Laser enhanced wire bonding for semiconductor device packages

Abstract

The embodiment of the invention relates to laser enhanced wire bonding of a semiconductor device package. An example apparatus (Figure 5C) includes a wire bonding tool including a capillary (Figure 5C, 551) having a central opening, the capillary configured to receive a bonding wire (553) in the central opening; a first laser path (563) formed in the capillary tube, the first laser path configured to focus a first laser beam (564) on an end of the bond wire to form an airless sphere; and a second laser path (561) formed in the capillary tube, the second laser path configured to focus a second laser beam (562) on a bonding location below the capillary tube.

Description

Technical Field

[0001] The present disclosure relates generally to semiconductor device packages, and more particularly to semiconductor device packages that include a semiconductor die coupled to leads of a package substrate using bond wires and wire bonding processes. Background Art

[0002] Semiconductor device packaging is widely used in a variety of applications. In a wire-bonded semiconductor device package, a semiconductor die or multiple semiconductor dies are mounted to a packaging substrate. The packaging substrate can be a lead frame with conductive leads spaced apart from the die mounting pads. The semiconductor die is attached to the die mounting pads, wherein the bonding pads on the semiconductor die face away from the die mounting pads. In order to electrically connect the bonding pads on the semiconductor die to the conductive leads, a wire bonding process is typically used. In the wire bonding process, a capillary is positioned above the device. The capillary has a bond wire spool connected to provide a bond wire through a small central opening in the capillary. The capillary is a hard material, such as ceramic or other dielectrics.

[0003] A flame or electric arc may be used to melt the exposed end of a bond wire extending a short distance through the capillary. A ball of molten material, known as a "free air ball," is formed at the end of the bond wire protruding from the capillary. The capillary and the package substrate (which contains the semiconductor die mounted thereto) move relative to each other. In an example wire bonder tool, the capillary may move in the "Z" direction (i.e., vertically) (because the elements are typically oriented), while the capillary, which may be mounted on an arm or support, or a package substrate such as a unit lead frame or an array or grid of lead frames, moves in the "XY" direction, i.e., in two directions in a horizontal plane (because the elements are typically oriented).

[0004] To form a wire bond, a capillary carrying a bond wire forces a free air ball of molten bond wire material onto a bond pad of a semiconductor die. The bond pad may be copper, aluminum, gold, or an alloy of these. Recently, copper bond pads are used more frequently because copper conductors are commonly formed in semiconductor damascene conductor processes. Aluminum bond pads are also used. In some example processes, the bond pad may include a thin plating layer for enhancing bonding by reducing corrosion and oxidation of the bond pad. In example semiconductor manufacturing processes, a gold, nickel, or palladium layer, or a combination of these, may be used.

[0005] Thermal ultrasonic wire bonding is often used. In thermal ultrasonic wire bonding, ultrasonic energy is applied to the capillary from an ultrasonic generator (USG) attached to the capillary during the ball bonding process. The ultrasonic energy vibrates the capillary while mechanically pressing the molten ball onto the bonding pad, and simultaneously, heating (e.g., using a heating block where the package substrate is located) the package substrate and the semiconductor die, so that the wire bonding process uses mechanical pressure from the capillary, ultrasonic energy applied to the capillary, and heat to form a bond. Ultrasonic vibrations are used in part to ensure that any oxidation or corrosion formed on the surface of the bonding pad is "broken through" and that reliable mechanical and electrical bonds are formed. In addition, the package substrate (in the example, the lead frame) and the semiconductor die are heated during bonding, which further increases the possibility of forming a reliable bond. In some example processes, for example, in the case of using copper or copper-plated bonding wires, the process is performed in an oxygen-deficient atmosphere by using an inert gas such as nitrogen placed around the element. This oxygen-free atmosphere delays or reduces the oxidation of copper wires and copper conductors. While using elevated temperatures improves bond reliability, elevated temperatures also accelerate oxidation of copper in air. An inert atmosphere addresses these issues by forming the bond in an oxygen-free environment.

[0006] After forming the ball bond, the capillary moves vertically and laterally away from the bonding pad while the bonding wire extends through the opening in the capillary. The capillary may be movable, or the package substrate and the capillary may be movable relative to each other. When the capillary moves to a position where a second bond will be formed on a lead or conductor, the bonding wire forms a loop from the end of the capillary and may be in an arc or curved shape on the element. The capillary then mechanically forces a portion of the extended bonding wire to reach a conductor (e.g., a lead frame lead) and performs stitch bonding by applying mechanical pressure, ultrasonic energy, and heat. The capillary then leaves the stitch bonding and uses a fixture to fix the bonding wire as the capillary moves, so that the bonding wire breaks at a short distance from the stitch bonding, thereby forming a small tail extending from the stitch bonding. The exposed end of the bonding wire is then melted again to form another free air ball, and the process is repeated for each of the wire bonding connections required to couple the bonding pad of the semiconductor die to the leads of the package substrate. Wire bonding can be automated, and the wire bonds required for the semiconductor die can be performed quickly, such as in a few seconds or less per semiconductor die, depending on the number of bond wires required. The wire bonder can use machine vision and automated visual inspection to quickly perform wire bonding. An operator can provide assistance, or the process can be fully automated. Thousands of wire bonds can be performed in a few seconds.

[0007] Once the wire bonds are formed, a molding compound (e.g., epoxy molding compound (EMC)), a thermosetting material, may be used to cover the semiconductor die and the portion of the package substrate containing the bonding wires and a portion of the leads to form a semiconductor device package. During the molding process, a portion of the leads are exposed from the molding compound to form terminals. In one example package type, a dual in-line package (DIP) package, the leads are formed on the side portions (usually at or near the middle of the side of the molded semiconductor device package) to leave the device terminals of the molding compound. The DIP terminals are formed to extend at an angle (e.g., a normal angle) to the bottom surface of the package and are formed for, for example, pins inserted into a socket, or for through-hole mounting by inserting into a plated-through hole in a printed circuit board or module. The DIP leads may be formed to have legs for surface mounting using solder. In another commonly used package type, a quad flat no-lead (QFN) package, the leads are exposed from the mold compound on the board side surface of the semiconductor device package but do not extend away from the molded package body to save board area when compared to, for example, the terminals of a DIP package. QFN packages are increasingly used to save board area.

