sinterable film exhibit unfavorable mechanical, thermal, and / or electrical properties. Higher amounts may result in oxidation and / or agglomeration of the metal particles.

[0041] The metal particles are preferably capped with a capping agent, more preferably selected from one or more of fatty acids, fatty amines, and starches. The presence of the capping agent may prevent oxidation and / or agglomeration of the metal particles.

[0042] The sinterable film preferably contains 0.1 to 20 wt. % capping agent, more preferably 0.5 to 0.8 wt. % capping agent, or 0.8 to 1.5 wt. % capping agent. Lower amounts of capping agent may be insufficient to prevent oxidation and / or agglomeration of the metal particles. Higher amounts may increase the amount of organic matter present in the sinterable joint formed from the sinterable film, which may adversely affect the mechanical, thermal, or electrical properties of the joint.

[0043] Preferably, the metal particles comprise silver particles, and the sinterable film is substantially free (more preferably completely free) of copper, aluminum, glass, carbon, and graphite particles.

[0044] The sinterable film preferably does not include a silver foil layer.

[0045] The sinterable film preferably includes a binder, more preferably a binder having a softening point between 50 and 170°C, and even more preferably between 70 and 120°C. A higher softening point may increase the amount of binder remaining in the sintered joint, which may adversely affect the mechanical, thermal, and / or electrical properties of the sintered joint. In addition, a higher softening point may make the particles of the metal powder less likely to sinter. A lower softening point may cause the sintered film to lose its structural integrity during pick-up or placement.

[0046] The binder preferably comprises a resin and / or rosin, more preferably hydrogenated rosin. The presence of such species may remove surface oxides from the substrate and / or metal particles.

[0047] The sinterable film preferably contains 0.5 to 5 wt. % binder. Lower amounts may be insufficient to act as a binder, while higher amounts may increase the amount of organic material present in the sintered joint.

[0048] The sinterable film preferably includes a solvent, more preferably selected from one or more of terpineol, butyl carbitol, and isopropanol. The solvent is capable of dissolving the binder. Such solvents may substantially evaporate during typical sintering temperatures, thereby reducing the amount of organic material present in the final sintered joint.

[0049] The sinterable film preferably contains sufficient solvent to dissolve the binder. The sinterable film preferably contains up to 70% by weight of solvent, more preferably 1-60% by weight of solvent, and even more preferably 10-30% by weight of solvent. A low amount of solvent may not fully dissolve the binder. A high amount may increase the amount of organic material present in the final sintered joint.

[0050] The attachment is carried out at a temperature of 130-170°C and / or a pressure of 2-5 MPa and / or for a time of 100-2000 ms, preferably 100-800 ms. Such conditions may be particularly effective for attaching a sinterable film to a substrate. For example, the conditions may promote infusion of metal particles into the substrate and / or may result in evaporation of the solvent. Higher temperatures and / or pressures and / or longer times may result in sintering of the metal particles. Lower temperatures and / or pressures and / or shorter times may result in insufficient attachment.

[0051] In a further aspect, the present invention provides a method of applying a sinterable film to a substrate during a surface mount technology (SMT) process, the method comprising: Providing a substrate; providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; placing the preform in contact with a substrate, the contact being via the sinterable film; attaching the sinterable film to a substrate; and separating the support membrane from the sinterable membrane; Placement is performed using a pick and place machine, During placement and attachment, the pick and place machine contacts the second surface of the support film but does not contact the sinterable film.

[0052] The advantages and preferred features of the first aspect apply equally to this aspect.

