Recently, copperball bonding to ic metallization has received considerable attention primarily because of. During the past 5 years there has been a major transition in our industry from ball bonding with gold wire to the use of copper, palladiumcoated copper, or silver wire. Tis journey to highvolume copper wire bonding production 3 october 2014 operations in chip assembly and test at. Fine pitch copper wire bonding on copper bond pad process. 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. Process monitoring shows all measurement data are all within the current defined specification values. It has higher mechanical strength for better wire bond looping performance which is the key for high io count devices. Freescale copper wire analysis, results and implementation. Parameters optimization of copper wire bonding on thin. Copper wire bonding concerns and best practices bonding process the cu bonding process faces challenges due to the oxidation and hardness of cu. 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. Copper wire bonding bonding copper wire to aluminum pads was previously evaluated as a method for reducing costs. Wire bonding is the method of making interconnections between an integrated circuit ic or other semiconductor device and its packaging during semiconductor device fabrication. The basic steps of ball bonding include the formation of.
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. Tis journey to highvolume copper wire bonding production. Harman, nist fellowes electronics and electrical engineering laboratory semiconductor electronics division812 national institute of. This difference in hardness, of copper is high enough to induce bond pad metal lift or worse silicon damage. The main advantage for gold wire wedge bonding is the possibility to avoid the. This is an accepted version of a paper published in. 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 bond force, electric flame off, current. Wire bonds provide electrical signals and power for the ic. Copper and gold wire bonding course description wire bonding is a welding process that is the dominant chip interconnection method. Gold wire provides the ability to use a ball and stitch process. Wire bonding technology can either be categorized by the bonding method ballwedge or wedgewedge or the actual mechanism that creates the metallic interconnection between wire and substrate thermocompression.
However, with this new technology, changes in the bonding processes as well as bonding metallurgy can affect product reliability. Use of copper bonding wire reduces material costs by 90% to resolve the issue of steeply rising gold prices impacting profits. Copper wire bond failure mechanisms randy schueller, ph. G g h03 wire bonding to advanced copperlok integrated circuits, materials, problems, and proposed solutions george g. 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 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. A novel flip chip bonding technology using au stud bump. Copper wire packaging reliability for automotive and high. However, the hardness of copper makes it difficult to use in many applications such as those with fragile bond pad structures. Gold and aluminum are the commonly used wire materials, in addition, copper and silver have also been used. Recent developments in copper bonding, like the availability of soft cu wires and the understanding of the effects of fab parameters on ball hardness. 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. Background microelectronic wire bonding is a process used to interconnect integrated circuits ics on microchips to substrates or boards. The bonding machine parameter settings require higher bonding forces and cutting tool concepts, applicable for the use of copper bonding wire.
Though copper wire bonding developed nearly 30 years ago, it has only recently gained in popularity due to the rapid increase in the price of gold, which is now about 7,000 times that of copper reference 1. The next section will examine the technological advantages and disadvantages of both copper and gold bonding wire. Although copper bond wire designs are moving forward for commercial applications, there are concerns with quality and reliability when using copper bond wires in highreliability military electronics with a long mission life. In general, the copper wire bonding process is very similar with gold wire bonding as it basically uses the same wire bonder equipment with minor hardware and software retrofits. Leo higgins iii 1 25april 2011 introduction since the end of 2009, the semiconductor industry has seen a sharp increase in the use of copper as a bonding wire.
With the references provided, readers may explore more deeply by reading the original articles. The copper bonding kit consists of a nitrogen nozzle for free air ball fab formation and a flow meter for the inert gas. Powercu soft bonding wire undergoes special processing steps thus heraeus is able to generate extreme soft copper. Wire bonding to advanced copperlok integrated circuits. Corrosion study and intermetallics formation in gold and. 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. Pdf challenges and developments of copper wire bonding. Showcase of wire bonding research centre for advanced materials. Bond conductor size shall be determined by the ampere rating of the service entrance equipment as shown on the grounding and bonding table. This wire bonder was retrofitted with a simple copper wire bonding kit. Copper wire bonding concerns and best practices article pdf available in journal of electronic materials 428 august 20 with 6,059 reads how we measure reads. Pdf copper wire bonding concerns and best practices.
