Solder printing

Abstract

A method (100) includes performing (106) a non-screen printing process to deposit solder on a lead frame or on conductive features of a semiconductor die or wafer, or on or in conductive vias of a laminate structure. The method (100) also includes bonding (110) the semiconductor die to the lead frame, performing (112) a thermal process to reflow the solder, performing (114) a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame, and separating (116) the packaged electronic device from the remainder of the lead frame.

Description

Background Art

[0001] Packaged electronic devices include integrated circuits (ICs) and single-component devices having a semiconductor die and a package structure with externally accessible leads for connection to a printed circuit board or socket. Some package types include a starting leadframe with a metal structure for the final product leads and wirebond connections between the die pads and the leads. Ball grid array (BGA) devices have solder balls connected to copper pads on a substrate or interposer structure, such as a printed circuit board (PCB) to which the die is attached. Wafer-level chip-scale packages (WCSPs) include a die with electrode pads, such as copper pads or solder pillars soldered to a conductive redistribution layer (RDL). Tin-silver (Sn, Ag) solder is typically plated on selected portions of the leadframe for subsequent soldering to the copper pillars of the semiconductor die. Although Sn, Ag solder can be plated to facilitate compact package designs, its current capacity is limited, and the Sn, Ag solder connections from the die copper pillars to the leadframe or from the die copper pillars to the WCSP RDL can fail due to electromigration. Tin-silver-copper (Sn, Ag, Cu or SAC solder) has better current capacity than Sn and Ag solders, but does not work in plating applications. SAC solder can be screen printed, but this method has misalignment and manufacturability issues. Summary of the Invention

[0002] According to one aspect, a method includes performing a non-screen printing process that deposits solder on a lead frame or on a conductive feature of a semiconductor die or wafer, or on a conductive through-hole in a laminate structure. In one example, the non-screen printing process deposits solder on the lead frame or on a conductive feature of a semiconductor die or wafer, and the method also includes bonding the semiconductor die to the lead frame, performing a thermal process to reflow the solder, performing a molding process to form a package structure that encapsulates the semiconductor die and a portion of the lead frame, and separating the packaged electronic device from the remainder of the lead frame. In one example, the method also includes depositing flux on the solder after performing the non-screen printing process and before bonding the semiconductor die to the lead frame. In one embodiment, the flux is deposited by performing a second non-screen printing process that deposits the flux on the solder. In one example, the non-screen printing process deposits solder mixed with the flux. In one example, a non-screen printing process deposits solder as an alloy of tin (Sn), silver (Ag), and copper (Cu). In one example, the non-screen printing process uses a heated print head to deposit the solder as an alloy mixture of molten particles. In one example, the non-screen printing process deposits the solder as particles in a solvent. In one embodiment, the non-screen printing process deposits the solder using the following apparatus: a first print head that deposits tin particles in a first solvent; a second print head that deposits silver particles in a second solvent; and a third print head that deposits copper particles in a third solvent. In one example, the non-screen printing process deposits the solder as an alloy by printing molten first particles using a heated first print head; and printing molten second particles using a heated second print head. In one example, the non-screen printing process is an inkjet printing process. In one example, the non-screen printing process is an electrostatic printing process. In one example, the non-screen printing process deposits the solder using a first print head that deposits first particles in a first solvent and a second print head that deposits second particles in a second solvent.

[0003] In another aspect, a method includes performing a non-screen printing process to deposit solder on an uneven surface of a lead frame or leads of a packaged electronic device. In one example, the non-screen printing process is an inkjet printing process. In another example, the non-screen printing process is an electrostatic printing process. In another example, performing the non-screen printing process includes controlling a spacing distance between a print head and the uneven surface of the lead frame or leads of the packaged electronic device based on a contour of the uneven surface.

[0004] In another aspect, a method includes performing a non-screen printing process to deposit solder on or in a conductive via of a laminate structure. In one example, the non-screen printing process is an inkjet printing process. In one example, the non-screen printing process is an electrostatic printing process.

[0005] In another aspect, an electronic device includes a conductive structure such as a lead frame, a semiconductor die, a wafer, or a substrate, and a solder layer on the conductive structure, the solder layer including co-diffused metal nanoparticles of two metals, the nanoparticles having diameters of 20 nm or greater and 20 μm or less, respectively. In one example, a concentration ratio of the two metals in the solder layer varies along at least one direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a flow chart of a method of manufacturing a packaged electronic device.

[0007] Figure 2 yes Figure 1 A flow chart of an example non-screen solder printing process in a method.

[0008] Figure 3 yes Figure 1 Flowchart of another example non-screen solder printing process in a method.

[0009] Figure 4 yes Figure 1 Flowchart of another example non-screen solder printing process in a method.

[0010] Figure 5 yes Figure 1 Flowchart of another example non-screen solder printing process in a method.

[0011] Figure 6-Figure 16 is based on Figure 1 and Figure 5 A partial cross-sectional side view of a packaged electronic device manufactured by a method.

[0012] Figure 17 yes Figure 6-Figure 16 A perspective view of a packaged electronic device.

[0013] Figure 18 and Figure 19 is based on Figure 1 A partial cross-sectional side view of a lead frame having an etched stepped profile deposited without screen printing according to another example of a method.

[0014] Figure 20 is based on Figure 1A partial cross-sectional side view of another example of a method of singulating a packaged electronic device having sawn leads with angled profiles deposited without screen printing.

[0015] Figure 21 is based on Figure 1 A partial cross-sectional side view of a laminate structure having conductive vias deposited by non-screen printing solder according to another example of a method.

[0016] Figure 22-Figure 27 is based on Figure 1 A partial cross-sectional side view of another example of a method of singulating a packaged electronic device having sawn leads with angled profiles that undergo non-screen printing solder deposition and heat treatment to form a packaged electronic device having varying lateral and vertical solder composition ratios across and vertically through the membrane.