[0053] In a further aspect, the present invention provides a method for forming a stack of sinterable films on a substrate during a surface mount technology (SMT) process, the method comprising: applying a first sinterable film to a substrate using a method described herein; and sequentially depositing one or more additional sinterable films on the first sinterable film, each of the one or more additional sinterable films comprising: providing a further preform including a further support film, the further support film having a first surface and a second surface opposite the first surface, the further support film having a further sinterable film of metal particles deposited on the first surface but not on the second surface; picking up a further preform via the second surface using a placement head of the pick and place machine; For a first of the one or more additional sinterable films: placing each additional preform in contact with the first sinterable film using a pick and place machine, the contact being via the additional sinterable film; attaching a further sinterable film to the first sinterable film; Separating the support membrane from the further sinterable membrane; For subsequent further sinterable films: using a pick and place machine to place each additional preform in contact with the immediately preceding additional sinterable film, the contact being via the additional sinterable film of the respective preform of the second or subsequent additional sinterable film; attaching a further sinterable film to the immediately preceding further sinterable film; and separating the support film from the further sinterable film.

[0054] The advantages and preferred features of the first aspect apply equally to this aspect.

[0055] The thickness of the stacked sinterable films can be controlled by controlling the number of stacked sinterable films. Controlling the thickness of the stack allows for control of the thickness of the sintered bond formed from the stack. A thicker sintered bond can be beneficial, for example, when the substrate and die joined by the bond exhibit different coefficients of thermal expansion (CTE).

[0056] In a preferred embodiment, the first sinterable film is formed from the same material as the one or more further sinterable films, in which case the mechanical, thermal and / or electrical properties of the sintered joint may be substantially constant across its thickness.

[0057] In an alternative preferred embodiment, the first sinterable film is formed from a material having different mechanical, thermal, and / or electrical properties than at least one of the one or more additional sinterable films. In this case, the mechanical, thermal, and / or electrical properties of the sintered joint may vary across its thickness. For example, if the joint is used to join a substrate and a die having different coefficients of thermal expansion (CTE), the CTE of the metal of the metal particles in the sinterable film can be controlled so that the CTE of the sintered joint varies across its thickness, i.e., the CTE of the substrate-side portion of the joint is closer to the CTE of the substrate, and the CTE of the die-side portion of the joint is closer to the CTE of the die. Examples of suitable metals include iron-nickel alloys, copper-tungsten alloys, and copper-molybdenum alloys. In another example, it may be desirable to introduce a sacrificial failure region into the joint to provide predictable failure and aid in module life prediction. Such a sacrificial zone can be introduced by ensuring that at least one of the sinterable films contains metal particles whose metal has a lower tensile strength and / or yield strength than the metal of the metal particles in the other sinterable films.

[0058] In a preferred embodiment, two additional sinterable membranes are stacked on the first sinterable membrane to form a stack having an inner sinterable membrane and two outer sinterable membranes, the inner sinterable membrane being formed from a material (i.e., metal particles) having different mechanical and / or thermal properties than the material forming the two outer sinterable membranes. Preferably, the metal of the metal particles of the inner sinterable membrane has a lower tensile strength and / or yield strength than the metal of the metal particles of the outer sinterable membranes. When the stack is sintered, the inner sinterable membrane may result in a sacrificial failure region.

[0059] Preferably, the method further comprises applying additive particles between the first sinterable film and the further sinterable film and / or between the further sinterable films.

[0060] The additive particles preferably comprise particles having a higher thermal conductivity than the materials of the first sinterable film and the one or more further sinterable films, thereby increasing the thermal conductivity of the sintered joint, which can be beneficial when heat needs to be removed from the die to the substrate.

[0061] The particles having a higher thermal conductivity than the material of the first sinterable film and the one or more further sinterable films preferably comprise diamond. Particles such as diamond can be dispersed in the film of sinterable particles.

[0062] The additive particles include particles having a different Young's modulus than the materials of the first sinterable film and the one or more further sinterable films, which can reduce the overall stress on the sintered joint, thereby improving the reliability of the joint.

[0063] In a further aspect, the present invention provides a method of attaching a die to a substrate, the method comprising: applying a sinterable film to a substrate using the methods described herein, or forming a stack of sinterable films on a substrate using the methods described herein; contacting the die with a sinterable film or a stack of sinterable films; and sintering the sinterable film or stack of sinterable films to attach the die to the substrate.

[0064] The advantages and preferred features of this embodiment apply equally to this embodiment.

[0065] In a preferred embodiment, the width of the sinterable film is smaller than the width of the die and the width of the substrate, which can result in undercutting, which can be beneficial, for example, if the die includes edge passivation.

