Patent Application
20120032354
The present invention relates generally to semiconductor device packaging and interconnection technologies. In particular wedge bonding technologies are discussed. More particularly, apparatus, methods, software, hardware, and systems are described for achieving high-speed wedge bonding of wire bonds.
In the field of semiconductor packaging, wirebonding can be used to interconnect integrated circuits and other associated components together. In particular, two main modes of wirebonding are in common usage. Ball bonding and wedge bonding. Both methods are well known in the art and have been in use for many years. As is known, ball bonding is commonly known and is frequently used with gold materials. However gold is relatively expensive. Additionally, such gold ball bonding requires surface plating (for example using silver) and heat to maintain good adhesion to bond pad materials. Additionally, attempts have been made to use ball bonding with copper wire alloys. However, at the high temperatures required for copper ball formation oxide formation is a common problem. The problem is quite pronounced as copper oxides are insulating materials that have proven difficult to bond. Additionally, deformation of the electrical connections made at high temperatures lead to reliability issues. Methods of avoiding oxide formation require the use of oxygen free ambient conditions. This comes with its own set of problems. Similar oxide formation issues make aluminum a difficult material for ball bonding applications as well. An advantage to ball bonding is its high rate of processing speed. In many applications, average bonding speeds of the order of 12-14 bonds per second can be attained.
However, because some materials are difficult to work with using high temperature ball bonding, an alternative wedge bonding approach can be used. A disadvantage of such prior art wedge bonding technique is that it is a comparatively slow process with average bonding speeds of the order of 2-3 bonds per second being common.
Moreover, although ball bonding and wedge bonding have been used in the industry for many years, wedge bonding has up until this point been a relatively slow process even after 30 years of use. Accordingly, ways of improving wedge bonding speeds would be advantageous. Thus, while existing systems and methods work well for many applications, there is an increasing demand for wedge bonding methodologies that enable increased speed using a variety of materials including aluminum. This disclosure addresses some of those needs.
In a first aspect, and embodiment of the invention describes a method for high-speed wirebonding that comprises positioning a distal end of a wirebonding capillary near a first bonding site and extruding a length of bonding wire through an aperture in the distal end of the capillary to generate an extruded length of bonding wire. A movable deflector is imposed against the extruded length of bonding wire to form a bent portion of the bonding wire proximal to an end portion of the bonding wire. Then the capillary is moved toward the first bonding site such that the bent portion of the bonding wire moves into contact with first bonding site. A first wedge bonding involves bonding the bent portion of the bonding wire with the first bonding site to form a first wire bond such that the bonding wire of the wire bond has a long tail, said long tail having a length that is longer that about two diameters of the bonding wire. Moving the capillary to a second bonding site and then second wedge bonding another portion of the bonding wire with a second bonding to form a second wire bond such that the bonding wire of the wire bond has another tail comprising a short tail, said short tail having a length that is less that about one and a half diameters of the bonding wire in many cases the second bond results in no tail at all.
Another aspect involves another embodiment of the invention which describes method for high-speed wirebonding. The method involves a “reverse” bonding approach for establishing wire bonds between two bonding sites. A process of this type can include positioning a distal end of a wirebonding capillary near a first bonding site. Extruding a length of bonding wire from an aperture in the end of the capillary. Deflecting the extruded length of bonding wire to bend the bonding wire to form a bent portion at an end of the bonding wire. Moving the bent portion of the bonding wire into contact with first bonding site. Wedge bonding the bent portion of the bonding wire with the first bonding site. The first bonding site can be a bond pad arranged on a semiconductor die. In one approach, the wedge bonding can comprise, compressing and/or ultra-sonic bonding the bent portion of the bonding wire to the first bonding site. Such bonding can also employ thermosonic bonding. To further continue, the capillary can be moved away from the first bonding site toward a second bonding site where another end of the bonding wire is wedge bonded to the second bonding site to establish a wire bond connection between the first and second bonding sites.
In another aspect, an embodiment of the invention describes method for high-speed wirebonding. The method involves positioning a distal end of a wirebonding capillary near a first bonding site. Extruding a length of bonding wire from an aperture in the end of the capillary. Imposing a movable deflector against the extruded length of bonding wire to bend the bonding wire to form a bent portion at an end of the bonding wire. Moving the bent portion of the bonding wire into contact with first bonding site. Wedge bonding the bent portion of the bonding wire with the first bonding site. In one approach, the wedge bonding can comprise, compressing and/or ultra-sonic bonding the bent portion of the bonding wire between the bonding site and a facing surface of the capillary and ultrasonically bonding the bent portion of the bonding wire to the first bonding site. To further continue an example method, the capillary can be moved away from the first bonding site toward a second bonding site where another end of the bonding wire is wedge bonded to the second bonding site to establish a wire bond connection between the first and second bonding sites.
In another aspect, embodiments of the invention include a wirebonding apparatus comprising a support for holding wirebonding substrates, a wirebonding capillary with an aperture for carrying and extruding bond wire and enabling bond wire attachment to wirebonding substrates, a movable deflector element arranged to enable movement of the deflector element to bend an extruded length of bonding wire such that the bent extruded length of bonding wire can be articulated at different bond line angles while maintaining a constant rotational orientation for the capillary, and a controller configured to enable control the operation of the wirebonding apparatus.
