Nonconductive adhesive surface

XPS is used to evaluate surfaces prior to bonding yielding information which may relate to bond performance, as well as to study failure surfaces. The added advantage in XPS is that more sample types can be analyzed, such as nonconductive adhesive surfaces without the problems of charging found with other techniques such as AES, SIMS, and ISS. For this reason XPS is often the method of choice in post-fracture analysis. 

The oxide layer that forms on aluminum is more complex than with other metal substrates. Aluminum is a very reactive surface, and oxide forms almost instantaneously when a freshly machined aluminum surface is exposed to the atmosphere. Fortunately, the oxide is extremely stable, and it adheres to the base metal with strength higher than could be provided by most adhesives. The oxide is also cohesively strong and electrically nonconductive. These surface characteristics make aluminum a desirable metal for adhesive bonding, and they are the reasons why many adhesive comparisons and studies are done with aluminum substrates. 

The AES technique provides rapid surface analysis, but is not widely used on fracture surfaces due to beam damage and charging of nonconductive adhesives. On the other hand, the use of AES in the analysis of adherend surfaces has been widespread. An advantage of AES is... 

Copper has good electrical conductivity and high adhesion property in conductive adhesive systems. However, copper tends to form a nonconductive oxide surface layer (Zhao et al. 2007). 

These two aspects, bleeding and tailing, have also been considered for using adhesives in surface-mount technology. Various nonconductive adhesives are currently used to hold the components during the... 

If the adhesive contains no conductive fiiier, eiectrical conductivity relies on contact between the joining partners with adhesive-fiim thicknesses of the same order of magnitude as the surface roughnesses. Poiyimides and epoxy resins are good materiais for nonconductive adhesives, on account of their property profiies. Compared to adhesives admixed with conductive fiiiers, materiai costs are much iower on account of the iower price for the adhesive and the reduction in consumption. 

Connections made with insulating adhesives free of fillers are electrically conductive if the partners are in contact with each other in adhesive no thicker than the surface roughness (< 10 pm). In principle the process is very similar to that of anisotropic adhesive gluing. The glue is applied by a dispenser or by print application of a paste. The electrically nonconductive adhesive can be applied allover across multiple connections. This implies low requirements for the process as such and therefore good affinity for fine-pitch applications. Once the partners to be joined have been positioned, the adhesive cures under pressure and temperature within a matter of seconds. 

Solutions of chitosan salts are well known for their adhesive properties (53). Chitosan itself adheres well to nonconducting surfaces, such as paper, rayon, cellophane, wood, leather, rubber, and glass, but not to metal surfaces (57,58). For smooth surfaces, a stronger bond is formed by first applying a thin primer... 

On the other hand, the deposition of metal layer on polymer surface is more problematic because the adhesion of metal deposition on a polymer surface is not so simple depending on how the metal layer is deposited, and also on the structure of the deposited metal layer. Metallized insulators such as polymeric and ceramic materials are widely used in the appliance, automotive, and electronics industries. Metallization of nonconducting substrates is technically difficult because of the structural incompatibility between the substrate and metallizing material, in terms of both chemical bonding and properties. The abrupt mismatch at the interface between them has been blamed for the major portion of failures of metallized parts under operating conditions. 

The adhesion of the polymer to the electrode surface is another consideration. For example, the polymer can be generated at an electrode such as tantalum, where it will not deposit. In our laboratories38 we have used the fact that deposition of PPy onto tantalum is difficult in the design of an electrochemical slurry cell to coat silica particles. The polymer generated at the tantalum anode does not deposit there instead, it deposits on the more receptive (silica particle) surfaces in the electrochemical cell. This represents a unique polymerization process whereby the polymer is generated electrochemically in an environment that allows nonconductive substrates to be coated, resulting in unique composite structures. 

Thus, the transport of hydrated ions and chemical debonding processes can be studied by means of the SKP. Fig. 31.6 shows the potential distribution measured with the SKP when a thin electrolyte layer enters the interface between an adhesive and an iron surface covered by a thin (about 6 nm) nonconducting SiOx layer precipitated by a plasma-polymerization process [51, 52]. The SiO layer inhibits the electron-transfer reaction. Consequently, no corrosive degradation of the interface takes place (see Section 31.3.2.1). However, as the adhesion of the epoxy adhesive to the siUca-Uke layer is weak, the polymer is replaced by... 

Since the adhesive matrix is a nonconductive material, interconnection joints rely to some extent on pressure to assure contact for conventional ACAs. Adhesive interconnections therefore exhibit different failure mechanisms compared to soldered connections, where the formation of intermetallic compoimds and coarsening of grains are associated with the main mechanisms. Basically there are two main failure mechanisms that can affect the contacts. The first is the formation of an insulating film on either the contact areas or conductive particle surfaces. The second is the loss of mechanical contact between the conductive elements due to either a loss of adherence or relaxation of the compressive force. 

A piece of copper adhesive tape (5 x 60 mm) with conductive glue (Ted Pella, Inc.) is first affixed on a small adhesive nonconductive aluminum square and then to the lower Au coated surface of a 5 x 5 mm piece of peeled membrane, so that only a small part is in contact with the copper tape. (This is because the conductive glue on the copper tape contains Ni particles which could damage the gold layer ). 

The use of both nonconductive epoxy adhesives and anisotropic conductive adhesives as a solder replacement for SMT was studied [121]. Quad flat pack components were connected to FR4 substrates and then subjected to temperature cycling. None of the tested adhesives passed the temperature cycling test in accordance with the military standard 883C [121]. Failure analysis indicated that impressions made in the contact area depend on the contact force and surface preparation. At very low contact forces, the presence of insulating oxide layers on the metal surfaces increased the contact resistance dramatically. However, as the contact force was increased, the contact resistance dropped rapidly [122]. 

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