[0008] Copper bonding wires are increasingly being used. Copper bonding wires have low resistivity and are less expensive than gold and silver, which can also be used. Copper wire bonding faces some challenges in forming reliable bonds due to oxidation of copper. Copper bonding wires are harder than gold bonding wires. Mechanical pressure on the copper wires and ultrasonic vibrations applied to the bonding pads can damage the bonding pads, leading to reliability issues. Copper bonding wires and copper bonding pads can oxidize, so plating of other metals such as gold, nickel, and palladium is often used to enhance bonding. Copper bonding wires can be plated with palladium (palladium-coated copper or "PCC") to reduce oxidation; however, this method increases costs. The use of ultrasonic energy in the copper wire bonding process can also damage the plating material used as a thin electroplating layer on the copper bonding pad, resulting in bonding defects and reduced reliability of the wire bonding. The use of ultrasonic energy also requires an ultrasonic generator as part of the wire bonding tool. The use of elevated temperatures applied to the leadframe leads also heats the semiconductor die, which may cause thermal stresses to sensitive devices formed within the semiconductor die, for example certain sensors and temperature sensitive devices with low thermal processing budgets may be adversely affected by the wire bonder heating process. The die may warp due to thermal cycling of the wire bonder. A reliable and economical wire bonding process is needed, and a wire bonding process that is efficient and reliable for copper wire bonding is needed. Summary of the invention

[0009] An example method is described including: using a first laser to form a free air ball of molten material on an end of a bond wire; using a second laser to form a melt region on a bond pad of a semiconductor die at a bonding location; forming a ball bond between the free air ball and the melt region of the bond pad; moving a capillary away from the ball bond while extending the bond wire; moving the capillary over the lead over a stitch bond location; using a second laser to form a melt region in a heat affected zone on the lead at the stitch bond location; and using the capillary to contact the melt region on the lead with the bond wire and form a stitch bond between the bond wire and the melt region on the lead while heating the bond wire using the first laser.

[0010] In an additional description example, an apparatus includes: a lead frame having a die pad and leads spaced apart from the die pad; a semiconductor die mounted to the die pad and having a bonding pad facing away from the lead frame; and wire bonds electrically coupling the bonding pad to the leads. The wire bonds further include: a ball bond formed on the bonding pad, the ball bond having a metal-to-metal bond between the ball and the bonding pad, the bonding pad having a heat affected zone with a diameter of less than 100 microns under the ball bond; a bond wire extending from the ball bond; a stitch bond formed on the lead between the lead and the bond wire, the stitch bond being a metal-to-metal bond; and a molding compound covering the semiconductor die, the wire bond, and a portion of the lead of the lead frame to form a semiconductor device package.

[0011] In another example, an apparatus includes a wire bonding tool, the wire bonding tool including: a capillary having a central opening, the capillary configured to receive a bonding wire in the central opening; a first laser path formed in the capillary, the first laser path configured to focus a first laser on an end of the bonding wire to form a free air ball; and a second laser path formed in the capillary, the second laser path configured to focus a second laser on a bonding location below the capillary. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figures 1A to 1B Semiconductor dies on a semiconductor wafer and individual semiconductor dies from the semiconductor wafer for use with the arrangement are shown in a projection view and a close-up projection view, respectively.

[0013] Figure 2 A quad flat no-lead (QFN) semiconductor device package suitable for arrangement is shown in a projection view from the board side.

[0014] Figure 3A In side view or bottom view of the board and Figure 3B Semiconductor device packages suitable for example arrangements are shown in cross-sectional views.

[0015] Figures 4A to 4E Selected steps for forming a semiconductor device package suitable for deployment are shown in a series of views.

[0016] Figures 5A to 5H Selected steps for forming a wire bond using an arranged method and wire bonding tool are depicted in a series of views.

[0017] Figure 6 Absorption of laser energy by materials that may be used with the arrangement is graphically depicted.

[0018] Figure 7 A method for forming a bond wire connection using an example laser enhanced wire bonding arrangement is depicted in a flow chart. DETAILED DESCRIPTION

[0019] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The drawings are not necessarily drawn to scale.

[0020] Elements are described herein as being “coupled.” The term “coupled” encompasses directly connected elements and indirectly connected elements, as well as elements that are still electrically connected even if coupled with intervening elements, conductors, or wires.

[0021] The term "semiconductor die" is used herein. A semiconductor die may include passive devices such as resistors, inductors, filters, sensors, or active devices such as transistors. A semiconductor die may be an integrated circuit having hundreds or thousands of transistors coupled to form functional circuits such as a microprocessor or memory device. A semiconductor die may include elements such as Hall elements for sensing magnetic fields.

[0022] The term "semiconductor device package" is used herein. The semiconductor device package has at least one semiconductor die electrically coupled to a terminal, and has a package body that protects and covers the semiconductor die. The semiconductor device package may include additional elements. Passive components such as sensors, antennas, capacitors, coils, inductors, and resistors may be included. In some example arrangements, multiple semiconductor dies are packaged together. Circuit systems that combine functions such as sensors, amplifier semiconductor dies, and logic semiconductor dies (such as controller dies or digital filters) may be packaged together to form a single semiconductor device package. The semiconductor die is mounted to a package substrate carrying conductive leads. A portion of the conductive leads forms an external terminal or pin of the packaged device. In a wire-bonded semiconductor device package for use in an arrangement, wire bonding couples the conductive leads attached to the package substrate to bonding pads on the semiconductor die. The semiconductor device package may have a package body formed by a thermosetting epoxy resin in a molding process or by using an epoxy resin, a plastic, or a resin that is liquid at room temperature and then cured. The package body may provide a hermetic package for a packaged device. The package body may be formed in a mold using an encapsulation process, however, a portion of the leads of the package substrate are not covered during the encapsulation, these exposed lead portions providing external terminals or pins for the semiconductor device package.

[0023] The term "package substrate" is used herein. A package substrate is a substrate arranged to receive a semiconductor die and to support the semiconductor die in a complete semiconductor device package. The package substrate may include a conductive lead frame, which may be formed of copper, aluminum, stainless steel, steel, and alloys (e.g., alloy 42 and copper alloy). The conductive leads are positioned for coupling to bonding pads on the semiconductor die. The package substrate may be a direct bonded copper (DBC) substrate, or a ceramic substrate with copper traces. The conductive leads are mounted to the package substrate and extend from the package substrate. Electrical connections from the bonding pads of the semiconductor die to the leads are formed using wire bonding or wedge bonding. The lead frame may be provided in strips, grids, or arrays. The conductive lead frame may be provided as a panel or grid of strips or arrays of unit lead frame portions in rows and columns. The semiconductor die may be placed on corresponding unit lead frame portions in the unit lead frame portions within the strip or array for parallel processing to increase throughput. The lead frame leads may have plated portions in areas designated for wire bonding connections to the semiconductor die, for example silver plating may be used.

[0024] When encapsulating semiconductor devices, molding compounds can be used to partially cover the packaging substrate, cover components, cover one or more semiconductor dies, and cover wire bonding or other electrical connections from one or more semiconductor dies to the packaging substrate. This molding process may be referred to as "encapsulation", but some parts of the packaging substrate are not covered in the molding compound during encapsulation. For example, in an arrangement, the encapsulated part is exposed from the molding compound to form a lead of a terminal or pin. Encapsulation is usually a compression molding process, in which thermosetting molding compounds such as epoxy resins can be used. The molding compound used in electronic packaging is sometimes referred to as "epoxy molding compound" or "EMC". In an example process, a room temperature solid or powder EMC can be heated to a liquid state, and then the liquid molding compound can be pressed into a mold cavity through a runner or channel to perform transfer molding. A unit mold shaped to surround an individual device can be used, or block molding can be used to mold several semiconductor devices into a single block shape. The molding process simultaneously forms multiple semiconductor device packages for several semiconductor devices. The devices to be molded may be provided in an array or matrix of a few, hundreds, or even thousands of devices in rows and columns on a lead frame strip.The semiconductor devices and lead frames are then molded simultaneously to increase processing throughput.

