Failure surface analysis

The XPS analysis of the samples primed at 34% RH indicated that there was a consistent failure of the wedge samples which occurred mainly within the alkoxide layer in all systems. Partial hydrolysis may have resulted in the formaton of a weak hydrated oxide layer and was the zone through which the crack propagated to debond the samples. Based on the relative humidity in the chamber during the priming process and the failure surface analysis results, it was concluded that this level of 34% RH was not sufficient to complete the hydrolysis of the alkoxides and produce a stabilized oxide structure. As noted above, however, the wedge crack results did not indicate any instability. 

A brief review of each technique will be followed by a discussion of results illustrating the application of the particular technique to adhesion. Examples are given of surface characterization of pretreated adherends, adhesive/adherend interactions, failure surface analysis, and correlation of these results to bond performance. Good summaries of the four major surface analytical techniques, namely XPS, AES, ISS, and SIMS, are given by Hercules(5) and Hofmann.( ) (See also Chapter 6 by Davis.)... 

SIMS yields compositional information for both surface characterization prior to bonding and for failure surface analysis. 

Failure surface analysis by XPS coupled by SEM can lead to the determination of the locus of failure in the system. The XPS results were obtained for failure surfaces of Ti-6-4 bonded in a... 

In aluminum alloy (2024-T3)-epoxy joints, for exanqrle, the initial oxide produced on the aluminum substrate is usually amorphous AI2O3. Upon exposure to moisture, AI2O3 is converted to aluminum hydroxide with a chemical composition between that of boehmite (AI2O3H2O) and pseudoboehmite (A1203-2H20). Failure surface analysis reveals that the hydroxide layer is normally attached to the adhesive side, suggesting that adhesion of the hydroxide to aluminum is very weak. Thus, once a hydroxide is formed, it is separated easily from the substrate, causing failure of the joint. 

The most useful application of ISS is in the detection and identification of sur-fece contamination, which is one of the major causes of product failures and problems in product development. The surface composition of a solid material is almost always different than its bulk. Therefore, surface chemistry is usually the study of unknown surfaces of solid materials. To better understand the concept of surface analysis, which is used very loosely among many scientists, we must first establish a definition for that term. This is particularly Important when considering ISS... 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

Contamination can be present not only as a surface deposit or a surface feature but can also be located within the bulk of a manufactured part. The selection of an appropriate series of analytical techniques, applied to failure, defect, and contamination analysis projects, is influenced by the location of the contamination or defect and the optical properties of the manufactured component. Microscopic analysis of opaque parts is limited to surface analysis... 

This is a surface analysis technique, used, for example, in examining causes of bonding failure. 

A surface analysis technique used in bonding failure analysis, for example. 

In order to accurately determine the locus of failure of adhesion systems, the chemisti y of the fracture surfaces must be analyzed using surface-sensitive characterization techniques. Many surface analysis techniques are presently available and each technique is based on an intrinsic property of the surface atoms or molecules. Lee155 , Czanderna 156) and Park 157) have reviewed these techniques. However, they suggest that one be aware that new techniques and applications are continually being introduced. 

The locus of failure after peel testing was determined using XPS analysis of both the silicon wafer and the polyimide failure surfaces. This analysis was also done as a function of the humidity. 

Figure 4. XPS locus of failure analysis of PMDA-ODA on SiO,. (A) PI failure surface C(ls) and N(l ) data, (B) SiO, failure surface C(ls) and N(l ) data.

PMDA-ODA on Al 0,. A minor improvement is noticed in the peel force of PMDA-ODA on Al20, when APS is applied to the surface. From the surface analysis results one can see that the APS was not retained on the IPA cleaned sapphire surface to any detectable level, which is likely the cause for no significant improvement in the peel force. The minor improvement in the results may have to do with a possible surface cleaning effect of the sapphire surface with APS solution. The data in Table 3 show that the failure locus has not changed significantly by the APS or T H exposure, being essentially in the polyimide film close to the polyimide/ceramic interface. 

The failure surfaces were analyzed using XPS. The results from the XPS analysis of the samples primed with each of the four alkoxides at 34% RH and the control sample, each bonded with PES and immersed in DI water at 100°C are listed in... 

XPS analysis of failure surfaces of wedge samples primed at 34% RH and bonded with PES and placed in a 100°C water bath... 

The XPS analysis of the failure surfaces of the wedge samples primed at 51% RH and bonded with PES and immersed in DI water at 100°C are reported in Table 3. The concentration of sulfur in all of the primed samples bonded with PES was about 5% and suggests that failure occurred primarily within the adhesive. The atomic concentrations of aluminum, silicon, and titanium were below 0.5%, precluding assignment of failure within the alkoxide layer. The control sample failed at the interface between the steel and the adhesive. 

As surface scientists, material scientists and chemists It would be useful at this time to step back and reflect on what Impact further miniaturization will have on us. Of particular interest to us Is the analysis of process performance and device yields using surface analysis techniques. With further miniaturization will it be possible to make meaningful analyses on device failures In an attempt to answer such questions ast why did this device fall or will It soon be necessary to speak In more general terms and develop answers In terms of probabilities. 

The first consideration in defect analysis is whether the part has been handled after removal from service. Handling can alter the appearance or contaminate it to the point that either failure analysis could not be conducted or the root cause could not be determined. Surface analysis techniques are sensitive to handling and cannot distinguish between the changes caused by the failure and contamination. The best practice is to minimize handling the part and keep track of the history of the part. There are certain steps that frequently have to be taken such as decontamination of parts that have been in contact with corrosive, toxic, or flammable chemicals. A log should be considered to keep track of what has been done to the part, which may help explain any unforeseen consequences of part handling. 

Material Composition 1. Analysis of composition of the polymer and additives 2. Degree of crystalhnity, molecular weight, molecular weight distribution, and degree of fusion 3. Identification of contaminants at the failure point 4. Surface analysis... 

XPS is one of the most widely used surface and materials analysis techniques in both academia and industry. Applications include semiconductor wafer defect analysis, identification of surface contamination in industrial processes, adhesion chemistry analysis, analysis of fracture or failure surfaces, and analysis of the strength and type of carbon bonding in polymers. 

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