In another aspect, embodiments of the invention describe a movable deflector element module for use in wirebonding operations. One such module includes a deflection member configured to enable movement in an x axis and y axis direction. The member includes an aperture oriented in a z-axis with the aperture having inner wall that defines a wire contact surface having a plurality of wire guide features. Also, a deflection actuator is configured to move the deflection member in said x and y axis directions as directed by a control element configured to specify x and y axis movement for the deflection actuator.
In another aspect, embodiments of the invention describe a capillary element for use in high speed wirebonding operations. One such capillary comprises a capillary including a facing surface at a tip end of the capillary. Also including an aperture that penetrates through the capillary to an opening in the facing surface of the shaft to enable a bond wire to pass through the aperture exiting the opening in the facing surface. The facing surface defines a substantially ring-shaped roughened surface area with a substantially flat surface angled in a range of about 0° to about 4°.
General aspects of the invention include, but are not limited to methods, systems, apparatus, and computer program products for enabling improved high speed wedge bonding of wire bonds.
The invention and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
a) and 1(b) are views of a prior art wedge bonding bond head as shown in side and top section view.
c) is a top down diagrammatic view of a prior art bonding tool showing the changing rotational orientation of the wedge bonding tool as it progresses around a die forming a series of wire bonds.
a) is a block diagram illustrating an operational relationship between an inventive deflector element and associated actuator element in a deflector module in accordance with the principles of the present invention.
b) is illustration of a specific embodiment of a deflector module in accordance with the principles of the present invention.
c)-3(e) are a set of illustrations depicting a method embodiment of using selected embodiments of a deflector module to position and deflect a wire bond wire in accordance with the principles of the present invention.
a)-4(g) are a set of illustrations illustrating one example process embodiment of using a wedge bonding tool in accordance with the principles of the present invention in conjunction with a deflector element to form directional wire bonds used for connecting IC elements with external connectors such as a leadframe.
h) shows an example of a bond angle and an alignment approach for one embodiment of wedge bonding in accordance with the principles of the invention.
a) and 5(b) show an example embodiment of deflector element and aperture in accord with one example embodiment of the invention.
a) & 7(b) illustrate some aspects of one embodiment of a wedge bonding capillary suitable for employment in accordance with the principles of the invention.
c) & 7(d) illustrate some aspects of one embodiment of a wedge bonding capillary illustrating one possible type of capillary guide features suitable for employment in accordance with the principles of the invention.
a) & 8(b) are side views of a wire bonding process as performed in some aspects of one embodiment of a wedge bonding capillary suitable for employment in accordance with the principles of the invention.
c) is a plan view of a portion of a substrate including plurality of bond sites having a specified pitch.
d) is a section view of substrate having a bond pad and an overlying layer and an opening to expose a portion of the bond pad.
a) & 9(b) are side section views of a bonding capillary used to bond a bond wire to a bonding site in accordance with the principles of the invention.
In the drawings, like reference numerals are sometimes used to designate like structural elements. It should also be appreciated that the depictions in the figures are diagrammatic and not to scale.
Reference is made to particular embodiments of the invention. Examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with particular embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. To contrary, the disclosure is intended to extend to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
Unless otherwise indicated, all numbers expressing quantities of ingredients, dimensions reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”.
In this application and the claims, the use of the singular includes the plural unless specifically stated otherwise. In addition, use of “or” means both “and” and also, “or”, unless stated otherwise. Moreover, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements and components comprising one unit and elements and components that comprise more than one unit unless specifically stated otherwise.
Aspects of the invention pertain to methods and apparatus for enabling high speed wedge bonding in semiconductor wirebonding applications. It is noted that in the prior art, wedge bonding techniques for bonding aluminum wire onto aluminum pads are slow. For example, the prior art wedge bonding techniques are slower than ball bonding with gold by some 30% or more. Switching from gold to copper wires can have significant cost savings, but the throughput is still slow. Although better with respect to silver, it is still some 15% slower. Additionally, the inability to establish high quality aluminum bonds has led manufacturers to use copper bond wires. Although suitable for many purposes, copper wirebonding can have some drawbacks. To begin, it is a harder metal than aluminum (hardness of copper and aluminum are 369 and 167, respectively). Thus, greater force must be applied to obtain a good bond using copper wire. When used in relatively rugged environments it is normally not an issue. However, in more delicate situations the force on the bond head can lead to damage to materials and substrate under a bond pad onto which the copper wire is bonded. This is particularly troubling when the underlying substrate is a semiconductor die. Similar problems are encountered with gold and silver wires. Additionally, a more pointed capillary head is typically used with these materials than with aluminum. As a result the force is more concentrated, thus leading to a higher likelihood of damage. In order to reduce likelihood of damage while wedge bonding copper (or other materials) a copper buffering layer is used to cushion the surface thereby minimizing damage to the underlying structure. The time and effort put into forming the copper layer increases cost and slows down the process of wirebonding.