[0017] Figure 28 yes Figure 22-Figure 27 A partial cross-sectional side view of a packaged electronic device having a varying SAC ratio across the membrane and vertically through the solder. DETAILED DESCRIPTION

[0018] In the drawings, like reference numerals refer to like elements throughout, and the various features are not necessarily drawn to scale. One or more operational characteristics of various circuits, systems, and / or components are described below in the context of functionality that, in some cases, results from the configuration and / or interconnection of various structures when the circuits are powered and operating.

[0019] Figure 1 A method 100 is shown that can be used to manufacture packaged electronic devices. Method 100 includes (among other things) printing solder on a lead frame or on a conductive feature of a semiconductor die or wafer, and / or on or in a conductive via. The examples described use non-screen printing processes, including but not limited to inkjet printing, offset or transfer printing, electrostatic printing, and the like. The non-screen printing process in certain embodiments includes inkjet or electrostatic printing techniques and one or more print heads to provide controlled placement and composition of printed solder, either alone or in combination with printed deposition of flux in the electronic device manufacturing process, to facilitate small packages and small feature sizes without the need for lead frame plating, and to allow the use of various solder alloys, including SAC solders that have better current capacity than Sn and Ag solders. Method 100 includes lead frame fabrication at 102 and wafer processing at 104. The illustrated examples include printing the solder alloy before or after die singulation.

[0020] In one embodiment, die singulation is performed at 105, followed by solder printing at 106. In another embodiment, solder printing is performed at 106, followed by die singulation at 107. In one example, solder printing at 106 includes printing a solder alloy (e.g., a SAC of any desired stoichiometric ratio) onto the lead frame and / or the die copper pillars of the processed wafer or singulated die. At 108, method 100 includes depositing flux on the printed solder, such as by dipping, printing, dispensing, etc. The lead frame is bonded to the die at 110, and a reflow process is performed at 112. A molding operation or process is performed at 114, followed by device separation at 116, and any desired final testing is performed at 118.

[0021] Figure 2-Figure 5 Shows that the Figure 1 Different example solder and / or flux deposition examples used at 106 and 108 in FIG. Figure 2 Shows that the Figure 1 An example non-screen solder printing process 200 is used at 106 and 108 in FIG. This example includes inkjet printing a solder alloy and flux as a suspension onto a lead frame and / or onto the copper posts of a processed wafer or singulated die. In one embodiment, the solder alloy is an alloy of tin, silver, and copper (e.g., SAC) in any desired stoichiometric ratio. Figure 3 Shows that the Figure 1 Another example non-screen solder printing process 300, 302 used at 106 and 108 in the method 100 of . This example includes printing a solder alloy (e.g., SAC) onto the lead frame and / or the die copper pillar at 300, and printing a flux onto the lead frame and / or the die copper pillar at 302. Figure 4 Shows that the Figure 1 Another example non-screen solder printing process 400, 402 used at 106 and 108 in the method 100 of . This example includes printing a solder alloy onto the lead frame and / or the die copper pillar at 400 and dipping the lead frame and / or the die copper pillar with flux at 402. Figure 5 Shows that the Figure 1 Another example non-screen solder printing process 500, 501, 502 is used at 106 and 108 in FIG. At 500, a solder alloy is printed onto a lead frame and / or a die copper pillar at 500. In this example, the printed solder alloy is baked at 501. At 502, the lead frame and / or the die copper pillar are dipped in flux.

[0022] Figure 6-Figure 16 Shown according to Figure 1 Example method 100 and Figure 5A packaged electronic device manufactured according to an embodiment of the present invention. Figure 6 The processed lead frame 600 (eg, Figure 1 102 in ). A lead frame in one example is a sheet or strip having multiple die areas that are ultimately separated (singulated) from one another but remain integrated during certain steps of the integrated circuit manufacturing process. In one example, the lead frame 600 is machined into a selectively coated copper structure having a copper portion 602 and an oxide layer or coating 604 on selected exterior surfaces of the metal structure 602. In one example, a stamping step is used to construct the die attach pads, leads, and other features to form a patterned copper metal structure 602. Certain examples include uneven surfaces, for example, by etching selected portions of the stamped copper structure to form step features to promote molding compound adhesion in the finished integrated circuit product (e.g., below Figure 18 and Figure 19 In one example, the stamped structure is exposed to an oxidizing environment at a controlled temperature to form a copper oxide layer 604Cu. x O, such as cupric oxide (CuO) or cuprous oxide (Cu2O). Figure 7 A processed semiconductor wafer (e.g., Figure 1 104 in FIG. 10. The die portion 700 includes a semiconductor portion 701 (e.g., silicon) and a conductive feature 702 (e.g., a copper pad or pillar). As previously described, solder printing, flux application, and bonding of the lead frame 600 to the die portion 700 may be performed prior to die singulation (e.g., at Figure 1 In a WCSP embodiment, die separation is performed simultaneously with device separation (e.g., Figure 1 116 in ), and before molding and device separation, the lead frame or dielectric / RDL structure and the processed wafer are bonded and the solder is reflowed (e.g., Figure 1 110 and 112 in the figure).

[0023] Figure 8 and Figure 9 An example is shown in which a non-screen printing process 800 is performed using a print head 802 that is controlled to translate in a controlled lateral direction or path 804 while directing solder in a vertical direction 806 toward the top side of the lead frame 600 to deposit solder 810 on the lead frame 600. In one example, the process is performed using an inkjet print head 802 having a position control device, such as a printer configured to translate and control the print head 802 in three dimensions (e.g., the X and Y directions shown in the figure and the vertical direction 806). Figure 8 and Figure 9 In one embodiment, the printing system translates the print head 800 in the XZ plane while controlling the Y-direction spacing between the top side of the lead frame 600 and the print head 802. In one example, the printing system also controls the delivery of solder from the nozzle of the print head to, for example, turn printing on and off, thereby facilitating precise, high-resolution control of where the solder 810 is printed and where it is not printed. In addition, the non-screen printing process 800 provides control over the thickness of the deposited solder (e.g., in the Y-direction) by one or more of the deposition rate and the time that the print head 802 is positioned over a particular area of ​​the lead frame 600. This facilitates printing the solder to different thicknesses at different locations in certain embodiments. In one example, the print head 802 translates in the XZ plane along a raster scan path 804 while being spaced a controlled distance in the Y-direction above the top side of the lead frame 600 while printing a continuous or pulsed stream of solder 810. In certain embodiments (e.g., above Figure 2 200 in the figure), a non-screen printing process 800 deposits solder 810 mixed with flux.