[0066] Preferably, the die includes an edge passivation, and the die contacts the sinterable film such that the sinterable film does not contact the edge passivation.

[0067] In a further aspect, the present invention provides a method for attaching a clip, bond pad, or upper bridge structure to a die, the method comprising: providing a die attached to a substrate; applying a sinterable film to a die; contacting the sinterable film with a clip, bond pad, or upper bridge structure; Sintering the sinterable film to attach the clip, bond pad, or upper bridge structure to the die; Applying the sinterable film to the die providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using a placement head of a pick and place machine; placing the preform in contact with the die using a pick and place machine, the contact being via the second surface; attaching a sinterable film to a die; and separating the support film from the sinterable film.

[0068] The advantages and preferred features of the first aspect apply equally to this aspect.

[0069] As mentioned above, in contrast to conventional methods, the method of the present invention can apply a sinterable film to a die attached to a substrate, which can facilitate the attachment of clips, bond pads, or upper bridge structures to the die.

[0070] In this embodiment, the sinterable film preferably comprises a stack of sinterable films.

[0071] In a further aspect, the present invention provides a method for attaching a clip, bond pad, or upper bridge structure to a die, the method comprising: attaching the die to a substrate using a method described herein; applying a sinterable film to a die; contacting the sinterable film with a clip, bond pad, or upper bridge structure; Sintering the sinterable film to attach the clip, bond pad, or upper bridge structure to the die; Applying the sinterable film to the die providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using a placement head of a pick and place machine; placing the preform in contact with the die using a pick and place machine, the contact being via the sinterable film; attaching a sinterable film to a die; and separating the support film from the sinterable film.

[0072] The advantages and preferred features of the first aspect apply equally to this aspect.

[0073] As mentioned above, in contrast to conventional methods, the method of the present invention can apply a sinterable film to a die attached to a substrate, which can facilitate the attachment of clips, bond pads, or upper bridge structures to the die.

[0074] In this embodiment, the sinterable film preferably comprises a stack of sinterable films.

[0075] In a further aspect, the present invention provides a method for manufacturing an electronic device, the method comprising: attaching the die to a substrate using a method described herein; Attaching a clip, bond pad, or upper bridge structure to the die using the methods described herein.

[0076] The advantages and preferred features of the first aspect apply equally to this aspect.

[0077] Preferably, the electronic device is a power module.

