CN110891616A

CN110891616A - Mechanism investigation and prevention of AL bond pad corrosion in CU wire bond device assemblies

Info

Publication number: CN110891616A
Application number: CN201880041781.5A
Authority: CN
Inventors: 奥利弗·明-仁·钱; 尼克·罗丝
Original assignee: University of North Texas
Current assignee: University of North Texas
Priority date: 2017-05-26
Filing date: 2018-05-25
Publication date: 2020-03-17
Also published as: WO2018218217A2; JP2020521878A; WO2018218217A3

Abstract

Severe corrosion on aluminum (Al) bond pads with a "mud-crack" appearance in copper (Cu) wire bond assemblies can be a critical failure mode, especially under harsh conditions such as an automotive environment. Such corrosion may be associated with, for example, chloride ions (Cl)^‑) Is correlated with the presence of the contaminant. However, the exact corrosion activation mechanism remains unclear and thus effective corrosion protection is not achieved. A novel immersion corrosion screening metrology is utilized as an in situ characterization tool to establish the corrosion mechanism directly related to Cu wire bond devices. With this bonding to AlThe improved understanding of the pad corrosion mechanism has led to significant progress towards developing effective corrosion protection strategies to improve and ensure overall package reliability.

Description

Mechanism investigation and prevention of AL bond pad corrosion in CU wire bond device assemblies

Cross Reference to Related Applications

This application claims priority and benefit of U.S. provisional patent application No.62/511,863, filed on 26.5.2017 and entitled "MECHANISTIC INVESTIGATION ANDPREVENTION OF AL BOND PAD CORROSION IN CU WIRE-bound DEVICE association," the disclosure of which is hereby incorporated by reference in its entirety.

Technical Field

The present disclosure relates generally to bi-metal devices, and more particularly to techniques for reducing corrosion of bi-metal devices including copper and aluminum.

Background

Copper (Cu) has rapidly replaced gold (Au) as a preferred wire bond material in microelectronic packages due to its higher electrical conductivity, lower cost and better mechanical strength, which results in reduced pad size and pad pitch. However, corrosion related failures need to be minimized to ensure package reliability. In particular, aluminum (Al) bond pads are particularly susceptible to corrosion and have a characteristic "mud-cracked" appearance. Especially under severe conditions such as an automotive environment, such corrosion can be a serious failure mode of Cu wire bond assemblies. The emerging trend for wearable electronics also imposes new stricter package reliability requirements to ensure protection against sweat/mud/rain corrosion under all terrain non-stop use conditions. In addition, the recent transition to non-lead SAC (Sn-Ag-Cu) solders requires the use of a stronger flux (2-3%) and higher reflow temperatures (-260 ℃), which may leave flux residues and ionic contamination to cause corrosion. Although this type of Al bond pad corrosion is often associated with materials such as halides (Cl)^-、Br^-、F^-) The presence of contaminants, but the basic corrosion mechanism remains unclear and effective corrosion protection is therefore not achieved.

Disclosure of Invention

The present disclosure provides halide-induced Al bond pads for improved package reliability and reduced Cu wire bondingCorrosion protection strategy for the corrosion mechanism. Previous corrosion protection strategies focused on CU-like components from faulty wire-bond devices after autoclave testing₉Al₄CuAl and CuAl₂An interfacial layer of an intermetallic compound of (2). However, the true cause of corrosion vulnerability is best revealed by careful monitoring of the active corrosion progress. In aspects of the present disclosure, a novel immersion corrosion screening metrology is presented as an in situ characterization tool in conjunction with SEM, optical microscopy, and other characterization techniques to establish the corrosion mechanism directly related to Cu wire bond devices. The disclosed immersion corrosion screening can be viewed as accelerating extreme moisture stress testing. In a properly molded package, the degree of adsorbed water and ionic impurities at the mold compound/die interface will be less severe.

By monitoring the active etch in real time, the surface AlO can be observed_xDendrite formation/growth and active hydrogen (H)₂) And (4) gas is separated out. In some aspects, immersion corrosion screening in accordance with aspects of the present disclosure has recognized H₂The precipitation plays a key role in extracting electrons from the Al bond pad to drive the corrosion cycle. These observations provide mechanistic insight followed by formation of a signal configured to eliminate the H₂A new corrosion inhibition strategy for half reactions evolved. In some aspects, the corrosion inhibition strategy can apply a selected surface treatment to substantially increase H⁺/H₂Activation energy barrier for cathode reaction. Testing of the corrosion inhibition strategy proposed by aspects of the present disclosure has demonstrated that surface treatment is very effective for eliminating severe Al pad spalling corrosion in acidic chloride test solutions with unmolded Cu wire bond components. The novel surface treatments according to aspects of the present disclosure have been demonstrated to exhibit good corrosion resistance after annealing at temperatures around 175 ℃. In some aspects, the selected surface coating may be applied at a pre-molding step in a manufacturing compatible wire bonding and molding assembly line.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

