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1.
A copper pad oxidizes easily at elevated temperatures during thermosonic wire bonding for chips with copper interconnects.
The bondability and bonding strength of a gold wire onto a bare copper pad are seriously degraded by the formation of a copper
oxide film. A new bonding approach is proposed to overcome this intrinsic drawback of the copper pad. A silver layer is deposited
as a bonding layer on the surface of copper pads. Both the ball-shear force and the wire-pull force of a gold wire bonded
onto copper pads with silver bonding layers far exceed the minimum values stated in the JEDEC standard and MIL specifications.
The silver bonding layer improves bonding between the gold ball and copper pads. The reliability of gold ball bonds on a bond
pad is verified in a high-temperature storage (HTS) test. The bonding strength increases with the storage time and far exceeds
that required by the relevant industrial codes. The superior bondability and high strength after the HTS test were interpreted
with reference to the results of electron probe x-ray microanalyzer (EPMA) analysis. This use of a silver bonding layer may
make the fabrication of copper chips simpler than by other protective schemes. 相似文献
2.
Development of a thermosonic wire-bonding process for gold wire bonding to copper pads using argon shielding 总被引:2,自引:0,他引:2
To improve the bondability and ensure the reliability of Au/Cu ball bonds of the thermosonic (TS) wire-bonding process, an
argon-shielding atmosphere was applied to prevent the copper pad from oxidizing. With argon shielding in the TS wire-bonding
process, 100% gold wire attached on a copper pad can be achieved at the bonding temperature of 180°C and above. The ball-shear
and wire-pull forces far exceed the minimum requirements specified in the related industrial codes. In a suitable range of
bonding parameters, increasing bonding parameters resulted in greater bonding strength. However, if bonding parameters exceed
the suitable range, the bonding strength is deteriorated. The reliability of the high-temperature storage (HTS) test for Au/Cu
ball bonds was verified in this study. The bonding strength of Au/Cu ball bonds increases slightly with prolonged storage
duration because of diffusion between the gold ball and copper pad during the HTS test. As a whole, argon shielding is a successful
way to ensure the Au/Cu ball bond in the TS wire-bonding process applied for packaging of chips with copper interconnects. 相似文献
3.
Thermosonic bonding of gold wire onto a copper pad with titanium thin-film deposition 总被引:1,自引:0,他引:1
A novel thermosonic (TS) bonding process for gold wire bonded onto chips with copper interconnects was successfully developed
by depositing a thin, titanium passivation layer on a copper pad. The copper pad oxidizes easily at elevated temperature during
TS wire bonding. The bondability and bonding strength of the Au ball onto copper pads are significantly deteriorated if a
copper-oxide film exists. To overcome this intrinsic drawback of the copper pad, a titanium thin film was deposited onto the
copper pad to improve the bondability and bonding strength. The thickness of the titanium passivation layer is crucial to
bondability and bonding strength. An appropriate, titanium film thickness of 3.7 nm is proposed in this work. One hundred
percent bondability and high bonding strength was achieved. A thicker titanium film results in poor bond-ability and lower
bonding strength, because the thicker titanium film cannot be removed by an appropriate range of ultrasonic power during TS
bonding. The protective mechanism of the titanium passivation layer was interpreted by the results of field-emission Auger
electron spectroscopy (FEAES) and electron spectroscopy for chemical analysis (ESCA). Titanium dioxide (TiO2), formed during the die-saw and die-mount processes, plays an important role in preventing the copper pad from oxidizing.
Reliability of the high-temperature storage (HTS) test for a gold ball bonded on the copper pad with a 3.7-nm titanium passivation
layer was verified. The bonding strength did not degrade after prolonged storage at elevated temperature. This novel process
could be applied to chips with copper interconnect packaging in the TS wire-bonding process. 相似文献
4.