Additionally, the unique aspects and advantages of this invention enable high speed wedge bonding that is on par with ball bonding speeds. Using the processes described herein, wedge bonding speeds of on the order of 7-8 bonds per second can be achieved. Substantially higher than the speeds achievable with the prior art wedge bonding techniques. Accordingly, aspects of the invention enable high speed wedge bonding of aluminum wire to aluminum bonding surfaces. Additionally, such a process can be performed at room temperature instead of the elevated temperatures needed for copper and gold wirebonding.
The diagrammatic illustrations of
a) and 1(b) illustrate a facing surface 101f of the bond head 101.
As shown in
In examining a first wire bond connection 122 connecting one of the pads 111 with a first external connector 112 the wire bond 122 defines a bond line between the two contact locations. Here we arbitrarily identify the bond line 122 as having angle of 0°. The diagrammatic illustration includes a first bubble 131 that shows a top down view of the associated bond head 101 and the bond wire 102. During wedge bonding, the bond head is moved in direction 141 from the bond pad 111 toward the final bonding site at connector 112. In the wedge bonding process, this process is repeated for each pair of pads and contact for the die 110. Thus, the bonding proceeds around the circumference of the die until completed.
For example, as the process has moved clockwise around the die another wire bond 123 is briefly discussed. A second external bond site 113 is wire bonded with an associated one of the pads 111 thereby defining the wire bond 123 and its associated bond line. With reference to the first bond line (122) it is shown that the bond angle has changed. Here that angle change 135 is represented as 90°. Thus the bond line 123 lies at 90° from the first bond line 122. This has consequences in how the wire bond is formed. The diagrammatic illustration includes a second bubble 132 that shows a top down view of the associated of the same bond head 101 and a bond wire 102. Because the bond line is significantly changed, the rotational orientation of the bond head 101 must also significantly rotate. This rotation enables wedge bonding between the external bond site 113 and its associated bond pad. During wedge bonding, the bond head 101 is moved in second direction 142 from the bond pad 111 toward the final bonding site at connector 113.
Likewise, as the process continues moving clockwise around the die another wire bond 124 is briefly discussed. Here, an example third external bond site 114 is shown wire bonded with an associated one of the pads 111 thereby defining the wire bond 124 and its associated bond line. With reference the to the first bond line (122), it is shown here that the bond angle 136 has further to about 120°. Thus the bond line 124 lies at 90° from the first bond line 122. Again, this has consequences in how the wire bond is formed. The diagrammatic illustration includes a third bubble 133 that shows a top down view of the associated of the same bond head 101 and a bond wire 102. Because the bond line is again significantly changed, the rotational orientation of the bond head 101 must also significantly rotate. At this point the rotation is about 120 degrees. Also, as before, this rotation enables wedge bonding between the external bond site 114 and its associated bond pad. During wedge bonding, the bond head 101 is moved in third direction 143 from the bond pad 111 toward the final bonding site at connector 114. And so it continues until the die 110 is completely bonded.
It is very important to consider that the bond head 101 realignment process takes a considerable amount of time. In fact, it is what accounts for the majority of the disparity in bond rates between the ball bonding process (e.g., about 14 bonds/s) and the prior art wedge bonding process (e.g., about 2-3 bonds/s). Accordingly, an approach for removing this step from the process has considerable advantage in a wedge bonding process.
Accordingly,
The wedge bonding module 210 typically includes a control arm 211 that can include an ultrasonic head (not shown in this view) with a capillary 213 used as a bonding tool mounted on a distal end thereon. The module 210 can include a linear motor (not shown) that drives the capillary 213 and bonding arm 211 (as can optionally move the deflector module 220) in the vertical direction, that is, in the Z-direction. The linear motor is but one of many examples of a suitable motive device that can be used to accomplish the desired movement in the module 210. This Z-axis movement enables the bond tool 213 to apply wire to various locations on the substrate 202. An XY table 214 is used as an XY positioning unit that holds the bonding module 210 (including control arm 211, bonding capillary 213, deflector module 220, and image pickup unit 204) and moves the module two-dimensionally a substantially horizontally arranged X-direction and Y-direction, and positions the same capillary 213 for wirebonding.
The control module 230 can include one or more microprocessors for controlling the entire wirebonding apparatus 210. For example, a drive device 231 can provide control signals to the bonding head 213 and the XY table 214 in response to a command signal from a controller 232. Commonly, software (or firmware) is executed on a microprocessor of the controller 232 and the operation of wirebonding or the like is performed by implementing the program. A support 205 holds the IC device 202 so that it can be wire bonded to another substrate. In this depicted embodiment, the other substrate comprises a leadframe 203. Additionally, in some embodiments, the support can include a heater unit. In one implementation, the semiconductor chip 202 is mounted on a leadframe 203 which can be mounted on the heater plate of a heater unit at the top of the support 205. The leadframe 203 can be heated by the heater unit.
Also, the wirebonding apparatus 200 typically includes an operation panel 233 having, for example, data input features that can include, but are not limited to track balls, alphanumeric value entering keys, and operating switches for enabling input and output of data such as process parameters and further display of the data for operation of the device 200. Such data can be input into the controller 232 to, for example using a track ball, enable manual movement of the XY table 214. The control unit 232 and the operation panel 233 are collectively referred to as an operating unit, hereinafter. The wirebonding apparatus 200 can be operated manually or automatically by the operation of the operating unit.