Drawings

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:

fig. 1A is an image showing dendrite progression due to aluminum (Al) corrosion;

FIG. 1B shows the formation of chloride (Cl)^-) An image of a mud crack morphology formed at the surface of the Al wafer caused by the induced corrosion;

fig. 1C is a scanning electron microscope image showing islands formed on the surface of an etched Al wafer;

FIG. 2 is a diagram showing aspects of surface elemental composition of an etched Al wafer;

FIG. 3A is a series of images showing the progression of corrosion in copper (Cu)/Al micro-patterns and Al wafers;

FIG. 3B is a graph showing the results of energy dispersive x-ray spectroscopy (EDX) analysis of Cu/Al micro-patterns and corrosion in Al wafers;

FIG. 4A is a graph showing the results of gas chromatography-mass spectrometry (GC-MS) analysis of gas generated from a blank sample without reactive corrosion;

FIG. 4B is a graph showing the results of GC-MS analysis of gases generated due to active corrosion of Al in a Cu/Al system;

FIG. 5 is a series of SEM images showing aspects of hydrogen evolution during corrosion of Al in a Cu/Al bimetallic system;

fig. 6A is an image showing a device to study corrosion of an Al pad;

fig. 6B is an image showing an aspect of corrosion of the Al pad;

fig. 6C is an image showing an aspect of wire bond peeling due to corrosion of the Al pad;

FIG. 6D is an image showing additional aspects of wire bond debonding due to corrosion of the Al pad;

fig. 7 is a diagram showing an aspect of a Cu line bonded to an Al pad;

fig. 8A is an image showing a Cu wire bonding device;

fig. 8B is an image showing corrosion of a Cu wire bond device;

fig. 8C is an image showing the use of an inhibitor compound to reduce corrosion and protect a Cu wire bond device according to aspects of the present disclosure;

fig. 9A is an image showing corrosion of an untreated Cu dot sample on an AL (0.5% Cu) substrate;

fig. 9B is an image showing improved thermal stability and corrosion protection of Cu dot/AL (0.5% Cu) samples treated with inhibitors according to aspects of the present disclosure;

FIG. 10A is a series of images showing the results of corrosion screening of Cu micro-dots without inhibitor coating;

FIG. 10B is a series of images showing the results of corrosion screening of Cu micro-dots without inhibitor coating and annealed without inhibitor coating;

fig. 10C is a series of images showing results of corrosion screening of Cu micro-dots after applying a sprayed inhibitor and annealing, in accordance with aspects of the present disclosure;

fig. 10D is a series of images showing results of corrosion screening of Cu micro-dots after applying vapor deposited inhibitors and annealing in accordance with aspects of the present disclosure;

fig. 11 is a flow chart showing an internal chloride contamination loading and testing scheme for Cu wire bond devices after the molding process;

fig. 12 is a graph showing electrical test data for a specimen of a molded Cu wire bond device after autoclave stress testing; and

fig. 13 is a flow chart of a method for reducing corrosion of a Cu wire bond device according to aspects of the present disclosure.

Detailed Description

Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the present invention, are given by way of illustration only, not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.

Fig. 1A-1C illustrate aspects of aluminum (Al) corrosion observed during a study of real-time corrosion in a Cu/Al bimetallic system, which was performed using a novel metric known as micropattern corrosion screening. The micropattern corrosion screening technique for investigation was prepared by sputtering Cu dots (50 nm thick, 130 μm diameter) onto a 1.2 μm thick aluminum wafer (99.5% Al + 0.5% Cu) substrate. All micropatterns were prepared by microspot masking using a danton vacuum Desktop Pro sputtering unit. Real-time examination of the corrosion process was performed by a Nikon Eclipse LV150 microscope. Samples were constantly monitored (Cu/Al micro pattern and Cu wire bond device both submerged in test environment solution (pH 5, 0-20ppm Cl)^-Solution) to neutralize the sample surface to obtain an indication of the surface corrosion process. FEI Nova 200NanoLab Scanning Electron Microscope (SEM) provides high resolution imaging of the corroded sample. Surface elemental composition information is obtained by an energy dispersive X-ray spectroscopy (EDX) system. Hydrogen (H) was detected by gas chromatography mass spectrometry with a Finnigan Trace GC Ultra equipped with a quaternary mass filter (GC-MS)₂) And (4) precipitating. The inhibitor surface treatment of the micropattern and Cu wire bond devices was performed by spray coating and chemical vapor deposition processes. A solution of the corrosion inhibitor compound is sprayed by using a pneumatic sprayer at a pressure of 70psi at a distance of-30 centimeters (cm)Spraying is performed onto the sample surface. Chemical vapor deposition was performed by heating the micropattern sample and corrosion inhibitor in situ for 6-10 minutes near the melting point of the compound. After an additional thermal anneal (>175 deg.C), the corrosion inhibitor treated micropattern samples were tested in an acidic chloride solution to evaluate corrosion inhibition.

