Adhesion failure analysis

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

Figure 8. XPS analysis of elemental composition as a function of sputter depth (a) zinc phosphated steel (b) interfacial substrate surface of zinc phosphated steel after adhesion failure of epoxyester coating in cathodic polarization testing. Reproduced from Ref. copyright 1983, American Chemical Society.

XPS analysis (Fig. 6), in conjunction with SEM examination of the failed debonded sides, identified the true modes of failure. The SAA control (hydrated oxide on both sides under SEM high A1 and 0 levels on both sides) failed within the oxide. Examination of the specimen treated with multilayer-forming 5000 ppm NTMP solution (distinct "metal" and "adhesive" sides under SEM high A1 and 0, low C levels on "metal" side high C, low A1 and 0 levels on "adhesive" side) indicated that the failure occurred between the metal and the adhesive (i.e., adhesive failure). 

PMDA-ODA on Si02. It is clear from Fig. 3 that the adhesion of PMDA-ODA to SiO, surface is significantly improved by the application of APS. This is not only seen initially but also after exposure to extended times at T H conditions, i.e. the reliability of the interface has been improved. Notice the spontaneous delamination (zero peel strength) of the PMDA-ODA film from non-APS treated silica surface after only 100 h in T H. It should be pointed out here that the 100 h exposure was the first point at which the samples were removed from the T H test chamber. It is possible that the delamination may have occurred much earlier than the 100 h reported here. Table 2 shows the locus of failure analysis results for the interfaces after initial peel and after exposure to T H for 100 (no APS only) and 700 h. 

PLASTEC is one of 20 information analysis centers sponsored by the Department of Defense to provide the defense community with a variety of technical information services applicable to plastics, adhesives, and organic matrix composites. For the last 21 years, PLASTEC has served the defense community with authoritative information and advice in such forms as engineering assistance, responses to technical inquiries, special investigations, field trouble shooting, failure analysis, literature searches, state-of-the-art reports, data compilations, and handbooks. PLASTEC has also been heavily involved in standardization activities. In recent years, PLASTEC has been permitted to serve private industry. 

A standard test report usually documents the resulting measurements, such as tensile shear strength and peel strength. It should also indicate all the pertinent conditions that are required to ensure reproducibility in subsequent testing. It is often very useful to describe the failure mode of the tested specimens. An analysis of the type (or mode) of failure is an extremely valuable tool to determine the cause of adhesive failure. The failed joint should be visually examined to determine where and to what extent failure occurred. The percent of the failure that is in the adhesion mode and that in the cohesion mode should be provided. A description of the failure mode itself (location, percent coverage, uniformity, etc.) is often quite useful. The purpose of this exercise is to establish the weak link in the joint to better understand the mechanism of failure. 

A more dramatic failure results in peel strengths of 0-10 g/mm and is characterized as an adhesive failure at the polyimide/metal oxide interface.This was the only failure mode observed in Ti and Zr films. Isotopically tagged water used with SIMS analysis shows that on annealing water reacts with the Ti with oxygen segregating to the metal/polyimide interface and hydrogen penetrating into the bulk of the Ti, in these samples. 

The mechanism of adhesion is also an important factor in failure analysis in composites [31]. Some adhesives work due to a physical entanglement of the resin into the wood structure whereas others require a free hydroxyl group on one of the cell wall polymers to participate in a chemical reaction with the resin. Substitution of hydroxyl groups was shown to decrease adhesion between chemically modified veneers due to the loss of hydroxyl functionality [32]. Resins that are water-soluble and depend on a hydrophilic substrate for penetration will be less efficient in chemically modified wood due to the decreased hydrophilic nature of the celt wall resulting from modification [33]. 

The interfacial debond occurs after the through-thickness cracking of the films. It is activated by transverse contraction of the substrate which induces the buckling of the strips of the cracked films. The analysis of this particular adhesion failure mechanism provides insights concerning the interfacial strength of... 

To determine adhesive failure, it was necessary to apply appropriate algorithms to the data For quantitative analysis data were imported to a spreadsheet, smoothed to remove noise from the LVDTs, and then sorted to remove edge effects. Because there was considerable warp in all specimens due to the durability test, a parabolic function was fit to this distortion and subtracted from the raw data to produce a flat bondline. The data were again sorted (in ascending order) to produce a cumulative frequency distribution of surface irregularities (wood failure). Conceptually, a thickness tolerance could then be specified to define the bondline region as well as a depth tolerance for shallow wood failure. The relative population of data within these regions represented the percent e of adhesive, shallow, and deep wood failure. 