The wedge bonding module 210 which drives the bonding arm 211 vertically in the Z-direction includes a position detection sensor 216 for detecting the position of the bonding arm 211, and the position detection sensor 216 is adapted to output the position of the capillary 213 mounted to the distal end of the bonding arm 211 from the position of a preset original point of the bonding arm 211 to the control device 232. The linear motor of the wedge bonding module 210 drives the bonding arm vertically in response to instructions from the controller 232 which also controls the magnitude and the duration of a load to be applied to the capillary 211 at the time of bonding.
Additionally, an ultrasonic oscillator (not shown) can be located within the arm 211 which, in one embodiment, can use a piezoelectric transducer to cause the capillary 213 to generate the requisite ultrasonic oscillations that can be applied to the capillary 213, for example, upon reception of a control signal from the controller 232.
Additionally, the controller 232 provides signals to the deflector module 220 that enable it to deflect wire extruded from the capillary 213 in accord with certain aspects of the invention. This will be discussed in greater detail in the following paragraphs.
In general, the wirebonding apparatus 200 is configured to connect bond pads of the IC device 202 to external bonding sites, for example, bonding sites on a leadframe 203. These bond connections are made using bond wire such as aluminum wire. Also, gold and copper can be used in accord with this invention. Aluminum being attractive because it is a softer material than both copper and gold thus reducing stress on the underlying substrate (the die 202) during wedge bonding. The approach disclosed in this application has several advantages over prior art methods. Unlike ball bonding, the present invention can be practiced at room temperature thus removing a large array of heat related problems from the system. Additionally, the need for non-oxygen ambient is also removed from the system. Also, it provides a high-speed method for achieving wedge bonding which has been a slow process for over 30 years. Thus, this invention meets a long unmet need and is particularly advantageous when used with materials like aluminum bonding wires.
A novel feature of the invention includes a deflector element 220 which is position in an operational arrangement with a bonding capillary 213. Typically, but not exclusively, the deflector element 220 is mounted with the bonding arm 211. The deflector element 220 comprises a movable deflector member and an associated actuator that enables controlled motion for the movable deflector member. The motion of the movable deflector member is intended to execute x-axis and y-axis movement and bending of an extruded portion of a bond wire extending from a capillary 213.
In general, the deflector element 220 and capillary 213 are controlled by software and hardware enabling their integrated operation with the wirebonding recipe of the bonding processes executed by the apparatus 200.
Such a movable deflector member can comprise one or more separate elements configured alone or in combination to enable such x, y movement and bending in a bond wire. The actuator can comprise a drive motor(s), magnetic actuators, and other motive elements.
b) is a diagrammatic depiction schematically illustrating an embodiment of a deflector element 220. In particular there is a movable deflector member 311 and an associated actuator system 312. In this particular embodiment, the member 311 includes an aperture 313 used to manipulate the position of the bond wire. In such case the bond wire is deflected by the inner surfaces of the aperture 313. For example, the aperture 313 is made in a working end of a deflector wand 311 that includes an arm portion 311a used to engage the working end with the actuator 312. The actuator system can comprise any system of motive devices suitable for moving the deflector member (or wand) 311 in the desired directions.
c) & 3(d) are diagrammatic depictions of the deflector member 311 embodiment such as shown in
d) is a bottom up view of an example embodiment. The aperture 313 of the deflector member 311 includes an inner surface 313d that can operatively deflect the bond wire 314. Also, the cross-section 315 of
e) is a simplified view (as in
It is particularly pointed out that the deflection of the wire 314 is achieved by the relative motion of the wire with respect to the deflector 311. In other words, it can be that the capillary 213 itself is moved relative to a stationary deflector 311.
a)-4(g) illustrate an implementation of a process used to establish a high speed wedge bond.
a) shows a capillary 213 in position above a bond pad 401 preparatory to bonding a wire 314 to the pad. This view is similar to the cross-section axis 315 shown in
In one feature of the invention, the facing surface of the capillary 317 is a substantially flat surface. The surface 317 generally having a face angle of in the range of about 0-4°. This is important because it is desirable to have the greatest amount of surface area of the facing surface applied against a bend bonding wire.
In describing the process, the capillary 213 is positioned above the desired bonding site 401, a portion of wire 314e is extruded from the wire in a desired length. For example, the length 314e is on the order of a radius of a flat facing surface 317 of the capillary. For example, using an 8 mil diameter capillary, the extruded portion 314e can be on the order of about 3-4 mils in length. The bonding wire can be made of any material and any thickness. Gold, copper, aluminum, and allots of the same provide some examples of suitable materials. Such wires are on the order of 15 μm to 2 mil as well as other thicknesses. In one example, a capillary 213 extrudes a portion of a bond wire 314e a desired length through the aperture 313 and then fixed in length. For example, the wire can be extruded through an open wire clamp to the desired length, then the wire clamp fixes the wire in place (stabilizing the length) and then relative movement of the deflector and capillary bend the wire as appropriate.