The annealing textures of copper interconnects depend upon their deposition textures and geometries. The copper interconnects
are subjected to tensile stresses even at room temperature, which in turn gives rise to strain energies. The stress distributions
in interconnects are not homogeneous due to trenches, resulting in non-fiber-type textures after annealing. To better understand
the formation of the non-fiber-type textures, the textures of specimens of 0.2–6 μm in trench width with 0.2 μm in space were
measured, and the strain energy and stress distributions have been simulated. The simulation results indicate that strain
energy density is highest at the upper corners of trench. Therefore, the grain growth rate at the upper corners is fastest,
resulting in the {111}〈110〉 annealing texture. As the trench width increases, the influence of stresses in the trench increases,
even though the strain energy density in the trench is relatively low. In this case the {111}〈112〉 component increases, even
though the formation of the {111}〈110〉 orientation cannot be excluded. 相似文献
5.
Two capillary solutions for ultra-fine-pitch wire bonding and insulated wire bonding 总被引:2,自引:0,他引:2
K.S. Goh 《Microelectronic Engineering》2007,84(2):362-367
In this article, the new challenges and requirements in wire bonding are discussed, the problems in ultra-fine-pitch wire bonding and insulated wire bonding are analyzed, and then two capillary solutions to the problems are presented. Actual bonding experiments using the new capillaries were carried out and the results were satisfactory. Compared to the standard design, a new capillary design has a larger inner chamfer, a larger chamfer diameter and a smaller chamfer angle. This new capillary design has proved to improve the ball bondability and smaller ball size control for ultra-fine pitch wire bonding. A unique surface characteristic on the capillary tip surface has also been derived. The new finishing process developed creates a new surface morphology, which has relatively deep lines with no fixed directions. Compared to the standard capillary, this capillary has less slipping between the wire and the capillary tip surface in contact, and provides better coupling effect between them and better ultrasonic energy transfer. This capillary has been used to effectively improve the bondability of the stitch bonds for insulated wire bonding. 相似文献
6.
Ultrasonic in situ force signals from integrated piezo-resistive microsensors were used previously to describe the interfacial stick-slip motion as the most important mechanism in thermosonic Au wire ball bonding to Al pads. The same experimental method is applied here with a hard and a soft Cu wire type. The signals are compared with those obtained from ball bonds with standard Au wire. Prior to carrying out the microsensor measurements, the bonding processes are optimized to obtain consistent bonded ball diameters of 60 μm yielding average shear strengths of at least 110 MPa at a process temperature of 110 °C. The results of the process optimization show that the shear strength cpk values of Cu ball bonds are almost twice as large as that of the Au ball bonds. The in situ ultrasonic force during Cu ball bonding process is found to be about 30% higher than that measured during the Au ball bonding process. The analysis of the microsensor signal harmonics leads to the conclusion that the stick-slip frictional behavior is significantly less pronounced in the Cu ball bonding process. The bond growth with Cu is approximately 2.5 times faster than with Au. Ball bonds made with the softer Cu wire show higher shear strengths while experiencing about 5% lower ultrasonic force than those made with the harder Cu wire. 相似文献
7.
8.
Wire bonding is one of the main processes of the LED packaging which provides electrical interconnection between the LED chip and lead frame. The gold wire bonding process has been widely used in LED packaging industry currently. However, due to the high cost of gold wire, copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving. In this paper, the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation. This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging. 相似文献
9.
Wire bonding is one of the main processes of the LED packaging which provides electrical interconnection between the LED chip and lead frame.The gold wire bonding process has been widely used in LED packaging industry currently.However,due to the high cost of gold wire,copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving.In this paper,the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation.This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging. 相似文献
10.
11.
Electroless copper grains were deposited on a Pd seed layer under varying bath conditions. The seed layer was determined to
have a (111) texture using grazing incident x-ray (GIX) diffraction. Multiple nucleation sites in the grain boundaries were
imaged using a scanning tunneling microscope. Continual copper growth produced row-like structures. The texture of the electrolessly
deposited copper (ED-Cu) grains were determined to be (111). No radial grain orientation for the Pd seed layer or the ED-Cu
thin film was detected using GIX diffraction. Atomic force microscope images indicated continual Cu nucleation throughout
the deposition process. PdH was formed as a by-product of the electroless deposition process, and detected by x-ray diffraction. 相似文献
12.
