Fine pitch probing and wire bonding and reliability of. Pdf copper wire bonding of microelectronic parts has developed as a means to cut the costs of using the more mature technology of gold wire bonding find, read and cite all the research you. With billions of units shipped, ti offers packaging solutions that deliver the performance, reliability, quality and cost advantages of copper. However, with this new technology, changes in the bonding processes as well as bonding metallurgy can affect product reliability. Copper wire bond failure mechanisms randy schueller, ph. D material properties that effect wire bonding to copper through thin inorganic films. Copper wire bonding refers to the wire bonding process that employs copper wires for interconnection, instead of the gold and aluminum wires traditionally used in semiconductor packaging. Bare cu and pd coated cu wires are bonded on the 1st and 2nd bond side on both bga and qfn. Harris julyaugust 2001, june 2002 setting bonding parameters 1. Cu wire bonding university of california, berkeley. For information about wire bonding equipment, please visit our corporate site at. Softer fab and higher bond reliability after aging 2000 hours. With a history of building its own chip assembly equipment, ti was able to experiment with copper wire bonding independently to evaluate the results and benefits.
Copper and gold wire bonding course description wire bonding is a welding process that is the dominant chip interconnection method. Bond conductor size shall be determined by the ampere rating of the service entrance equipment as shown on the grounding and bonding table. Tis extensive relationships with at tool and materials. No exposed oxide, no cracked glass max 25% probepad ratio probeball bond ratio is not specified large variation in probe mark sizes. The copper bonding kit consisted of a nitrogen nozzle fixture at the fab free air ball formation area and a flow meter for inert gas. Wire bonding is a technique widely used to provide electri cal interconnection between semiconductor chips and relative metal pads on substrates or lead.
Wedge bonding technique can be used for both aluminum wire and gold wire bonding applications. It was shown that during wire bonding, the sam has been removed and a metal to metal weld has been formed. Exclusive technology feature failure analysis on power. This paper presents an extensive evaluation of electroless nipd and nipdau bond pads that offer a much more robust alternative to the standard al pad. Tis journey to highvolume copper wire bonding production 3 october 2014 operations in chip assembly and test at. Developing robust, finepitch copper wire bonding processes to assemble these new copper devices requires complete process optimization, encompassing the wire bonder,bonding tools,and bonding wire. Copper wire bonding concerns and best practices bonding process the cu bonding process faces challenges due to the oxidation and hardness of cu. Using this approach, direct wire bonding onto copper bond pad with both gold and copper wires have been achieved. The buffer is selected with a combination of the buffer switch i, ii, iii and the rightmost thumbwheel switch position. Fine pitch probing and wire bonding and reliability of aluminum capped copper bond pads page 4 inspection criteria for probe mark damage loose criteria for inspecting probe mark damage on pad.
This technique provides more control over loop height and bond placement. Silver wire has a wide process window that improves manufacturability for devices with fragile bond pad structures. Typically the whole wire bonding process consists of five stages. Wire bonding on 2s modules of the phase2 cms detector cern. Silver wire is softer than pcc resulting in lower alsplash and lower risk of bond pad damage. Power and time relate to the ultrasonic generator settings used to ultrasonically soften, the bonding wire. Copper wire is harder than au wire and oxidizes in air. The cucoral bonding wire is a composite wire type with a copper core and aluminum coating. Among the challenges to copper wire bonding is the damage to bond pads that had been engineered for wire bonding with the softer gold wire.
Copper wire bonding of microelectronic parts has developed as a means to cut the costs of using the more mature technology of gold wire bonding. The material mix of aluminum and copper provides excellent electrical and mechanical properties. Research focusing on methods of softening the cu wire and its free air ball fab during bonding were reported in. Diameter 15um to 50um cu copper alloy wire p3233 high reliability copper alloy bonding wire provides wider second bond process window and lower resistivity than bare copper.
Copper is rapidly gaining a foothold as an interconnection material in semiconductor packaging because of its obvious advantages over gold, which include. Data sheet copper wire bonding copper wire benefits jdevices has extensive experience in cu wire products dating back to 2007, resulting in mature and capable cu wire bonding capability. Designmethodologyapproach dozens of journal and conference. This is reflected by the longterm behavior during both passive temperature cycling tests and especially. Although less common, wire bonding can be used to connect an ic to other electronics or to connect from one printed circuit board pcb to another. Both gold au and copper cu wire have been used for wire bonding to aluminum al bond pads on ics for many years intermetallic compound imc formation provides adhesion between wires and pad. Copper wire has two main drawbacks that have retarded its replacement of au wire. Wire bonding to advanced copper, lowk integrated circuits. The minimum thickness of the aluminum layer remaining under the copper wire bonds is a critical factor for the long term reliability of copper wire bonded products. In the past gold wire was the dominant material in use but in 2015 copper and palladium coated copper wire captured more than 51% of the total market. However, copper wire bonding has been around a long time and while it has been used a great deal for larger diameter wires 30. Direct gold and copper wires bonding on copper sciencedirect. Gold wire provides the ability to use a ball and stitch process. Wirebonding is an electrical interconnection technique using thin wire and a combination of heat, pressure andor ultrasonic energy.
