System and method for solder paste printing on components

Abstract

The present invention provides systems and methods in which dot-shaped portions of a material (e.g., a viscous material such as solder paste) are printed or otherwise transferred onto an electronic component at a first printing unit, and the electronic component is subsequently placed onto a substrate, with the portions of viscous material between the electronic component and the substrate. Optionally, the printing unit that dot-prints the material onto the electronic component includes a coating system that forms a uniform layer of the material on a donor substrate, and the material is transferred from the donor substrate to the electronic component in individual dot-shaped portions by the printing unit. The system may also include an imaging unit to assist in the overall process.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent No. 62 / 981,900, filed on February 26, 2020. Technical Field

[0003] The present invention relates to a system and method for printing solder paste from a coated film onto an electronic component and placing the electronic component on a substrate with the solder paste therebetween. Background Art

[0004] Surface mount technology (SMT) is a field of electronic assembly used to mount electronic components to the surface of a printed circuit board (PCB) rather than inserting the components through holes in the PCB as in conventional assembly. SMT was developed to reduce manufacturing costs and allow for efficient use of PCB space. Due to the introduction of surface mount technology and increasing automation, it is now possible to assemble highly complex electronic circuits into smaller and smaller assemblies with good repeatability.

[0005] The surface mount soldering process involves placing the electrical contacts of an electronic component or substrate, a small amount of solder paste, and solder-wettable pads adjacent to each other on a printed circuit board. The material is then heated until the solder reflows, thereby forming an electrical connection between the solder-wettable pads and the electrical contacts of the electronic component. Once the solder reflows, it forms both an electrical and mechanical connection between the electronic component and the printed circuit board. Compared to other interconnection methods, this process has many advantages because components can be interconnected simultaneously, and the process is repeatable, low-cost, and easily adaptable to large-scale production.

[0006] One of the most important parts of the surface mount assembly process is applying solder paste to the printed circuit board. The goal of this process is to accurately deposit the correct amount of solder onto each of the pads to be soldered. Typically, this is achieved by screen printing the solder paste through a stencil or foil, but it can also be achieved by jet printing. It is generally believed that this part of the process (if not properly controlled) can account for the majority of assembly defects.

[0007] Solder paste itself is a mixture of flux components and powdered solder metal alloys, which is widely used in the electronics industry. At room temperature, solder paste has enough flexibility that it can be made to conform to almost any shape. At the same time, it has enough "tacky" to make it easy to adhere to any surface it is placed in contact with. These properties make solder paste useful for surface mount soldering and can also be used to form solder bumps on electronic components such as ball grid array packages or on printed circuit boards.

[0008] Solder paste printing is a critical stage in today's surface mount assembly process. When using a stencil or film for printing, several factors can negatively impact the process, leading to defects in the final product. For example, the stencil itself must be very accurate: a stencil that is too thick will result in solder bridges, while one that is too thin will result in insufficient solder being applied. Similarly, when the stencil aperture is too large, solder bridges can occur, while when the stencil aperture is too small, insufficient solder paste will be applied. It's generally considered best to use a circular stencil aperture that is slightly smaller than the PCB pad size to prevent bridging defects during reflow. However, defects can occur during stencil production.

[0009] The squeegee used for screen printing should also be optimized: the squeegee angle affects the vertical force applied to the solder paste. If the angle is too small, the solder paste will not be squeezed into the stencil orifices. If the squeegee pressure is too low, it will prevent the solder paste from being applied cleanly to the stencil, while if the squeegee pressure is too high, it will cause more solder paste to leak.

[0010] Another key point is that the higher the printing speed, the less time it takes to apply the solder paste through the stencil orifice surface, and therefore a higher printing speed may result in an insufficient amount of solder being applied. In current processes, the printing speed should be controlled at approximately 20 mm / s to 40 mm / s, and therefore the maximum speed is currently limited by the printing process.

[0011] Because solder paste is a high-viscosity thixotropic material, and therefore jetting is quite complicated due to the fact that most jet heads are designed for low-viscosity materials and are easily clogged, the use of jet printing for this process has been limited. However, extensive work in this field shows that jetting and dispensing are very promising methods. For example, see the following documents: WO 2007 / 084888 A2, US PGPUB 2011 / 0017841 A1, U.S. Patent No. 9,808,822 B2, and U.S. Patent No. 8,740,040 B2. Although very promising, the jetting of viscous materials can produce some unwanted debris and form defects in the final assembly. Compared to laser-based processes, it is also a slow process that depends on the mechanics of the dispenser. Summary of the Invention

[0012] The present inventors have recognized that it is desirable to jet print solder paste material, but in a manner that does not cause defects in the final assembly. To this end, the inventors have developed systems and methods that involve jetting solder paste directly onto electronic components during or prior to the "pick and place" stage of mounting the components on a PCB, thereby solving the problem of jetting failure while avoiding the problems caused by the screen printing process.