[0024] The non-screen printing process 800 deposits (eg, prints) solder 810 on selected portions of the upper side of the lead frame 600, such as Figure 8 and Figure 9as shown. Different embodiments include fine printing, such as printing feature sizes of about 200 μm or larger. In the illustrated example, the non-screen printing process 800 is an inkjet printing process. The inkjet embodiment of the non-screen printing process 800 is advantageous for effectively printing feature sizes on the order of 100 microns to 10-50 microns. In another example, the non-screen printing process 800 is an electrostatic printing process. The electrostatic jet printing embodiment of the non-screen printing process 800 provides finer resolution, such as printing feature sizes as low as 10-50 μm or lower to the sub-micron level. In one example, the non-screen printing process 800 uses a heated print head 802 to deposit the solder 810 as an alloy mixture of molten particles, for example, the printing temperature is controlled to be above the melting temperature of the alloy particles. In one embodiment, the non-screen printing process 800 deposits the solder 810 as an alloy of tin (Sn), silver (Ag), and copper (Cu), such as SAC 305 solder or SAC 405 solder, using a print head 802 provided with tin, silver, and copper particles, and heated to a temperature at or above the melting temperature of the tin, silver, and copper. In another embodiment, the non-screen printing process 800 deposits the solder 810 as an alloy by printing melted first particles using a heated first print head 802 and printing melted second particles using a heated second print head 802. In another embodiment, the non-screen printing process 800 deposits an alloy of three metals (e.g., tin, silver, and copper) using separate heated print heads 802 with melted tin, silver, and copper, respectively.

[0025] In another example, the non-screen printing process 800 deposits the solder 810 as particles in a solvent (e.g., a dispersant) such as water, oil, ethanol, etc. In one embodiment of this example, the print head 802 is not heated. In one example, the non-screen printing process 800 deposits the solder 810 as an alloy mixture of different particles in a solvent, such as a mixture of tin, silver, and copper in water, oil, ethanol, or other solvents, with or without heating. In another embodiment of this example, the non-screen printing process 800 deposits the solder 810 using a first print head 802 that deposits first particles in a first solvent and a second print head 802 that deposits second particles in a second solvent. In one example, the non-screen printing process 800 uses a third print head 802 that deposits third particles in a third solvent. In different embodiments, the solvents can be the same or different. In one example, a non-screen printing process 800 deposits solder 810 using a first print head 802 that deposits tin particles in a first solvent, a second print head 802 that deposits silver particles in a second solvent, and a third print head 802 that deposits copper particles in a third solvent. In one embodiment, the three alloy components are printed sequentially, and the solvents evaporate (or are baked, such as above). Figure 5501 in the figure) to form a printed alloy solder 810. In one example, the non-screen printing process 800 controls the particle concentration of the constituent alloy particles in each print head and / or the printing thickness of the constituent printed layer to control the final alloy stoichiometry.

[0026] Figure 10 and Figure 11 An example is shown in which a non-screen printing process 1000 is performed using a print head 1002 that is controlled to translate along a controlled lateral direction or path 1004 while directing solder along a vertical direction 1006 toward the bottom side of a semiconductor die or wafer 700 to deposit solder 1010 on the die or wafer 700. In one example, the process 1000 is performed using an inkjet print head 1002 having a position control device, such as a printer configured to translate and control the print head 1002 in three dimensions (e.g., the X and Y directions shown in the figure and the vertical direction 1006). Figure 10 and Figure 11 In one embodiment, the printing system translates the print head 1000 in the XZ plane while controlling the Y-direction spacing between the top side of the die or wafer 700 and the print head 1002. In one example, the printing system also controls the delivery of solder from the nozzle of the print head so as to, for example, turn printing on and off, thereby facilitating precise, high-resolution control of where the solder 1010 is printed and where it is not printed. In addition, the non-screen printing process 1000 provides control over the thickness of the deposited solder (e.g., in the Y-direction) by one or more of the deposition rate and the time that the print head 1002 is positioned over a particular area of ​​the die or wafer 700. This facilitates printing solder to different thicknesses at different locations in certain embodiments. In one example, the print head 1002 translates in the XZ plane along a raster scan path 1004 while being spaced a controlled distance in the Y-direction above the top side of the die or wafer 700 while printing a continuous or pulsed stream of solder 1010. In certain embodiments (e.g., above Figure 2 200 in the figure), a non-screen printing process 1000 deposits solder 1010 mixed with flux.

[0027] like Figure 10 and Figure 11As shown, the printing process 1000 deposits (e.g., prints) solder 1010 on selected portions of the upper side of the die or wafer 700. In the illustrated example, the non-screen printing process 1000 is an inkjet printing process. In another example, the printing process 1000 is an electrostatic printing process. In one example, the non-screen printing process 1000 uses a heated print head 1002 to deposit the solder 1010 as an alloy mixture of molten particles, for example, the printing temperature is controlled to be higher than the melting temperature of the alloy particles. In one embodiment, the non-screen printing process 1000 uses a print head 1002 provided with tin, silver, and copper particles to deposit the solder 1010 as an alloy of tin, silver, and copper, and is heated to a temperature at or above the melting temperature of the tin, silver, and copper. In another embodiment, the non-screen printing process 1000 deposits the solder 1010 as an alloy by printing molten first particles using a heated first print head 1002 and printing molten second particles using a heated second print head 1002. In another embodiment, the non-screen printing process 1000 deposits an alloy of three metals (eg, tin, silver, and copper) using separate heated print heads 1002 with respective melted tin, silver, and copper.

