Systems and methods for inserting molds for transparent substrates.

Abstract

Invention details;

Description

DIE PLACEMENT SYSTEM AND METHOD FOR TRANSPARENTSUBSTRATESInventors: Rainer Schramm Cyriac DevasiaRELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 443,866, filed February 7, 2023. This application is herein incorporated by reference, in its entirety, for all purposes.FIELD OF THE DISCLOSURE

[0002] The invention relates to micro-electronic packaging, and, more particularly, to a system and method for ensuring the precise positioning of a die to a substrate.BACKGROUND

[0003] The manufacture of integrated circuits (ICs) and other very small devices requires the precise positioning of individual ICs and / or other elements, such as optical elements, either of which is referred to herein as a die, on a substrate. These dies must be placed on and fixed to specific locations on a substrate such that they become electronically and / or optically connected to other components with which they are designed to interact.

[0004] The machine responsible for placing the dies on a substrate is referred to as a die placement system, thermo-compression bonding system, and, sometimes, a “die bonder” while placement of dies onto a substrate or a printed circuit board is generally referred to in the industry as a die placement, die attach, or die bonding operation. During a die placement operation, die positioning must be very precise and accurate to ensure that interconnections between the die and substrate are properly established.

[0005] Traditional alignment methods used in microelectronics use a localized camera system prior to placement to ensure high precision. Such localized camera systems either include multiple cameras, one to look down at the substrate and one to look up at the die (for aligning features onthe die bottom) or a single camera configured to look down at the substrate and die (for aligning features on top of the die) just prior to placement. In some cases, a single camera configured to look down at the substrate can be used to align the substrate with a feature on the die bottom, however, this requires that a portion of the die remain visible from the top during placement, which limits the geometry of placement tooling and may not be feasible for certain dies.

[0006] In systems requiring two cameras, the additional camera adds expense and complexity while taking up valuable space and making packaging of other elements of the system more difficult.

[0007] Additionally, there is a need to confirm accurate placement, both before and after curing of any epoxy used for bonding, to allow for repositioning and to prevent defective components from being shipped or subjected to further testing.

[0008] What is needed, therefore, are systems and methods that would allow for the use of a single camera to align features on a die bottom with corresponding features on a substrate while also allowing for correct placement to be confirmed.SUMMARY

[0009] Herein described are die bonding systems and methods of use that allow a die to be aligned with a substrate using an alignment camera configured to peer through the substrate, thereby also allowing proper placement to be confirmed, both before and after curing of an epoxy in an epoxy bonding operation.

[0010] Embodiments utilize a glass substrate in combination with an optical alignment camera while other embodiments utilize silicon substrates in combination with Short Wavelength Infrared (SWIR) cameras. Additional embodiments comprising other types of camera systems in combination with substrates that those camera systems are capable of peering through would be apparent to one of ordinary skill in the art and their use should understood to be within the scope of the teachings provided herein.

[0011] The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used inthe specification has been selected principally for readability and instructional purposes and not to limit the scope of the inventive subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is an illustration depicting a glass substrate with etched features, in accordance with embodiments of the present disclosure;

[0013] Figures 2A and 2B are illustrations depicting a die being attached to an etched feature of the substrate depicted in Figure 1, in accordance with embodiments of the present disclosure;

[0014] Figure 3A is an illustration depicting a glass substrate held in place by vacuum pedestals with a fixed UV source and an alignment camera disposed on an actuator positioned below the substrate, with the embodiment shown in Figure 3B replacing the fixed UV source with a UV source disposed on an actuator, in accordance with embodiments of the present disclosure;

[0015] Figures 4A and 4B are illustrations depicting a glass substrate held in place by vacuum pedestals with an alignment camera also on an actuator offering multiple degrees of freedom positioned below the substrate, with the embodiment shown in Figure 4B also including an optical element disposed on an actuator and configured to controllably direct laser energy towards the substrate, in accordance with embodiments of the present disclosure;

[0016] Figure 5 is a flowchart describing a method of bonding a die to a substrate, in accordance with embodiments of the present disclosure; and

[0017] Figure 6 is a schematic describing pyrometer and laser combining optics used in embodiments of the present disclosure.

