Search

This paper deals with the interfacial adhesion properties of Ti-6Al-4V alloy substrates, prepared by using different treatment protocols selected on the basis of their different effectiveness, and bonded using a structural, high-strength epoxy adhesive. The alternative pre-bonding treatments were sodium hydroxide anodization and low-pressure-plasma treatment, the effects of which were compared to that of a base preparation via solvent degreasing of the substrates’ surface. The treated surfaces were joined according to standard protocols, and then tested for shear strength. The mechanical results were then correlated to surface characteristics of the substrates such as oxidation state and wettability. Parallel scanning Kelvin-probe measurements allowed us to focus our attention on the possible role of the electrical properties of the substrates. We observed that each treatment entails different behavior of the electrical potential of the surface, which correlates with the mechanical strength of the joints. The results suggest that an evaluation of the surface potential of titanium-alloy substrates might be a promising, indicative supplementary parameter for the evaluation of their pre-bonding surface conditions, allowing correlations with presence/absence of an oxide layer at the resin-substrate interface.

During the last 25 years, major shifts occurred in the electronic assembly industry, such as the transition to contract manufacturing and reduction or elimination of in house manufacturing, the switch from solvent cleaned rosin fluxes to low solids no-clean fluxes and the big shift from leaded solder to Lead-Free solders. The preferred method for cleaning high reliability surface mount assemblies was to employ a suitable solvent batch or inline machine, to clean traditional leaded rosin flux wave solder solvent wash process (Figure 1).1 The fluxes would be reduced from the Printed Circuit Board Assembly (PCBA) with a solvent degreasing process. Visually the board would appear very clean because of the reduction of the amber flux, but when the boards were placed in a water environment the clear flux residue around the leads would turn white. Traditional rosin flux, left a clear film on the board and sealed in the board fabrication and flux activators and visually appeared clean. This is because the solvents used to clean the flux only removed the top 2/3rds off the surface and left a clear film.PCBA cleanliness was monitored using visual inspection and a ROSE (Resistivity OF Solvent Extraction) test system of a process that meet product validation. The ROSE test measured the amount of equivalent m grams of NaCl/sq. cm, by immersing the PCBA in a solution of 75% IPA/25% water.2 This total board average cleanliness reading was a result of the change in the conductivity and the algorithm used to calculate the detectable contamination.3 IPA was selected as weaker solvent that was in the degreasers to soften the rosin and measure the extractable activators and yet safe to labels and ink ID markings.The use of this ROSE monitor for historical rosin-based fluxes with solvent cleaned assemblies appeared to meet the needs of the time, but when the entire chemistry of electronic assembly changed, including fluxes (no solids), laminates, soldermask and not cleaning, this tool was not able to correlate to field performance as a predictor of reliability.Process monitoring of the new no-clean or cleaned processes that passed a ROSE test on the production floor may, or may not, pass during environmental testing, or perform well in the field. As technology has expanded in areas of use, miniaturization and circuit sensitivity, the traditional total board average cleanliness has not correlated to the failure areas that are under a component, between vias, pads, or leads requiring a new definition of cleanliness and how it is assessed.4, , This can be seen in IPC 5702 and 5704 that the IPC recommends that each company determine what level of cleanliness that they require to be included on their print and has not established cleanliness guidelines.6The proliferation of electronics in all aspects of life including medical, wearables, telecom, cell and automobiles is on an exponential growth curve.7, , As electronics complexity increases (Figure 2), the spacing between conductors is decreasing and the circuitry is more sensitive to parasitic leakage caused by the presence of semi-conductive ionic and organic materials.This paper will explore the ever more demanding cleanliness requirements of PCBAs and methods to monitor and assess the cleanliness of electronic assemblies today.

Surface treatment is necessary in a host of industries to attain a defect-free surface. In medical and semiconductor fields, for example, clean surfaces are essential to provide good adhesion across multiple interfaces. Conventional treatment methods such as wet chemical cleaning or solvent degreasing can effectively increase the wettability of surfaces and thereby the adhesion, or decrease the contact resistivity. However, a massive disadvantage of these techniques is that they leave the treated surface contaminated with traces of process chemicals and generate residues that are difficult to dispose of and are harmful to the environment. Due to the health concerns of these techniques, dry cleaning techniques such as plasma cleaning are currently being explored by researchers around the globe. In this chapter, a comprehensive review of the current and past work on plasma cleaning applications along with the fundamentals and advantages of plasma cleaning will be discussed.

Studies on ultrasound-assisted processes are gaining importance due to its effectiveness and facilitating green method in processing. Degreasing of skin/hide prior to tanning process is an important unit operation. Presence of large amounts of natural fat at the interior of skin/hide matrix makes degreasing process a challenging one. Conventionally, organic solvent and/or detergent based degreasing process are employed leading to environmental problems. In the present paper, the use of power ultrasound in aqueous degreasing process has been studied and compared with different degreasing systems. Glutaraldehyde pre-tanning has also been employed for carrying out the degreasing process at ultrasonic bath temperature. The results indicate that there is a significant increase in the degreasing efficiency due to the application of ultrasound. About 2-fold increase in fat removal has been observed due to the use of ultrasound as compared to control under the given process conditions. Comparing the degreasing efficiencies of the solvent with aqueous based ultrasonic processes, about 80% of the solvent degreasing efficiency could be obtained for aqueous degreasing process. This novel ultrasonic process helps in making aqueous degreasing process a viable option, which is eco-friendly even dispensing with temperature control measures.