[0013] In one embodiment of the present invention, a solder paste printing system is configured for printing solder directly onto electronic components held across a very well-defined gap by a "pick and place" machine. The system may include one or more imaging devices for monitoring and controlling various processes.

[0014] In some embodiments of the present invention, the printing system includes a coating system that forms a uniform layer of printed material on a substrate. In the presence of, the coating system may include a syringe and air or mechanical pump for printing the material, which drives the material onto a donor or carrier substrate. The donor substrate is then moved toward and through the well-defined gap between a roller or a knife to form a uniform layer of printed material with a thickness defined by the gap. Alternatively, the coating system may include a screen printing module in which the material is coated on a stencil of a screen or a film with well-defined holes, and a scraper or a scraper is used to transfer the material to the substrate in a soft or hard-jointed manner. In a further embodiment of the present invention, the coating system may include a dispenser or inkjet head, gravure printing system or micro-gravure printing system, a slot die system for printing the material onto the substrate, or a roller coating system for coating a highly uniform layer of material to be printed on the substrate. The coating system may be housed in a closed room with a controlled environment (cold or hot) to prevent solvents from evaporating from the printed material or to prevent material oxidation, thereby extending the life of the material. Furthermore, the coating system can include more than one material, thereby creating the possibility of printing multiple materials onto an intermediate substrate in a controlled sequence and enabling the printing of more than one material onto a final substrate. Within the coating system, the donor substrate can be translated in a controlled manner, bidirectionally or otherwise, for example, while opening the gap between the coating rollers, creating the possibility of re-coating the same area of the donor substrate with printed material without contaminating the rollers and reducing or eliminating the amount of substrate consumed during the initial printing process, thereby avoiding waste.

[0015] In various embodiments of the present invention, the printed material may be a solder paste or other metal paste, a metal paste or a ceramic paste, an adhesive, a polymer material, or a mixture of polymer and monomer materials for printed electronics.

[0016] The printing process can use a laser-based system that includes a high-frequency laser to enable the material to be ejected from one substrate to another. Either can use a laser-assisted deposition system / laser dispensing system that rotates 0 to 90 degrees or 90 to 180 degrees from the main axis of the gravity field in which it is located, thereby simplifying the mechanical structure without reducing the printing quality.

[0017] In some embodiments of the present invention, the printing unit includes a gap control unit configured to maintain a very well-defined gap between the donor substrate and the electronic component. For example, a very well-defined gap between the coated substrate and the electronic component can be maintained by a plane of three actuators at the corners of the control unit (which allows both translation and rotation), as mentioned in US PGPUB2005 / 109734A1, US Patent No. 6,122,036A, WO2016 / 198291 and EP 3,219,412 A1. Such actuators can be used at the corners of the control unit for both the coated substrate and the electronic component to allow translation and rotation in two planes, where the two planes are independent or overlap each other.

[0018] In another embodiment of the present invention, a very well-defined gap between the donor substrate and the electronic component is achieved by providing a fixed gap between the two.

[0019] In some embodiments of the present invention, the intermediate substrate may be a continuous transparent film substrate, a transparent film substrate coated with a metal layer or a metal layer and a dielectric layer, or a transparent solid substrate.

[0020] In some embodiments of the present invention, a pick-and-place machine holds the electronic component beneath the printing system and transfers it to the PCB. Additionally, the printed image can be processed by an imaging system. Such an imaging system can be a microscope or a charge-coupled device (CCD) that photographs the printed material dots on the electronic component and measures them in two dimensions, then processes the measurement data for accurate deposition on the final substrate. Alternatively, the imaging system can be a three-dimensional (3D) microscope that photographs the printed material dots on an intermediate substrate and measures them in three dimensions, then transfers the measurement data to the pick-and-place unit for accurate deposition on the final substrate. In further embodiments of the present invention, the imaging system is two microscopes or CCDs, arranged so that one can image the printed material dots on the electronic component and measure them in two dimensions (e.g., length and width), while the other measures them in a third dimension (e.g., height), then transfers all measurement data to the pick-and-place unit for accurate deposition on the final substrate. In any case, the imaging system can be included during and / or after the printing process and can acquire images of the electronic component. In one embodiment of the present invention, the imaging system at the printing unit may employ mirrors to obtain images from the surface of the electronic component and / or the main laser channel of the printing unit to simultaneously image both the dot size and the target area of the final substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

[0022] Figure 1 Conceptually depicted is a system configured in accordance with an embodiment of the present invention that employs a narrow-gap laser-based printing system to provide high-resolution and high-speed printing of solder paste, and a “pick and place” placement system to achieve very high yields and accurately and securely place electronic components on a PCB board.