[0025] The term "scribe lane" is used herein. A scribe lane is a portion of a semiconductor wafer between semiconductor dies. The term "scribe street" is sometimes used. Once semiconductor processing is completed and the semiconductor device is complete, the semiconductor device is separated into individual semiconductor dies by cutting the semiconductor wafer along the scribe lane. The separated dies can then be removed and disposed of individually for further processing. This process of removing dies from the wafer is called "singling" or sometimes "dividing". The scribe lanes are arranged on four sides of the semiconductor die, and when the dies are singulated from each other, rectangular semiconductor dies are formed.

[0026] The term "saw street" is used herein. A saw street is an area defined between molded electronic devices that is used to allow a saw (such as a mechanical blade, laser, or other cutting tool) to pass between the molded electronic devices to separate the devices from each other. This process is another form of singulation. When the molded electronic devices are provided in the form of a strip and one device is adjacent to another device along the strip, the saw street is parallel and perpendicular to the length of the strip. When the molded electronic devices are provided in the form of an array of devices in rows and columns, the saw street includes two sets of parallel saw streets that are perpendicular to each other, and the saw will traverse the molded electronic devices in two different directions to cut the packaged electronic devices in the array apart from each other.

[0027] In the arrangement, the wire bonding process uses laser energy. The wire bonder capillary of the example arrangement may include one or more laser paths positioned as part of the capillary or adjacent to the capillary. In the example arrangement, a first laser beam is focused to form a free air ball on the end of a bond wire extending from the capillary. A second laser beam is focused on a bonding location such as a bonding pad surface. When performing ball bonding, a first laser is used to form a molten bond on the end of the bond wire, not a conventional electric flame (EFO) arc method or a welding torch, and simultaneously, a second laser beam is focused on the bonding pad surface. When a copper bonding wire is used with a copper bonding pad, a copper-to-copper ball bond is formed by forming a small molten copper surface on the bonding pad and forcing the molten end of the bonding wire to reach therein. Because the wire bonding process forms a small melting area on the bonding pad, the corrosion and oxidation problems faced by existing thermal ultrasonic wire bonders are solved without the need for ultrasonic energy and without the need to heat the entire semiconductor die. Local heating of the bond pad at the bonding location using a laser provides reliable copper-to-copper bonding (when copper bond wires are used with copper bond pads) and eliminates damage to the copper bond pads by reducing or eliminating vibrations when used without the arrangement. Copper plated bond wires and gold, silver or aluminum bond wires with copper or aluminum bond pads can also be used with the arrangement.

[0028] After forming the ball bond, the laser in the capillary can also be used to form a stitch bond on the lead of the package substrate. A second laser can be focused on the bonding position on the conductive lead where the stitch bond is to be formed, and a small melting area is produced. Then, a stitch bond for the bonding wire is formed on the copper lead at the bonding position. Since the conductive lead has a molten surface at the position where the stitch bond is to be formed, a reliable metal-to-metal bond, such as a copper-to-copper bond, is also formed without the need for ultrasonic energy used in conventional thermal ultrasonic wire bonders. The laser can be an ultraviolet laser, such as a 380 nanometer laser, or a blue laser, such as a 445 nanometer laser, for example, laser energy of these frequencies is well absorbed by both copper and gold conductors, and reliable copper-to-copper welding has been demonstrated. Lasers of other frequencies can be used. Commercially available blue lasers can be used with the described arrangement at a reasonable cost.

[0029] Reliable and cost-effective copper-to-copper wire bonding is achieved using the arrangement using copper bonding wire and copper bonding pads. Alternatives include gold bonding wire and gold-to-gold wire bonding. The need for cladding on the copper bonding wire is reduced or eliminated, thereby reducing costs. The need for an ultrasonic generator for the wire bonder is also eliminated, also reducing the cost of the equipment. Laser sources that can be used with the arrangement are commercially available and have proven to be reliable.

[0030] Performing wire bonding on semiconductor dies and package substrates using the arrangement creates a small heat affected zone (HAZ) where ball bonding and stitch bonding will occur, and this small HAZ can be quickly cooled after the bonding operation. Rapid cooling of the bonds then increases wire bonding speed, increasing throughput and yield, further reducing device cost. Additionally, in an example process, using the arrangement can eliminate the need to perform bonding on the package substrate and semiconductor device positioned on a heating block, thereby reducing the cost of the wire bonder tool and reducing thermal stress on the semiconductor die.

[0031] Figure 1A and 1B A semiconductor wafer 101 (the semiconductor wafer having semiconductor devices formed thereon) is shown in two projection views ( Figure 1A ) and individual semiconductor die 105 ( Figure 1B ).exist Figure 1A , a semiconductor wafer 101 having an array of semiconductor die 105 formed in rows and columns on a device side surface is shown. The semiconductor die 105 may be formed using processes commonly used in semiconductor manufacturing facilities, including ion implantation, substrate doping, thermal annealing, oxidation, dielectric and metal deposition, sputtering, photolithography, patterning, etching, stripping, chemical mechanical polishing (CMP), electroplating, and other processes for manufacturing semiconductor devices on a wafer. Slice streets 103 and 104, which run perpendicular to each other and in parallel groups across the wafer 101, separate rows and columns of complete semiconductor die 105 and provide areas for segmenting the semiconductor wafer 101 so as to separate the semiconductor die 105 from each other.

[0032] Figure 1B Individual semiconductor dies 105 are shown after singulation from semiconductor wafer 101, having bonding pads 108, which are conductive pads electrically coupled to devices (not shown) formed on the device-side surface of semiconductor die 105. Bonding pads 108 are positioned for connection to leads of a semiconductor device package.

[0033] Figure 2A quad flat no-lead (QFN) semiconductor device package 200 suitable for arrangement is depicted in a projection view from the board side. In the illustrated example, the semiconductor device package 200 has a terminal 211 for surface mounting to the board using solder. The die pad 213 is exposed from the mold compound 223 forming the package body and can be used as a thermal path to remove excess heat from the semiconductor die (not visible) mounted in the semiconductor device package 200. Other leadless semiconductor packages can be used with arrangements such as small outline no-lead (SON) packages. Alternatively, leaded packages such as small outline integrated circuits (SOIC) or dual in-line packages (DIP) semiconductor packages can be used with arrangements. In order to reduce the size and volume of systems formed using semiconductor devices, there is a constant need to reduce the size of semiconductor packages. Leadless semiconductor device packages occupy less board area for package mounting and are increasingly used. Although the illustrated example is for leadless packages, the arrangement can also be used with lead frames for leaded semiconductor device packages.

[0034] Figure 3A A semiconductor device package 300 for use with an example arrangement is shown in a bottom view of the board side surface. Figure 3A , an example QFN package is shown. Terminals 311 (with Figure 2 The terminal 211 in FIG. 3 is a portion of the lead frame lead 315, and the terminal 311 is a portion of the lead 315 exposed from the molding compound 323. The die pad 313 is also a portion of the lead frame and has full thickness, and thus the board side surface of the die pad 313 is exposed from the molding compound 323.