[0028] In another example, Figure 10 and Figure 11 The non-screen printing process 1000 in the example deposits solder 1010 as particles in a solvent (e.g., a dispersant) such as water, oil, ethanol, etc. In one embodiment of this example, the print head 1002 is not heated. In one example, the non-screen printing process 1000 deposits solder 1010 as an alloy mixture of different particles in a solvent, such as a mixture of tin, silver, and copper in water, oil, ethanol, or other solvent, with or without heating. In another embodiment of this example, the printing process 1000 deposits solder 1010 using a first print head 1002 that deposits first particles in a first solvent and a second print head 1002 that deposits second particles in a second solvent. In one example, the non-screen printing process 1000 uses a third print head 1002 that deposits third particles in a third solvent. In different embodiments, the solvents can be the same or different. In one example, the non-screen printing process 1000 deposits solder 1010 in three passes using a first print head 1002 that deposits tin particles in a first solvent, a second print head 1002 that deposits silver particles in a second solvent, and a third print head 1002 that deposits copper particles in a third solvent. In one embodiment, the three alloy components are printed sequentially using the respective print heads 1002 and associated solvents, and the solvents evaporate (or are baked, such as above). Figure 5501 in the figure) to form printed alloy solder 1010 on the copper pillar. In one example, the non-screen printing process 1000 controls the particle concentration of the constituent alloy particles in each print head and / or the printing thickness of the constituent printed layer to control the final alloy stoichiometry.

[0029] Figure 12 and Figure 13 A flux dipping process 1200 is shown that dips the die or wafer 700 to form flux 1202 on the printed solder 1010 on the copper pillars 702 (e.g., above). Figure 5 In this example, the die or wafer 700 is inverted with the copper pillars 702 and printed solder 101 facing downwards. Figure 12 As shown, the die or wafer 700 is lowered to immerse the ends of the solder printed copper pillars 702 into a container of liquid flux 1202 and then Figure 13 It is shown lifted to leave an impregnated layer of flux 1202 on the underside of the printed solder 1010 on the bottom of the copper pillar 702.

[0030] Figure 14 and Figure 15 The attachment of semiconductor die 700 and lead frame 600 is shown, which includes Figure 14 The bonding process 1400 in the embodiment of the present invention is to bond the semiconductor die 700 to the lead frame 600 (e.g., the lead frame 600 shown in FIG. Figure 1 110 in the illustrated example). In the illustrated example, the solder printed lead frame 600 is positioned in a fixture and the flux-impregnated die or wafer 700 is lowered onto the lead frame 600 to bond the flux-impregnated bottom of the printed solder 1010 to the printed solder 810 of the lead frame 600, as shown. Figure 14 shown. Figure 15 A thermal process 1500 is shown (e.g., Figure 1 112 in the ), which melts the solder 810 and 1010, and uses Figure 14 The flux 1202 in the lead frame reflows the solder 810 and 1010 to form solder joints 1502 between opposing sides of the copper pillars 702 and portions of the top side of the lead frame copper portion 602 .

[0031] Figure 16 A molding process 1600 (eg, in the Figure 1 114 in the figure), package structure 1602 encapsulates semiconductor die 700 and a portion of lead frame 600. In this example, portions of lead features 602 are exposed outside of molded package structure 1602 to allow the finished IC package electronic device to be soldered to a host printed circuit board (not shown). Figure 17The packaged electronic device 1700 is shown after the corresponding device separation from the remaining portion of the lead frame 600 and the Figure 1 An example of a finished packaged electronic device 1700 after any final testing at 116 and 118 in FIG.

[0032] Now refer to Figures 18-20 In a further example, non-screen solder printing includes performing a non-screen printing process that deposits solder on an uneven surface of a lead frame or an uneven surface of a lead of a packaged electronic device. In one example, the non-screen printing process prints solder (e.g., SAC solder) on a surface having an average roughness of approximately 100 μm or greater to accommodate solder printing on a half-etched lead frame and its lead features (including, in some embodiments, saw-cut tapered surfaces of the lead features). Figure 18 and Figure 19 An example of a non-screen solder printing process 1800 using a print head 1802 is shown that is controlled to translate along a controlled lateral direction or path 1804 while directing the solder along a vertical direction 1806 to deposit solder 1810 on the top side of a half-etched lead frame 1820. The lead frame 1820 in one example is a sheet or strip having multiple die areas that are ultimately separated (singulated) from one another but remain integrated during certain steps of the integrated circuit manufacturing process. In one example, the lead frame 1820 is machined into a selectively coated copper structure having a copper portion 1822 and an oxide layer or coating 1824 on selected outer surfaces of the metal structure 1822. In one example, a stamping step is used to construct the die attach pads, leads, and other features, thereby forming a patterned copper metal structure 1822. In addition, some portions of the top side of the lead frame are etched to approximately half the Y-direction thickness of other portions (e.g., etched by half) to provide an uneven surface for the lead frame 1820 or for uneven surfaces of leads of a packaged electronic device fabricated using the lead frame 1820. Various embodiments of the non-screen printing process 1800 are used in different examples, such as inkjet printing, electrostatic printing processes, etc., using single or multiple print heads 1802, with or without heating, with or without solvent, with or without flux, such as the printing processes 800 and 1000 described above. Furthermore, the non-screen printing process 1800 can be used in various embodiments to print any type of solder, including alloys such as the SAC solder described above.

[0033] Figure 18 and Figure 19The non-screen printing process 1800 in FIG. 1 deposits solder 1810 on the uneven surface of the step feature portion of the lead frame 1820. In this example, the lead frame 1820 includes uneven surfaces of the leads 1822 of the finished electronic device, which are formed by half etching during the lead frame processing. The non-screen printing process 1800 in this example includes controlling the spacing distance D between the print head 1802 and the uneven surface of the lead frame 1820. Figure 18 As shown, a non-screen printing process 1800 in one example prints solder 1810 having a substantially uniform thickness on an uneven surface of a lead of a packaged electronic device by controlling a spacing distance D according to the contours of the uneven surface. In one example, the non-screen printing process 1800 controls or adjusts the spacing distance D to a substantially constant value based on Y-axis position feedback information about the position of the print head relative to a base or fixture holding a lead frame 1820. In one example, an uneven surface (such as Figure 18 and Figure 19 ) is programmed into a position control device for the printing process 1800, and the position control device adjusts the Y-axis position of the print head 1802 to maintain a substantially constant standoff distance D. In some embodiments, the non-screen printing process 1800 includes controlling the delivery of solder from a nozzle of the print head 1802, including adjusting the deposition rate in a substantially continuous manner to print solder 1810 having different thicknesses at different locations on the lead frame 1820.