[0023] Figure 2a and 2b Schematically depicts the Figure 1 A conceptual overview is presented to configure various aspects of the system.

[0024] Figure 3 Draws the basis Figure 2a-2b The schematic diagram shown is an example of a system arrangement that uses a coated substrate, a laser-based printing system, a "pick and place" machine to hold the electronic components, and an optional imaging system prior to placement of the electronic components.

[0025] Figure 4a and 4b Depicted is a method of depositing a material onto a film substrate by a syringe according to some embodiments of the present invention. Figure 4a ) and passing the material through a well-defined gap to form a uniform layer ( Figure 4b ) to form a uniform film.

[0026] Figure 5 Aspects of using a primary laser channel or mirror to image a point on a solid or film substrate are depicted according to some embodiments of the present invention. DETAILED DESCRIPTION

[0027] The present invention relates to systems and methods for printing solder paste at high resolution on top of electronic components at very high rates, for example, printing solder paste directly on top of the electronic components from a coated film, and subsequently placing the electronic components directly onto a substrate (e.g., a PCB or other substrate). The printing process can be performed using a laser assisted deposition / laser dispensing system to achieve high resolution at high speeds. The electronic components can be any electronic components used in SMT processes, for example, capacitors, resistors, diodes, chips, complete integrated circuits, or any other components. The placement of the electronic components on the substrate can be performed using a "pick and place" machine that holds the components and exposes the back side of the components to print solder paste thereon, and places the components on the PCB with the printed solder paste between the components and the substrate.

[0028] In some cases, multiple materials can be printed onto an electronic component. For example, after printing a first material in the manner described above, the electronic component can be maintained beneath the printing unit until a second (or additional) material is dispensed onto the electronic component from the coated film at one or more locations. The second (or additional) material can be applied to the coated film before or after the first material is printed onto the electronic component. Using this method, multiple materials can be printed onto the electronic component approximately simultaneously. It is even possible to have multiple coated films within a single printing area simultaneously, allowing the various materials coated on multiple films to be printed approximately simultaneously by scanning a laser or other print head over the coated films while maintaining the electronic component within the single printing area. An example of using multiple materials with an electronic component is adhesive printing. In such cases, the mixture of two materials can trigger a reaction between the materials (as with epoxyamine or silanol-platinum catalysts). To this end, the materials do not mix at the coated substrate, but only after printing onto the electronic component. This avoids clogging of the print head and other undesirable side effects.

[0029] Before describing the present invention in detail, Figure 1 As is helpful, the figure provides a conceptual overview of a system 10 according to an embodiment of the present invention that employs a narrow or contact gap printing system 12 for printing solder paste (or other material) directly onto an electronic component, performing pre-print processing and / or inspection 14, and positioning the component with the solder paste printed thereon for pick-up and placement on a PCB or other substrate 16. As further described below, the narrow or contact gap printing system may include initially applying the solder paste to a donor substrate. As part of the pre-print processing and / or inspection 14, the solder paste printed on the component may be observed by one or more imaging devices for monitoring and controlling the initial and subsequent processes. Then, when the component is placed on a PCB or other substrate (with the previously printed solder paste disposed between the component and the PCB), the positioning process may also be observed by one or more imaging devices.

[0030] In one embodiment of the procedure, during the first printing process 12, solder paste is distributed on the component in the form of dots (e.g., small, generally circular spots or droplets), and the solder joints on the component are observed by an imaging system before the component is placed on the PCB (wherein the solder joints are located between the component and the PCB). The solder joints can be printed onto the component by a laser-assisted deposition / laser dispensing system printing unit, in which a fast frequency laser is used to spray the solder joints from a uniform layer of solder paste on a coated substrate onto the component. The spraying of the material is carried out in a well-defined and stable manner to maintain a low dot size distribution. In such an arrangement, the coated substrate plays an important role in the stability of the system. Therefore, an additional coating system can be added before the first printing unit. Such a coating system can be a traditional coating system based on a micro-gravure or slot die coater, or a roller coating system. It can also be a coating system based on screen printing, a dispenser, or an inkjet system.

[0031] Figure 2a and 2b Schematically depicts the Figure 1 The conceptual overview presented provides aspects of various systems 20a, 20b that can be configured. Each of these systems separates the solder jetting process from the component placement process.

[0032] exist Figure 2b , printing system 20b includes a coating system 22 that forms a uniform layer 26 of material to be printed (e.g., solder paste) on a donor substrate 28. In one embodiment of the invention, coating system 22 includes a syringe and an air or mechanical pump that drives the material onto the donor substrate 28 to be printed. Subsequently, a motor, rollers, or the like is used to move the donor substrate 28 toward a well-defined gap between the rollers or knives to form a uniform layer 26 of material to be printed having a thickness defined by the gap. In some embodiments of the invention, the donor substrate 28 can be translated bi-directionally in a controlled manner while opening the gap between the coater rollers, creating the possibility of re-coating the same area of the donor substrate with material to be printed without contaminating the rollers and reducing or eliminating the amount of substrate consumed during the initial printing process, thereby avoiding waste.