[0078] The invention will now be further described with reference to the following numbered clauses: 1. A method for applying a sinterable film to a substrate, the method comprising: Providing a substrate; providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; placing the preform in contact with a substrate, the contact being via the sinterable film; attaching the sinterable film to a substrate; and separating the support membrane from the sinterable membrane. 2. The method of clause 1, wherein the support membrane comprises a polymer or the support membrane comprises a polymer support membrane. 3. The method of clause 1 or 2, wherein the substrate is selected from a direct bonded copper (DBC) substrate, an active metal brazed (AMB) substrate, a semiconductor surface in the form of a gate pad, or a source pad, or a drain pad, or a collector pad, a silicon wafer substrate, a silicon wafer substrate, a heat spreader, a metal connector, and a piezoelectric substrate. 4. The method of any of clauses 1-3, wherein the preforms are square, rectangular, circular in shape, and have general dimensions ranging from 0.5mm wide to 40mm wide in shapes that match the approximate dimensions of the substrate to which they are attached. 5. The method of any one of clauses 1 to 4, wherein the support membrane has a thickness of 40 to 80 μm. 6. The method of any one of clauses 1 to 5, wherein the sinterable film has a thickness of 30 to 120 μm. 7. The method of any of clauses 1-6, wherein the sinterable film preferably comprises metal particles selected from one or more of silver, silver alloys, gold, gold alloys, copper, copper alloys, palladium, palladium alloys, nickel, nickel alloys, aluminum, and aluminum alloys. 8. The method of any of clauses 1 to 7, wherein the metal particles have a longest dimension of 1 to 1000 nm, preferably 2 to 500 nm, more preferably 5 to 100 nm, and even more preferably 10 to 60 nm. 9. The method of any one of clauses 1 to 8, wherein the sinterable film comprises 30 to 95 wt. % metal particles. 10. The method of any of clauses 1-9, wherein the metal particles are capped with a capping agent preferably selected from one or more of a fatty acid, a fatty amine, and a starch. 11. The method according to clause 10, wherein the sinterable film comprises 0.1 to 20 wt. % of the capping agent, preferably 0.5 to 0.8 wt. % of the capping agent or 0.8 to 1.5 wt. % of the capping agent. 14. The method of any of clauses 1 to 13, wherein the sinterable film comprises a binder having a softening point preferably between 50 and 170°C, preferably between 70 and 120°C. 15. The method of claim 14, wherein the binder comprises a resin and / or rosin, preferably hydrogenated rosin. 16. The method of claim 14 or 15, wherein the sinterable film comprises 0.5 to 5 wt. % of a binder. 17. The method of any of clauses 1-16, wherein the sinterable film preferably comprises a solvent selected from one or more of terpineol, butyl carbitol, and isopropanol. 18. The method of clause 17, wherein the sinterable film comprises up to 70% by weight of solvent, preferably 1-60% by weight of solvent, more preferably 10-30% by weight of solvent. 19. The method according to any of clauses 1 to 18, wherein the attaching is carried out at a temperature of 130 to 170°C and / or at a pressure of 2 to 5 MPa and / or for a time period of 100 to 2000 ms, preferably 100 to 800 ms. 20. Placement is done using a pick and place machine, 20. The method of any of clauses 1-19, wherein during placement and attachment, the pick and place machine contacts the second surface of the support film but does not contact the sinterable film. twenty one. Placement is done using an automated pick and place machine, 21. The method of any of clauses 1-20, wherein during the pick-up, place-and-attach process, the pick-and-place machine contacts the second surface of the support film but does not contact the sinterable film. 22. The method of clause 20 or 21, wherein the pick and place machine is equipped with a bonding head tool having vacuum and air purge capabilities. 23. The method of any of clauses 20 to 22, wherein during placement, attachment and / or separation, the pick and place machine, preferably the bonding head tool of the pick and place machine, is maintained in contact with the second surface using a vacuum. 24. The method of clause 23, wherein separating the support film from the sinterable film is performed by moving a placement head of a pick and place machine away from the sinterable film while maintaining the vacuum. 25. The method of clause 24, wherein the support film is discarded from the pick and place machine by removing / reversing the vacuum. 26. The method of any one of clauses 1 to 25, performed during a surface mount technology (SMT) process. 27. The method of any of clauses 1-26, wherein placing the preform in contact with the substrate comprises placing the preform in contact with a cavity / recess in the substrate. 28. providing a further preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a further sinterable film of metal particles deposited on the first surface but not on the second surface; placing a further preform in contact with the sinterable film, the contact being via the further sinterable film; attaching a further sinterable film to the sinterable film; 28. The method of any of clauses 1-27, further comprising separating the support membrane from the further sinterable membrane. 29. The method of any of clauses 1 to 28, further comprising contacting the sinterable silver film or the further sinterable silver film with a component preferably selected from a die, a wafer, a bond pad, a secondary ceramic substrate, a copper wire, and a copper ribbon. 30. The method of clause 29, further comprising sintering the sinterable film, and optionally further sinterable films, to attach the component to the substrate. [Brief explanation of the drawings]

[0079] The invention will now be further described with reference to the following drawings. [Figure 1] 1 shows an image of paste printed on top of a die according to conventional methods. [Figure 2] 1 shows a schematic diagram of a preform according to the invention; [Figure 3] 1 shows a schematic diagram of the method according to the present invention. [Figure 4] 4 shows an image of a sinterable film applied to a substrate using the method shown in FIG. 3. [Figure 5] 1 shows a schematic diagram of the method according to the present invention. [Figure 6] 6 shows an image of a sinterable film applied to a substrate using the method shown in FIG. 5. [Figure 7] 1 shows a schematic diagram of the method according to the present invention. [Figure 8] Figure 7 shows an SEM image of a die sintered on top of a copper substrate using the method. [Figure 9]1 shows a schematic diagram of the method according to the present invention. [Figure 10] 1 shows a schematic diagram of the method according to the present invention. [Figure 11] 1 shows a schematic diagram of the method according to the present invention. [Figure 12] 1 shows a schematic diagram of the method according to the present invention.