[0034] Figure 20 Shown according to Figure 1 Another example of method 100 of singulating packaged electronic devices having sawn leads having an angled profile that undergoes a non-screen printing process 2000 is provided. This example uses the lead frame 600 and semiconductor die portion 701 described above, wherein the outer sidewalls of the lead features 602 of the starting lead frame 602 include chamfers formed, for example, during package singulation sawing. In one example, the cut portion of the lead features 602 facilitates soldering to a host printed circuit board (not shown) by allowing solder to flow at the bottom of the lead features 602 and along a portion of the sidewalls of the lead features 602. This facilitates processing wettable flank surfaces by controlled vertical printing and / or angled printing at non-zero printing angles relative to the top and bottom of the packaged electronic device structure.

[0035] like Figure 20As shown, non-screen printing process 2000 uses a print head 2002 that is controlled to translate along a controlled lateral direction or path 2004 while directing solder along a vertical direction 2006 to deposit solder 2010 on the top side of a singulated packaged electronic device. Various embodiments using non-screen printing process 2000 (such as inkjet printing, electrostatic printing processes, etc.) have single or multiple print heads 2002, with or without heating, with or without solvent, and with or without flux, such as non-screen printing processes 800, 1000, and 1800 described above. Furthermore, non-screen printing process 2000 can be used in various embodiments to print any type of solder, including alloys such as the SAC solder described above. Non-screen printing process 2000 in this example prints solder 2010 along angled and horizontal portions of lead features 602, including printing solder 2010 over any intermediate coating material 604 in this example. In one example, the non-screen printing process 2000 includes controlling the standoff distance between the print head 2002 and the uneven surface of the singulated packaged electronic device. Figure 20 As shown, a non-screen printing process 2000 in one example prints solder 2010 having a substantially uniform thickness on an uneven surface of a lead of a packaged electronic device by controlling a spacing distance D according to the contour of the uneven surface. The non-screen printing process 2000 in one example controls or adjusts the spacing distance D to a substantially constant value based on Y-axis position feedback information about the position of the print head relative to a base or fixture holding a lead frame 2020. In one example, an uneven surface (such as Figure 20 ) is programmed into a position control device for the non-screen printing process 2000, and the position control device adjusts the Y-axis position of the print head 2002. In some embodiments, the non-screen printing process 2000 includes controlling the delivery of solder from a nozzle of the print head 2002, including adjusting the deposition rate in a substantially continuous manner to print solder 2010 having different thicknesses at different locations on the lead frame 600.

[0036] Figure 21Another aspect is shown in which a non-screen solder printing process 2100 is performed to deposit solder 2110 on or in conductive vias 2131 and 2132 of a laminate structure 2120. In this example, the non-screen printing process 2100 uses a print head 2102 that is controlled to translate along a controlled lateral direction or path 2104 while directing the solder along a vertical direction 2106 to deposit the solder 2110 on or in the vias of the laminate structure 2120. The laminate structure 2120 in this example includes a first dielectric layer 2121 and a second dielectric layer 2122. Conductive vias 2124 (e.g., copper) extend between the top and bottom sides of the first dielectric layer 2121. Some of the vias 2124 contact copper wiring features 2126 (e.g., lines or traces) that extend between the top side of the first dielectric layer 2121 and the bottom side of the second dielectric layer 1222. Vias 2131 and 2132 extend between the bottom and top sides of the second dielectric structure 2122. Various embodiments using a non-screen printing process 2100 (such as inkjet printing, electrostatic printing, etc.) have single or multiple print heads 2102, with or without heating, with or without solvent, and with or without flux, such as the printing processes 800, 1000, 1800, and 2000 described above. In addition, the non-screen printing process 2100 is used in various embodiments to print any type of solder, including alloys such as the SAC solder described above. The non-screen printing process 2100 in this example selectively prints solder 2110 on the top edge of the first through-hole 2131, where the solder 2110 in this example extends outward from the lip of the through-hole 2131 along some portions of the second dielectric layer 2122, but the solder 2110 is not printed in the inner cavity of the through-hole 2131. Figure 21 The non-screen printing process 2100 in FIG. 2 prints solder 2110 on the top edge of the second through-hole 2132. In this example, the non-screen printing process 2100 also prints solder 2110 into the interior cavity of the second through-hole 2132. In one example, the non-screen printing process 2100 controls the print head 2102 to remain over the center of the through-hole 2132 for a sufficient time to completely fill the interior cavity of the through-hole 2132, although this is not a requirement in all possible implementations.

[0037] Now refer to Figures 22-46 , Figure 22-Figure 27 Another singulated packaged electronic device undergoing solder print deposition and thermal processing to form a packaged electronic device is shown that includes a solder layer having a profiled or varying ratio and composition gradient laterally across the solder and / or vertically across the solder. Figure 28 Shown Figure 22-Figure 27A finished packaged electronic device having varying lateral and vertical composition ratios across and vertically through the solder. Figures 28-46 A partial cross-sectional side view of a further non-limiting example of an electronic device having printed solders with different composition profiles is shown. A non-screen printing process in one example forms nanoparticles of two or more different composition materials, such as tin-silver-copper (Sn, Ag, Cu). The printed deposition in this example forms individual Sn, Ag, and Cu particles mixed together, for example, by printing simultaneously or individually using individual print heads. In one example, the above method produces a printed solder by dispersing metal nanoparticles in a solution, and then print-depositing the solution by, for example, one or more print heads as described above. The deposited nanoparticle film is not 100% dense at the time of deposition, but forms nanoparticles located in a stack, for example, with a diameter in the range of about 20 nm to 20 μm.

