Bonding module pins to an electronic substrate

A method includes disposing a terminal pin on an electronic substrate with a base region of the terminal pin in contact with a circuit trace on an electronic substrate, and ultrasonically coupling the base region of the terminal pin to the circuit trace.

TECHNICAL FIELD

This description relates to power device module packages.

BACKGROUND

It may be desirable in some applications to engineer and manufacture power devices to provide sufficient performance, cost, and reliability. A semiconductor power device can be often manufactured discretely as opposed to being integrated in an integrated circuit (IC) process. Typically, the power device die is mounted on a printed circuit board to form a circuit, and enclosed in a power module package. Packaging technologies for a power module package can include lead frame, die attach, electrical interconnections, and encapsulation. Power module pins attached to the printed circuit board extending through the power module package can form the external electrical connections (e.g., power supply, signal, and ground leads (terminals)) to the enclosed circuit.

The semiconductor packaging technologies can only degrade the performance of a power device and circuit by adding thermal and electrical resistance, inductance, size, cost, and reliability problems. Thus, a need exists for systems, methods, and apparatus to address the shortfalls of present technology and to provide other new and innovative features.

SUMMARY

A method includes disposing a terminal pin on an electronic substrate with a base region of the terminal pin in contact with a circuit trace on the electronic substrate, and ultrasonically coupling the base region of the terminal pin to the circuit trace.

In an aspect, disposing the terminal pin on the electronic substrate includes picking up the terminal pin from a rack using a sonotrode probe, and moving the picked-up terminal pin to a location on the electronic substrate in a pick-and-place operation. The terminal pin has at least one compressible shape feature, and picking up the terminal pin from the rack includes press-fitting the terminal pin in a lumen in the sonotrode probe by compressing the at least one compressible shape feature. The at least one compressible shape feature may include at least one of a groove-and-ridge section disposed in the body region of the terminal pin, an eye-of-needle structure disposed in the tip region of the terminal pin, and a chamfer transitioning from the body region to a flange in the base region of the terminal pin.

In an aspect, directing ultrasonic energy to the base region of the terminal pin in contact with the circuit trace includes using the sonotrode to direct ultrasonic waves to the base region in contact with the circuit trace.

DESCRIPTION

In some implementations, the modules and packages described herein include high power devices that are assembled together into a single package. For example, the packages can include multiple semiconductor die (e.g., silicon semiconductor die, silicon carbide (SiC) semiconductor die, insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field effect transistor (MOSFET) die, etc.) that may be assembled together to provide high performance, reliability, and/or improvement in thermal management while maintaining proper electrical performance of the submodule or package.

In some implementations, the packages described herein can be used in applications with high voltages (e.g., higher than 600 V), high current densities (e.g., between 100 A to 800 A (e.g., 400 A)), and/or high switching frequencies (e.g., greater than 1 kHz). In some implementations, the packages can be used in a variety of applications including, for example, automotive applications (e.g., automotive high power module (AHPM), electrical vehicles, and hybrid electrical vehicles), computer applications, industrial equipment, traction invertors, on-board charging applications, inverter applications, and/or so forth. In some implementations, one or more of the semiconductor die described herein can include, or can be, at least a portion of an automotive high power module (AHPM) power device.

Inverters for industrial applications (e.g., automotive inverters) can incorporate a wide variety of components, including insulated-gate bipolar transistor (IGBT) power devices, fast recovery diodes (FRDs), high-voltage DC line capacitors, main circuit bus bars, a power module drive circuit board, a motor control circuit board, three-phase current sensors, and DC and heavy-current AC connectors, etc.

Terminal pins are useful connectors for devices mounted on, and circuits formed on, electronic substrates. An electronic substrate, for example, can be a printed circuit board with circuit trace(s) (e.g., a metal or copper traces), can be a direct bonded metal (DBM) substrate (e.g., direct-bonded copper (DBC)) having circuit trace(s) formed (e.g., printed) on a side (or both sides), and/or so forth. Circuit components (semiconductor device die, resistive elements, capacitors, inductors, interconnections, terminal pins etc.) may be disposed on the circuit trace(s) to form an electronic circuit.