The bond angle required to connect the bond pad 401 to a desired external bonding site is determined. This enables the correct x, y deflection to be applied to the bent portion of the wire 403. Then, as shown in
After bending, as shown in
The application further contemplates a more flexible bonding approach that uses a relative motion between the deflector 311 and the capillary 213 to bend the wire to attain the bent portion 403. For example, the deflector 311 can be moved relative to a stationary capillary 213 to bend the wire 314e to attain the desired bonding angle as already indicated. However, the capillary 213 can also be moved relative to a stationary deflector 311 to bend the wire 314e to attain the desired bonding angle. Or embodiments that use some degree of motion for both the capillary 213 and the deflector 311 together can be used to generate the desired relative motion between the deflector 311 and the capillary 213 to bend the wire to attain the bent portion 403 can be used.
Then, as shown in
Thus, as is shown in
Once bonded, as shown in
Additionally, when the wire portion 403 (314e) is bent in direction 402 (See, e.g.,
It is pointed out that the wire can be positioned and held in place using standard clamp and wire tensioners as can be found in ball bonding tools. The clamp holds the wire in place while the deflector bends the wire into the desired configuration and then releases the wire once it is positioned at the desired bonding site. Moreover, in some embodiments the wire tensioner (or other associated vacuum systems) can be dispensed with altogether.
a) shows another embodiment of a deflector aperture. In this depiction, a deflector arm 511a supports a working end 512 of a deflector element 511. In particular, a different embodiment of aperture is shown. The aperture 513 comprises a flower-shaped aperture 513 arranged with a plurality of wire guiding features 514. The inner surface of the aperture 513 is shaped generally like a “flower” having petal portions. These petal portions 514 are the guide features 514. They are arranged such that when the aperture is moved across (402) the extruded wire (e.g., 314e) the wire can be generally centered at a nadir 515 of one of the features 514. Importantly, the presence of apexes 516 between the petals can prevent the wire from deviating from one petal to another as the deflector moves across the capillary. As shown in this embodiment, the aperture 513 includes 8 “petals” that serve as the guide features 514. Different embodiments can, of course, have more or fewer petals. Also, a wide range of petal shapes or configurations can be employed as might be suggested to one of ordinary skill by this disclosure.
An example depiction of the operation of a guide feature 514 is shown with reference to
It is specifically pointed out that many different implementations of such guide features can be used. For example, the inner surface of the aperture can comprise a set of slots or grooves in the inner surface to engage and fix the wire during wirebonding. In one example implementation a series of notches can be arranged in a spaced apart arrangement around the inner surface of the aperture. For example, the spacing can be such that grooves are spaced every 5°, 4°, 3°, 2°, 1°, or even tighter. It is pointed out that these intervals are examples only and that the invention is not limited to these intervals with those of ordinary skill appreciating that the spacing can be set at any desired interval. It is also pointed out, that alignment features can also be arranged on the capillaries. However, the inventors note that it is advantageous to place them on the deflector element. This is because the formation of the guide features is time consuming and difficult. Additionally, the lifespan of an average capillary is considerably less than that of a deflector. Thus, although the invention contemplates the placement of alignment features on the capillaries and/or the deflector element 511, there are certain advantages to placing them on the longer lived deflector element.
In a continuing description of the invention one method of applying this technology is described. In one embodiment, a method of employing a wirebonding apparatus 200 in accordance with an aspect of the invention is described. This embodiment describes a wedge bonding method and associated method of establishing wire bonds between bond sites. An aspect of this invention will be discussed in association with the embodiment addressed in the flow diagram of
Once the die (or other target subject) is positioned on the inventive wedge bonding tool bonding can begin. It is to be noted that appropriate adjustments and software instructions can be applied to the tool 200.
Accordingly, the distal end of a wirebonding capillary is positioned near a first bonding site (Step 601). The capillary supports a bonding wire and can have an entire strand of appropriate wire in readiness for a bonding process. The wire can be of any material, with aluminum, copper, and even gold providing attractive materials. Aluminum in particular provides some process advantages. In particular, aluminum is soft and also aluminum is compatible with many bond pad and bonding site materials (e.g., copper). Accordingly, it is not necessary to plate the target bond pads to obtain good bond adhesion between wire and pad as is the case with some other materials (e.g., gold). Generally, such positioning involved positioning the capillary right above the bond site. The capillary head must be positioned above the bond pad a distance that is thicker (e.g., 316) than the thickness (height) of the associated deflector arm (e.g., 311). Thus, for a deflector arm 30 mils thick, the capillary head will be at least 35 mil and possibly much higher above the bond pad. In one example implementation the capillary head (the tip of the capillary) is positioned about 50 mils above the target surface (the bond site) in readiness for bonding. In general, the capillary head is a distance above the bond pad that takes into consideration the height of the deflector above the bond pad, the thickness of the deflector, the thickness of the wire, and any desired tolerances.