[0035] Figure 3B Shown in cross section Figure 3A The semiconductor device package 300. Figure 3B, a semiconductor die 305 is shown mounted to the device side surface of a die pad 313 by a die attach material 325, the die pad being the central portion of a lead frame 337. The lead frame 337 has leads 315 having inner ends proximate to and spaced apart from the die pad 313. The lead frame 337 may be copper, copper plated, alloy 42, stainless steel, or other conductive metals and alloys. In an example arrangement, a copper lead frame is used. For example, the lead frame 337 may be partially etched or stamped from a thin sheet material. The leads 315 are formed with a partial thickness at the inner ends and with a full lead frame thickness at the terminal ends, the terminals 311 being formed by exposing a portion of the leads 315 from the mold compound 323. The leads 315 may be formed in a partial etching process. In the partial etching process, the area of ​​the lead frame 337 can be completely etched to form a space or hole, or the lead frame can be selectively partially etched from one side or from the opposite side to form areas of different thicknesses. For example, a sheet material of copper foil can be used as a starting material and patterned using a complete etching and partial etching process. Stamping can be used to pattern the lead frame. The area to be welded of the copper lead frame can be plated or tinned to prevent corrosion and improve weldability. The area for wire bonding connection can be plated to increase bonding strength, and also reduce or eliminate diffusion and oxidation or tarnishing. Plating can include gold, palladium, nickel, silver, tin and combination layers, such as chemical nickel immersion gold (ENIG) and electroless nickel, electroless palladium and immersion gold (ENEPIG). Silver point plating can be used.

[0036] The semiconductor die 305 is electrically connected to the leads 315 of the lead frame 337 by bonding wires forming wire bonds 319. Wire bonds 319 are conductive wires connected from bonding pads on the semiconductor die 305 to the leads 315 in the wire bonding tool. Gold, copper, palladium-coated copper, aluminum, or silver bonding wires can be used for wire bonding connections. In an example, a copper bonding wire with a diameter of about 20 microns is used. Depending on the material selected for the bonding wire and the desired electrical properties of the bonding wire, bonding wires of other diameters can be used. Applicable examples include 15 microns, 20 microns, 25.4 microns, 33 microns, and 50 microns in diameter for copper and palladium-coated copper bonding wires.

[0037] In an example wire bonding process, wire bonding begins with the exposed end of a bond wire extending from an opening in a capillary of a wire bonding tool. The capillary is a hard material, such as a ceramic. Aluminum oxide (aluminum oxide), aluminum zirconium or other ceramics can be used. The capillary has a bottom surface configured to press the bond wire against a bonding pad or lead during bonding. In a conventional bonder, a heat source such as a flame or (more frequently) an electric spark is used to melt the exposed end of the bond wire under the capillary to form a free air ball on the end of the bond wire. Then, mechanical pressure is applied using the surface of the capillary to mechanically press the free air ball onto the bonding pad, and in many instances, ultrasonic energy is applied during ball bonding to produce a bond between the ball formed on the end of the bond wire and the bonding pad. Semiconductor devices and lead frames can be heated to further improve bonding in conventional wire bonders. The bonding pad can be formed of a metallized material used in semiconductor processes, including aluminum and copper bonding pads and alloys of these. In a conventional wire bonder, the wire bonding tool may include a heater block to support and heat the semiconductor die and lead frame to provide thermosonic wire bonding using a combination of heat, mechanical pressure, and ultrasonic energy to form the bond.

[0038] After the ball is bonded to the bond pad, the capillary of the wire bonding tool moves over a portion of the conductive lead to the stitch bond position, and the stitch bond can be formed on the surface of the lead. As the capillary moves, the bond wire is allowed to extend from the ball bond on the bond pad through the capillary opening, and the bond wire is formed in an arc over the lead frame and the semiconductor die, and then the bond wire is pulled down to the stitch bond position on the lead of the lead frame. The capillary then performs a mechanical stitch bond to the lead by pressing the bond wire against the lead using ultrasonic energy again. As the capillary moves away from the stitch bond on the lead, the bond wire is then cut at a short distance from the lead. A short tail extending from the end of the capillary is left, and the process can be repeated for the next wire bond.

[0039] In an arrangement further described below, a wire bonding process uses a laser in the wire bonding process. In the described example process, a first laser is used to form a free air ball at the end of the bonding wire, and a second laser is used to produce a molten portion of a bonding pad or conductor for forming a metal bond. Since the laser produces a molten pool of material at the bonding location on the bonding pad and the conductive lead, the need for ultrasonic energy for effective wire bonding is eliminated. The advantage generated by using the arrangement is that damage to the bonding pad material caused by the ultrasonic energy of the moving capillary is reduced or eliminated, and the use of the arrangement eliminates the need for an ultrasonic generator, which reduces the cost of the wire bonder tool. The use of a laser to produce a copper molten pool, such as in the case of a copper free air ball on a copper bonding wire, causes a copper-to-copper bond without any intermetallic compounds (IMC) that may occur in a conventional wire bonding process. A copper-to-copper bond is formed, which has a low resistivity, thereby improving performance. The small heat-affected zone generated by using a focused laser on the bonding pad and the conductive lead reduces or eliminates the need to heat the entire semiconductor die and lead frame. Rapid cooling after forming a bond due to a small heat affected zone enables faster and faster bonding operations as the capillary can be moved quickly to the next bond, thereby increasing throughput and reducing per-device cost. Thermal stress on sensitive components fabricated in semiconductor dies can also be reduced by using the described arrangement.

[0040] Figures 4A to 4E Selected steps for forming a packaged semiconductor device such as may be used with an example arrangement are depicted in a series of views.

[0041] Figure 4A Lead frame 337 is shown in cross-section mounted on tape 310 for packaging process. Lead frame 337 may be formed by a stamping or etching process of a sheet material for a lead frame and may have copper, copper alloy, Alloy 42, stainless steel, steel, or another conductor. In an example, lead frame 337 is copper or copper alloy. Lead frame 337 has a die pad 313 and leads 315 spaced apart from die pad 313. During processing, the leads may be moved by being in Figure 4A External removable connecting rods or barrier rods (not shown) are temporarily connected to each other for support during processing.

[0042] Band 310 may be a removable adhesive film, such as INNOX Advanced Materials Company, Limited, which can be purchased from South Korea. In an example process, band 310 may be a polyimide film with an adhesive and a release film covering. In an automated process, a tape machine may be used to apply the band to the plate side surface of the lead frame. Band 310 may include a strippable adhesive so that when band 310 is removed after molding, the adhesive is easily removed or removed together with the band. Due to heat applied during a process such as molding, the band is preferably heat-resistant. Other removable films such as UV strippable films may be used. Lead frame 337 and band 310 may be combined and provided to the packaging process as a supply assembly, and this portion of the process may be performed independently of the semiconductor manufacturing process, and performed at various locations, and asynchronously performed relative to the rest of the process.

[0043] Figure 4B Shown after additional processing Figure 4A 337 of the lead frame. In preparation for the subsequent die mounting step, a die attach material 325 is first formed on the device side surface of the die pad 313 of the lead frame 337. The die attach material 325 can be a die attach epoxy. The die attach epoxy can be dispensed in liquid or gel form through a needle dispenser, and alternatively, the die attach epoxy can be dispensed using an inkjet or "drop on demand" system or by using a template. The die attach material 325 can be a die attach tape or film. Since the die pad 313 has a board side surface that will be exposed from the molding compound in the complete semiconductor device package (see Figure 3B The die attach material 325 may be electrically conductive. ...