The presence of chloride ions may cause corrosion of aluminum (with 0.5% Cu), hereinafter referred to as Al samples for short. Immersion corrosion screening shows the progress of corrosion of Al, which begins with the formation of dendrites on the Al surface and the corrosion continues to result in the formation of a morphology similar to mud cracks. It was observed that the concentration of chloride ions in the solution had a direct effect on the progress of the corrosion of Al (with 0.5% Cu). Observe Al samples at 20ppm Cl^-Corrosion at pH 4 at concentration and images were taken after 96 hours of immersion as shown in fig. 1A-1C. For example, fig. 1A is an image showing the observed dendrite progression due to Al corrosion. FIG. 1B is an image showing a close-up view of dendrite formation and reveals that the formation is due to severe chloride ions (Cl)^-) The induced corrosion causes a mud crack morphology to form at the surface of the Al wafer. Fig. 1C is an SEM image of an etched Al wafer and shows islands of etched aluminum surface with severe mud cracking formed.

As part of the analysis, EDX was used to examine the surface elemental composition of the corroded Al samples. The results of this analysis are shown graphically in figure 2 and tables 1 and 2 below. Table 1 shows the surface elemental composition of a mudcrack of an eroded sample (e.g., mudcrack 202 of fig. 2) and table 2 shows the surface elemental composition of an island of an eroded sample (e.g., mudcrack 204 of fig. 2).

TABLE 1

TABLE 2

Element(s)	By weight%	Atom%
			O	36.51	49.63
Al	52.60	42.40
			Si	6.12	4.74
S	4.77	3.23
			Total of	100.00	100.00

As briefly mentioned above, for exposure to 20ppm Cl at pH 4^-Up to 96 hours of Al samples, the data shown in fig. 2 associated with corroded samples was obtained using EDX. In the same panel as in fig. 2, an SEM image of the eroded sample is shown. As shown in fig. 2 and tables 1 and 2, the corroded samples show a high oxygen signal with almost a 1:1 ratio to Al, compared to a slightly lower O to Al ratio of 1:2 at the island regions, indicating severe oxidation in the region where the mud cracking occurred. To compareThe surface of the original Al (with 0.5% Cu) sample exhibited a 1: 70O: Al composition ratio, indicating that the Al corrosion in the crack region was more aggressive, which resulted in more corrosion in the crack region than in the Al island high region.

The progress of corrosion of Cu/Al micro patterns and Al wafers was investigated side-by-side using the immersion corrosion screening technique described above. In fig. 3A, an image comparing the corrosion progression observed in Al (e.g., Al region 302) and Cu/Al bimetallic systems (e.g., Cu/Al region 304) is shown, and in fig. 3B, a plot of the observed EDX representing a corroded Cu/Al micropattern is shown. Note that even with the use of the thinner 2ppm Cl^-Active Al corrosion was also observed along the Cu/Al bimetallic contact in as little as 10 minutes for a solution with a pH of 5. Similar to fig. 1A-1C, the severity of Al corrosion driven by Cu/Al bimetallic contacts can be seen by strong dendrite formation and mud cracking around Cu spots on the Al surface. In contrast, Al wafers do not experience this severe corrosion under the same conditions and exhibit only minor surface roughening at the same time mark.

This difference in the severity of corrosion shows the important effect of the Cu/Al bimetallic contact. The Cu and Al whose positions in the galvanic series are separated form a galvanic couple, with the less noble metal Al becoming the anode and the more noble metal Cu becoming the cathode. In the presence of Cl^-And moisture, the electrochemical cell is completed and corrosion occurs rapidly. On the other hand, Al does not have such a powerful driving force to obtain a rapid corrosion state. When immersed in a more concentrated 20ppm Cl^-In the middle, it takes about twice as long (e.g., 96 hours) to heavily corrode the Al wafer. The screening data also shows different corrosion progression in the Cu/Al and Al systems. In a Cu/Al system, corrosion starts at the Cu/Al interface and continues to form dendrites. Later, as expected, when immersed in an acidic chloride solution, Al corrosion was greatly accelerated in micropatterned samples with Cu/Al bi-metals (e.g., as shown in Cu/Al region 304) compared to Al wafers immersed in the same solution (e.g., as shown in Al region 302). As shown in FIG. 3A, even with the use of the more dilute 2ppm Cl^-pH 5 solution, at least 1Active Al corrosion was also observed along the Cu/Al bimetallic contact within 0 minutes. Similar to the corrosion shown in fig. 1A-1C, the severity of Al corrosion driven by Cu/Al bimetallic contacts can be seen by strong dendrite formation and mud cracking around Cu spots on the Al surface. In contrast, Al wafers do not experience such severe corrosion under the same conditions, and exhibit only minor surface roughening at the same time mark, as shown (e.g., as shown by Al region 302). This difference in corrosion severity shows the important effect of the Cu/Al bi-metal on Al in the Cu/Al system, which also ends up forming a mud crack morphology at about 44 hours, as shown in fig. 3A. An O to Al ratio of over 2:1 was observed using EDX, as shown in FIG. 3B.

