Insulated bond wire assembly for integrated circuits

An insulated bond wire to connect integrated circuits to each other or to substrates. Insulated bond wires may allow bond wires connecting integrated circuits and substrates to cross without shorting. Because bond wires may be crossed, integrated circuit assemblies with crossing bond wires may not need to be redesigned to avoid the wire crossings. In addition, insulated bond wires may also allow for closer spacing between bond wires due to reduced electronic interference between the wires. Closer spacing may allow for more input and output ports on an integrated circuit and thus increase its functionality.

FIELD OF THE INVENTION

The present invention relates to integrated circuits and in particular, insulated bond wires.

BACKGROUND OF THE RELATED ART

Integrated circuit assemblies may use bare bond wires to connect to each other and to underlying substrates. The bare bond wires may connect circuits on integrated circuits to circuits on substrates or other integrated circuits through types of bond pads, such as metal pads and lead frame posts. The bare bond wires may be made of gold, silver, aluminum, or copper.

To install the bare bond wires, a cutting machine may cut ultra thin bare bond wire into predetermined lengths. A bonding machine may then ultrasonically bond each end of the bare bond wire to the bond pad or lead frame post on either an integrated circuit or a substrate. The bond pads may be 100 microns by 100 microns square. The minimum distance the bonding machine can move between the bond pads usually restricts a minimum spacing between the bare bond wires. After making the needed connections with the bare bond wires, hot plastic may be molded over the integrated circuit assembly and cooled.

Using bare bond wires on integrated circuits and substrates has many disadvantages. Because the bare bond wires may short if they come in contact with each other, the integrated circuits are typically designed such that the bare bond wires connecting one integrated circuit to another do not cross each other. A change in design of one integrated circuit or substrate may mean that the other integrated circuits or substrates in the integrated circuit assembly have to be redesigned to keep the bare bond wires from crossing. The redesign of the integrated circuits and substrates may be especially tedious if different vendors manufacture their components.

The bare bond wires that sag may pose additional problems. If the bare bond wires sag into other bare bond wires, the touching bare bond wires may short. In addition, if the bare bond wires sag into an edge of the integrated circuit, the bare bond wires may short as well. The problems with the bare bond wires sagging may become worse if hot plastic is molded over the integrated circuit assembly that uses the bare bond wires. If the hot plastic is molded over the integrated circuit assembly, the hot plastic may push the bare bond wires together, potentially causing them to short. Also, the hot plastic may push the bare bond wires into the edge of the integrated circuit causing the bare bond wires to short.

Another potential problem encountered by the bare bond wires is electronic interference. Current in the bare bond wires may cause electronic interference with the current in neighboring bare bond wires. Accordingly, the bare bond wires may need to be spaced far enough apart to minimize the effects of electronic interference from neighboring bare bond wires.

DETAILED DESCRIPTION OF THE INVENTION

The following description makes reference to numerous specific details in order to provide a thorough understanding of the present invention. However, it is to be noted that not every specific detail need be employed to practice the present invention. Additionally, well-known details, such as particular materials or methods, have not been described in order to avoid obscuring the present invention.

Referring toFIG. 1, an embodiment of the invention using insulated bond wires to connect an integrated circuit to an underlying substrate is shown. Bare bond wire materials may be gold, silver, aluminum, or copper. Insulated bond wire5, having bare bond wire7coated in insulating material6, such as a polymer, may be used to connect the integrated circuit3to the underlying substrate2. Possible insulating materials6include, but are not limited to, polyvinyl, polytetrafluoroethylene, fluorinated ethylene propylene, and polyimide. The underlying substrate2may also be a second integrated circuit. Examples of the underlying substrates2that may be connected to the integrated circuit3include, but are not limited to, printable circuit boards, aluminum lead frames, and fine pitch ball grid arrays. To connect the integrated circuit3to the underlying substrate2, a first end of the insulated bond wire5may be connected to a lead frame post9(a type of bond pad) on the underlying substrate2, and an end of the insulated bond wire5may be connected to the bond pad10on the integrated circuit3. The bond pads10on the integrated circuit3may be a type of address pin, such as, but not limited to power supply pins, input pins, output pins, input/output pins, control pins, or clock pins. The bond pad10and the lead frame post9may be made of metal or other materials as known in the art.