[0038] Energy (such as heating) is then applied to melt the nanoparticles together at, for example, a low temperature (e.g., about 80°C). Printing of such nanoparticles facilitates melting of the SAC at lower temperatures, a major advantage in manufacturing. Heating causes the nanoparticles to diffuse into each other and form a final solder structure, for example, a layer comprising co-diffused Sn, Ag, and Cu (or Sn(X)Ag(Y)Cu(Z) nanoparticles) with diameters ranging from 20nm to 20μm. The solder layer in one example has different SAC ratios across the entire film (e.g., Sn(X)Ag(Y)Cu(Z), where X, Y, and / or Z vary laterally and / or vertically across the entire film). In one example, a packaged electronic device includes SAC solder on a conductive structure. In some examples, the solder extends over the remainder of the starting lead frame after singulation of the lead frame, IC terminals, device, or package, conductive pads or features of a substrate, conductive pads or features of a processed semiconductor wafer, or conductive pads or features of a singulated semiconductor die. In some examples, the solder is a SAC solder having a higher Ag ratio at the bottom of the film than at the top of the film, for example, formed by adjusting the Ag print head while maintaining the Cu and Sn print heads ejecting at the same volume per unit area. In other examples, the concentration ratios of two or more components of the solder vary in one, two, or three mutually orthogonal directions in three-dimensional space, for example, including Figures 22-46 The X and Y directions and / or any third (e.g., "Z") direction, or a combination thereof.

[0039] Figure 22-26An example process for producing packaged electronic devices during printing of different solder segments is shown, some of which have different ratios of tin, silver, and copper, some of which are stacked to form a vertical distribution, some of which are formed as distributed solder segments for compound lateral distribution in different lateral regions, and some of which have different thicknesses. Figure 27 shows the thermal process after solder printing, and Figure 28 The final finished packaged electronic product is shown. Figures 29-46 Several non-limiting examples of distribution ratios of two metal compositions are shown for example printed and thermally co-diffused solder layers formed on corresponding conductive features of a packaged electronic device.

[0040] Figure 22 A non-screen printing process 2200 is shown in which an alloy of three metals (e.g., tin, silver, and copper) is deposited using a separate heated print head, which is shown as a single unit 2202 that translates along a lateral direction 2204 and deposits material along a printing direction 2206 to form a first solder segment 2210. Figure 22 A singulated packaged electronic device having a package structure 1602 (eg, mold compound) and sawn leads having an angled profile is shown undergoing a non-screen solder printing process 2200 . Figures 22-28 The example device in uses the lead frame 600 and semiconductor die portion 701 described above, wherein the outer sidewalls of the lead features 602 of the starting lead frame 602 include chamfers, such as those formed during package singulation sawing. In one example, the cut portion of the lead features 602 facilitates soldering to a host printed circuit board (not shown) by allowing solder to flow at the bottom of the lead features 602 and along a portion of the sidewalls of the lead features 602. This facilitates processing of wettable flank surfaces by controlled vertical printing and / or angled printing at non-zero printing angles relative to the top and bottom of the packaged electronic device structure.

[0041] like Figure 22As shown, non-screen printing process 2200 translates print head unit 2202 along a controlled lateral direction or path 2204 while directing solder along a vertical direction 2206 to deposit solder 2010 on the angled portion of the top side of the singulated packaged electronic device. Various embodiments of non-screen printing process 2200 can be used, such as inkjet printing, electrostatic printing processes, and the like, with single or multiple print head units 2202, with or without heating, with or without solvent, and with or without flux, such as non-screen printing processes 800, 1000, and 1800 described above. Furthermore, non-screen printing process 2200, in various embodiments, can be used to print any type of solder, including alloys such as the SAC solder described above. Non-screen printing process 2200 in this example prints solder segments 2010 along the angled and horizontal portions of lead features 602, including printing solder segments 2010 over any intermediate coating material 604 in this example. The non-screen printing process 2200 in one example includes controlling the standoff distance between the print head 2202 and the uneven surface of the lead feature 602 .

[0042] like Figure 22 As shown, a non-screen printing process 2000 in one example prints solder segments 2010 having a substantially uniform thickness on an uneven surface of a lead of a packaged electronic device according to the contours of the uneven surface. In some embodiments, the non-screen printing process 2000 includes controlling the delivery of solder from a nozzle of a print head unit 2202, including adjusting a deposition rate in a substantially continuous manner, to print solder segments 2010 having different thicknesses at different locations on the lead frame 600.

[0043] Craft 2200 Figure 23-26 Continuing in order to print additional solder segments 2220, 2230, 2240, and 2250. These additional solder segments illustrate example profile concentration ratios, including shading or dot density in the figure, which indicates a generally continuously varying ratio of two of the three constituent metal materials forming the solder segment (e.g., the ratio of silver concentration divided by copper concentration, etc.). In a specific example, the concentration of any one of the three example constituent metal materials can vary from 0% to 100% in any linear, nonlinear, or step-wise manner in different examples. Figure 23 A second solder segment 2220 is formed in the solder segment 2220, which in this example includes a distribution of silver concentration that is equal to or close to 0% at the bottom of the solder segment 2220 and increases toward or to 100% at or near the top of the solder segment 2220. Although this and other distributed solder segments are generally shown as continuous in the figures, other distributions are possible, such as stepped distributions, etc. In one example, Figure 23The vertical profile shown in FIG is implemented by dynamically changing the mixture of the constituent metals at each lateral position in a single pass by the print head unit 2202. In another possible embodiment, the non-screen printing process 2200 implements the vertical profile in a multi-pass manner (e.g., changing the concentration ratio profile along the printing direction 2206), for example, printing along the printing direction 2204 at a first concentration ratio (e.g., silver concentration equal to or close to 0%), and performing multiple repeated passes to gradually increase the thickness of the deposited solder segment 2220 by gradually increasing the silver concentration ratio (e.g., the concentrations of the other two constituent metals of the solder 2220 are correspondingly reduced).