More importantly, the in situ corrosion screening described above shows for the first time the rapid gas bubbling associated with the active corrosion of Al in Cu/Al systems. Gas chromatography-mass spectrometry (GC-MS) analysis was performed on the evolved gases and the results are shown in fig. 4A and 4B. Fig. 4A shows the results of performing GC-MS on a blank sample and fig. 4B shows the gases generated by the etching process. The results of the GC-MS analysis provided a clear signal for hydrogen.

The hydrogen evolution reaction plays an important role in severe Al corrosion. Once hydrogen evolution occurs, it promotes oxidation of Al to early dendrite formation, as shown above in fig. 3A and 3B. Once dendrites form, intergranular corrosion progression proceeds laterally and downward to cause spalling corrosion. Hydrogen evolution can also lead to internal stress build-up, leading to a violent eruption, as shown in fig. 5, which fig. 5 shows SEM images of hydrogen evolution during corrosion of Al in a Cu/Al bimetallic system (left), at the hydrogen evolution site (middle), and at the Cu/Al interface site (right).

Exposing the underlying unprotected Al to hydrogen evolution further leads to corrosion. As shown in fig. 3, the hydrogen evolution is always followed by severe corrosion, forming dendrites and eventually mud cracks. As will be described in more detail below, the newly discovered hydrogen evolution that accompanies severe Al corrosion provides important insight to help establish the corrosion mechanism and create an effective preventative strategy.

The immersion screening metrology described above was also applied to study corrosion occurring in industrial Cu wire bonded devices. Devices with palladium (Pd) -coated Cu lines bonded to Al pads were used to investigate the corrosion of the Al pads. This study is shown in fig. 6A-6D, which illustrate the process of immersion screening of Pd coated Cu wire bonded devices.

Fig. 6A is an image showing a Pd coated Cu wire bond device prior to immersion. Fig. 6B is an image showing corrosion starting with hydrogen evolution, which occurs within about 6 minutes of the immersion screening process, and fig. 6C is an image showing first wire bond peeling, which occurs within about 7 minutes of the immersion screening process. Fig. 6D is an image showing 10% line striping that occurred within approximately 43 minutes of the immersion screening process. As shown in fig. 6, the corrosion progression of the wire bond device is similar to that of the lab-made Cu/Al bimetallic micropatterned system. Corrosion always starts at the Al pad of the Cu wire bond and proceeds along the Al contact lead, with hydrogen evolution. This indicates that the additional Pd coating on the Cu line bonded to the Al pad is not effective in preventing Al corrosion, which was induced in the above studies using acidic chloride conditions. This also indicates that the bimetallic contact between the Cu ball and the Al pad plays an important role in Al pad corrosion in Cu wire bond devices.

This Cl^-The severity of the induced Al corrosion can be seen from the time frame of the corrosion screening event. At 5ppm Cl^-First signs of corrosion with hydrogen evolution were noted after immersion in a solution at pH 5 for as little as 6 minutes, as shown in fig. 6B. The first wire bond peel occurred at 7 minutes as shown in fig. 6C, and it took only 43 minutes to peel 10% or more of all Cu lines from the Al pad as shown in fig. 6D.

The mechanism of galvanic corrosion that occurs when different metal contacts are exposed to an electrolyte (such as chloride ions) has been previously reported. In the present case of Cu wire bonded devices, in Cl^-Large electrochemical potential difference between Al and Cu in the presence of ions: (>+2.0V) resulted in severe Al bond pad corrosion being observed. However, in Cl^-In the absence of ions, the surface oxide coating on the Al metal provides good passivation protection against continued Al corrosion.