[0044] Figure 4C Another cross-sectional view shows the die after the die mounting operation. Figure 4B313. In an example process, a pick-and-place tool or other die handling tool may be used to place the semiconductor die 305 on the die attach material 325 to mount the semiconductor die 305 to the die pad 313. The semiconductor die 305 is shown with a bonding pad 308, which may be aluminum, copper, alloy, or plated metal, exposed and facing away from the die pad 313 to prepare for wire bonding. In the illustrated example arrangement, the bonding pad 308 has copper or a copper alloy. The leads 315 are spaced apart from the die pad 313 and the semiconductor die 305. The leads 315 have a partial thickness at the inner end and a full thickness of the lead frame 337 at the outer end away from the semiconductor die 305.

[0045] Figure 4D Another cross section is shown after additional processing. Figure 4C The semiconductor die 305 and the lead frame 337 are shown. Figure 4D As shown in , a wire bond 319 has been formed between the bonding pad 308 and the upper surface of the lead 315. In an example wire bonding process, the wire bonding tool has a capillary having a surface for ball bonding and pin bonding on the surface, and having a central opening. The capillary can be made of ceramic, metal or other hard materials. Example capillary materials include ceramics, such as alumina, or aluminum zirconium. Tungsten can be used. The end of the bonding wire is protruded a short distance through the capillary opening. In the arrangement, the first laser is focused on the end of the bonding wire and is used to heat the end of the bonding wire to form a ball. In the arrangement, the second laser is focused on the bonding position on the bonding pad and simultaneously with the ball formation, or synchronously, the second laser forms a molten pool in the bonding pad surface at the bonding position. The wire bonder moves the capillary over the bonding pad and uses mechanical pressure to force the ball against the molten surface of the bonding pad and forms a ball bond to the bonding pad.

[0046] In a specific example arrangement, a copper bonding wire is used with a copper bonding pad, and a copper-to-copper bond is formed between the ball and the bonding pad. The bonding wire remains attached to the ball bonding. When the capillary moves over the bonding pad, the bonding wire extends through the opening in the capillary and forms an arc or curved shape. The capillary extends the bonding wire over the lead frame and aligns with the predetermined bonding position, and is positioned over the lead. The laser is focused on the bonding point and a melting area is formed on the lead at the bonding point. The capillary then presses the bonding wire against the lead and forms a stitch bond on the lead. Similarly, in an example, the lead frame has a copper lead, and a copper bonding wire is used so that a copper-to-copper bond is formed between the bonding wire and the molten pool on the copper lead. When the capillary moves from the stitch bond, the bonding wire is cut and the cut end of the bonding wire extending from the capillary is used to form the next ball, which is a repeated process. The wire bond may have a short tail extending from the stitch bond. Figures 5A to 5H The use of lasers and capillaries in the method of arrangement is further described in detail.

[0047] Figure 4E Another cross section is shown through the Figure 4D The semiconductor device package 300 is formed by additionally processing the semiconductor die 305. Figure 4E 3, mold compound 323 has been formed over semiconductor die 305, wire bonds 319, and portions of lead frame 337. Portions of leads 315 (e.g., board side surfaces of the outer ends of the leads) are exposed from the mold compound using full thickness to form terminals 311 (see, e.g., Figure 3A The terminal 311 is arranged for surface mounting the package to a system board. The board side surface of the die pad 313 is also exposed from the molding compound. The molding compound can be an epoxy molding compound (EMC), epoxy resin, resin or plastic.

[0048] In an example molding process, a transfer mold is used. A solid thermosetting resin, which can be a pellet or powder, is heated to a liquid state. A punch forces the now liquid molding compound through runners into the mold in the mold recesses, where the lead frame is positioned to hold the semiconductor die, bond wires, and leads in place while the molding compound flows into the mold. The molding compound is then allowed to solidify and cool into a solid package around the semiconductor die and lead frame. Figure 4E As shown in FIG, after the molding step, the band 310 remains in place. Figures 3A to 3B , the tape 310 is removed from the board side surface of the semiconductor device package. A singulation step may be performed to cut unit devices from a lead frame strip or array and singulate the semiconductor device packages from each other.

[0049] Figures 5A to 5H A method of arrangement using a laser assisted wire bonding process is depicted in a series of steps.

[0050] exist Figure 5A , a capillary 551 of a wire bonding tool is shown positioned over a bonding pad 508 of a semiconductor die 505. The semiconductor die 505 is shown mounted on a die pad 513 of a lead frame 537 that is connected to, for example, a semiconductor die 505. Figure 4E The die attach material 525 is used to mount the semiconductor die 505 to the die pad 513. The leads 515 of the lead frame 537 are spaced apart from the die pad 513 and are configured for wire bonding. Figure 5AIn the embodiment of the present invention, the capillary 551 is enhanced by using a first laser source 573 and a second laser source 571. The laser sources may be mounted to the capillary or mounted to direct the laser beam to the capillary using, for example, an optical fiber for directing the laser beam.

[0051] Capillary 551 has a central opening through which bonding wire 553 extends. Bonding wire 553 may be gold, copper, copper-plated, silver or aluminum. In the illustrated example, copper bonding wire is used. Bonding wire 553 may have a diameter between 8 and 70 microns. The opening in capillary 551 is larger than the bonding wire diameter to allow the bonding wire to pass through it, and may be between 35 and 100 microns. Wire clamp 557 is arranged to selectively fix bonding wire 553, or wire clamp 557 may be opened to extend the bonding wire. Bonding wire 553 is provided by a spool or other wire supply source (not shown). The size of the bottom end of capillary 551 is set to fit within the bonding pad opening, and the diameter may be less than 100 microns, for example 50 to 100 microns.

[0052] In an aspect of the arrangement, the capillary 551 is arranged for use with laser energy and has a lens or optical cover 559 at the bottom that allows transmission of light from the laser sources 573, 571. In the illustrated example, a first laser path 563 is used to direct laser energy from the first laser source 573 to the end of the bond wire 553 to allow the desired free air ball to be formed by melting the end of the bond wire 553. A second laser path 561 is formed in a portion of the capillary 551 and has a medium for laser transmission, such as an optical cable for laser energy, and is positioned to receive a laser beam from a second laser source 571 and direct the laser beam to a bonding location on the bond pad 508. Figure 5A The example arrangement shown in has two laser paths, a first laser path 563 of a first laser 573 for directing a laser beam from the first laser source 573 for forming a free air ball, and a second laser path 561 for using the second laser source 571 to melt a bonding pad in a first heat affected zone or on a lead of a lead frame conductor to form a second heat affected zone at a stitch bonding location. In an alternative arrangement, a single laser is used with a beam splitter or mirror to direct the laser beam to the two laser paths. In the illustrated example, the capillary 551 includes laser paths 563 and 561. In an additional alternative arrangement, the laser may be mounted separately from the capillary 551, and the laser may be focused on an appropriate location as described below. The fiber laser path may be mounted on the capillary or have a separate mount so that the laser is focused on an appropriate point during the bonding process. A single laser source may be used to generate multiple beams used in the method. In an additional alternative arrangement, a third or even fourth laser source may be used to generate laser beams for different steps in the method.