A length of wire is extruded from the aperture in the end of the capillary (Step 603). In one implementation, a bond wire is fed down through an inner diameter of the capillary to extend a distance beyond a facing surface of the capillary. The extruded length can be on the order of about the radius of the capillary face. Thus, for a capillary having a diameter of about 6 mils, an extruded length of up to 3-4 mils can be used. It is pointed out that greater or shorter extruded lengths can be used. In particular, for greater diameter capillaries greater lengths can be used and vice versa. As mentioned above, aluminum, copper, gold and other materials can be used with aluminum being a particularly attractive candidate. Additionally, a wide range of wire thicknesses can be employed with this methodology. One example range of wire thicknesses can include wire diameters ranging from about 5 μm to about 2 mils and other thicknesses. One example can be a 50 μm aluminum wire extruded to a length of about 3 mils using a capillary having a diameter of about 6 mils. Of course this is but one example with many others apparent to those of ordinary skill
Once the desired length of wire is extruded, a movable deflector is imposed against the extruded length of bonding wire to bend the bonding wire to form a bent portion at an end of the bonding wire (Step 605). A deflector (for example, a deflector 311 as is shown in
Additionally, the bending process requires that the deflector pass beneath the capillary. For example, in one embodiment the facing surface of the capillary can lie a distance of about 1.1 to about 1.5 wire diameters above the top surface of the deflector 311. Of course, the distance can be less or greater. The general idea being that the desired amount of bend is imparted to the bent portion of wire 403 by the motion of the deflector under the capillary.
Once bent, the deflector is repositioned such that the capillary can pass through the aperture of the deflector. Then the capillary is moved through the aperture toward the bonding site such that the bent portion of the bonding wire is moved into contact with the first bonding site (Step 607). Additionally, the facing surface of the capillary compresses the bent portion of the bonding wire between the bonding site and a facing surface of the capillary to establish a wedge bond of the bonding wire with the first bonding site (Step 609). This process is typically enhanced using ultrasonic energy. For example ultrasonic bonding of aluminum bonding wires enables the direct bonding of the wires to an aluminum bond pad or scrubbing can enhance the bond between the wire and bonding surface. Also, in some embodiments thermosonic bonding can be used enhance the bond between the wire and bonding surface. Such can enable the bonding of aluminum, Al/Ag or Au wires enabling with Al bond pads and bonding surfaces. This will be discussed in some detail below with respect to certain capillary heads. This process results in a low temperature wedge bond that can be established in any direction without need for changing the rotational orientation of the capillary. This first novel aspect of this embodiment is completed in the formation of this novel type of wedge bond.
Once the bond is established, the method can move the bonding wire to a second bonding site to establish a completed wire bond electrical connection with another circuit element. For example, the capillary is moved away from the first bonding site (the location of the first bond) toward a second bonding site (where the bond that completes the connection can be made) (Step 611). The capillary is then moved and positioned in an operative arrangement with the second bonding site and then the wire is wedge bonded to the second bonding site to establish a wire bond connecting the first and second bonding sites (Step 613). A standard wedge bonding technique can be used here and the wire can be broken off in a standard fashion to complete the bond. At this point the capillary can be removed to another bonding site to repeat the process. Importantly, the rotational orientation of the capillary is not changed in this move.
a) is a cross-section view of one example of a capillary device 213 suitable for use with some embodiments described in this specification. The capillary 213 can be made of any material. But when used with aluminum wire, a hard material like aluminum oxide crystals (ruby, sapphire, etc.) can provide an excellent capillary material. In aluminum applications such materials are harder than aluminum oxide materials that sometimes form on bond wires. Such oxides are damaging to prior art ceramic capillaries. And such ruby materials also suffer from less aluminum build up. Additionally, similar advantages can be obtained with tungsten carbide capillary materials. It is pointed out that this technology has applicability beyond aluminum wedge bonding and can be used with copper, gold, silvers, their alloys as well as various other materials. In addition to the materials described above, in some implementations capillaries formed of ceramics (e.g., zirconia ceramic and others) can also be used.
In one important attribute, the face surface 701 of the capillary is flat or very near flat. The face angle 702 (not drawn to scale) that describes an angle that the facing surface 701 makes with a perfectly flat plane should be less than about 4-5°. This very flat surface enables a maximum contact area of the surface 701 with the bent wire. Additional implementations can include faces with slight inverse angles (those having surfaces that become higher as they extend inward from the face edges). In general, these more flat surfaces are very different from capillaries used to ball bond gold wires. Such ball bonding capillaries are designed to optimize ball formation. Accordingly, they have relatively steep face angles. In a typical gold ball bonding application the face angle will be 8°, 12°, 15°, or even steeper. These tools cannot provide the needed contact area required to enable the present methodology. Additionally, when using gold processes, the facing surface 701 is very smooth. However, in an aluminum bonding capillary, a great deal of “scrubbing” is required to break up the surface oxides present on aluminum wires. Hence a rough surface is required. This is amplified through the effect of ultrasonic scrubbing. Such a roughened matte surface can be used with a ruby or tungsten carbide capillary.
It is also noted that a pattern of raised features can be used to good effect in this manner. For example a criss-crossed (cross-hatched) pattern of raised features (e.g., a waffle-shaped pattern) can provide good results.