[0018] These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. The accompanying drawings are not intended to be drawn to scale. For purposes of clarity, not every component may be labeled in every drawing.DETAILED DESCRIPTION

[0019] As a preliminary matter, the word “transparent,” as used herein, should be understood to refer to a material that allows light or other energy therethrough, such that objects behind thetransparent one can be observed by the alignment camera(s) discussed herein. While, in some cases, this refers to the use of a glass substrate with optical alignment camera(s), it should also be understood to include the use of an optically-opaque substrate, such as silicon, and an Infrared (IR) alignment camera, in embodiments a Short Wavelength IR alignment camera, a mm wave alignment camera, or any other type of alignment camera that would allow a die to be observed therethrough.

[0020] Now regarding die placement systems generally, traditional die placement systems used in microelectronics packaging typically use a localized camera system to align features of a die and substrate prior to placement and ensure high precision. Localized camera systems that currently include multiple cameras, one to look down at the substrate and one to look up at the die, which is needed for aligning features on the die bottom, can be simplified in cases where the substrate is transparent to the camera in use.

[0021] The die placement system 300 described herein utilizes a novel alignment camera layout that simplifies and reduces the cost of the die placement system 300 while freeing up valuable space thereon. More specifically, by utilizing a single alignment camera 302 configured to look up, through a transparent substrate 100 (i.e. a substrate that is transparent to the alignment camera 302) while simultaneously viewing a feature, features and / or alignment marks on a bottom of a die 102 and corresponding and / or complimentary feature, features 104, and / or alignment mark(s) on a top of a substrate 100, alignment of a die 102 and substrate 100 can be effectively achieved and / or confirmed / measured without requiring a second camera positioned above the substrate 100. This layout reduces cost, complexity, and packaging requirements while maintaining, or even improving on, alignment accuracy.

[0022] Figure 1 is an illustration depicting a substrate 100 with etched features 104 on which a die 102 is configured to be placed. In embodiments, the substrate 100 is glass. An etched feature 104 with die 102 attached thereto and etched feature 104 without die 102 are shown in more detail in Figures 2A and 2B, respectively.

[0023] Now referring to Figure 3A, Figure 3A depicts a die placement system 300 holding a substrate 100 in place using vacuum pedestals 304 and an alignment camera 302 disposed on an actuator 310 positioned below the substrate and configured to allow at least vertical motion of the camera, relative to the substrate 100. In such embodiments, the vacuum pedestals 304 secure thesubstrate 100 to the die placement system 300 using vacuum. The die 102 may be brought into contact with the substrate 100 using a gantry-mounted die bond head 308 or similar arrangement common in die bonding. Where the die placement system is used for epoxy bonding, a fixed UV source 306 comprising a ring of Light-Emitting Diodes (LEDs) or similar may be used for curing, a ring being used to avoid interference with the alignment camera 302.

[0024] Figure 3B depicts a die placement system 300 identical to that of Figure 3A, except that in Figure 3B the fixed UV source 306 is replaced by a UV source that can be moved along at least an X and Y axis (i.e. in the planes parallel to the substrate 100). This feature enables the UV source 306 to direct UV light to an interface between the die 102 and substrate 100 during an epoxy bonding operation, to cure the epoxy, and to move to the side, allowing the alignment camera to view the die 102 and substrate 100.

[0025] Notably, a UV source is only needed where UV-cured epoxy is being utilized and any type of die bonding requiring precise alignment of a die 102 and substrate 100 where transparent substrates can be used would benefit from the teachings described herein.