[0053] In the illustrated example, two lasers are used. Using two lasers, one laser for free air ball formation and one laser for bonding locations, eliminates the need for using an EFO system in a conventional ball bonder for ball bonding operations. Furthermore, during stitch bonding operations, two lasers are used in the method of the arrangement, one laser to create a melted area in the second heat affected zone on the leads of the package substrate, and another laser to heat the bond wire at the stitch location during stitch bonding.

[0054] Figure 5B Illustration of subsequent operations in the wire bonding cycle Figure 5A Components. Figure 5B In the embodiment of the present invention, a first laser source 573 outputs a laser beam 564 which is guided by a laser path 563 in the capillary 551 to apply laser energy to form a free air ball on the end of the bond wire 553 under the lens 559 of the capillary 551. At the same time or synchronously, a second laser source 571 outputs a second laser beam 562 which is guided by the second laser path 561 to the bonding location on the bond pad 508. In one method of using the arrangement, the two lasers are powered simultaneously. In another method, the two lasers may be operated independently but in rapid succession in any order so that during the formation of the melted area on the bond pad 508, the free air ball formed on the bond wire 553 will melt. Figures 5A to 5B 4 , a semiconductor die 505 , a lead frame 537 , leads 515 , a die pad 513 , and a die attach material 525 are shown, which are supported by a die support 510 .

[0055] The second laser beam 562 may have a focal spot on the bonding pad 508 with a diameter between 50 and 200 microns, similar in size to the diameter of a free air ball. This laser spot will form a small heat affected zone in the bonding pad 508, for example, less than 200 microns (see Figure 5C The first heat affected zone 567 in the ball bond). Since the heat affected zone at the bonding location is smaller (compared to heating the entire bond pad, as is done in a conventional bonding process), the ball bond will cure and harden quickly, allowing the speed of the bonding process to be increased. The use of laser enhanced wire bonding in the arrangement limits the heating of the semiconductor die to a small heat affected zone at the surface of the bond pad, thereby reducing thermal stress on other components in the semiconductor die (compared to conventional wire bonding, which is performed where the lead frame and semiconductor die are heated as a whole). During stitch bonding, a similar second small heat affected zone is formed on the leads of the lead frame, again reducing thermal stress on the components. In addition, the laser enhanced wire bonding method using the arrangement can reduce or eliminate the need for a heating device during wire bonding, for example, wire bonding can be performed at ambient temperature or room temperature (between 15°C and 40°C) without the need to use heaters used in conventional wire bonding tools to heat the semiconductor die and lead frame.

[0056] Figure 5C FIG. 1 shows free air ball formation using two laser beam arrangements and forming a molten area in the first heat affected zone 567 of the bond pad 508. Figure 5B Components. Figure 5C , a free air ball 565 is shown formed on the end of a bond wire 553 extending from a capillary 551, and a melted region or heat affected zone 567 of a bond pad 508 is also shown. The free air ball 565 and the melted region 567 are formed by the operation of a second laser source 571 transmitting a laser beam 562 and a first laser source 573 transmitting a laser beam 564. The laser beam 562 is focused to melt a small portion of the copper bond pad 508 to form the heat affected zone 567, and the laser beam 564 is focused to form the free air ball on the end of the copper bond wire 553. Figure 5A 5 shows a semiconductor die 505, a lead frame 537, leads 515, a die pad 513, and a die attach material 525, which is supported by a die support 510. The laser beams 564 and 562 quickly melt the materials, and the use of the second laser beam 562 to form a molten area in the heat affected zone 567 on the bond pad 508 eliminates the need to "clean" the bond pad 508 to break up any oxidation or tarnish that may have formed on the surface of the bond pad 508, thereby eliminating the need to use conventional ultrasonic energy. Eliminating the use of ultrasonic energy reduces the cost of the bonding tool and reduces damage to the plating on the bond pad used to reduce corrosion and defects.

[0057] Although not shown for simplicity of illustration, copper wire bonding may be performed in an oxygen-deficient environment to reduce oxidation during bonding. Since copper bonding wires and copper bond pads are susceptible to oxidation, nitrogen or other oxygen-free gas may be applied to the bonding area during the bonding process to further delay or prevent oxidation. The laser enhanced wire bonding of the arrangement may enable wire bonding without the need for a heater block to heat the semiconductor die and lead frame, which reduces the temperature during bonding, and this aspect of the arrangement also advantageously reduces unnecessary copper oxidation, which is accelerated at higher temperatures.

[0058] When the molten free air ball 565 contacts the molten area in the heat affected zone 567 of the bond pad 508, the arrangement is used to achieve a copper-to-copper bond between the bond wire 553 and the bond pad 508. The capillary 551 moves the molten free air ball 565 to the molten area 567 to form a copper-to-copper bond, in the example where a copper bond wire is used for the bond wire 553, and a copper bond pad is used for the bond pad 508. The die pad 513, the lead 515 of the lead frame 537, and the die support 510 are shown in FIG. Figure 5A Arranged as shown in Figure 5CAs shown in , two laser beams 564 and 562 may be applied simultaneously during the ball bonding step to ensure that the molten free air ball interfaces with the molten area of ​​the bond pad and forms a copper-to-copper bond.

[0059] Figure 5D Figure 1 shows the subsequent steps in the wire bonding process. Figure 5C Components. Figure 5D , a ball bond 570 is shown formed on the bond pad 508 at the heat affected zone 567. The molten area in the heat affected zone 567 will cool and harden and have a diameter of less than 200 microns, which corresponds to the laser spot size. Figure 5D As shown in , the capillary 551 has been moved upward from the bonding pad 508 so that the bonding wire 553 extends to the position where the bonding wire loop will be formed, thereby setting the loop height. The looped shape of the bonding wire used in the wire bonding allows the wire bonding to extend laterally above the semiconductor die 505, while the bonding wire 519 is spaced apart from the die and the die edge, thereby preventing short circuits that may otherwise occur. By selectively clamping the bonding wire 553 and extending the bonding wire through the capillary 551, the clamp 557 can be used to shape the bonding wire 553. The melting area in the ball bond 570 and the heat affected zone 567 is several times larger than the diameter of the bonding wire, for example, 2 to 3 times larger, which is a small area affected by the laser energy. The melting area in the ball bond 570 and the heat affected zone 567 will cool rapidly and the bonding process can proceed to the next bond quickly, thereby increasing the throughput (when compared to conventional wire bonding without a laser). The bond between ball bond 570 and bond pad 508 is a copper-to-copper bond made in a molten state and is a strong and low resistance metal-to-metal bond. Figure 5D In the embodiment, the lead frame 537, the lead 515, the die pad 513, the die bonding material 525 and the die support 510 are as shown in FIG. Figure 5A It should be noted that while the illustrated example steps are described using copper bond wires, gold also absorbs and heats in response to blue laser energy, and laser enhanced wire bonding can be used with gold or gold alloy bond wires and gold bond pads, for example to form gold-to-gold ball bonds.