Based on the data obtained during the above experiments, a corrosion resistance mechanism was proposed, as shown in fig. 7. The corrosion-resistant mechanism shown in fig. 7 is configured to account for the acidic chloride-induced Al bond pad corrosion described above. In fig. 7, Cu line 702, Al surface 704, Cu ball 706, and Al bond pad 708 are shown. The Cu ball 706 and the Al bond pad 708 may form a Cu/Al bimetal interface. In some aspects, the Al surface 704 may be covered by a mixed aluminum oxide/hydroxide layer when exposed to moisture. Under acidic conditions, the surface charge of the alumina/aluminum hydroxide may be positive, which results in attraction of negative ions such as Cl^-. Absorbed Cl^-The ions can be made by converting the exposed alumina/aluminum hydroxide to aluminum chloride (AlCl) which has very high solubility in water (46g/100mL)₃) Causing the passivation oxide to dissolve. In the absence of the passivation oxide, the exposed Al bond pad 708 bonded to the Cu line (e.g., Cu line 702) may be driven by a large potential difference to oxidize quickly. Hydrolysis of aluminum chloride on the surface generates locally concentrated protons to efficiently capture electrons from Al oxidation, resulting in the observed hydrogen formation. As shown, this hydrogen evolution can accumulate large physical stresses, resulting in "volcanic eruption" like damage, which further exposes the underlying and unprotected Al to Cl^-Induced corrosion. With H₂The gas continues to leave the system and the Al pad corrosion becomes non-self-limiting and rapidly self-promotes the formation of the observed "mud crack" morphology that severely corrodes the Al bond pad.

In any case, active corrosion requires efficient electron transfer between the anode and cathode in a localized corrosion cell. Corrosion protection strategies according to aspects of the present disclosure are directed to modifying the Al/Cu bimetallic system using selected surface treatments to prevent this newly discovered cathodic half-reaction of hydrogen evolution. According to some aspects, the Cu/Al micropatterned surface may be treated with a thin (e.g., less than 3 μm) selected corrosion inhibitor coating that can significantly increase H₂The precipitated energy barrier and prevents active Al corrosion cycling.

Referring to FIGS. 8A-8C, various images are shown illustrating application by applicationThe treatment of inhibitor coatings according to aspects of the present disclosure provides improvements. Fig. 8A is an image showing a Cu wire bonding device; FIG. 8B is a Cl plot at 5ppm pH 5 illustrating a Cu wire bonded device not treated with an inhibitor compound according to the present disclosure^-Images after approximately 17 hours of immersion in solution; and fig. 8C is a Cl at 5ppm pH 5 illustrating a Cu wire bonded device treated with an inhibitor compound according to the present disclosure^-Images after approximately 12 days immersion in solution. As shown in fig. 8B and 8C, the selected inhibitor compounds may completely prevent hydrogen evolution and provide extended corrosion protection to Cu wire bond devices.

In the absence of the inhibitor compound, hydrogen evolution and Al pad corrosion quickly (e.g., less than 10 minutes) began and complete peeling of all Cu wires was achieved at 17 hours of immersion, as shown in fig. 8B. however, with the inclusion of the inhibitor compound, corrosion was completely prevented and the Al pad and Cu wire bonds remained intact even after 12 days, this may be due to the covalently bound inhibitor raising the potential barrier to the hydrogen evolution reaction, thereby preventing Al corrosion. in some aspects of the present disclosure, the inhibitor compound may include fluorescein, cetyl trimethylammonium bromide, 3-hydroxyflavone, cerium dibutyl phosphate, 8-hydroxyquinoline, sodium benzoate, tolyltriazole, benzotriazole, amino-oxazole-thiol, glutaric acid, polyvinyl alcohol, thiourea, phenylthiourea, 4-carboxyphenylthiourea, 1, 4-naphthoquinone, indole, tryptamine, tryptophan, monoethanolamine, thioacetamide, quinaldinic acid, α -benzoin oxime, 2- (2-hydroxyphenyl) benzoxazole, dithiooxamide, bis-copper dihydrazone, iron butynoxide, 2-carbothioamide, thiobenzamide, 4-thiobenamide, thiobenazolecarboxamide, and thiobenoxacor.

In some aspects, package-friendly application methods can be used to apply a laboratory-proven corrosion-inhibiting coating to Cu wire-bonded devices in an assembly line production environment. In an industrial environment, the inhibitor coating may be subjected to a series of severe temperature conditions after application of the inhibitor coating but before the encapsulation process may be completed. For example, the wire bond device coated with the selected inhibitor may be exposed to a temperature of about 175 ℃ for about 5-10 minutes during the molding process. Temperatures of about 220-260 c may also be experienced for 10-15 minutes during the wire bonding and solder reflow process. The applied surface treatment (e.g., inhibitor compound) should be configured to withstand these higher temperatures. Preliminary thermal stress testing of the inhibitor coating according to aspects of the present disclosure was performed under autoclave test conditions to evaluate its thermal stability and resulting corrosion protection. Fig. 9A and 9B are images showing inhibitor treated Cu dot samples tested in a pressure cooker at about 121 ℃, 2 atmospheres, and 100% relative humidity. Under these harsh conditions, the samples treated with the inhibitor coating resist corrosion for almost 4-8 days.