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. Silver bonding wire exhibits excellent durability, conductivity and speed of production. In particular, copper wire is a preferred bonding wire material for highcurrent or highpower applications, since it can carry more current for a given wire diameter. Cu wire bonding university of california, berkeley. Potential failure modes of copper bond wires include corrosion, intermetallic growth, oxidation, susceptibility to. 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.
An inert atmosphere, typically forming gas, is required to prevent cu oxidation. The semiconductor metallization usually contains cu layers with 550. 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. However, copper wire bonding has been around a long time and while it has been used a great deal for larger diameter wires 30. Wire bonding is generally considered the most costeffective and. With the use of copper in the metallization, it became much more difficult to form a metallurgical bond. Its well known that, compared to gold, copper has better electrical and thermal properties. At the beginning of the wire cycle, the bonding tool travels down to the first bond location steps 1. Wire bonding is a standard interconnection technique used for electrically connecting microchips to the terminals of a chip package or directly to a substrate harman, 2010.
Wire bonding is a solid state welding process, where two metallic materials are in intimate contact, and the rate of metallic interdiffusion is a function of temperature, force, ultrasonic power, and time. Common wire bonding surfaces gold wire bonding enepig electroless nickel electroless palladium immersion gold 11. The bond pad cleanliness and oxidation levels are important for the ball bond first bond. Bare copper, palladium coated copper pcc, au coated pcc au pcc and silver ag alloy wires have emerged as alternatives to gold bond wires. Copper and gold wire bonding tj green associates llc. Tis extensive relationships with at tool and materials.
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. Bonding wires for semiconductor technology pdf heraeus. The main application of wire bonding technology is to create electrical. In wire bonding, the attachment of a bond wire to a bond pad is realized by a joining.
This technique provides more control over loop height and bond placement. Parameters optimization of copper wire bonding on thin small outline package 15 without oxidation while some fabs formed under flow rate 0. With just a small capital investment, material costs can be reduced by 80%. Copper also has about 25% higher thermal conductivity than gold 385401 w m 1 k 1 for cu and 314318 w m 1 k 1 for au. 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 for first and second bond formation. Pdf copper wire bonding of microelectronic parts has developed as a means to cut the costs of using the. With the acquisition of the bonding wire business of. Barriers need to be overcome in cu wire bonding due to the high oxidation rate and hardness of cu wires. Challenges and developments of copper wire bonding technology article pdf available in microelectronics reliability 526. If copper were an easy dropin replacement for gold the industry would have made the change long ago.
The development of a new copper wire bonding process for fine pitch applications is currently in progress. Jdevices cu wire products have excellent quality and reliability on par with au wire. Direct gold and copper wires bonding on copper sciencedirect. Copper based wires are low cost and have excellent electrical resistivity. It also has higher thermal and electrical conductivity.
A schematic of the copper wire bond setup is shown in fig. With the recent increase in gold au wire cost, cu wire is an attractive way to manage overall package cost. Bonding these wires to different pad materials produces different metallurgical systems. Sample fabs formed under different flow rates are illustrated in figure 3. Figure 6 wire bond to aluminumsilicon metallization. Development of proper bonding schedules for copper containing metallizations will result in the formation of a. However, in recent years the price of au has greatly increased, fueling the demand for highvolume wire bonding. However, with this new technology, changes in the bonding processes as well as bonding metallurgy can affect.
Freescale copper wire analysis, results and implementation dr. Instead of gold wire, it is replaced by copper wire, though not limited. Operator motion of the micropositioner if a manual bonder is used. Fine pitch copper wire bonding process and materials study. International traffic in arms regulations or the u. Advantages of cu wire bonding the main advantage of cu wire bonding is the lower cost. The composition of the premix inert gas used is 95%n2 with 5%h2. Bare cu and pd coated cu wires are bonded on the 1st and 2nd bond side on both bga and qfn.
They are very reliable, have advanced bondability and are suitable for fine structures. Copper wire bonding concerns and best practices pdf free. As the copper wire is harder, the copper fab is 30 percent harder than a gold fab. Softer fab and higher bond reliability after aging 2000 hours. Reliability of copper wire bonding for power devices. Unfortunately copper has a few mechanical property differences that make it more difficult to use as a wire bond material.
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