In example power modules or packages, the electronic substrates may be enclosed in a housing or casing (e.g., a plastic cover or molding). The terminal pins may be attached to pads on the electronic substrate and extend through the housing or casing to form external electrical interconnections (e.g., power, signal or ground terminals) of the power modules or packages. The terminal pins may be made of, for example, copper, nickel, aluminum, or other metals or metallic alloys. The terminal pins may be plated with, for example, silver, palladium, nickel or gold.

In packaging technologies, the terminal pins are attached to pads on the electronic substrate before packaging, for example, using soldering techniques. The soldering techniques may involve using solder alloy as adhesive material and heating for solder reflow (to bind pins to the pads on the electronic substrate). A pin may have a flat face that may be soldered, for example, to a copper track of the electronic substrate. The other end of the pin may be available for making a connection terminal outside of the package (after packaging).

The soldering techniques for attaching pins to the electronic substrate may involve reheating and cooling cycles (e.g., during pin attachment solder reflow process). The reheating and cooling cycles can degrade interfaces of other components (e.g., die attach interface) already attached to the electronic substrate. Further, solder intermetallic growth can pose reliability problems.

The present disclosure describes, systems and methods using ultrasonic bonding (e.g., welding) to attach terminal pins to an electronic substrate or an electronic substrate.

A terminal pin may have a rod-like or needle-like shape extending from a pin tip region to a base region (e.g., a base with a substantially flat face). For ultrasonic bonding, the terminal pin may be placed on a portion (e.g., a metal pad) of the circuit trace with the flat face of the base in contact with the metal pad. A tool, for example, an ultrasonic sonotrode (also known as ultrasonic tip, probe, horn or finger), may direct ultrasonic energy (waves) to the base region of the pin with the flat face of the base in contact with the metal pad. The applied ultrasonic energy may ultrasonically bond (e.g., weld) the terminal pin to the electronic substrate (e.g., DBM substrate) along the flat face of the base in contact with the metal pad.

In some implementations, the sonotrode may be configured to apply ultrasonic energy by directing longitudinal ultrasound waves to the base region of the pin with the flat face of the base in contact with the metal pad. The longitudinal ultrasound waves may be generated, for example, by longitudinal movements of ultrasound transducers in the sonotrode along a vertical axis. A speed or vibrational frequency of the longitudinal movements of ultrasound transducers movements of ultrasound transducers may be of the order of several kHz (e.g., in the range of about 20 kHz to 80 kHz).

In some implementations, the sonotrode may configured to apply ultrasound energy by directing torsional ultrasound waves (i.e., tangential vibrations) to the base region of the pin with the flat face of the base in contact with the metal pad. The torsional ultrasound waves may be generated, for example, by rotational or twisting movements of ultrasound transducers in the sonotrode about the vertical axis. A speed or vibrational frequency of the rotational or twisting movements of ultrasound transducers may be of the order of several kHz (e.g., in the range of about 20 kHz to 80 kHz).

FIGS.1A through1Dshow, for example, ultrasonic welding of a needle-like terminal pin110placed on a metal pad120using a sonotrode130.

Terminal pin110may have a pin tip region112and a base region114. Base region114(also can be referred to as head region) may have a with a substantially flat surface116. Terminal pin110may be disposed (e.g., disposed vertically, disposed substantially vertically) so that substantially flat surface116of base region114is in contact with a surface122of metal pad120.

Sonotrode130may include a hollow probe132having a probe tip or edge134. Hollow probe132may have a tubular structure with a lumen extending inward from probe tip or edge134. Sonotrode130may aligned to receive terminal pin110in hollow probe132. For ultrasonically welding terminal pin110to metal pad120, sonotrode130may be lowered over terminal pin110so that probe edge134is close to base region114in contact with metal pad120.

