Polyimide failure

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. 

The N(ls) peak on the sapphire failure surfaces indicates presence of imide (peak at 400.7-401.0 eV), which suggests presence of polyimide on the sapphire failure surface. This is supported by the C(ls) data which show the presence of the carbonyl C(ls) species as well as jr-to-jr transition peak due to aromatic species. Since the polyimide failure surface shows only C(ls), N(ls), and O(ls) peaks in relative abundance, characteristic to the polyimide, it can be said that... 

The locus of failure in all PMDA-ODA/MgO cases is consistently a mixed mode type leaving ceramic on the polyimide failure surface, and leaving polyimide on the ceramic failure surface. APS application prior to polyimide coating does not change the failure locus or the peel strength behavior of these interfaces. 

Another common location for creep failures of encapsulated assemblies is at sharp corners or edges. Many encapsulants such as polyimides must be applied in thin coats, and coverage of points, edges, or corners is difficult or impossible. Sharp corners, characteristic of most thin-film devices provide ideal conditions for the initiation of creep failures due to the resulting irregularity of the encapsulant coverage. 

Imide passivated linear devices was determined from I-V characteristics of statistically significant numbers of devices following severe PTHB test (i.e., 15 psi, 120°C, 100% relative hvimidity, and 30 V bias). Two coat (3 p) polyimide passivation provided almost twice the mean time to failure of 1 p thick PSG passivation. Polyimide protection against high humidity (13,14) and Na" " diffusion (15) has been reported previously. 

F-BDAF Tg for various blend compositions, see Fig. 14. The microphase-separated morphology further manifests itself in the self-adhesion behavior of polyimide films derived from such mixtures. For mixture containing at least 25 wt% of the flexible component, peel tests of polyimide bilayer samples prepared by solution casting, bulk failure of the test specimens was observed. Since the flexible component contained fluorine, the samples could be examined by X-ray photoelectron spectroscopy to determine the surface composition. At only 10% loading, the flexible component comprised 100% of the top 75 A of the sample. The surface segregation of the flexible component is believed to be responsible for the adhesion improvements. 

No significant difference is observed in the locus of failure data for the APS treated samples presented in Table 2. A closer look at the XPS high resolution scans as shown in Fig. 4 supports the interpretation that the failure is within the polyimide close to the PI-APS interface, but not at it. This is in particular verified by the presence of C=0 C(ls) peak at about 288.9 eV, ji-to-jr transition peak, and the N( 1 s) peak at 400.8 eV due to imide nitrogens. 

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. 

Polyimide-Polyimide Adhesion. To study polyimide-polyimide adhesion (10). a thin layer (200 A) of gold was sputter-coated onto one side (20% of the total area) of the polyimide sample to initiate peel (polyimide has a poor adhesion to gold). The surface of the polyimide in the exposed area was modified to the polyamic acid surface. PMDA-ODA polyamic acid in NMP solvent was spin-coated to the surface-modified (to polyamic acid) polyimide film, and subsequently cured at 400 °C under nitrogen. Thickness of the adherate layer (peel layer) after curing is approximately 20 um and the width of the peel layers is 5 mm. The peel strengths were measured by 90° peel of the top polyimide layer. The failure occurs at the interface between... 

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. 

Profilometer measurements of the impacted specimens revealed general distortion of the film in and around the region of impact. By profilo-metric measurements on both sides of the film, the amount of wear in the contact zone was estimated. This technique provided a comparison of wear behavior to within 15 or 20 /mi. In several cases the experiments were continued until the film was worn through. In such cases the number of impacts to failure also provided a means of comparing wear behavior. In terms of these techniques it was found that the poly (vinyl fluoride) had the best wear resistance, followed by the polyimide. For example, tests conducted with the larger hammer indicated that for the same thickness, the poly (vinyl fluoride) had approximately one-half the depth rate of wear exhibited by the polyimide. 

The purpose of this paper is to present a technique whereby manufacturing process dynamics for structural polymers can be accurately defined through efficient laboratory rheological characterization. Structural polymers, in this paper, refer principally to the thermosetting epoxides, phenolics and polyimides. This type of test pattern, however, is generally applicable to the production and utilization of most polymers. The engineering applications associated with these polymers involves primary and secondary aerospace articles. In this situation, failure to meet performance criteria could result in catastrophic loss of the vehicle and associated cargo. 

In order for a polyimide to be useful as an interlevel dielectric or protective overcoat (passivant), additional demanding property requirements must be met In the case of the passivant, the material must be an excellent electrical insulator, must adhere well to the substrate, and must provide a barrier for transport of chemical species that could attack the underlying device. It has been demonstrated that polyimide filrns can be excellent bulk barriers to contaminant ion motion (such as sodium) [10], but polyimides do absorb moisture [11,12], and if the absorbed moisture affects adhesion to the substrate, then reliability problems can result at sites where adhesion fails. However, in the absence of adhesion failure, the bulk electrical resistance of the polyimide at ordinary device operating temperatures and voltages appears to be high enough to prevent electrochemical corrosion [13]. 

Both siloxane-polyimide copolymers and BPADA-derived copolymers exhibited excellent solubility in a variety of dipolar aprotic solvents, including tetrahydrofuran, n-methylpyrrolidone, and dimethyl sulfoxide, as well as chlorinated hydrocarbons such as o-dichlorobenzene and methylene chloride. The polymers and copolymers were typical thermoplastics exhibiting little elongation at failure. The tensile properties are summarized in Table II. 

In panel (d) a strikingly different type of defect structure is encountered, the so-called tears. It should be noted that these correspond to much larger defects (compare the scan size). In the work of Russell and coworkers it was found that three types of failure were present in the rubbed polyimide films, namely scratches, tears, and strings of islands, all of which are aligned along the mbbing direction. Local overshearing of the film was held responsible for the observed formation of... 

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