[0033] In a further embodiment, the coating system 22 may include a screen printing module, wherein a screen or stencil with well-defined holes is used to coat the donor substrate 28, a scraper or squeegee is used to apply the viscous material thereto, and the viscous material is subsequently transferred to the donor substrate 28 in a soft or hard bond manner. Alternatively, the coating system 22 may include a dispenser or inkjet head to print the viscous material onto the donor substrate 28. Alternatively, the coating system 22 may be a gravure printing system or a micro-gravure printing system that coats a highly uniform layer 26 of material to be printed on the donor substrate 28. In one embodiment of the present invention, the coating system 22 is a slot die system that coats a highly uniform layer 26 of material to be printed on the donor substrate 28. In another embodiment of the present invention, the coating system 22 is a roller coating system that coats a highly uniform layer 26 of material to be printed on the donor substrate 28. Although not shown in detail, Figure 2a The printing system 20a may also include a coating system, such as coating system 22 , as part of the laser-based printing system 30 .

[0034] like Figure 2a As shown in FIG, in one embodiment of the present invention, a laser-based printing system 30 (which may include a laser-based printing unit 32 and, optionally, a coating system 22) may be housed within a sealed chamber 34 with a controlled environment (cold or hot) to prevent solvent evaporation from the material to be printed or to prevent oxidation of the material, thereby extending the life of the material. In some embodiments of the present invention, the coating system 22 contains more than one material, thereby creating the possibility of printing multiple materials onto an electrical component in a controlled sequence and enabling the printing of more than one material onto a final substrate 38.

[0035] Return to Figure 2b , a laser-based printing unit 32 prints dots 24 of solder paste from the coated substrate 28 directly onto the electrical contacts of the electrical component 34. The laser-based printing unit 32 used in the narrow gap / contact printing process 30 may include a laser-based system including a high-frequency laser configured to eject portions of a layer of coated material 26 from the donor substrate 28 to the electrical component 34 via a laser-assisted deposition / laser-dispensing system. The laser-assisted deposition system / laser-dispensing system may be rotated from 0 to 90 degrees or 90 to 180 degrees from the main axis of the gravity field in which it is located, thereby enabling simplification of the mechanical structure without compromising print quality.

[0036] Alternatively, without using a coating system, the narrow gap / contact printing process 30 may employ an inkjet head system capable of jetting solder paste directly onto the electrical component 34. Alternatively, the narrow gap / contact printing process 30 may employ a dispenser head system capable of printing material directly onto the electrical component 34. Further, the narrow gap / contact printing process 30 may employ an offset printing module, a gravure printing module, or any conventional printing technology to print material directly onto the electrical component 34. For example, the narrow gap / contact printing process 30 may employ a screen printing module, wherein the material to be printed is applied to a stencil such as a screen or film having well-defined apertures, and a doctor blade or squeegee is used to transfer the material to the electrical component 34 in a soft or hard bond manner, thereby forming an array of dots of the material to be printed on the electrical component 34.

[0037] In some embodiments of the present invention, the first printing unit 32 employed in the narrow gap printing process 30 includes a very well-defined gap control unit between the donor substrate 28 and the electrical component 34. In one embodiment, a set of three actuators at the corners of the control unit (which allows both translation and rotation) is used to maintain a very well-defined gap between the donor substrate 28 and the electrical component 34, as described in US PGPUB 2005 / 109734 A1, US Patent No. 6,122,036A, WO 2016 / 198291, and EP 3,219,412 A1, which are incorporated herein by reference. Multiple sets of three actuator units can be used at the corners of the control unit for both the donor substrate and the electrical component 34 to allow translation and rotation in two planes, where the two planes are independent or overlapping. Alternatively, a very well-defined gap between the donor substrate 28 and the electrical component 34 can be maintained by providing fixed support below the donor substrate and / or the electrical component 34.

[0038] In some embodiments of the present invention, after the electrical components 34 are printed in the first printing unit 32, the printed electrical components 34 may be returned to the first printing unit 32 for a second printing of the adhesive material. In any case, after being printed with the adhesive material (in the form of dots 24 or other arrangements), the electrical components 34 are moved from the first printing unit 32 toward a substrate 38 (e.g., a PCB), where they are placed between the respective electrical components 34 and the substrate 38 along with the printed solder paste and / or other adhesive material.