In order to achieve copper wafer bonding with good quality, surface conditions of copper films are important factors. In this
work, the effects of surface conditions, such as surface roughness and oxide formation on the bond strength, were investigated
under different bonding conditions. Prior to bonding, copper film surfaces were kept in the atmosphere for less than 1 min,
3 days, and 7 days, respectively, to form different thicknesses of oxide on the surface. Some copper wafers were cleaned using
HCl before bonding in order to remove the surface oxide. Surface roughness of copper films with and without HCl cleaning was
examined. Since surface cleaning before bonding removes oxides but creates surface roughness, it is important to study the
corresponding bond strength under different bonding conditions. These results offer the required information for the process
design of copper wafer bonding in three-dimensional integration applications. 相似文献
13.
It is conventionally believed that wire bonding initiates at the periphery of the contact area and no bonding occurs in the central area. However, this paper demonstrated that two bonding patterns exist, and are determined by bonding processes. If a selected pre-ultrasonic energy is applied, intermetallic compounds initiate in both peripheral and central area of bonds. However, if a pre-ultrasonic energy is absent, intermetallic compounds are only present at the peripheral area as conventionally reported. The application of the pre-ultrasonic energy significantly improves bonding strength, from 66.8 to 94.5 MPa for 20 μm Au wire bonds, due to the intermetallic compounds of greater structured integrity. Two different mechanisms are respectively proposed to account for the intermetallic formation in the center and periphery of the bond interface. 相似文献
14.
D. Martin Knotter Ingrid A. RinkWim A.P. Claassen Jos H.M. Philipsen 《Microelectronic Engineering》2011,88(12):3452-3458
The impact of fluoride and AlOx contaminants on the quality of wire bonding (Au to Al welding) has been measured. No or minor impact of these contaminants has been found with a standard ball shear test. Despite an accelerated lifetime test, the shear strength remains above the required specification limits. Intermetallic coverage, the percentage of the interface between the bond ball and the bond pad where welding resulted in intermetallic diffusion, gives a better picture of the quality decay, but this method is too elaborate for production control and specification limits are unclear. 相似文献
15.
Corrosion inhibition by self-assembled monolayers for enhanced wire bonding on Cu surfaces 总被引:3,自引:0,他引:3
Caroline M. Whelan Michael Kinsella Laureen Carbonell Hong Meng Ho Karen Maex 《Microelectronic Engineering》2003,70(2-4):551-557
Corrosion inhibition by thiol-derived self-assembled monolayers (SAMs) on Cu surfaces has been characterised using contact angle measurements, X-ray photoelectron spectroscopy, voltammetry, and thermal desorption spectroscopy. Factors influencing SAM formation were investigated to develop an optimised wafer level process. XPS confirms the formation of thiolate species bonded to a mixed metallic Cu and cuprous oxide surface. Stability studies as a function of temperature and electrochemical potential demonstrate promising passivation properties. The feasibility of exploiting SAMs in microelectronics applications was demonstrated by the enhancement of Cu wire bonding onto Cu bond pads. 相似文献
16.