As shown inFIG. 1, because at least one of a pair of bond wires11,12is insulated, first bond wire11and second bond wire12can cross at bond wire crossing13. The insulating material between the insulated bond wires11,12may prevent current from shorting between one insulated bond wire to the other. If both of the bond wires11,12were not coated in the insulating materials, a short may occur at the bond wire crossing13where the bond wires11,12may be touching. The first bond wire11may be connected to the integrated circuit3and the substrate2by a first end connected to bond pad24and a second end connected to a bond pad25. The bond wire12may be connected to the integrated circuit3and the substrate2by a first end connected to bond pad23and a second end connected to a bond pad26. Without insulating material the short may have had to be prevented by redesigning the integrated circuit3or the underlying substrate2. Either the bond pads23,24may have had to be switched or lead frame posts25,26may have had to be switched. The bond wires11,12may allow the integrated circuit3and the underlying substrate2to be connected without having to be redesigned.

Insulating material can be coated onto bare bond wires using several possible methods.FIG. 2shows a flowchart of one embodiment of a method to coat the insulating material onto the bare bond wire. At block50, a machine may extrude the bare bond wire using methods known in the art. The bare bond wires may have diameters in the range of approximately 0.5 to 2 mils. However, other bare bond wire diameters may be used. At block51, liquid insulating material may be coated onto the bare bond wire as the bare bond wire is being extruded or, in another embodiment of the invention, the bare bond wire may be extruded and then dipped or pulled through a bath of the liquid insulating material. At decision block52, a manufacturer may determine whether to cure or cool the insulating material based on what the insulating material is. For example, if the insulating material is a thermoset polymer, at block54, the insulating material may be cured on the bare bond wire to form an insulated coating. The insulating material may also be cooled on the bare bond wire at block53. At block55, the manufacturer may dry the insulating material, if needed, after the insulating material has been cooled or cured. Other methods of coating the insulating material on the bare bond wire not described herein are also within the scope of the invention.

The thickness of the insulating material connected to the bare bond wires may vary depending on factors such as, but not limited to, the thickness of the bare bond wire and the type of insulating material used. The insulated bond wires in contact after installation on the integrated circuit should have a sufficient thickness of the insulating material connected to them to prevent shorts. For example, if a polymer is used as the insulating material, a thickness in the range of approximately 0.2 micrometers to 0.6 micrometers may be used. However, other insulating material thicknesses may also be used.

Referring toFIG. 3, an embodiment of the invention having multiple integrated circuits connected to an underlying substrate is shown. First integrated circuit3may be connected to second integrated circuit4through first insulated bond wire27and second insulated bond wire28. Second integrated circuit4may also be connected to the underlying substrate2by the insulated bond wire22. The underlying substrate2may also be another integrated circuit. With several integrated circuits3,4forming an integrated circuit assembly, the number of potential insulated bond wire crossings may increase. As shown inFIG. 3, the insulated bond wire22may cross other insulated bond wires on the integrated circuit assembly at bond wire crossings19,20,21. Also, the insulated bond wire may cross other bond wires that do not have insulating material on them. The insulating material on one of two crossing bond wires should prevent a short between them. If the insulated bond wire22did not have insulating material coating it, the integrated circuits3,4and the underlying substrate2may have had to be redesigned. The bond pads on the integrated circuits and the lead frame posts on the underlying substrate2may have needed to be shifted to prevent the bond wire crossings19,20,21. The redesign may have required extensive cooperation between the manufacturers of the integrated circuits3,4and the manufacturers of the underlying substrate2.