[0044] like Figure 24 and Figure 25 As shown, the example continues process 2200 to further deposit a third solder segment 2230 having an opposite vertical silver concentration profile (e.g., equal to or close to 100% at the bottom of the solder segment 2230, gradually decreasing to equal to or close to 0% at the top of the solder segment 2230). Figure 25 As further shown in FIG, the process 2200 in this example also includes depositing a fourth solder segment 2240 over portions of the third solder segment 2230. The example solder segment 2240 in this example also has a vertical silver concentration profile with a higher silver concentration at the bottom and a lower silver concentration at the top. The combination of the underlying profiled solder segment 2230 and the overlying profiled solder segment 2240 creates a composite vertically profiled solder structure 2230 / 2240 having a concentration profile of silver content along the vertical (Y) direction.

[0045] Craft 2200 Figure 26 and Figure 27 Continuing in order to deposit the fifth solder segment 2250, each of which includes a laterally distributed silver concentration. In the illustrated example, as the print head unit 2202 translates along direction 2204 (e.g., in Figure 26 and Figure 27 The silver concentration in each printed segment 2250 increases (e.g., from 0% or nearly 0% at the right end of the segment 2250 to 100% or nearly 100% at the left end of the segment 2250). Figure 26 and Figure 27As further shown in FIG, process 2600 prints solder segment 2250 to a vertical thickness (e.g., in the Y direction) that is greater than the vertical thickness of solder segment 2240. As previously described, the printed deposition of solder segments 2210, 2220, 2230, 2240, and 2250 provides a structure including individual Sn, Ag, and Cu particles intermixed together, wherein the deposited nanoparticle film is not 100% dense as deposited, but rather forms nanoparticles stacked upon one another, e.g., having diameters in the range of approximately 20 nm to 20 μm.

[0046] exist Figure 27 A thermal heating process 2700 is performed in the printed solder segments 2210, 2220, 2230, 2240, and 2250 to melt the nanoparticles together. In one example, the thermal process controls the temperature of the deposited solder segments to a low temperature, such as at or near 80°C (e.g., ±2°C), which causes the nanoparticles to diffuse into each other and produce Figure 27 The final solder segment structures 2210, 2220, 2230, 2240 and 2250 in FIG. 2 respectively include Figure 28 The final product packaged electronic device 2800 is shown as co-diffused Sn, Ag, and Cu (or Sn(X)Ag(Y)Cu(Z) nanoparticles) with diameters ranging from 20 nm to 20 μm.

[0047] Figures 29-46 Several non-limiting examples of profile ratios of two metal compositions for example printed and thermally co-diffused solder layers formed on respective conductive features of packaged electronic devices are shown. In these examples, for the SAC solder example, darker areas with high dot density indicate high concentration ratios of silver relative to the other constituent metals, tin and copper, while lighter areas with no or low dot density indicate low concentration ratios of silver relative to the other constituent metals. Various embodiments of profiled printed solder segments may include variations in more than one constituent metal relative to the other metals, and any number of ratiometric profiles, any desired shapes, gradients, etc., may be implemented in various example packaged electronic devices, including stepped, nonlinear, linear, exponential profiles, and the like. Figures 29-46The examples of packaged electronic devices are non-limiting and are merely examples of a few of many possible implementations in which solder structures 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, and 4600 are on or formed on conductive structures 602, such as lead frames, IC terminals, remaining portions of a starting lead frame after device or package singulation, conductive pads or features of a substrate, or conductive pads or features of a processed semiconductor wafer, or conductive pads or features of a singulated semiconductor die, etc.

[0048] The described examples provide solder printing, such as SAC solder printed using inkjet or electrostatic printing processes, which facilitates manufacturability and performance improvements of electronic devices. Some described examples facilitate the use of multiple nozzles (such as printing solder, flux, and solder mask) to change printed materials in a single pass. Certain embodiments also facilitate controlled variation of printed material thickness, for example, using inkjet or electrostatic printing to compensate for solder column size or other solder thickness differences. In addition, the described techniques facilitate the use of different unplated copper lead frame materials and improved current carrying capacity of solder alloys such as SAC solder. The described non-screen printing process allows the use of solder that cannot be plated and provides improved control, positioning, process yield, and flexibility for precise control of printed area feature size and thickness. In addition, the described examples facilitate the placement of capacitors and inductors while arranging semiconductor dies, even though such passive components may have different solder requirements than the semiconductor dies. As described above, many different embodiments are possible, including printing the solder particles and flux as a suspension, printing the solder particles first and then printing the flux, printing the solder particles first and then performing a flux dip, and printing the solder particles, baking the printed solder particles, and then printing the flux or performing a flux dip. The printing process and equipment can be modified through updated software with little or no impact on the cost of retooling, labor, or materials, and has advantages over screen printing in terms of adaptability. Printing techniques can be used instead of plating, thereby enabling the formation of larger pillars and denser copper on silicon without the need to plate the lead frame during processing, while improving thermal conductivity through the lead frame compared to plated tin-lead solder (e.g., 360 W / mK vs. 190 W / mK Watts per meter). In addition, the non-screen printing process described allows thicker solder to be deposited in some locations (e.g., to account for different sizes of copper pillars on the semiconductor die) to achieve better final device flatness, and inkjet or other non-screen printing processes are advantageous for arranging other components with different solder requirements. Furthermore, solder mask printing facilitates optimal flow during device manufacturing. Furthermore, inkjet, electrostatic, or other non-screen printing processes use significantly less material than screen printing, and printing avoids problems associated with stencil dirtiness, staining, stretching, or other stencil defects or degradation. Furthermore, printing can be used to print on non-flat surfaces (e.g., cavities, lead flanks, half-etched lead frame features, etc.), and printing can be directly onto core posts or columns. As described above, certain examples also facilitate printing through-silicon vias (thru-silicon vias). Furthermore, automated printing is fast, allowing, for example, solder to be printed on selected locations on a processed wafer in 30 seconds or less.Furthermore, multiple print heads can perform printing of a single alloy as a single operation, with or without heat, and with or without solvent, whereas stencil or screen printing techniques involve multiple operations and use more materials.