FIG.1Ashows, for example, pin tip region112of terminal pin110introduced in hollow probe132.FIG.1Bshows, for example, sonotrode130lowered over terminal pin110so that edge134is close to base region114in contact with metal pad120. In this position, as shown inFIG.1C, sonotrode130may be activated to direct ultrasonic waves (e.g., longitudinal ultrasonic waves136and/or torsional ultrasonic waves137) to base region114in contact with metal pad120. In example implementations, the ultrasonic waves (e.g., longitudinal ultrasonic waves136and/or torsional ultrasonic waves137) may have a frequency, for example, in the range of about from 20 kHz to 80 kHz, and a small amplitude of vibration (e.g., about 13 to 130 micrometers). The ultrasonic waves (e.g., longitudinal ultrasonic waves136and/or torsional ultrasonic waves137) may give energy directly to a welding contact area (e.g., surface116), with little diffraction. In response to the high frequency and the amplitude of the ultrasonic waves, a resulting friction along surface116may bind (weld) base region114to metal pad120.FIG.1Dillustrates terminal pin110with base region114welded to metal pad120(as base region114W) after repositioning of the sonotrode.

In example implementations, terminal pins (e.g., terminal pin120) may be coupled (e.g., welded), in situ, on a, for example, an electronic substrate that already has several mounted circuit components (semiconductor device die, resistive elements, capacitors, inductors, interconnections, other terminal pins, etc.).FIG.2shows for example, an electronic substrate200with a printed circuit trace210. Several circuit components (e.g., die220, interconnections230, etc.) of a circuit (e.g., a power circuit) may be disposed on circuit trace210. Terminal pins250may be ultrasonically welded or bonded to circuit trace210, in situ, using, for example, sonotrode130.FIG.2shows, for example, a terminal pin252in a process of being ultrasonically welded or bonded to circuit trace210using sonotrode130.

In example implementations, a system for ultrasonically welding terminal pins to an electronic circuit trace on an electronic substrate may include a sonotrode coupled to an x-y-z placement tool.

FIG.3schematically shows an example system300for ultrasonically welding terminal pins (e.g., terminal pin310) to an electronic circuit trace on an electronic substrate. System300may include a stage350(e.g., an XY stage) for holding the electronic substrate352, and a sonotrode330powered by ultrasonic power generator332. Hollow probe tip334of sonotrode330may include locking mechanisms (e.g., a chuck, a pressure-fit) (not shown) for automatically holding and releasing terminal pin310. Sonotrode330may be coupled to a motorized three-dimensional (3D) positioner334(e.g., an XYZ positioner configured to move the sonotrode330probe along X, Y, Z axes). Three-dimensional positioner334may include a position detector (e.g., a camera)(not shown) for detecting positions electronic substrate352(held on stage350). Three-dimensional positioner334may be further configured to drive sonotrode330to pick-and-place terminal pins onto electronic substrate352, for welding.

Terminal pins used to form external electrical interconnections (e.g., power, signal or ground terminals) of the power modules or packages may have different shapes, for example, in consideration of the weld characteristics when attached to electronic substrates. Further, the shapes of the terminal pins may be adapted to activate locking mechanisms (e.g., a chuck, press-fit, etc.) to hold the terminal pins in probe tip336of sonotrode330.

FIGS.4A through6Bshow examples of terminal pins having shapes configured in consideration of the weld characteristics when attached to electronic substrates. Further, the terminal pins may have shape features (e.g., locking mechanisms) for holding and releasing the terminal pins in probe tip336.

FIG.4Ashows a plan view, andFIG.4Bshows a perspective view, of a terminal pin410with a shape adapted in consideration of the welding characteristics when attached to electronic substrates. Terminal pin410also includes shape features for fixedly coupling (e.g., press-fitting) in probe tip336. Although some implementations refer to press-fitting, these implementations can include any type of fixed coupling.

Terminal pin410may include a pin tip region412, a pin body region414, and a pin base region416. In example implementations, pin body region414may be a rod-like cylindrical body414-b(shank). Cylindrical body414-bmay have a diameter d in the range of about a fraction of a millimeter to a few millimeters (e.g., 0.4 mm to 2 mm). Pin tip region412may include an extension of the cylindrical body ending in pointed end412-t. The extension of the cylindrical body in the pin tip region below pointed end412-tmay include a grooves-and-ridges section (section412-gr) having, for example, one or more circumferential grooves (and ridges). Further, pin base region416may include a flat flange416-fcapping cylindrical body414-bof pin body region414. Flange416-fmay be shaped like a circular, oval, or rectangular plate. In the example shown inFIGS.4A and4B, flange416-fis a flat plate with a circular shape.