[0026] Figure 4A depicts another variation on the die placement system of Figures 3 A and 3B, wherein the alignment camera utilizes two actuators 310 to enable motion in two axis, in embodiments the X and Y axis. This feature allows the alignment camera 302 to find substrate 100 and die 102 features on, for example, opposite ends of each part, providing additional alignment precision.

[0027] Figure 4B depicts the die placement system of Figure 4A with a laser 400 and actuated mirror 410 configured to be actuated in after placement to direct laser energy towards the interface between the die 102 and substrate 100. Alternatively, a beam splitter with the appropriate coatings can be used without the need for an actuated mirror 410. This configuration provides the high heat necessary for, for example, reflow operations.

[0028] In embodiments, the substrate is moved to the vacuum pedestals using an XY or XY- Theta table. In other embodiments, however, the substrate is left stationary and the die placement system 300 is moved below the substrate 100, an arrangement that tends to be more space-efficient for systems with limited space on the machine deck.

[0029] In embodiments, the vacuum pedestals 304 are configured to move up and down, in embodiments by less than 5mm, to allow the substrate 100 to be moved along an X and Y axis.

[0030] In embodiments, a heated ring is used to apply heat around a bonding area to minimize thermal shocks, which is especially important during laser reflow operations.

[0031] In embodiments, the alignment camera 302 is mounted on an actuator 310 configured to allow the alignment camera 302 to be moved along a Z axis, allowing the alignment camera 302 to be moved to focus on the substrate 100 feature and the die 102 feature being aligned.

[0032] In embodiments, the alignment camera 302 is a Short-Wavelength Infrared (SWIR) camera, whose wavelength is preferably >1260nm. This allows the alignment camera 302 to be used with silicon and similar substrates. In addition to finding features on a top layer, such techniques can also be used to find features and / or markings on intermediate layers of a substrate 100 and / or die 102. In embodiments, this is accomplished using by moving the alignment camera 302 in Z, relative to the die 102 / substrate 100 to focus on a layer of interest; the bottom surface of the die 102 may be presented a small distance up in Z from its final placement position.

[0033] Regarding the actual act of attaching a die 102 to a substrate 100, a variety of methods could be applied. This disclosure, however, focuses on attaching dies using either epoxy and a UV source 306 or a laser to locally heat the substrate / die to reflow the layer on the bottom of the die or on top of the wafer, similar to performing a localized eutectic reflow, also called (LAB) laser assisted bonding.

[0034] A general method of aligning a die feature to a substrate feature using the systems described herein comprises using a die placement system 300 to pick up a die 102, in embodiments using a die bond head 308, and moving it to a nominal bonding location above a transparent substrate 100. An alignment camera system 302 installed below the transparent substrate 100 then images a substrate feature 104 and a die feature to be joined and calculates the difference in location, i.e. the offset, therebetween. The die bond head 308 or other conveyance mechanism then moves the die 102 by the required amount to center / align the features on the substrate 100 and die 102 (in embodiments, the substrate 100 could be lifted off of the vacuum pedestals 304 and moved, such as by an XY table). The die bond head 308 is then moved down to bring the die 102 on top of the substrate 100 for final attach, after which a UV source 306 or laser 400 and mirror 410 can be moved below the die feature and substrate feature to be joined and activated to bond the die feature to the substrate feature.

