Qualitative adhesion tests

Many of the qualitative adhesion tests vary with plate thickness. As indicated above, adhesion is better for thinner deposits. That, it was stated, has to do with the stress present in deposited films. A specified plating thickness should therefore be a given parameter requirement for adhesion testing. 

Adhesion tests can be broken into two categories qualitative and quantitative. They vary from a simple Scotch tape test to a complicated flyer tape test, which requires precision-machined specimens and a very expensive testing facility. Quantitative (such as peeling) tests have been developed for coatings on plastics (12), but not to the same extent for metal-to-metal systems. The quantitative testing systems in limited use, mainly in the electronics industry, are not commonly present in production plants but have been used to aid in process development. For quality control purposes, qualitative tests for metal-to-metal adhesion (13) are usually adequate. The adhesion of some plated metal parts is improved with baking for 1 to 4 h at relatively low (120 to 320°C) temperatures. 

ASTM D3808-01 Standard practice for qualitative determination of adhesion of adhesives to substrates by spot adhesion test method. 

Qualitative Determination of Adhesion of Adhesives to Substrates by Spot Adhesion Test Method, Practice for (D 3808)... 

A common mode of coating failure is delamination at the coating-substrate interface. The strength of this interface is measured using adhesion tests that range from the simple adhesion scratch test to the more sophisticated tests based on fracture and/or contact mechanics. Many of the qualitative tests, such as the Adhesion Tape Test, are covered in the ASTM standards (e.g. [43-45]). These should be used only for comparative purposes, where a quick evaluation of adhesion is required. 

As noted earlier and readily seen by the complexity of variables, adhesion testing is a very inexact science. Many tests have been devised in order to characterize the adhesion property. These include both qualitative and quantitative test methods. Examples of qualitative tests are the Scotch tape test and razor blade tests which certify that the adhesion exceeds some... 

The rate of adhesion loss in tests of paint performance can be greatly influenced by coating formulation and resin type (24) this is illustrated qualitatively by the results shown in Table II. To a first approximation, the anodic inhibitor pigments commonly used in... 

For all materials, the adhesive mechanism and the plastic deformation should be the main processes. During testing, the variation in friction coefficient values could be influenced by the specific AM behavior. Since AM corresponds to the crosslink density of a composite, for a qualitative assessment it can be concluded that the crosslink density decreases with increasing absorbed dose. PTFE500kGy-EPDM showed much lower AM and f90 values. It can be inferred that the state of cure is strongly dependent on the irradiation dose absorbed by the PTFE powder. 

The success of the tap test depends on the skill and experience of the operator, the background noise level, and the type of structure. Some improvement in the tap test can be achieved by using a solenoid-operated hammer and a microphone pickup. The resulting electric signals can be analyzed on the basis of amplitude and frequency. However, the tap test, in its most successful mode, measures only the qualitative characteristics of the joint. It tells whether adhesive is in the joint or not, providing an acoustical path from substrate to substrate or it tells if the adhesive is undercured or filled with air, thereby causing a mechanically damped path for the acoustical signal. The tap test provides no quantitative information and no information about the presence and/or nature of a weak boundary layer. 

Typical materials analysed using this technique include glass, uranium oxides, steel, platinum, geological samples, ceramic materials and plastics (Figure 7.21). Excellent information is obtained where surface composition is important, e.g. catalysts, presence of toxic elements, surface analysis in the application of adhesives, etc. It can be used as a quick qualitative test for the analysis of semiconductor components as specified as part of WEEE and RoHS compliance. 

The adhesive properties of thin films are a crucial material property, because mi-cromachined structures generally consist of several layers deposited on top of one another. Insufficient adhesion inevitably leads to device failure. Only a few methods for measuring adhesion strength are mentioned in the literature. A widespread qualitative test of film adhesion is the tape test, in which a piece of adhesive tape is pressed on the surface and then pulled off. If the film adhesion is good, no material... 

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