[0060] Figure 5E Figure 1 shows the subsequent steps in the wire bonding process. Figure 5D Components. Figure 5E, wire bond 519 is shown extending from ball bond 570 on bond pad 508 at heat affected zone 567. Capillary 551 has now been moved laterally away from ball bond 570 so that bond wire 553 extends and forms wire bond 519 as a curved loop. Capillary 551 is positioned over lead 515 of lead frame 537 and carries bond wire 553 in preparation for stitch bonding on lead 515. Clamp 557 is shown open, but can be selectively closed to allow capillary 551 to pull bond wire 553 into a desired shape. Die pad 513, semiconductor die 505, die attach material 525, die support 510, and laser sources 573 and 571 are all as in FIG. Figures 5A to 5D As shown in .

[0061] Fig. 5F Figure 1 shows the subsequent steps in the wire bonding process. Figure 5E Components. Fig. 5F , laser beam 562 is shown as forming a melted portion in a heat affected zone 572 on lead 515 in preparation for a stitch bonding operation. Capillary 551 is positioned above the stitch bonding location. Laser beam 562 is shown as being directed from a second laser source 571 through a laser path 561 in capillary 551. In an alternative arrangement, laser beam 562 may be provided via an optical path rather than capillary 551. Lens 559 transmits laser energy and may include optical elements to focus laser beam 562. Fixture 557 is shown as securing bonding wire 553 in position in preparation for a stitch bonding operation. Die pad 513, semiconductor die 505, die attach material 525, and die support 510 are all shown. Figures 5A to 5E As shown in .

[0062] Figure 5G Illustration showing stitch bond formation in a laser enhanced wire bonding process showing an example arrangement Fig. 5F Components. Figure 5G, laser beam 562 is shown as forming a melted area in heat-affected zone 572 on lead 515. Bond wire 553 is moved through capillary 551 to form a stitch bond on lead 515 by placing bond wire 553 in the melted portion of heat-affected zone 572 on the surface of lead 515. At the same time, first laser source 573 transmits laser beam 564 for heating and partially melting bond wire 553 at the stitch bond location. The molten metal in lead 515 will bond to the heated and partially melted bond wire 553 to form a stitch bond. Once the stitch bond is formed, laser beams 564 and 562 can be stopped and the molten metal is allowed to solidify by cooling. Since the melted area for stitch bonding is a small heat-affected zone on lead 515, the stitch bond will harden quickly because the rest of lead 515 is not heated. This rapid solidification is an advantage of using the arrangement as compared to the heated lead frame method used in conventional bonders without the use of laser enhanced wire bonding. The die pad 513, semiconductor die 505, die attach material 525, and die support 510 are all as shown in FIG. Figures 5A to 5F As shown in .

[0063] Figure 5H Schematic diagram showing wire bonding 519 after a bonding process using an arrangement Figure 5G Components. Figure 5H , wire bond 519 extends from ball bond 570 on bond pad 508 to stitch bond 574 formed on lead 515. Capillary 551 is shown after wire clamp 557 is used to break bond wire 553 and form a new end on bond wire 553 for subsequent ball bond. The process of forming a wire bond 519 by a capillary 551 may be repeated for each wire bond 519 required to complete the electrical connection of the semiconductor die to the lead frame lead. Figures 5A to 5H The process shown.

[0064] Due to the use of the arrangement a small heat affected zone is generated (see Figure 5H Instead of using a heater block to heat the entire lead frame and semiconductor die, the time for cooling ball bonds and stitch bonds is reduced, and the capillary 551 can be quickly moved from one bonding site to another, thereby increasing processing throughput.

[0065] exist Figure 5H, capillary 551 is shown with first and second laser paths 563, 561, as well as bond wire 553 and wire clamp 557. A lens or optical cover 559 is shown on the bottom of capillary 551. In additional alternative arrangements, the alternative laser paths are part of capillary 551, and laser sources 573, 571 may be mounted independently of capillary 551. In other arrangements, a single laser may be used with a beam splitter, mirrors, and optical fibers to form two laser beams.

[0066] When the arrangement is used with copper bonding wires and copper bonding pads, as is increasingly being used, copper-to-copper bonds are formed at ball bond and stitch bond locations. These bonds are formed as metal-to-metal bonds without the need for ultrasonic energy and without the use of a heater block. Because the laser enhanced wire bonding of the arrangement achieves metal bonding without the need for ultrasonic energy, damage to the bonding pads that has been observed in thermosonic wire bonding is reduced or eliminated. By using the arrangement, thermal stresses on components in the semiconductor die are reduced because the semiconductor die may not be heated during the wire bonding process, but rather only the ball bond and stitch bond locations are heated by the laser.

[0067] Although the examples described above are described as using copper bonding wires and copper bonding pads, the arrangement can also be used with other materials. For example, gold bonding wires are commonly used and can be used with the arrangement. Aluminum bonding pads can be used with copper or gold bonding wires. Plating on the bonding pads can be used, including nickel, gold and palladium layers to increase bonding and reduce oxidation, tarnishing and copper diffusion.

[0068] The wavelength used in the laser of the arrangement may vary, but may be selected to be a frequency that is highly absorbed by the materials used in the bond wires, bond pads and leads of the package substrate.

[0069] Figure 6 The XY graph shows the absorption of laser energy of different wavelengths by metal materials used in semiconductor processes. Figure 6 As shown in , for laser light with wavelengths between 200 and 500 nanometers (0.3 to 0.5 micrometers), both copper and gold have good absorption rates of about 60%. Curve 601 represents copper, and curve 603 represents gold.

[0070] Copper and gold absorb ultraviolet (wavelengths between 200 and 389 nanometers), violet (wavelengths between 390 and 419 nanometers), and blue (wavelengths between 420 and 499 nanometers) lasers very well. Blue lasers at 445 nanometer wavelength have been shown to exhibit good heating and absorption (especially by copper) and are readily commercially available. Using these commercially available lasers in the described arrangement provides an economical approach to implementing a wire bonding tool utilizing laser energy enhancement.

[0071] Figure 7 A flowchart is shown for forming and Figures 5A to 5H The steps in the illustrated sequence of FIG. 701 correspond to the steps in the arrangement. At step 701, the method begins by forming a free air ball of molten material on the end of a bonding wire extending through a capillary using a first laser. (See, e.g., Figure 5C The free air ball 565 in FIG. 5 ). The free air ball may be formed using a laser beam from a first laser source, as described above and in Figure 5C In an alternative approach, the EFO system can be used to form free air balloons.

[0072] At step 703, the method continues by forming a melted region on a bond pad of the semiconductor die at a bonding location using a second laser. (See Figure 5C The melting area in the heat affected zone 567 on the bonding pad 508). Figure 5C As shown in , forming the free air ball and forming the molten region can be performed simultaneously, alternatively, these steps can be performed simultaneously in any order.

[0073] The method then proceeds to step 705, moving the capillary and bringing the melted region into contact with the free air ball. At step 707, the method continues by forming a ball bond between the free air ball and the melted region of the bonding pad. (See Figure 5C , wherein the capillary 551 carries the free air ball 565 to contact the melted area of ​​the heat affected zone 567, and Figure 5D , where ball bond 570 is shown as being on bond pad 508).