A chamfer416-cmay be used to transition from the cylindrical body of pin body region414to flange416-c. Terminal pin410may have a flange-to-tip length L and a body diameter db, chamfer416-cmay have a diameter dc, and grooves-and-ridges section may have a diameter dgr. The grooves (or recesses) can have a diameter less than the diameter dgr.

In example implementations, flange416-fmay have a diameter df in the range of about a fraction of a millimeter to a few millimeters (e.g., 0.4 mm to 2 mm wide). A diameter of the flange416-fis larger than the diameter dc of the chamfer416-c. The diameter dc of chamfer416-cis larger than the diameter db of the body of the terminal pin410.

FIG.4Cis an exploded view of base region416of terminal pin410illustrating an example orientation and example dimensions of chamfer416-f, pin body region414and flange416-f. As shown inFIG.4C, pin body region414may include a cylindrical body having a diameter d. Flange416-fmay have a diameter df and a thickness tf. The thickness tf is smaller than the diameter df. Chamfer416-cmay transition from the cylindrical body to the flange at an angle ca. Chamfer416-cmay have a diameter dc (at the flange) and a thickness tc. The thickness tc is smaller than the thickness tf in some implementations. Chamfer416-cmay transition from the cylindrical body to the flange at an angle ca.

In example implementations, flange416-fmay have a diameter df in the range of about a fraction of a millimeter to a few millimeters (e.g., 0.4 mm to 2 mm). Chamfer416-cmay transition from the cylindrical body to the flange at a chamfer angle ca in a range of 20 degrees to 70 degrees. Chamfer416-cmay have a diameter dc (at the flange) that is greater than the diameter d of the cylindrical body by about 0.2 mm to 0.6 mm.

The shape features of terminal pin410useful for fixedly coupling (e.g., press-fitting) in probe tip334may, for example, include grooves-and-ridges412-grand chamfer416-f.

FIG.5Ashows a plan view, andFIG.5Bshows a perspective view, of another terminal pin510with a shape adapted in consideration of the welding characteristics when attached to electronic substrates. Terminal pin510may have shape features for fixedly coupling (e.g., press-fitting) the terminal pin in probe tip334. Terminal pin510, like terminal pin410,FIGS.4A-4C) may include a pin body region414, and a pin base region416. Pin base region416may include a flat flange416-f. A chamfer (e.g., a chamfer416-c) may transition from cylindrical body414-bof pin body region414to flange416-f. Terminal pin510may further include a pin tip region512. Pin tip region512may have an eye-of-needle structure512t. The eye-of-needle structure512tmay be formed by providing a circular or oval hole (eyelet512-eon) in a flattened fish-shaped extension of the cylindrical body of pin body region414. Eye-of-needle structure512tmay have a lateral width Weon at the widest. In example implementations, Weon may be in the range of a fraction of millimeter to a few millimeters (e.g., 0.8 mm to 3 mm wide). Terminal pin510may have a flange-to-tip length L, and chamfer416-fmay have a diameter dc.

The shape features of terminal pin510useful for fixedly coupling (e.g., press-fitting) in probe tip334may, for example, include eye-of-needle structure512tand chamfer416-f.

In the example terminal pins (e.g., terminal pins110,410,510, etc.) described in the foregoing, the pin body region (e.g., region414) has been described as being a rod-like cylindrical body (e.g., cylindrical body414-b). In some example implementations, the pin body region may include structures or regions of non-cylindrical shape (e.g., an S-shaped ribbon structure, a double-eyelet eye-of-needle structure, etc.).FIG.5Cshows, for example, terminal pin510in which a portion of pin body region414is an S-shape ribbon structure414-S.FIG.5Dshows, for example, terminal pin510in which a portion of pin body region414is a double-eyelet eye-of-needle structure414-deon. The shapes and dimensions (not shown) of these non-cylindrical shapes (e.g., S-shaped ribbon structure414-S, double-eyelet eye-of-needle structure414-deon, etc.) may (like the dimensions of eye-of-needle structure512tand chamfer416-f) be conducive for fixedly coupling (e.g., press-fitting) terminal pin510in probe tip334.