[0039] In some embodiments of the present invention, during the movement of the electrical component 34 from the first printing unit 32 to the substrate 38 on which the component is placed, the material (e.g., solder paste) printed on the electrical component 34 can be processed by the imaging system 50 (see, e.g., Figure 2a). Such an imaging system 50 can be one or more microscopes, charge coupled devices (CCDs), and / or other imaging components that take a picture (or multiple pictures) of the printed dots of material 24 on the electrical component 34 and measure the dots in two or three dimensions. For example, the imaging system 50 may include: two microscopes or CCDs, which are arranged so that one of them can image the printed dots on the intermediate substrate and measure the dots in two dimensions (e.g., length and width), while the other one measures the dots in a third dimension (e.g., height). This measurement data can then be transferred to the pick and place machine 44 to ensure that the electrical component 34 is accurately deposited on the substrate 38. For example and as Figure 2a As shown, optical or other imaging inspection can reveal that while many of the dots 24 are suitable for transfer of the electrical components 34 to the substrate 38 (e.g., depicted in the figure with check marks), some of the dots 24 are misshapen or otherwise unsuitable for transfer to the final substrate 38 (e.g., depicted in the figure with "X"s). A controller (not shown) having access to this data can then operate the pick and place machine 44 to omit transfer of unsuitable ones of the unsuitable electrical components 34 to the substrate 38. An imaging system can also be included after placement of the electrical components 34 to ensure proper placement of those components. In one embodiment of the present invention, the imaging system is located at the printing unit 32, and a mirror or other optical component for obtaining an image from the surface of the electrical components 34 and / or the laser channels 52 of the printing unit can be used to image both the size of the dots and the electrical components.

[0040] Figure 3 An example of a system 60 configured in accordance with the present invention is shown. System 60 embodies aspects of systems 20a and 20b described above. Specifically, system 60 includes a coating system 22 that uses air or a mechanical pump (not shown) to drive solder paste 62 from a reservoir (e.g., a syringe 64) onto a donor substrate 28 to form a uniform layer 26 of solder paste (and / or other materials) 62 on the donor substrate 28. Rollers or gears 66 are then used to move the donor substrate 28 toward a well-defined gap 70 between rollers or knives 72 to form a uniform layer 26 of solder paste on the donor substrate 28, the uniform layer having a thickness defined by the gap 70.

[0041] The system 60 also includes a laser-based printing unit 32 configured to produce dots 24 of solder paste 62 on the electrical component 34. In this example, the donor substrate 28 can be a transparent film, and the laser-based printing unit 32 includes a laser module 74 containing a high-frequency laser that is arranged to eject portions of the layer of applied material 26 from the donor substrate 28 to form the dots 24 on the electrical component 34 by focusing a laser beam 76 onto the interface between the layers of material 26. The incident laser beam causes localized heating, followed by a phase change and high localized pressure that drives the solder paste 62 to be ejected onto the electrical component 34. After printing onto the electrical component 34, the printed electrical component can be returned for printing of a second (or additional) layer of solder paste 62, if needed or desired.

[0042] Alternatively, the donor substrate 28 may be a screen or grid, wherein the solder paste 62 is introduced into the holes of the screen by an applicator 72 (which may be a roller or a doctor blade). In such a case, an incident laser beam 76 from a laser module 74 causes the solder paste to be displaced from the holes in the screen onto the electrical components 34.

[0043] Once the dots 24 are printed on the electrical component 34, the component 34 is moved toward an inspection area of an imaging system 50 by, for example, a pick and place machine 44, which includes one or more 3D and / or 2D imaging components configured to take a picture of the printed dots 24 of solder paste and measure the dots in two or three dimensions. The measurement data can be used by the pick and place machine 44 to ensure that the component 34 is accurately deposited on the final substrate 38 and / or to return the component to the solder paste printing area to apply new or additional solder paste dots 24.

[0044] After inspection by the imaging system 50, if the existing solder joints 24 are deemed acceptable, the component 34 is moved by the pick and place machine 44 so as to be positioned over the area of the PCB substrate 38 where the component is to be placed. A two-dimensional platform 90 may be used to correctly position the PCB substrate 38 so that it is properly oriented to receive the component 34. The component 34 is then placed on the PCB substrate 38 with the solder joints 24 between the component and the PCB substrate to secure the component in place on the PCB substrate.

[0045] Although not shown, an additional inspection unit (similar to inspection unit 50) may be associated with the area where components 34 are placed on PCB substrate 38. The inspection unit may include a mirror or other optical component for obtaining an image from the surface of the PCB substrate to assist in aligning the PCB substrate beneath electronic components 34 via platform 90 and to assist in synchronizing the placement of electronic components on the PCB substrate.