In some aspects, various inhibitor application methods can be used in industrial implementations. For example, in some aspects, a pneumatic nebulizer can be used to spray samples with solutions containing different inhibitor concentrations at 70psi pressure. The sprayed samples were then annealed at about 175 ℃ for about 4 minutes and then at 5ppm Cl^-Test solutions with pH 5 were subjected to corrosion screening. Tests have shown that the sprayed samples resist corrosion for a longer period of time than untreated samples, however, Al corrosion can be observed at about 4 hours mark. In additional aspects, chemical vapor deposition techniques can be used to apply the inhibitor. A chemical vapor deposition technique for applying an inhibitor compound to Cu microdots on an Al wafer is implemented that includes heating the Cu microdots in situ on the Al wafer after applying the inhibitor compound at a selected temperature for a selected duration. An infrared spectrum was performed on the sample and it showed that the inhibitor compound formed strong covalent bonds with the Cu/Al micro sample. The ir absorption peak heights also reveal that chemical vapor deposition application methods can provide thinner and more uniform inhibitor coatings. During the test, the samples were again annealed at about 175 ℃ for 4 minutes and at 5ppm Cl^-Corrosion was tested in a solution with pH 5. The samples coated using the chemical deposition method exhibited excellent corrosion resistance in about 10 hours and no signs of Al corrosion were observed.

Referring to FIGS. 10A-10D, images illustrating pairs of inhibitor coatings applied by different methods are shownInfluence of corrosion resistance of the Cu/Al samples. In fig. 10A, images of different time periods during the test are shown, showing Cu micro-dots on Al without inhibitor coating at 5ppm Cl at pH 5^-Results of corrosion screening in solution, where the left image corresponds to 0 minutes, the right image corresponds to 2 hours, and the right image corresponds to 4 hours. In fig. 10B, images are shown at different time periods during the test, showing Cu micro-dots on Al at 5ppm Cl at pH 5 without inhibitor coating and without inhibitor coating annealed at 175 ℃ for 4 minutes^-Results of corrosion screening in solution, where the left image corresponds to 0 minutes, the right image corresponds to 2 hours, and the right image corresponds to 8 hours. In fig. 10C, images are shown at different time periods during the test, showing Cu micro-dots on Al at 5ppmpH of Cl of 5 after applying a sprayed inhibitor and annealing at 175 ℃ for 4 minutes according to aspects of the present disclosure^-Results of corrosion screening in solution, where the left image corresponds to 0 minutes, the right image corresponds to 2 hours, and the right image corresponds to 6 hours. In fig. 10D, images are shown at different time periods during the test, showing Cu micro-dots on Al at 5ppm Cl at pH 5 after applying a vapor deposited inhibitor coating and annealing at 175 ℃ for 4 minutes according to aspects of the present disclosure^-Results of corrosion screening in solution, where the left image corresponds to 0 minutes, the right image corresponds to 4 hours, and the right image corresponds to 10 hours. As shown in the images, the samples treated with the inhibitor coating according to the present disclosure exhibited less corrosion than the untreated samples.

Referring to fig. 11, a flow chart showing an internal chloride contamination loading and testing protocol for Cu wire bond devices after the molding process is shown. As shown in fig. 11, at step 1102, a Cu wire bond device 1112 is provided/obtained. At step 1104, the Cu wire bond device 1112 is loaded with sodium chloride (NaCl)_(aq)) As indicated at 1114. In one aspect, the Cu wire bond device can be loaded with about 1.25 μ L of NaCl_(aq). Note that the loading of Cu wire bond devices with NaCl is provided for purposes of illustration and not limitation, and other compounds and/or solutions may be utilized depending on the particular test being performed. Additionally, note that volumes less than or in excess of 1.25 μ L may be used to fill Cu wire bond devices, depending on the compound/solution utilized, the particular test being performed, and/or other testing considerations. After the loading step 1104, at step 1106, a loading solution (e.g., NaCl) may be allowed to flow_(aq)) And (6) drying. As the loading solution dries, crystals 1116 (e.g., NaCl crystals) may form on the Cu wire bond device 1112. Once dried, at step 1108, the Cu wire bond device 1112 may be molded and subjected to stress testing. In one aspect, a stress test may be configured according to a set of test parameters. The set of test parameters may include a temperature parameter, a time parameter, and the like. For example, testing of aspects of the present disclosure was performed using a temperature parameter (e.g., temperature parameter) of 130 ℃ for forty-eight hours (e.g., time parameter). After molding and stress testing, defect analysis of the Cu wire bond device may be performed at step 1110.