At this point in the analysis, it was possible to define a tolerance for bondline thickness, whereby all points within a prescribed tolerance would be considered adhesive failure, and all points outside this tolerance would be considered wood failure. Furthemtore, a second tolerance could be specified to distinguish shallow" wood failure fi-om deep" wood failure (Fig. 10). For the specimens evaluated in this study, two tolerances ( 40 pm and 60 pm) were selected for both the bondline thickness and the depth of shallow wood failure. A typical bondline thickness for block-shear specimens is about 80 pm, and the thickness of a small fiber bundle is 40-60 pm (or 2-5 fiber diameters). Table 1 summarizes the results from this analysis as well as the visual grading values obtained from the trained observers. 

Specimen 5 (Fig. 1) was selected for analysis because like specimen 1, it too is an obvious adhesive failure. However, unlike specimen 1, it contained several unique surface features that made it difficult to analyze. Among these were thick adhesive fragments, bondline voids (probably from air bubbles), and shallow (a few fibers) wood failure. Four of the observers declared near complete adhesive failure. However, one observer viewed it veiy differently (85 % wood failure). In this case, the profilometer analysis did not agree well with visual observations. This was due to considerable warp (cup and bow), which severely compromised the 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. 

There are other mechanisms such as fretting, fretting corrosion, and fretting CF, which is a combination of adhesive, corrosive, and abrasive forms of wear. Wear by all mechanisms except fatigue mechanism, occurs by gradual removal of material. One or more of these mechanisms may be operating in a particular machine. In many cases, wear may be initiated by one mechanism but may proceed by other mechanisms and thereby complicate failure analysis (60). 

FTIR may also be used as a quality-control test to determine whether an adhesive was under- or overcured," or it can be used as a failure analysis tool. In one failure analysis study, adhesive failure of a lid attached to a flip-chip package occurred. FTIR... 

Ong MC, Zhao XL, Joman PP, Chin JM, Master RN. Lid adhesive failure study for flip-chip packaging. In I5th Int. Symposium on Physical and Failure Analysis of Integrated Circuits 2008. 

Adhesives are a very diverse and complex group of materials. They can manifest themselves in many shapes and forms—they can be viscous liquids, powders, or cured products. Analysis or characterization is an essential step in working with adhesives. As a rule, such efforts are directed toward a specific purpose that may focus on structural determination, curing reaction, size of the molecule, material design at a molecular level, process control, or failure analysis. In this chapter we provide a general review of several physical methods frequently used for analysis of adhesives. In view of the prolific literature on the subject as well as the space constraints, it is not intended to give a comprehensive treatment of the theory and experimental aspects. The examples chosen for this review are illustrative and not exhaustive. 

Analysis of interfaces between materials, especially for failure analysis after aging and testing of adhesively bonded systems Study of the cure of adhesives. 

R.S. Court, M.P.F. Sutcliffe, S.M. Tavakoli, Ageing of adhesively bonded joints—fracture and failure analysis using video imaging techniques. Int. J. Adhes. Adhes. 21, 455-463... 

It has been shown that Impedance Spectroscopy (IS) is a promising, non-destructive tool for the analysis of incipient adhesion failure in metal-insulator structures. This contribution presents a complete analysis of experimental impedance spectra, carried out by using numerical simulation and analytical techniques. 

The target of the work was to improve the level of detail in the analysis of the experimental resjmnse function. Pitting the theoretical (but not the Electrochemical Equivalent Circuits-based) frequency response function to the experimental data is shown to provimetal-insulator interface. On these basis, changes in surface dif-fusivity values might be effectively used to track the evolution of the interface under T H tests, thereby providing a novel tool to predict adhesion failure. 

In previous publications 2 it has been shown that Low-Frequency Impedance Spectroscopy can be considered a promising, non-destructive toot for the evaluation and the analysis of incipient adhesion failure in some metal-insulator structures. The technique is based on the effect of the interface modifications on the diffusivity of chemical species such as water, which is ubiquitously present in polymers used for packaging. Since such... 

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