[0046] An alternative arrangement of the laser-based printing unit 32 may include a coating system 22 in which the solder paste 62 is driven from a reservoir (e.g., a syringe 64) to a roller using air or a mechanical pump. The thickness of the material layer on the roller can be maintained uniform using one or more knives that are displaced a defined distance above the surface of the roller. The roller may be concave or otherwise formed with a recess to accommodate a defined amount of material to be printed, wherein the amount is transferred to the printing roller when the two rollers contact each other in the material transfer area. Alternatively, the roller may have a screen or grid-like surface with holes, wherein the solder paste is introduced into such holes. When the roller completes its rotation through the printing area, it transfers the solder paste in the form of dots to the electrical components. After transferring the material from the roller, the roller may pass through an inspection area, and a knife or other tool may be used to remove any residual solder paste before applying new solder paste.

[0047] When transferring solder paste from the donor substrate 28 to the electronic component 34, for example, using one of the techniques described above, a very well-defined gap 112 can be maintained between the coated donor substrate 28 and the electronic component 34 by positioning the rollers 66 and / or the electronic component 34 to receive the solder paste. The width of the gap can be monitored by one or more inspection units (not shown) and maintained by an appropriate control system (not shown). Furthermore, although Figure 3 While the system is shown oriented in a vertical manner (relative to the deposition of solder paste dots 24 onto electronic components 34 and the deposition of electronic components 34 onto substrate 38), one or both of these operations can be performed at 90 degrees (or any other orientation) relative to the gravitational field in which the system 60 is located. By way of example, in the illustration, if the gravitational field is assumed to be from the top of the page to the bottom of the page, the laser-based printing unit can be configured to print solder paste dots 24 from the donor substrate 28 to the electronic components 34 at an angle orthogonal to the gravitational field. Such an arrangement can provide a more compact configuration than shown in the illustration.

[0048] Figure 4a and 4b Further depicted is the use of a syringe 64 ( Figure 4a ) placing a quantity of material 62 on the film substrate 28 and passing the material through a well-defined gap 126 to form a uniform layer 26 of solder paste ( Figure 4b ) forms a uniform layer 26 of solder paste on a donor substrate 28. A well-defined gap 126 is formed by bringing a pair of rollers 128a, 128b or knives close together using an appropriate control unit (e.g., a stepper motor or piezoelectric transducer).

[0049] Figure 5Various aspects of imaging solder paste dots 24 of an electronic component 34 using a main laser channel are depicted according to some embodiments of the present invention. In this example, dots 24 of solder paste have been printed on the electronic component 34, and a camera 196 is used to image the dots via the main laser channel. Alternatively, the camera 196 can be offset from the main laser channel and a semi-transparent mirror 198 inserted therein to reflect the image of the dots 24 toward the camera. Such imaging can be used to ensure that the dots of material are optimally placed on the electronic component. Similar imaging systems using cameras and mirrors can be used to monitor the placement of electronic components on a PCB substrate from the top and / or from the side (although there is no laser at this transfer point).

[0050] Thus, systems and methods for printing solder paste from a coated film onto an electronic component and placing the electronic component on a substrate with solder paste therebetween have been described. In various embodiments, these systems and methods employ a multi-step process in which solder paste is dispensed onto a donor substrate and then printed onto the electronic component before the electronic component is finally secured to the substrate. As the solder paste and / or electronic component undergo the various steps throughout the process, they may undergo one or more imaging steps. In order to achieve a very narrow dot size distribution when printing onto the electronic component, it is important to have a very clearly defined distance control between the coated donor substrate and the electronic component. To achieve this, any of several mechanical solutions can be used. For example, the distance between the coated donor substrate (which may be a film or foil) and the electronic component can be controlled by using a mechanical, clearly defined foil or two rollers adjacent to each other. Alternatively, the distance between the coated donor substrate and the electronic component can be decisively defined by having both the coated donor substrate and the electronic component located on the same machine.

[0051] To enhance jet placement and resolution during printing, an imaging system can be added to monitor the size and position of the printed dots on the electronic component and the final substrate. To this end, one or more imaging systems can be added to monitor both the electronic component and the final substrate. Such imaging systems can use a CCD, a microscope, or a 3D microscope and computer software to monitor the dot size and / or dot height on the electronic component at an angle perpendicular to the plane of the electronic component. Monitoring can be performed before and / or after the component is placed on the final substrate.

[0052] Although not illustrated in detail, it should be understood that the various components of the systems described herein operate under the control of one or more controllers, preferably processor-based controllers that operate under the instructions of machine-executable instructions stored on a tangible, machine-readable medium. Such controllers may include a microprocessor and memory, which are communicatively coupled to each other via a bus or other communication mechanism for transmitting information. The memory may include program code memory (such as read-only memory (ROM) or other static storage device) and dynamic memory (such as random access memory (RAM) or other dynamic storage device), and each may be coupled to the bus to provide and store information and instructions executed by the microprocessor. The dynamic memory may also be used to store temporary variables or other intermediate information during the execution of instructions by the microprocessor. Alternatively or in addition, a storage device (such as solid-state memory, magnetic disk, or optical disk) may be provided and coupled to the bus to store information and instructions. The controller may also include a display (for displaying information to a user) and various input devices (including an alphanumeric keyboard and a cursor control device (such as a mouse and / or touchpad)) as part of a user interface for the printing system. In addition, one or more communication interfaces may be included to provide two-way data communication to and from the printing system. For example, a network interface including a wired and / or wireless modem may be used to provide such communication.