FIG.6Ashows a plan view, andFIG.6Bshows a perspective view, of another terminal pin610with a shape adapted in consideration of the weld characteristics when attached to electronic substrates. Terminal pin610may have shape features for fixedly coupling (e.g., press-fitting) the terminal pin in probe tip334. Terminal pin610may include a pin tip region612, a pin body region614, and a pin base region616. Pin body region614may have a flat ribbon-like structure. Pin tip region612(like pin tip region412,FIGS.5A and5B) may have an eye-of-needle structure512t. The eye-of-needle structure may be formed by providing a circular or oval hole (eyelet512-eon) in an extension of the flat ribbon-like structure of pin body region614. Further, pin base region616may include a flat616-fcapping the cylindrical body of pin body region414. Flange616-fmay be shaped like a flat circular, oval, or rectangular plate. In the example shown inFIGS.6A and6B, flange616-fhas a flat rectangular shape. A chamfer616-cdisposed on one or more sides (e.g., lateral sides) of the flat ribbon-like body of pin body region414may be used to transition from pin body region614to flange616-f.

The shape features of terminal pin610useful for fixedly coupling (e.g., press-fitting) in probe tip334may, for example, include eye-of-needle structure512tand chamfer616-f.

Shape features of terminal pins410,510,610(e.g., grooves-and-ridges section412-gr, chamfer416-f, chamfer616-f, and eye-of-needle structure512t, etc.) may be adapted to be fixedly coupled (e.g., press-fit) and hold the pins in a lumen of a probe tip of a sonotrode. The shape features may have a diameter or width larger (slightly larger) than a diameter of the lumen. The shape features may be compressible (e.g., radially compressible). The shape features when compressed may have reduced diameters or widths allowing the terminal pins to be inserted in the lumen of the probe tip with little resistance.

FIG.7Aillustrates an example of a terminal pin (e.g., terminal pin510) fixedly coupled (e.g., press-fitted) in a probe tip720of sonotrode710. Probe tip720may include a lumen (e.g., an annular opening730of diameter D) extending from end face740into sonotrode710. Annular opening730may have an outwardly-sloping bevel surface740btransitioning to end face740.

As shown inFIG.7A, for example, terminal pin510may be press-fitted in annular opening730with eye-of-needle structure512tleading into annular opening730and flat flange416-fabout flush with end face740. Eye-of-needle structure512tmay have a lateral width Weon that may be about the same, but slightly wider than diameter D of annular opening730(i.e., Weon>D). With Weon slightly larger than D, the length L of terminal pin510may be inserted (e.g., press-fitted) longitudinally in annular opening730with little resistance (e.g., because of the compressibility eye-of-needle structure512t). Once inserted, having Weon slightly larger than D may cause eye-of-needle structure512tto create lateral pressure (e.g., against walls of annular opening730) to hold terminal pin510in place.

When eye-of-needle structure512tis compressed, the width Weon may be become smaller than D and thus free terminal pin510to slide in or out of annular opening730with little resistance.

Further, chamfer416-cmay have a diameter dc that may be about the same, but slightly larger than diameter D of annular opening730(i.e., dc>D). Further, chamfer angle ca of chamfer416-c(FIG.4C) may be about the same a slope angle ba of bevel740bof annular opening730.

When the length of terminal pin510is inserted in annular opening730(with flange416-fabout flush with end face740), chamfer416-c(having a diameter slightly larger than diameter D of annular opening730) may be press fit (e.g., like a bottle cork or stopper) in annular opening730to lock inserted terminal pin510in position. Surfaces of chamfer416-cmay be pressed in frictional contact with surfaces of bevel740bwith inserted terminal pin510locked in position. In example implementations, one or more surface finishes (e.g., rough, granular, or polished, etc.) may be included on end face740and/or bevel740b. In some implementations, the surface finishes on the end face740and/or bevel740bmay be included, for example, in consideration of the friction between surfaces of chamfer416-cand bevel740b, and the friction between surfaces of flange416-fand end face740when the surfaces are in frictional contact (e.g., when inserted terminal pin510is locked in position in annular opening730). In example implementations, one or more surface finishes (e.g., rough, granular, or polished, etc.) may be included on the flange416-fand/or chamfer416-c.