Also, as seen inFIG. 3, if the insulated bond wire22sags into an integrated circuit board edge38, the insulating material coating the bond wire22may prevent the bond wire22from shorting into the integrated circuit board edge38. Integrated circuits may be grounded so that the bare bond wire touching the integrated circuit board edge38may short. Bond wires may sag on the integrated circuit or if hot plastic is molded onto the integrated circuits3,4, the bare bond wire may be pushed into the integrated circuit board edge38even if it is not sagging. The insulating material on the insulated bond wires may prevent the bond wire22from sagging into or being pushed into the integrated circuit board edge38by the hot plastic. The insulating material may need to be made thick enough that the integrated circuit board edge38will not be able to cut all the way through the insulating material and make contact with the bond wire22.

Because insulating material may keep the bond wires from shorting to each other or the integrated circuit board edge38, bond wire pitch angle39may be made smaller. Without the insulating material, the bond wire pitch angles39may need to be great enough to prevent the bond wires from contacting other bond wires or the integrated circuit board edge38. With the insulating material, the insulated bond wires may be able to touch each other and the integrated circuit board edge38, and therefore, the bond wire pitch angles39may be made tighter. Tighter bond wire pitch angles may mean the integrated circuit assembly's final size can be smaller.

Referring toFIG. 4, a close-up of a ball bond on an embodiment of the invention is shown. Insulated bond wire5is connected to lead frame post9through ball bond8. In one embodiment of the invention, the ball bond8may be formed with an ultrasonic bond between an end of insulated bond wire7and the lead frame post9. Insulating material6may be removed from the insulated bond wire7a distance18from the end of the bond wire7. The insulated bond wire7without the insulating material on its ends may bond better to the bond pads or the lead frame posts9, however, the insulated bond wire7may also be connected to the bond pads or the lead frame posts9with the insulating material on its ends. The distance18may be in the range of approximately 0 to 20 microns or approximately five percent of the bond wire's total length. However, other distances18of the insulating material may be removed. In one embodiment of the invention, the insulating material6vaporizes off of the end of the bond wire7during the ultrasonic bonding process. In another embodiment of the invention, the insulating material6is stripped off of the end of the bond wire7before the ultrasonic bond is formed. A capillary may be used to cut and strip the end insulating material6off. Other methods of stripping the insulating material6off of the end of the bond wire7are within the scope of the invention. In another embodiment of the invention, a solvent may be applied to the end of the insulated bond wire5to dissolve the insulating material6off of the end of the bond wire7.

Referring toFIG. 5, an embodiment of the invention having two integrated circuits connected to each other and an underlying substrate2through insulated bond wire is shown. If bond wires29,30are coated in an insulating material, such as a polymer, distance16between the adjacent insulated bond wires29,30may be smaller than if the bond wires29,30were not coated in the insulating material. The insulating material coating the bond wires29,30may inhibit electronic interference between the bond wires29,30to allow the bond wires29,30to be brought closer together. Because the distance16can be decreased, distance17between lead frame posts34,35may also be decreased. Because the lead frame posts on the underlying substrate2can be brought closer together, the underlying substrate2may be capable of holding more lead frame posts and correspondingly have more outlets for input and output. The increased number of the outlets may increase the functionality of the underlying substrate2. Alternately, the underlying substrate2may be made smaller without losing its current level of functionality if it can place the lead frame posts closer together.

In the same way, distance14between insulated bond wires31,32may be smaller than if the insulated bond wires31,32were not coated in the insulating material. Because distance14can be minimized, distance15between bond pads36,37may also be minimized. The reduced space between the bond pads on the integrated circuit3means more bond pads may fit on the integrated circuit3and thereby increase the functionality of the integrated circuit3.

Insulated bond wires may increase reliability and flexibility for integrated circuits and integrated circuit designs. Insulated bond wires may cross other insulated bond wires, touch other insulated bond wires, or touch an integrated circuit board edge without shorting. These features of insulated bond wires may allow integrated circuits to attach to each other and other substrates with crossed bond wires where before, the integrated circuits or substrates may have had to be redesigned to prevent crossed wires. Insulated bond wires may also allow for smaller or more functional integrated circuits by allowing insulated bond wires to be closer together without electronically interfering with each other.

Although an exemplary embodiment of the invention has been shown and described in the form of insulated bond wires, many changes, modifications, and substitutions may be made without departing from the spirit and scope of the claimed invention.