However, in recent years the price of au has greatly increased, fueling the demand for highvolume wire bonding using cu wire, which can lead to signi. Tool force is the amount of weight applied to the bonding wire to mechanically couple the bonding wire to the bonding pad surface. These have been carried out without the use of plasma cleaning to remove the copper surface oxidation prior to wire bonding. Copper wire bonding concerns and best practices article pdf available in journal of electronic materials 428 august 20 with 6,181 reads how we measure reads. Corrosion study and intermetallics formation in gold and. This is a commonly available gas from main gas suppliers and is. Fine pitch copper wire bonding process and materials study. Copper wire bonding bonding copper wire to aluminum pads was previously evaluated as a method for reducing costs.
Tm external use 4 cu bond wire strategy fsl has converted consumer industrial microcontrollers to cu wire and are now initiating automotive conversions. In a materials stack of a thin inorganic film over a metal pad, one should choose the film to have both a low ultimate strength. International traffic in arms regulations or the u. Multiple surface metallizations within the same package. Copper wire bonding concerns and best practices pdf free. Pdf copper wire bonding concerns and best practices. Process monitoring shows all measurement data are all within the current defined specification values. The high hardness of cu wire increases the occurrence of chip damage during bonding 1,3,4. Some of the variations that challenge wire bonding are. Copper wire bonding book lays out the challenges involved in replacing gold with copper as a wire bond material, and includes the bonding process changesbond force, electric flame off, current and ultrasonic energy optimization, and bonding tools and equipment changes. The composition of the premix inert gas used is 95%n2 with 5%h2. With the recent increase in gold au wire cost, cu wire is an attractive way to manage overall package cost. Copper wire has higher thermal and electrical conductivity than. For ribbon wire, use the equivalent round wire diameter width which gives the same crosssectional area as the ribbon wire being tested.
Wire bonding is the method of making interconnections between an integrated circuit ic or other semiconductor device and its packaging during semiconductor device fabrication. Modeling of copper wire bonding process on high power leds. However, in recent years the price of au has greatly increased, fueling the demand for highvolume wire bonding. Tis journey to highvolume copper wire bonding production. Wire bonding using copper wire has many advantages over wire bonding using gold wire, which are summarised in table i. Bonding jumpers shall be installed around any section of nonmetallic duct, pipe, device or fitting that will break the continuity of the ground. Copper wire packaging reliability for automotive and high.
If copper is so good as a bonding wire, why didnt it. Copper wire bonding is fast becoming the preferred material for wire bonding in many semiconductor and microelectronic applications. Wire bonding is generally considered the most costeffective and. Effect of gas type and flow rate on cu free air ball. Physically robust interconnect design in cup bond pads. This critical volume provides an indepth presentation of copper wire bonding. Copper wire bonds also need to be studied to determine the thickness of t he efl tover d ie metallization after the wirebonding process. Wire bonding length defines the resistance, capacitance, and inductance of the wire.
The increasing need to reduce integrated circuit ic. The principle difference between the two processes is that the aluminum wire is bonded in an ultrasonic bonding process at room temperature, whereas gold wire wedge bonding is performed through a thermosonic bonding process with heating up to 150oc. Copper wire bonding book lays out the challenges involved in replacing gold with copper as a wire bond material, and includes the bonding process changes. Factsheet cucoral aluminum cladded copper wire for. Barriers need to be overcome in cu wire bonding due to the high oxidation rate and hardness of cu wires. An inert atmosphere, typically forming gas, is required to prevent cu oxidation.
Gold wire has been the most widely used wire in wire bonding. Usually, after the initial impact of fab on the bond pad, the ultrasonic vibration and the compression of. For condition g or h, the bond strength shall be determined by dividing the breaking force by the total of the nominal beam widths before bonding. Process quality improvement in thermosonic wire bonding. Therefore, gold au wire is still enjoying a huge circle of trust by being a reliable material. We present a novel ultrasonic wiretowire bonding method for bonding two micrometerthick metal wires together. Cu wire bonding has been widely accepted as a less expensive alternative to au. Quikpak can support prototype and preproduction volumes. A number of studies have been conducted on cu wire bonding 36 and the expected benefits of cu wire over au wire have been published 79. Evaluation of wire bonding performance, process conditions. Jdevices cu wire products have excellent quality and reliability on par with au wire.
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