FIG.7Bis an exploded view (of a portion ofFIG.7A) showing a press fit of eye-of-needle structure512thaving a width Weon in annular opening730having a diameter Dh (that is slightly smaller than Weon).

FIG.7Cis an exploded view (of a portion ofFIG.7A) showing a press fit of chamfer416-cin annular opening730of probe tip720(with chamfer416-chaving diameter dc that is slightly larger than diameter D of the annular opening).

In example implementations, a process of ultrasonically welding multiple terminal pins to an electronic substrate may be implemented as an automated pick-and-place assembly line process (e.g., in a semiconductor device packaging facility). The automated process may use the locking mechanisms of a sonotrode and the terminal pins (e.g., terminal pins410,510and610) to pick the terminal pins for placement on the electronic substrate. For example, as shown inFIG.8, system300(FIG.3) may include a stock of terminal pins (e.g., terminal pins410) arranged on a stand or rack810. Motorized XYZ positioner336may be configured to move sonotrode330in x, y and z directions to pick up a terminal pin (e.g., terminal pin410) from rack810, move the picked up terminal410to over electronic substrate, and place the picked up terminal on the electronic substrate for ultrasonic welding.

FIG.9pictorially illustrates movement of sonotrode330under control of XYZ positioner336to pick up terminal pins from rack810over a timeline T. At time t1, XYZ positioner336may align sonotrode330vertically over a terminal pin (e.g., terminal pin410) on rack810. At time t2, sonotrode330may descend over the terminal pin. At time t3, sonotrode330may further descend over the terminal pin to enclose and lock the terminal pin inside sonotrode330. Flange416-fmay be about flush with end face340of the sonotrode. At time t4, sonotrode330may ascend vertically to lift enclosed the terminal pin from rack810. At time t5, sonotrode330(including the enclosed terminal pin) may further ascend vertically to position sonotrode for further movement (e.g., position the terminal pin over the electronic substrate to the lift the terminal pin from rack810.

Sonotrode330may pick up a terminal pin (e.g., with a round body using, for example, a vacuum suction system. Pins with either a round body or a flat body (e.g., terminal pins410,510and610, etc.) may have one or more locking mechanism (e.g., a grooved tip, an eye-of-needle structure, a chamfer, etc.). A pin with a locking mechanism may be picked up by sonotrode330after activating the locking mechanism to lock the pin in the sonotrode.

FIG.10illustrates an example method1000for attaching a terminal pin to a circuit trace on an electronic substrate. Method1000includes disposing the terminal pin on the electronic substrate with a base region of the terminal pin in contact with the circuit trace on the electronic substrate (1010), and ultrasonically100welding the base region of the terminal pin to the circuit trace (1020).

In method1000, the terminal pin (e.g., terminal pin510) may include a rod-like pin body or shank, and a base region attached to the pin body. The base region may have a flat surface (e.g., surface116,FIG.1A). Disposing the terminal pin on the electronic substrate1001may include disposing the terminal pin with the flat surface of the base region in contact with the circuit trace on the electronic substrate.

Disposing the terminal pin on the electronic substrate1001may further include picking up the terminal pin from a stock or rack, and moving the picked-up terminal pin to a location on the electronic substrate in a pick-and-place operation. Picking up the terminal pin from the stock or rack may include using a sonotrode probe to pick up the terminal pin. A motorized XYZ positioner may move the sonotrode probe with the picked-up terminal to a location on the electronic substrate.

In method1000, welding the base region of the terminal pin to the circuit trace1020may include directing ultrasonic energy to the base region of the terminal pin in contact with the circuit trace. Directing ultrasonic energy to the base region of the terminal pin in contact with the circuit trace may include using a sonotrode to direct ultrasonic waves (e.g., longitudinal ultrasonic waves136and/or torsional ultrasonic waves137) to the base region in contact with the circuit trace. The ultrasonic energy may weld the base region to the circuit trace.

Some implementations may be implemented using various semiconductor processing and/or packaging techniques. Some implementations may be implemented using various types of semiconductor processing techniques associated with semiconductor substrates including, but not limited to, for example, Silicon (Si), Gallium Arsenide (GaAs), Gallium Nitride (GaN), and/or so forth.

It will be understood that although the terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, a “first” element could be termed a “second” element without departing from the teachings of the present implementations.