[0053] Then, in various embodiments, the present invention provides:

[0054] Systems and methods that enable solder paste or other viscous materials (e.g., high viscosity polymers, acrylics, epoxies, adhesives (e.g., urethane-based adhesives), pastes, or waxes) to be printed directly onto electronic components at high resolution and high speed using a laser-based printing unit and placing the components on a PCB or other substrate using "pick and place" techniques.

[0055] A system and method for printing a viscous material (such as solder paste, or any of the materials identified above) onto an electronic component (which is then placed on a final substrate) includes a printing unit and, optionally, a coating unit.

[0056] A system or method as in any of the preceding embodiments, wherein the printing unit is highly accurate, produces low to no debris, and is very fast.

[0057] A system or method as described in any of the foregoing embodiments, wherein the printing unit includes a coating system that forms a uniform layer of viscous material on the substrate, and the coating system includes a syringe of viscous material and an air or mechanical pump that drives the viscous material onto the carrier substrate and then moves the carrier substrate toward a well-defined gap between the roller and the knife (for example, using a motor or roller, etc.) to form a uniform layer of viscous material (whose thickness is defined by the gap) on the carrier substrate.

[0058] A system or method as described in any of the preceding embodiments, wherein the coating system includes a screen printing module, a dispenser or an inkjet head, a gravure printing system or a micro-gravure printing system, a slot die system, or a roller coating system, the coating system being within a sealed chamber with a controlled environment to extend the useful life of the viscous material.

[0059] A system or method as in any of the preceding embodiments, wherein the coating system comprises more than one material, thereby creating the possibility of printing multiple materials onto an electronic component in a controlled sequence.

[0060] A system or method as described in any of the foregoing embodiments, wherein the carrier substrate can be translated bi-directionally in a controlled manner while opening the gap between the coating rollers, thereby creating the possibility of re-coating the same area of the carrier substrate with viscous material multiple times without contaminating the rollers to reduce waste.

[0061] A system or method as in any of the preceding embodiments, wherein the viscous material is solder paste, metal paste, adhesive for printed electronics, or other viscous material.

[0062] A system or method as described in any of the preceding embodiments, wherein the printing unit is a laser-based system comprising a high-frequency laser to enable the ejection of viscous material from a coated substrate to the electronic component, and the printing unit is a laser-assisted deposition / laser-dispensing system that is rotated 0 to 90 degrees or 90 to 180 degrees from the main axis of the gravitational field in which it is located.

[0063] A system or method as described in any of the aforementioned embodiments, wherein the printing unit includes a very well-defined gap control unit between the coated substrate and the electronic component, wherein the gap control is achieved by: a plane of three actuators at the corners of the gap control unit that allows both translation and rotation, or a plane of three actuators at the corners of the gap control unit established for both the coated substrate and the electronic component to allow both translation and rotation in two planes and wherein the two planes are independent or overlap each other, or form a fixed mechanical gap.

[0064] A system or method as in any of the preceding embodiments, wherein a continuous transparent film substrate is used as a coated substrate for the system, and the transparent film substrate is coated with a metal layer or with a metal and a dielectric layer.

[0065] A system or method as in any of the preceding embodiments, wherein placement of electronic components is accomplished by a "pick and place machine" with and without an imaging system.

[0066] A system or method as described in any of the aforementioned embodiments, wherein either of the imaging systems is a microscope or CCD that takes pictures of solder paste on an electronic component and measures points in two dimensions; or a 3D microscope that takes pictures of printed solder paste on an electronic component and measures points in three dimensions; or two microscopes or CCDs that are arranged so that one can take pictures of printed solder paste on an electronic component and measure points in two dimensions, while the other measures the solder paste in a third dimension that is orthogonal to the other two dimensions, or wherein the imaging system is located in the printing unit itself and uses a mirror to image the surface of the electronic component, or uses a main laser channel to simultaneously image both the printed solder area size and the electronic component.