[0074] At step 709, the method continues by moving the capillary away from the ball bond while extending a bond wire from the ball bond and forming a wire bond loop in the bond wire extending from the ball bond. (See Figure 5D , where the capillary 551 moves away from the ball bond 570 and the bond wire 553 extends from the ball bond, and Figure 5E , where wire bond 519 is shown forming a loop extending from ball bond 570).

[0075] At step 711, the method continues by moving the capillary and extending the bond wire over the pin bonding location on the lead of the package substrate on which the semiconductor die is mounted. (See, e.g. Figure 5E , wherein the capillary 551 is positioned over the lead 515 of the lead frame 537 and the semiconductor die 505 is mounted on the die pad 513 of the lead frame 537).

[0076] At step 713, the method continues by using a second laser beam to form a melted region on the lead at the stitch bond location. (See, e.g. Fig. 5F , where the second laser beam is shown as forming a melted portion in the heat affected zone 572 on the lead 515 at the stitch bonding location).

[0077] At step 715, the method continues by contacting the melted region on the lead with the bond wire using a capillary and forming a stitch bond between the bond wire and the melted region on the lead while heating the bond wire using a first laser. (See Figure 5G , wherein a stitch bond is formed by placing a bonding wire 553 onto a melted portion in a heat affected zone 572 on a lead 515; and Figure 5H , where stitch bonding 574 is shown).

[0078] Figure 7 Steps 701, 703, 705, 707, 709, 711, 713, and 715 shown in the can be repeatedly performed in an automated wire bonder until all wire bonding connections between bond pads on a semiconductor die and leads of a lead frame are completed. Laser enhanced wire bonding using the described arrangement results in metal-to-metal bonding at ball bonds on bond pads and stitch bonds on leads without the need for ultrasonic energy and without the use of heater blocks, thereby improving bonding, reducing damage to bond pads, and reducing the cost of wire bonder tools.

[0079] Modifications to the described arrangements are possible, and other alternative arrangements are possible, within the scope of the claims.

Claims

1. A method comprising: using a first laser to form a free air ball of molten material on an end of a bond wire extending through the capillary; forming a melted region on a bond pad of the semiconductor die at a bonding location using a second laser; moving the capillary and bringing the melted region into contact with the free air ball; forming a ball bond between the free air ball and the melt region of the bond pad; moving the capillary away from the ball bond while causing the bond wire to extend from the ball bond and forming a wire bond loop in the bond wire extending from the ball bond; moving the capillary and extending the bond wire over a stitch bonding location on a lead of a package substrate on which the semiconductor die is mounted; forming a melted region in a heat affected zone on the lead at the stitch bonding location using the second laser; as well as The melted region in the heat-affected zone on the lead is brought into contact with the bonding wire using the capillary, and stitch bonding is formed between the bonding wire and the melted region on the lead while the bonding wire is heated using the first laser. 2 . The method of claim 1 , wherein the first laser and the second laser are attached to the capillary. 3 . The method of claim 2 , wherein forming the stitch bond comprises forming a copper-to-copper bond between a copper lead and a copper bond wire. 4 . The method of claim 1 , wherein the first laser and the second laser have wavelengths between 300 nanometers and 499 nanometers. The method of claim 1 , wherein the first laser is a blue laser having a wavelength of approximately 445 nanometers. The method according to claim 1 , wherein the bonding wire is copper, palladium-coated copper, gold, silver or aluminum. 7 . The method of claim 1 , wherein the bond wire comprises copper or a copper alloy, the bond pad comprises copper or a copper alloy, and the lead comprises copper or a copper alloy.

8. The method of claim 1, wherein the bond wire is copper and the bond pad is copper, the ball bond is a copper-to-copper bond, and the lead is copper or a copper alloy, and the stitch bond is a copper-to-copper bond.

9. The method of claim 1, wherein during the forming of the ball bonds, the semiconductor die is at a temperature between 15°C and 40°C. 10 . The method of claim 1 , wherein forming the free air ball using the first laser and forming the melted portion of the bonding pad using the second laser are performed simultaneously. 11 . The method of claim 1 , wherein forming a melted area on a wire using the second laser and heating the bonding wire using the first laser while forming a stitch bond are performed simultaneously. The method according to claim 1 , wherein the bonding wire is gold or a gold alloy.

13. The method of claim 12, wherein the bond pad is gold or a gold alloy and the ball bond is a gold-to-gold bond.

14. The method of claim 1, wherein forming the ball bond and forming the stitch bond are performed without applying ultrasonic energy to the capillary. 15 . The method of claim 1 , wherein forming a melt region on a bonding pad of the semiconductor die at a bonding location using a second laser comprises forming a first heat affected zone having a diameter less than 100 microns in the melt region. 16 . The method of claim 1 , wherein forming a melt region on the lead at a stitch bonding location using the second laser comprises forming a second heat affected zone having a diameter of less than 100 microns in the melt region on the lead.

17. An apparatus comprising: a lead frame having a die pad and leads spaced apart from the die pad; a semiconductor die mounted to the die pad and having a bonding pad facing away from the lead frame; A wire bond electrically coupling the bond pad to a lead, the wire bond comprising: a ball bond formed on the bond pad, the ball bond having a metal-to-metal bond between the ball and the bond pad, the bond pad having a first heat affected zone having a diameter of less than 100 microns beneath the ball bond; a bond wire extending from the ball bond; a stitch bond formed on the lead between the lead and the bonding wire, the stitch bond being a metal-to-metal bond having a second heat-affected zone on the lead with a diameter of less than 100 microns; and A molding compound covers the semiconductor die, the wire bonds, and a portion of the leads of the lead frame to form a semiconductor device package.

18. The apparatus of claim 17, wherein the lead frame is copper or a copper alloy.

19. The apparatus of claim 17, wherein the bond wire is copper, palladium-coated copper, silver, aluminum, or gold.

20. The apparatus of claim 19, wherein the bond wire is copper or a copper alloy.

21. The apparatus of claim 20, wherein the ball bond is a copper-to-copper bond.

22. The apparatus of claim 21, wherein the stitch bond is a copper-to-copper bond.

23. A wire bonding tool comprising: a capillary having a central opening, the capillary configured to receive a bond wire in the central opening; a first laser path formed in the capillary, the first laser path configured to focus a first laser beam on a distal end of the bond wire as the bond wire extends from the opening; and A second laser path is formed in the capillary, the second laser path being configured to focus a second laser beam on a bonding location beneath the capillary.

24. The wire bonding tool of claim 23, further comprising a first laser source configured to transmit the first laser beam through the first laser path.

25. The wire bonding tool of claim 24, further comprising a second laser source configured to transmit the second laser beam through the second laser path.

26. The wire bonding tool of claim 25, wherein the first laser source and the second laser source transmit laser beams having wavelengths between 300 nanometers and 499 nanometers.

27. The wire bonding tool of claim 25, wherein the first laser source and the second laser source transmit the first laser beam and the second laser beam at a wavelength between 440 and 470 nanometers.

28. The wire bonding tool of claim 23, wherein the capillary is not coupled to a sonic energy source or an ultrasonic energy source.

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