[0080] Referring to Figure 1, there is shown paste applied to a die using conventional printing methods. As can be seen, there are problems with paste leakage and stencil separation.

[0081] Referring to Figure 2, there is shown a schematic diagram of a preform (generally designated A) comprising a support film B having a first surface C and a second surface D. The first surface is coated with a sinterable film of metal particles E.

[0082] Referring to Figure 3, a schematic diagram of the method according to the present invention is shown. In step 1, a pick-and-place bonding head uses a vacuum to pick up the preform A shown in Figure 2 by the support film B. In step 2, the preform A is brought into contact with a substrate / die at a temperature of 150°C to attach a sinterable film E. In step 3, while maintaining the vacuum, the bonding head is moved away from the substrate / die to separate the support film from the sinterable film. Finally, as shown on the right side of Figure 3, the support film is discarded by turning off the vacuum.

[0083] Referring to Figure 4, there are images of a sinterable film applied to the top side of a die using the method shown in Figure 3. The image on the left shows a macro image with the polymer support film removed and set to one side, while the laser scanned image on the right shows good uniformity and flatness.

[0084] Referring to FIG. 5, a method for forming a stack of sinterable films on a substrate during a surface mount technology (SMT) process is shown. A preform is applied to a substrate using a pick-and-place machine. The support film is then removed from the sinterable film. A second sinterable film is then applied to the first sinterable film, followed by a third sinterable film. A die is then applied to the stack of sinterable films. The second sinterable film has different material properties than the first and third sinterable films. The sinterable film is then sintered to form a sintered bond between the die and the substrate. In FIG. 5, the order of steps is as follows: place the laminate preform, place the peel-off barrier polymer sheet, place the second layer, place the third layer, place the die, and sinter the multilayer preform.

[0085] Referring to FIG. 6, an SEM image of a stack of five sinterable films formed during the method illustrated in FIG. 5 is shown.

[0086] Referring to FIG. 7, a schematic diagram of the method according to the present invention is shown. The width of the sinterable film can be the same as the width of the die (top) or smaller than the width of the die (bottom). If the width of the sinterable film is smaller than the width of the die, an undercut will be formed. In FIG. 6, the first step is the placement process of the laminated preform. In the top scheme, the first step is to place a die that is exactly the same size as the preform, and the second step is to sinter without overprinting / overlamination. In the bottom scheme, the first step is to place an oversized die, and the second step is to sinter with an undercut. FIG. 8 shows an SEM image of a die sintered on top of a copper substrate using the method according to the present invention to achieve an undercut of approximately 65 μm.

[0087] Referring to Figure 9, a schematic diagram of a method for attaching a clip to a die according to the present invention is shown. A sinterable film is attached to a substrate, and then the die is placed on the sinterable film. The sequence of steps is to place a laminate preform, place the die, proceed to sintering, place the laminate preform on the substrate and sintered die, place the clip on the laminate preform, and sinter the clip. Clip attachment can enable high current and low inductance circuits.

[0088] 10, a schematic diagram of a method for attaching bond pads to a die in accordance with the present invention is shown. The sequence of steps is to place a laminate preform, place the die, place the laminate preform on the die, place the bond pad on top of the laminate preform, sinter both preforms simultaneously, and bond the preform to the top of the pad. The bond pad provides a buffer layer between the sensitive top metal of the die and harsh interconnect methods such as copper wire or copper ribbon bonding, which require high force and ultrasonic energy.