Referring to fig. 12, a graph is shown showing the results of electrical test data for a sample of molded Cu wire bond devices after autoclave stress testing. As shown in FIG. 12, the results of the electrical failure analysis demonstrate that the inhibitor coating is very effective for preventing Al bond pad corrosion due to the use of NaCl as described above with respect to FIG. 11_(aq)Severe internal Cl caused by Cu loaded wire bond devices^-Ionic contamination was expected. Conductivity testing was performed after autoclave stress testing based on applying 2 volt input/output to the surface treated molded wire bond device. As shown in fig. 12, excellent conductivity was observed even though the device suffered severe contamination due to internal chloride ions. This demonstrates that the selected inhibitor treatment is effective to prevent corrosion of Cu lines and Al pads exposed in the presence of chloride ions. Note that during testing, the unprotected control devices experienced extensive Cu ball delamination and open circuit catastrophic failure.

Referring to fig. 13, a flow diagram is shown illustrating a method 1300 for reducing corrosion of Cu wire bonded devices according to aspects of the present disclosure, the method including providing at least one aluminum substrate, and at 1320, disposing one or more copper elements on the at least one aluminum substrate, in one aspect, disposing one or more copper elements on the at least one aluminum substrate may include coupling the one or more copper elements to bond pads of the at least one aluminum substrate, at 1330, the method 1300 includes applying a coating to the at least one aluminum substrate and the one or more copper elements, in one aspect, a coating may be applied to the aluminum substrate prior to disposing the one or more copper elements on the at least one aluminum substrate, for example, the aluminum substrate may be coated, and then one or more copper elements (such as Cu wires) may be disposed on or coupled to one or more regions of the aluminum substrate, such as wire bonding Cu to a bond pad of Al, as described above with reference to fig. 1-12, as described above, the coating may be configured to inhibit corrosion of one or more copper elements such as a thiobenzone coating, a thiobenzone, a thiobenzo.

In one aspect, the method 1300 may include subjecting at least one aluminum substrate and one or more copper elements to a molding process and/or an annealing process. The annealing process may be performed after the coating is applied. In one aspect, the method 1300 may include immersing at least one aluminum substrate and one or more copper elements in a solution for a period of time, and generating observation data associated with corrosion of the at least one aluminum substrate and one or more copper elements over the period of time. As described above, the solution may be configured to induce corrosion of the at least one aluminum substrate and the one or more copper elements. The observation data may include data representing the ability of the coating to inhibit corrosion of the at least one aluminum substrate and the one or more copper elements. For example, the observation data may include images, graphs, and/or other data generated using at least one of a Scanning Electron Microscope (SEM), an energy dispersive X-ray spectroscopy (EDX) system, and a gas chromatography-mass spectrometer (GC-MS), as described above with reference to fig. 1A-12.

As shown above, the corrosion mechanism according to aspects of the present disclosure may provide excellent corrosion protection by hindering cathodic hydrogen evolution. The selected inhibitor coating may be compatible and remain active under autoclave test conditions to prevent Al corrosion for at least 4-8 days. In addition, aspects of the present disclosure provide package-friendly application methods, such as spray coating, chemical vapor deposition, and the like, that provide good thermal stability and corrosion inhibition properties. Note that the specific techniques disclosed herein may also be applied to industrially prepared wire bonded device samples and to test and optimize process parameters for applying inhibitors to wire bonded devices in assembly line conditions.

Although the embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.

Claims

1. A system, the system comprising:

at least one aluminum substrate;

one or more copper elements disposed on the at least one aluminum substrate; and

a coating applied to the at least one aluminum substrate and the one or more copper elements and configured to inhibit corrosion of the at least one aluminum substrate and the one or more copper elements.

2. The system of claim 1, wherein the coating comprises at least one of fluorescein, cetyltrimethylammonium bromide, 3-hydroxyflavone, cerium dibutylphosphate, 8-hydroxyquinoline, sodium benzoate, tolyltriazole, benzotriazole, amino-azole-thiol, glutaric acid, polyvinyl alcohol, thiourea, phenylthiourea, 4-carboxyphenylthiourea, 1, 4-naphthoquinone, indole, tryptamine, tryptophan, monoethanolamine, thioacetamide, quinaldinic acid, α -benzoinoxime, 2- (2-hydroxyphenyl) benzoxazole, dithiooxamide, dicyclohexylcopper oxalyl dihydrazone, cupferron reagent, 2-butyne-1, 4-diol, benzamide, 4-aminobenzenesulfonamide, and thioacetamide.

3. The system of claim 1, wherein the one or more copper elements comprise at least one of copper balls and copper wires.