Claims

1. A system (20a, 20b, 60), comprising: A laser-based printing system (30) comprising a coating system (22) configured to form a uniform layer (26) of an adhesive material (62) on a donor substrate (28), and a laser-based printing unit (32) configured to print a plurality of dot-shaped portions (24) of the adhesive material (62) from the donor substrate (28) onto an electronic component (34); and a pick-and-place unit (16) configured to place the electronic component (34) having the dot-shaped portion (24) of the adhesive material (62) printed thereon onto a substrate (38) such that the dot-shaped portion (24) of the adhesive material (62) is disposed between the electronic component (34) and the substrate (38), wherein the laser-based printing unit (32) is configured to print the individual dot-shaped portions (24) of the adhesive material (62) from the donor substrate (28) onto the electronic component (34) while the electronic component (34) is held by the pick and place unit (16) such that a first gap (112) is maintained between the donor substrate (28) and the electronic component (34), and wherein the coating system (22) comprises a syringe (64) of the viscous material (62) arranged to drive the viscous material (62) onto the donor substrate (28), and the coating system (22) is further configured to convey the donor substrate (28) having the viscous material (62) thereon toward and through a second gap (126) between rollers (128a, 128b) or knives to form the uniform layer (26) of the viscous material (62) on the donor substrate (28), the uniform layer (26) of the viscous material (62) having a thickness defined by the second gap (126).

2. The system (20a, 20b, 60) of claim 1, wherein the coating system (22) is configured to apply more than one material to the donor substrate (28) in a plurality of printing procedures.

3. The system (20a, 20b, 60) of claim 1 or 2, wherein the viscous material (62) is one of the following: solder paste or adhesive.

4. The system (20a, 20b, 60) of claim 1 or 2, wherein the viscous material (62) is a polymer material.

5. The system (20a, 20b, 60) according to claim 1 or 2, wherein the viscous material (62) is one of the following: a metal paste, a ceramic paste, a wax material, an acrylic, or an epoxy resin.

6. The system (20a, 20b, 60) of claim 1 or 2, wherein the laser-based printing unit (32) comprises: (a) a high-frequency laser configured to eject the dot-shaped portion (24) of the viscous material (62) from the donor substrate (28) to the electronic component (34); (b) an inkjet head system configured to eject the dot-shaped portion (24) of the viscous material (62) directly onto the electronic component (34); (c) a dispenser head system configured to print the dot-shaped portion (24) of the viscous material (62) directly onto the electronic component (34); (d) offset printing machine module; (e) gravure printing module; (f) another printing module configured to print the dot-shaped portions (24) of the adhesive material (62) directly onto the electronic component (34); or (g) A laser-assisted deposition / laser-dispensing system that is rotated from 0 to 90 degrees or from 90 to 180 degrees from the principal axis of the gravitational field in which it is located.

7. The system (20a, 20b, 60) of claim 1 or 2, further comprising one or more imaging systems (50) arranged to image: (i) the dot-shaped portions (24) of the adhesive material (62) printed on the electronic component (34) during movement of the electronic component (34) from the laser-based printing unit (32) to the substrate; (ii) the electronic component (34) after the electronic component (34) has been placed on the substrate (38); or (iii) both.

8. The system (20a, 20b, 60) of claim 7, wherein at least one of the one or more imaging systems (50) is configured to measure the dot-shaped portion (24) of the adhesive material (62) printed on the electronic component (34) in two or three dimensions during movement of the electronic component (34) from the laser-based printing unit (32) to the substrate (38).

9. A method for printing a material onto an electronic component, comprising: A coating system (22) using a laser-based printing system (30) forms a uniform layer (26) of a viscous material (62) on a donor substrate (28), wherein the coating system (22) comprises a syringe (64) of the viscous material (62), and wherein the step of forming the uniform layer (26) of the viscous material (62) comprises: driving the viscous material (62) from the syringe (64) onto the donor substrate (28); conveying the donor substrate (28) having the viscous material (62) thereon by the coating system (22) toward and through a second gap (126) between rollers (128a, 128b) or knives to form the uniform layer (26) of the viscous material (62) on the donor substrate (28), the uniform layer (26) of the viscous material (62) having a thickness defined by the second gap (126) between the rollers (128a, 128b) or knives; printing a plurality of dot-shaped portions (24) of the adhesive material (62) from the donor substrate (28) onto the electronic component (34) by a laser-based printing unit (32) of the laser-based printing system (30), while the electronic component (34) is held by a pick and place unit (16) such that a first gap (112) is maintained between the donor substrate (28) and the electronic component (34), and The electronic component (34) having the dot-shaped portions (24) of the adhesive material (62) printed thereon is transferred to a substrate (38) by a pick and place machine (44).

10. The method of claim 9, wherein the laser-based printing unit (32) uses a laser to eject the dot-shaped portions of material from the donor substrate (28) onto the electronic component (34).

11. The method of claim 9 or 10, further comprising imaging, using one or more imaging systems (50), (i) the dot-shaped portions (24) of adhesive material (62) printed on the electronic component (34); (ii) the substrate (38) after the electronic component (34) having the dot-shaped portions (24) of adhesive material (62) printed thereon has been placed on the substrate (38); or (iii) both.

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