[0089] 11, there is shown a schematic diagram of a method for attaching an upper bridge structure to a die in accordance with the present invention. The sequence of steps is to place a laminate preform, place a die and spacer, sinter the spacer and die, place a laminate preform, place an upper substrate, and sinter the substrate to the top side of the attachment. This method can result in a double-sided cooled module, where the drain and source connections of the die are sintered to the planar substrate to improve cooling capacity and increase the volumetric density of the power module.

[0090] 12, there is shown a schematic diagram of a method according to the present invention in which a sinterable film is applied to a cavity in a substrate. The sequence of steps is to place a laminate preform in the cavity, place a die on the preform in the cavity for sintering, place the laminate preform on the die for contact, and place a bridging contactor on top of the preform for sintering.

[0091] The foregoing detailed description has been provided by way of illustration and description and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments set forth herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. 1. A method of applying a sinterable film to a substrate during a surface mount technology (SMT) process, comprising: Providing a substrate; providing a preform including a support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using the placement head of the pick and place machine; placing the preform in contact with the substrate using the pick and place machine, the contact being via the sinterable film; attaching the sinterable film to the substrate; and separating the support film from the sinterable film.

2. providing a further preform including a further support film, the further support film having a first surface and a second surface opposite the first surface, the further support film having a further sinterable film of metal particles deposited on the first surface but not on the second surface; picking up the preform via the second surface of the further support film using the placement head of the pick and place machine; placing the preform in contact with the sinterable film using the pick and place machine, the contact being via the further sinterable film; attaching the further sinterable film to the sinterable film; The method of claim 1 , further comprising: separating the further support film from the further sinterable film.

3. the support membrane comprises a polymer or the support membrane comprises a polymer support membrane; and / or the substrate is selected from a direct bonded copper (DBC) substrate, an active metal braze (AMB) substrate, a semiconductor surface in the form of a gate pad, a source pad, a drain pad, a collector pad, a silicon wafer substrate, a heat spreader, a metal connector, and a piezoelectric substrate; and / or the preform has a longest dimension of between 0.5 mm and 40 mm; and / or the preform is in the shape of a square, rectangle, circle, or any polygon that fits the approximate dimensions of the substrate; and / or the thickness of the support film is 40 to 80 μm; and / or the thickness of the sinterable film is between 30 and 120 μm; and / or the metal particles comprise silver particles and the sinterable film is substantially free of copper, aluminum, glass, carbon, and graphite particles; and / or the sinterable film does not include a silver foil layer; and / or the attachment is carried out at a temperature of 130-170°C and / or at a pressure of 2-5 MPa and / or for a time of 100-2000 ms; and / or placing the preform in contact with the substrate comprises placing the preform in contact with a cavity or recess in the substrate; and / or picking up the preform through the support film using the placement head of the pick and place machine includes picking up the preform from a holding carrier; and / or 3. The method of claim 1 or 2, wherein the sinterable film comprises a solvent selected from one or more of terpineol, butyl carbitol, and isopropanol.

4. 10. The method of claim 1, wherein the metal particles are selected from one or more of silver, silver alloys, gold, gold alloys, copper, copper alloys, palladium, palladium alloys, nickel, nickel alloys, aluminum and aluminum alloys, silver-coated copper, and copper-coated silver.

5. The method of claim 4 wherein the metal particles are silver.

6. The method of claim 1, wherein the sinterable film comprises a binder having a softening point of 50 to 170°C.

7. The method of claim 6, wherein the sinterable film comprises a binder having a softening point of 70 to 120°C.

8. The method of claim 6 , wherein the binder comprises a resin and / or a rosin.

9. The method of claim 8 , wherein the binder comprises hydrogenated rosin.

10. The method of claim 6, wherein the sinterable film comprises 0.5 to 5 wt. % binder.

11. 1. A method for forming a stack of sinterable films on a substrate during a surface mount technology (SMT) process, the method comprising:

10. The method of claim 1, comprising: applying a first sinterable film to a substrate; and sequentially depositing one or more additional sinterable films on the first sinterable film, each of the one or more additional sinterable films comprising: providing a further preform including a further support film, the further support film having a first surface and a second surface opposite the first surface, the further support film having a further sinterable film of metal particles deposited on the first surface but not on the second surface; picking up the further preform via the second surface using a placement head of a pick and place machine; For a first of the one or more additional sinterable films: placing each of the additional preforms in contact with the first sinterable film using the pick and place machine, the contact being via the additional sinterable film; attaching the additional sinterable film to the first sinterable film; Separating the support film from the further sinterable film; For the subsequent further sinterable film, using the pick and place machine to place each additional preform in contact with the immediately preceding additional sinterable film, the contact being via the additional sinterable film of the respective preform of a second or subsequent additional sinterable film; attaching the further sinterable film to the immediately preceding further sinterable film; and separating the support film from the further sinterable film.

12. the first sinterable film is formed from the same material as the one or more further sinterable films; or 12. The method of claim 11, wherein the first sinterable film is formed from a material having different mechanical and / or thermal properties than at least one of the one or more further sinterable films.

13. 13. The method of claim 12, wherein two further sinterable films are stacked on the first sinterable film to form a stack having an inner sinterable film and two outer sinterable films, the inner sinterable film being formed from a material having different mechanical and / or thermal properties than the material forming the two outer sinterable films.

14. 14. The method according to any one of claims 11 to 13, wherein the method further comprises applying additive particles between the first sinterable film and further sinterable films and / or between further sinterable films.

15. 15. The method of claim 14, wherein the additive particles comprise particles having a higher thermal conductivity than a material of the first sinterable film and one or more further sinterable films.

16. 16. The method of claim 15, wherein the additive particles having a higher thermal conductivity than the material of the first sinterable film and one or more further sinterable films comprise diamond.

17. 15. The method of claim 14, wherein the additive particles comprise particles having a different Young's modulus than the material of the first sinterable film and one or more further sinterable films.

18. 1. A method of attaching a die to a substrate, comprising: applying a sinterable film to a substrate using the method of claim 1 or forming a stack of sinterable films on a substrate using the method of claim 11; contacting a die with the sinterable film or stack of sinterable films; and sintering the sinterable film or stack of sinterable films to attach the die to the substrate.

19. 20. The method of claim 18, wherein the width of the sinterable film is less than the width of the die and the width of the substrate.

20. 20. The method of claim 19, wherein the die includes an edge passivation, and the die contacts the sinterable film such that the sinterable film does not contact the edge passivation.

21. 1. A method of attaching a clip, bond pad, or upper bridge structure to a die, the method comprising: providing a die attached to a substrate; applying a sinterable film to the die; contacting the sinterable film with a clip, bond pad, or upper bridge structure; sintering the sinterable film to attach the clip, the bond pad, or the upper bridge structure to the die; applying the sinterable film to the die providing a preform including a support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using the placement head of the pick and place machine; placing the preform in contact with the die using the pick and place machine, the contact being via the second surface; attaching the sinterable film to the die; and separating the support film from the sinterable film.

22. 22. The method of claim 21, wherein the sinterable film comprises a stack of sinterable films.

23. 1. A method of attaching a clip, bond pad, or upper bridge structure to a die, the method comprising: Attaching a die to a substrate using the method of claim 18; applying a sinterable film to the die; contacting the sinterable film with a clip, bond pad, or upper bridge structure; sintering the sinterable film to attach the clip, the bond pad, or the upper bridge structure to the die; applying the sinterable film to the die 1. Providing a preform including a support film, the support film having a first surface and a second surface opposite the first surface, the support film having a sinterable film of metal particles deposited on the first surface but not on the second surface; providing a pick and place machine having a placement head; picking up the preform via the second surface using the placement head of the pick and place machine; placing the preform in contact with the die using the pick and place machine, the contact being via the sinterable film; attaching the sinterable film to the die; and separating the support film from the sinterable film.

24. 24. The method of claim 23, wherein the sinterable film comprises a stack of sinterable films.

25. 1. A method of manufacturing an electronic device, comprising: Attaching a die to a substrate using the method of claim 18; and attaching a clip, bond pad, or upper bridge structure to the die using the method of claim 23.

Images