4. The system of claim 1, wherein the coating is applied to the at least one aluminum substrate and the one or more copper elements prior to annealing the at least one aluminum substrate and the one or more copper elements.

5. A method, the method comprising:

providing at least one aluminum substrate;

disposing one or more copper elements on the at least one aluminum substrate; and

applying a coating to the at least one aluminum substrate and the one or more copper elements, the coating configured to inhibit corrosion of the at least one aluminum substrate and the one or more copper elements.

6. The method of claim 5, wherein the coating is applied to the at least one aluminum substrate using a spray coating technique.

7. The method of claim 5, wherein the coating is applied to the at least one aluminum substrate using a chemical vapor deposition technique.

8. The method of claim 5, wherein the coating comprises at least one of fluorescein, cetyltrimethylammonium bromide, 3-hydroxyflavone, cerium dibutylphosphate, 8-hydroxyquinoline, sodium benzoate, tolyltriazole, benzotriazole, amino-azole-thiol, glutaric acid, polyvinyl alcohol, thiourea, phenylthiourea, 4-carboxyphenylthiourea, 1, 4-naphthoquinone, indole, tryptamine, tryptophan, monoethanolamine, thioacetamide, quinaldinic acid, α -benzoinoxime, 2- (2-hydroxyphenyl) benzoxazole, dithiooxamide, dicyclohexylcopper oxalyl dihydrazone, cupferron reagent, 2-butyne-1, 4-diol, benzamide, 4-aminobenzenesulfonamide, and thioacetamide.

9. The method of claim 5, wherein the one or more copper elements comprise at least one of copper balls and copper wires.

10. The method of claim 5, wherein the method comprises subjecting the at least one aluminum substrate and the one or more copper elements to a molding process.

11. The method of claim 5, wherein the method comprises subjecting the at least one aluminum substrate and the one or more copper elements to an annealing process.

12. The method of claim 5, further comprising immersing the at least one aluminum substrate and the one or more copper elements in a solution for a period of time and generating observation data associated with the corrosion of the at least one aluminum substrate and the one or more copper elements over the period of time, wherein the solution is configured to induce corrosion of the at least one aluminum substrate and the one or more copper elements, and wherein the observation data comprises data representative of the ability of the coating to inhibit the corrosion of the at least one aluminum substrate and the one or more copper elements.

13. The method of claim 12, wherein the observation data is generated using at least one of a Scanning Electron Microscope (SEM), an energy dispersive X-ray spectroscopy (EDX) system, and a gas chromatography mass spectrometer (GC-MS).

14. A method, the method comprising:

providing at least one aluminum substrate;

disposing one or more copper elements on the at least one aluminum substrate;

applying a coating to the at least one aluminum substrate and the one or more copper elements, the coating configured to inhibit corrosion of the at least one aluminum substrate and the one or more copper elements;

immersing the at least one aluminum substrate and the one or more copper elements in a solution for a period of time, wherein the solution is configured to induce corrosion of the at least one aluminum substrate and the one or more copper elements; and

generating observation data associated with the corrosion of the at least one aluminum substrate and the one or more copper elements over the period of time, wherein the observation data comprises data representative of the ability of the coating to inhibit the corrosion of the at least one aluminum substrate and the one or more copper elements.

15. The method of claim 14, wherein the coating is applied to the at least one aluminum substrate using a spray coating technique.

16. The method of claim 14, wherein the coating is applied to the at least one aluminum substrate using a chemical vapor deposition technique.

17. The method of claim 14, wherein the coating comprises at least one of fluorescein, cetyltrimethylammonium bromide, 3-hydroxyflavone, cerium dibutylphosphate, 8-hydroxyquinoline, sodium benzoate, tolyltriazole, benzotriazole, amino-azole-thiol, glutaric acid, polyvinyl alcohol, thiourea, phenylthiourea, 4-carboxyphenylthiourea, 1, 4-naphthoquinone, indole, tryptamine, tryptophan, monoethanolamine, thioacetamide, quinaldinic acid, α -benzoinoxime, 2- (2-hydroxyphenyl) benzoxazole, dithiooxamide, dicyclohexylcopper oxalyl dihydrazone, cupferron reagent, 2-butyne-1, 4-diol, benzamide, 4-aminobenzenesulfonamide, and thioacetamide.

18. The method of claim 14, wherein the one or more copper elements comprise at least one of copper balls and copper wires.

19. The method of claim 14, wherein the method comprises subjecting the at least one aluminum substrate and the one or more copper elements to a molding process.

20. The method of claim 14, wherein the method comprises subjecting the at least one aluminum substrate and the one or more copper elements to an annealing process prior to immersing the at least one aluminum substrate and the one or more copper elements in the solution.