[0049] The above examples are merely illustrative of several possible implementations of various aspects of the present disclosure, and equivalent changes and / or modifications will occur to those skilled in the art upon reading and understanding this specification and the accompanying drawings. Modifications to the described examples are possible, and other implementations are also possible, within the scope of the claims.

Claims

1. A method comprising: performing a non-screen printing process that deposits solder on a lead frame or on conductive features of a semiconductor die or wafer; depositing flux on the solder after performing the non-screen printing process and before bonding the semiconductor die to the lead frame; bonding the semiconductor die to the lead frame; performing a thermal process to reflow the solder; performing a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame; as well as The packaged electronic device is separated from the remainder of the lead frame. 2 . The method of claim 1 , wherein depositing the flux on the solder comprises performing a second non-screen printing process to deposit the flux on the solder. The method of claim 1 , wherein the non-screen printing process deposits the solder mixed with a flux.

4. The method of claim 1, wherein the non-screen printing process deposits the solder as an alloy of tin (Sn), silver (Ag), and copper (Cu). The method of claim 1 , wherein the non-screen printing process deposits the solder as particles in a solvent.

6. The method of claim 5, wherein the non-screen printing process deposits the solder as an alloy of tin (Sn), silver (Ag), and copper (Cu).

7. The method of claim 6, wherein the non-screen printing process deposits the solder using: a first print head that deposits tin particles in a first solvent; a second print head that deposits silver particles in a second solvent; and a third print head that deposits copper particles in a third solvent.

8. The method of claim 1, wherein the non-screen printing process is an inkjet printing process.

9. A method comprising: performing a non-screen printing process that deposits solder on a lead frame or on conductive features of a semiconductor die or wafer, wherein the non-screen printing process deposits the solder as an alloy mixture of molten particles using a heated print head; bonding the semiconductor die to the lead frame; performing a thermal process to reflow the solder; performing a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame; as well as The packaged electronic device is separated from the remainder of the lead frame.

10. A method comprising: performing a non-screen printing process that deposits solder on a lead frame or on conductive features of a semiconductor die or wafer, wherein the non-screen printing process deposits the solder as an alloy by: printing melted first particles using a heated first print head; and printing the melted second particles using a heated second print head; bonding the semiconductor die to the lead frame; performing a thermal process to reflow the solder; performing a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame; as well as The packaged electronic device is separated from the remainder of the lead frame.

11. A method comprising: performing an electrostatic printing process that deposits solder on a lead frame or on conductive features of a semiconductor die or wafer; bonding the semiconductor die to the lead frame; performing a thermal process to reflow the solder; performing a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame; as well as The packaged electronic device is separated from the remainder of the lead frame.

12. A method comprising: performing a non-screen printing process that deposits solder on a lead frame or on conductive features of a semiconductor die or wafer, wherein the non-screen printing process deposits the solder using: a first print head that deposits first particles in a first solvent; and a second print head that deposits second particles in a second solvent; bonding the semiconductor die to the lead frame; performing a thermal process to reflow the solder; performing a molding process to form a package structure encapsulating the semiconductor die and a portion of the lead frame; as well as The packaged electronic device is separated from the remainder of the lead frame.

13. A method comprising: A non-screen printing process is performed that deposits solder on the stepped surface of a lead frame or the tapered surface of a lead of a packaged electronic device. The method of claim 13 , wherein the non-screen printing process is an inkjet printing process.

15. The method of claim 13, wherein the non-screen printing process is a xerographic printing process.

16. The method of claim 13, wherein performing the non-screen printing process comprises: A spacing distance between a print head and the stepped surface of the lead frame or the tapered surface of the lead of the packaged electronic device is controlled according to a profile of the stepped surface of the lead frame or the tapered surface of the lead of the packaged electronic device.

17. A method comprising: A non-screen printing process is performed that deposits solder on or in the conductive vias of the laminate structure.

18. The method of claim 17, wherein the non-screen printing process is an inkjet printing process.

19. A method comprising: A non-screen printing process is performed that deposits solder on or in the conductive vias of the laminate structure, wherein the non-screen printing process is an electrostatic printing process.

20. An electronic device comprising: a conductive structure of a lead frame or semiconductor die or wafer or substrate; as well as A solder layer on the conductive structure, the solder layer including co-diffused metal nanoparticles of two metals, wherein the diameters of the nanoparticles are 20 nm or more and 20 μm or less, respectively. 21 . The electronic device according to claim 20 , wherein a concentration ratio of the two metals in the solder layer varies along at least one direction.

22. The electronic device according to claim 21, wherein: The solder layer includes co-diffused metal nanoparticles of tin, silver, and copper; and A concentration ratio of two of tin, silver, and copper in the solder layer varies along the at least one direction. 23 . The electronic device according to claim 22 , wherein a concentration ratio of the two of tin, silver, and copper in the solder layer varies along two or more mutually orthogonal directions. 24 . The electronic device according to claim 20 , wherein a concentration ratio of the two metals in the solder layer varies along two or more mutually orthogonal directions.

25. A method comprising: providing a conductive structure of a lead frame or semiconductor die or wafer or substrate; as well as A solder layer is formed on the conductive structure. The solder layer includes co-diffused metal nanoparticles of two metals, wherein the diameters of the nanoparticles are 20 nm or more and 20 μm or less, respectively.

26. The method of claim 25, wherein a concentration ratio of the two metals in the solder layer varies along at least one direction.

27. The method of claim 26, wherein: The solder layer includes co-diffused metal nanoparticles of tin, silver, and copper; and A concentration ratio of two of tin, silver, and copper in the solder layer varies along the at least one direction.

28. The method of claim 27, wherein a concentration ratio of the two of tin, silver, and copper in the solder layer varies along two or more mutually orthogonal directions.

29. The method of claim 25, wherein a concentration ratio of the two metals in the solder layer varies along two or more mutually orthogonal directions.

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