J. -Y. Cho K. Mirpuri D. N. Lee J. -K. An J. A. Szpunar 《Journal of Electronic Materials》2005,34(1):53-61
To understand the effect of line width on textural and microstructural evolution of Cu damascene interconnect, three Cu interconnects
samples with different line widths are investigated. According to x-ray diffraction (XRD) results, the (111) texture is developed
in all investigated lines. Scattered {111}〈112〉 and {111}〈110〉 texture components are present in 0.18-μm-width interconnect
lines, and the {111}〈110〉 texture was developed in 2-μm-width interconnect lines. The directional changes of the (111) plane
orientation with increased line width were investigated by XRD. In addition, microstructure and grain-boundary character distribution
(GBCD) of Cu interconnect were measured using electron backscattered diffraction (EBSD) techniques. This measurement demonstrated
that a bamboo-like microstructure is developed in the narrow line, and a polygranular structure is developed in the wider
line. The fraction of ∑3 boundaries is increased as the line width increases but is decreased in the blanket film. A new interpretation
of textural evolution in damascene interconnect lines after annealing is suggested, based on the state of stress and growth
mechanisms of Cu deposits. 相似文献
17.
This paper presents an application of the grey-fuzzy Taguchi method to derive the optimum parameters for the fine-pitch copper (Cu) wire bonding process with multiple quality characteristics. Cu wire has become an important replacement material without the high manufacturing cost of gold for wire bonding processes in integrated circuit (IC) packaging. However, it sometimes fails to take advantage of the Cu material properties due to an insufficient understanding of the relationship between process inputs and outputs of the fine-pitch Cu wire bonding. To assure the accomplishment of cost savings without losing yield, the proposed grey-fuzzy Taguchi method is utilized with an L18 (21 × 37) experimental design and grey relational analysis (GRA) to evaluate the degree of relationship between process inputs and responses, followed by transforming the multiple quality characteristics into a single performance index using a fuzzy inference system. Finally, the process parameters are optimized by the Taguchi method. The proposed optimization methodology provides superior optimization performance compared to the grey-Taguchi method and the parameter setting used in mass production in terms of the conformation experiments. 相似文献
18.
19.
Thermosonic flip-chip bonding process with a nonconductive paste (NCP) was employed to improve the processability and bonding strength of the flip-chip onto flex substrates (FCOF). A non-conductive paste was deposited on the surface of the copper electrodes over the flex substrate, and a chip with eight gold bumps bonded onto the copper electrodes by the thermosonic flip-chip bonding process.For the chips and flex substrates assembly, ultrasonic power is important in the removal of some of the non-conductive paste on the surface of copper electrodes during thermosonic bonding. Accordingly, gold stud bumps in this study were directly bonded onto copper electrodes to form successful electrical paths between chips and the flex substrate. A particular ultrasonic power resulted in some metallurgical bonding between the gold bumps and the copper electrodes, increasing the bonding strength. The ultrasonic power was not only to remove the NCP from the copper electrodes, but also formed metallurgical bonds during the thermosonic flip-chip bonding process with NCP.In this study, the parameters of the bonding of chips onto flex substrates using thermosonic flip-chip bonding process with NCP were a bonding force of 4.9 N, a curing time of 40 s, a curing temperature of 140 °C and an ultrasonic power of 14.46 W. The processability and bonding strength of flip-chips on flex substrates using thermosonic bonding process with NCP was verified in this study. This process has great potential to be applied to the packaging of consumed electronic products. 相似文献
20.
《Microelectronics Reliability》2014,54(9-10):2006-2012
The effect of bonding parameters on the reliability of thick Al wire bond is investigated. Samples were prepared with 25 different designs with 5 different bonding parameters such as time, ultrasonic power, begin-force, end-force and touch-down steps (pre-compression) with 5 levels. The bond signals of ultrasonic generator were collected during bonding in order to obtain prior quality information of bonded wires. 3D X-ray tomography was then used to evaluate bond quality during passive thermal cycling between −55 °C and 125 °C. Tomography datasets were obtained from the as-bonded condition and during cycling. The results clearly show ultrasonic power, appropriate levels of begin-force and touch-down steps are all important for achieving a well attached and reliable bond. Analysis of the virtual cross-sections indicates a good correlation between the bond signal (i.e. the initial bond quality) and wire bond damage/degradation rate. An improved understanding of the wire bonding process was achieved by observing the effect of the complex interaction of bonding parameters on the ultrasonic generator signals and degradation rate under thermal cycling. 相似文献