[0035] The method described generally above is described more specifically in Figure 5. More specifically, Figure 5 describes how, in embodiments, the method of bonding a die feature to a substrate feature comprises: Moving a transparent substrate 100 using an XY-Theta positioning table 500; positioning the transparent substrate to bring a bond site on the substrate over a vacuum (build) pedestal 502; actuating the pedestal in Z and securing the transparent substrate thereto using vacuum, alternatively, the transparent substrate can be lowered onto a fixed vacuum pedestal and secured 504; dispensing UV epoxy at the bond site for UV epoxy attach, alternatively, other attach methods may be used to secure the die after placement 506; picking a die using a bond head and bringing the die to a nominal XY-Theta location, but at a higher Z distance 508; moving an alignment camera positioned below the transparent substrate to find features on the transparent substrate and the die 510; moving the die using the bond head in XY-Theta to align the die feature to the substrate feature(s) 512; moving the die bond head 308 down in Z to place the die 102 on the substrate 100 514; if needed, a post placement measurement step can be implemented with the alignment camera system 302 positioned below the transparent substrate 100 516; retracting the alignment camera 302 in Z 518; actuating a UV source 306 under the vacuum pedestal 304 and energizing it 520; retracting the UV source 306522; moving a die bond head 308 up in Z 524; and, if needed, a post cure measurement step can be implemented with the camera system 302 below the glass 526.

[0036] In embodiments, initial positioning is within a few microns and final alignment is within a few nanometers.

[0037] Where a laser 400 is used for heating, the simplest way to heat the substrate 100 and die 102 is to direct a fixed laser beam of a certain size / diameter to match the size of the die 102. The required dose of laser power can be delivered to the area under the die 102 to achieve the desired result, e.g. reflow. Conveniently, the wavelength of the laser 400 can be tailored to either only heat the substrate 100, heat both substrate 100 and die 102, or primarily heat metal layers at the interface between die 102 and substrate 100.

[0038] In embodiments, a pyrometer 612 can be placed in the laser beam path to get temperature feedback of the area being heated. The pyrometer feedback can either be used to actively set or modulate the laser power to achieve a desired temperature profile. Alternatively, the pyrometer 612 can be used to sense temperature to maintain process stability, but not actively modulate laserpower. Suitable lasers 400 for this application include, but are not limited to, near IR, shortwave IR, picosecond, and femtosecond fast pulse lasers.

[0039] For relatively large dies 102, where a larger area needs to be heated for certain operations, such as to achieve uniform eutectic reflow, simply expanding the laser beam drops the power density, forcing the need for a significantly higher power laser 400. This is not practical in many cases, since it may be cost prohibitive. In other cases, a sufficiently high-power laser 400 at the desired wavelength may not be available. For such cases, the laser beam can be moved at high speeds to cover an area that matches the die size with high-speed scanning optics. This method allows the system to programmatically handle different die geometries. The laser power as well as the scanning pattern can be programmatically selected for each die size and type.

[0040] The pyrometer 612 may be integrated with the scanning optics to allow for temperature feedback along the scanned laser beam path. The pyrometer feedback can be used for active laser power modulation or as a temperature sensor to ensure process stability.

[0041] A particularly suitable pyrometer and laser combining optic 600 is provided in Figure 6. The optic 600 comprises an optics box 622 having a focusing lens 604 disposed in an aperture intended to face a workpiece 602, e.g. a substrate 100, during use.

[0042] In embodiments, the optics box 622 is configured to direct laser energy to the focusing lens 604 and radiation of a suitable wavelength emitted from the workpiece 602 during laser heating to the pyrometer 612 via a series of optical elements. For example, a dichroic beam combiner 606 could be used to redirect the laser beam towards the workpiece 602 from below while allowing a return signal to pass through and reach the pyrometer 612.

[0043] In embodiments, the dichroic beam combiner 606 relies on a laser turning mirror 614, a laser focusing optic 616, and a laser optical fiber coupler 618 to optically connect a laser 400 to the focusing lens 604, and ultimately the workpiece 602.

[0044] In embodiments, the pyrometer signal is configured to pass through a pyrometer focusing lens 608 and pyrometer optical fiber coupler 610 after passing through the dichroic beam analyzer 606 before reaching the pyrometer 612.

[0045] The arrangements described herein provide a simpler and faster way to align and bond a die to a substrate and can be used in various types of die and other bonding and / or microelectronics packaging operations.

[0046] The foregoing description of the embodiments of the present disclosure has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto.

[0047] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the disclosure. Although operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

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