In another embodiment,
Referring to side section view of
Returning to a discussion of
Additionally, the chamfer angle in the present capillary is steeper than that of an ordinary ball bond capillary. This can be characterized by the interior chamfer angle (ICA) depicted in
Another aspect of the invention contemplates a “reverse” bonding process in which an order of bonding is performed the opposite of a commonly used in a standard wedge bonding process. Such an approach is different from that used in the art as presently practiced.
As commonly used in the prior art, standard wedge bonding proceeds as follows. Bonds are made between a lead of a leadframe and the target pad on the die. A first bonding surface (e.g., the die bond pad) is arranged on a semiconductor die and a second bonding is performed on the leadframe. Commonly, when the first wire bond is made at the die it is hazarded by the presence of a rather large and an undesirable tail end of indeterminate length. It can be quite long, as much as several wire diameters. Whereas, in present approach, the second bond is made at the lead. This approach can commonly be seen in existing wedge bonding technologies as well as other approaches.
In this approach, a longer tail is positioned at the die. This can have undesirable consequences. The risk of wire shorting, misconnection with improper bond sites, and other fabrication difficulties is increased. These conditions can be exacerbated when tight bond pitches and small bonding surfaces are used (such as with die based bonding surfaces). In such cases a premium is placed on small and accurate bonds of the bond wires. An approach for minimizing or removing the tails at the die is desired.
As shown in
This can, in one embodiment be remedied using an improved “reverse” wirebonding approach.
In typical use the wire is simply compressed and the broken away at the end of the wire bond. However, this process commonly leaves a shorter tail 801t such as shown here at the end of the bonding wire 803 at site 801. This tail 801t can be quite short, in some cases less that a single wire diameter in length. This compares favorably with the process of
c) can be used to clarify what is meant by pitch. For purposes of this disclosure, when looking at a pattern 825 of bonding sites (e.g., 821-824), a bond pad pitch is defined as a distance 835 between the centers of two adjacent pads (e.g., 821, 822). In many applications having a small bond pad pitch, the existence of bonding wire tails can be a large problem that can lead to shorting, fabrication difficulties, and other problems. The problems become steadily more severe when used at high pad densities. Such can be a large problem when encountered in high bond pad density substrates, such as on semiconductor die. Although such problems can be encountered in other substrates as well (e.g., leadframes and other substrates) Embodiments of the invention can address these problems.
A semiconductor die pad size is typically on the order of 100 μm (microns) or greater. This can be further constrained by the passivation pad opening, which can be on the order of the diameter of a capillary tip (901, 902). Additionally, a pad pitch, derived from the application constraints, prescribes the type of capillary one should use as well as the diameter of the bonding wire to be used. In one non-limiting example, a pitch 905 for a 100 μm×100 μm pad can be on the order of about 110 μm. It is expressly pointed out that this is but one example illustrating a general principle, with larger and smaller bond pads and pitches in common use. In a related situation, similar problems can also arise when very small bond pads are used. Again, the existence of tails can lead to shorting, fabrication difficulties, and other problems. The problems become steadily more severe when progressively smaller pads are used, such as on semiconductor die. Although such problems can be encountered in other substrates as well (again, e.g., leadframes and other substrates).
Another constraint deals with the issue of bonding sites being constrained by the size of an opening used to expose and underlying bonding surface.
In one common situation, a bonding site, especially but not exclusively, located on a semiconductor die, a pad size can be further constrained by an opening in an overlying layer that exposes a portion of the underlying bond pad. In one example, an underlying bond pad 854 is the order of 100 μm (microns) or greater. As illustrated in
a)-9(b) illustrate a wedge bonding process embodiment that can form wedge bonds of the present invention. In
In the present application, the first bond is applied to the larger sites that can support the presence of a longer tail and the second bond is applied to the small tightly constrained bond sites that cannot afford the presence of a tail.
With reference to
Once the target subject (which can include a die mounted on an associated substrate) is positioned on the inventive wedge bonding tool, wirebonding can begin. It is to be noted that appropriate adjustments and software instructions can be applied to the tool 200.
Accordingly, the distal end of a wirebonding capillary is positioned near a first bonding site (Step 1001). The first bonding site is generally less constrained, i.e., less sensitive to the presence of bonding wire tails. The capillary supports a bonding wire as described above. The wire can be of any material, with aluminum, copper, silver, and gold providing attractive materials as do alloy bonding wires. Aluminum in particular provides some process advantages for the reasons discussed above. The capillary head is positioned above the bond pad a distance that is thicker (e.g., 316) than the thickness (height) of the associated deflector arm (e.g., 311).
A length of wire is extruded from the aperture in the end of the capillary (Step 1003). In one implementation, a bond wire is fed down through an inner diameter of the capillary to extend a distance beyond a facing surface of the capillary. It is pointed out that where the bonding wire tail is to be minimized for the first bond, a shorter extruded length is typically used. Additionally, a wide range of wire thicknesses can be employed with this methodology. One example range of wire thicknesses can include wire diameters ranging from about 25 μm to about 50 μm and other diameters. One example can be a 50 μm aluminum wire extruded to a length of about 75 μm using a capillary having a diameter of about 6 mils. Of course this is but one example with many others apparent to those of ordinary skills.
Once the desired length of wire is extruded, a movable deflector is imposed against the extruded length of bonding wire to bend the bonding wire to form a bent portion at an end of the bonding wire (Step 1005). As described above, the deflector is brushed under the extruded portion of wire to form the bent portion of the wire to attain the desired orientation (bond angle) relative to the associated second bond site to which the wire is to be connected in the wirebonding process.
Once in position, the bent bonding wire is wedge bonded with the first bonding site (Step 1007). As indicated above, the process described here is particularly useful for small bond sites (e.g., bond pads that have dimensions less than 100 μm across or deep) or crowded bond pads. With reverse bonding, however, the first bond is on the lead finger of the leadframe, which is typically much larger than the die bond pad. Once bent, the deflector is repositioned to enable the capillary to pass through the deflector aperture and then the capillary is moved through the aperture toward the bonding site such that the bent portion of the bonding wire is moved into contact with the first bonding site. The facing surface of the capillary can compress the bent portion of the bonding wire between the bonding site and a facing surface of the capillary to establish a wedge bond of the bonding wire with the first bonding site. This process is typically enhanced using ultrasonic energy. For example ultrasonic bonding of aluminum bonding wires enables the direct bonding of the wires to an aluminum bond pad or scrubbing can enhance the bond between the wire and bonding surface. Advantageously, such a process can be formed at room temperatures. Also, in some embodiments, thermosonic bonding can be used enhance the bond between the wire and bonding surface. This can enable the bonding of aluminum (Al), copper (Cu), silver (Ag) or gold (Au) wires facilitating bonding to Al bond pads and bonding surfaces. In particular, such an approach is used with respect to gold wires and copper wires.
Once the bond is established, the bonding capillary and bonding wire is moved to a second bonding site to establish a completed wire bond electrical connection with another circuit element. For example, the capillary is moved away from the first bonding site (the location of the first bond) toward a second bonding site (Step 1009). It is pointed out that the second bonding site can be more tightly constrained than the first. That means that it can be more susceptible to the presents of a long bond tail. In such cases short of no bond tails are helpful. Examples of such bonding sites are those having small bonding surfaces, or having tight bond pitches, as well as other conditions where a bond having a short tail can be advantageous. In one particularly useful situation. The second bonding sites can be arranged on a semiconductor die. After the capillary is positioned, the second end of the bond wire is wedge bonded to the second bonding site to establish a wire bond connection between the first and second bonding sites (Step 1011). A standard wedge bonding technique can be used here and the wire can be broken off to complete the bond. Typically, no tail or a very small tail is formed at the second bonding site. Thus, by reversing the process, tails that may cause serious problems when formed in a crowed environment or one with small bonding sites is moved to a more spacious first bonding site, thereby removing a problem known to exist in other approaches. At this point the capillary can be removed to another bonding site to repeat the process.
Importantly, the rotational orientation of the capillary is not changed in this move. An advantage of this process is that unlike other wedge bonding processes, the disclosed process is fast. As explained above, prior art wedge bonding is substantially slower than ball bonding processes. Such is not the case in the present invention.
This process is particularly attractive because it can establish good wire bonds between aluminum (or gold or copper) bonding wires and aluminum bond pads (e.g., 801. 802). In particular, excellent bonds between aluminum pads and aluminum bonding wires can be achieved at room temperature using ultrasonic bonding using the capillary. Alternatively, direct bonds to aluminum bond pads can be made using gold (Au), silver (Ag), silver alloy, or copper (Cu) wires using thermosonic bonding.
The process can be adapted to a full range of bond wire thicknesses including those as thin as 15 μm. Additionally, in accordance with the present invention, the bonding processes can be implemented as a series of computer implemented operations. These instructions can be programmed as a computer readable instruction set that can be implemented by a processor of the wedge bonding apparatus 200. Also, the computer readable instructions can be stored on a non-transitory computer readable tangible medium. Examples, include, but are not limited to disk drives, flash memory, non-volatile memories in general, optical and magnetic disks, and many other such devices or media. In one implementation the computer readable instructions can be implemented as firmware resident on one or more devices.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
Various embodiments of the disclosure could also include permutations of the various elements recited in the claims as if each dependent claim was a multiple dependent claim incorporating the limitations of each of the preceding dependent claims as well as the independent claims. Such permutations are expressly within the scope of this disclosure.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.
The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
This application is a continuation-in-part of and claims priority to co-pending U.S. patent application Ser. No. 13/025,078, filed on Feb. 10, 2011 and entitled “Wire Bonding Method and Capillary Enabling High-Speed Wedge Bonding of Wire Bonds,” which is a divisional of U.S. patent application Ser. No. 12/851,981, filed on Aug. 6, 2010, now U.S. Pat. No. 7,918,378, issued on Apr. 5, 2011 and entitled “Wirebonding Method and Device Enabling High-Speed Wedge Bonding of Wire Bonds.” All of the foregoing are hereby incorporated by reference in their entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12851981 | Aug 2010 | US |
| Child | 13025078 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13025078 | Feb 2011 | US |
| Child | 13172622 | US |