Cryoblasting, which involves bombarding a substrate with carbon dioxide particles, has been shown to have considerable promise as a pretreatment for aluminium. Auger electron spectroscopy and contact angle measurements indicated the removal of organic material from the metal and electron microscopy indicated a roughening effect. Joint strengths obtained with a single-part epoxide were more than double those obtained after degreasing and were similar to those achieved after grit blasting or conversion coating. Cryoblasting could be used either as a “stand alone” alternative to solvent degreasing or as the first stage, to replace organic solvents, in a multi-stage pretreatment. It has also been shown to be effective with substrates other than aluminium.

With the increased usage of plastics in the automotive industry, the science of polymer (paint) to polymer (plastic) adhesion has gained increased recognition. This paper attempts to delineate the basics to attaining adhesion to plastics and to describe the current means by which adhesion to low surface free energy plastics is attained. Adhesion to very low surface free energy substrates, such as thermoplastic olefins (TPOs; blends of poly(propylene) and rubber), is most often accomplished through the use of a surface pretreatment. The surface pretreatment, for example plasma discharge, flaming, chemical etching, or solvent degreasing, modifies the chemistry of the plastic surface mainly through oxidation and surface roughening. The change in polarity of the surface then affords greater adhesion of subsequent topcoats. Adhesion to low surface free energy plastics can also be attained through the use of adhesion promoters. The adhesion promoter most commonly consists of chlorinated poly(olefin) dissolved in a nonpolar solvent. When applied to the low surface free energy plastic, the solvents can swell and diffuse into the surface. Mechanical interlocking with rubber domains below the surface accounts for afforded adhesion. Modern techniques available to the coatings chemist are described in relation to adhesion achieved. New chemistries developed to replace chlorinated poly(olefins) are reviewed.

Hazardous wastes are generated from cold solvent degreasing operations used in many industrial processes. The spent solvents are managed under Subtitle C of the Resource Conservation and Recovery Act (RCRA). With the land ban of spent solvents, disposal has become increasingly difficult. As a result, industries have begun investigating ways to avoid using RCRA listed cleaning solvents. The U.S. Environmental Protection Agency's (EPA) Pollution Prevention Research Branch along with APS Materials, Inc., a small metal finishing company, participated in a joint research project to evaluate the substitution of a dilute, terpene-based cleaner for 1,1,1-trichloroethane (TCA) and methanol, hazardous wastes F001 and F003 respectively, in their degreasing operations. This paper presents the results of a study evaluating the waste reduction/pollution prevention that can be achieved by substituting dilute limonene solutions for TCA and methanol in the cleaning of orthopedic implants (e.g. metal knee and hip joint replacements). This paper describes the original cleaning process, the modifications made to the process in using the dilute limonene solution, and the sampling plan used in evaluating the effectiveness of the solution. The paper presents qualitative results of the sampling tests and an economic evaluation of plant modifications.

Corrosion protection efficiency of any protective system depends not only on the nature and quality of the coating system used but also on the condition of the mrface on which it is to be applied. Various metal cleaning methods include (a) chemical cleaning — solvent degreasing, alkali cleaning and acid pickling (b) mechanical cleaning — shot blasting and (c) chemical conversion coatings — phosphating. Several of the recent advances in the field of prepaint treatment of steel have had as an objective the provision of an intrinsically fine, compact, well adhered zinc phosphate coating. Studies in this direction have been carried out in Central Building Research Institute, Roorkee and conditions for a suitable phosphating process have been optimised. Some work on the development of zinc rich paints based on both inorganic as well as organic binders have already been reported. The study has been extended by evaluating the performance of these zinc rich coatings on phosphated steel panels. In this report the performance of the above mentioned coatings when applied on the phosphated steel panels have been discussed. The studies reported include the preparation of the phosphated mild steel panels having three levels of coating wight ranging between 1.5–7.5 g/m2 (obtained by varying only the immersion time and keeping other parameters similar). A cost of zinc rich paint (75m?) based on either sodium silicate or chlorinated rubber binder was then applied on these panels along with the unphosphated ones. Comparison of the corrosion protection efficiency of the various systems thus obtained was carried out by using both laboratory and accelerated laboratory tests as well as by outdoor exposure studies. The performance of the coatings on phosphated panels has been remarkedly satisfactory as compared to the unphosphated panels. This is particularly so when the coating weight of the phosphate layer is between 4.5–7.5 g/m2; there is not any marked difference in the performance of paints applied on a phosphated layer with a coating weight of about 1.5 g/m2 as compared to the unphosphated panels.

Ultrasonics is one of the newest tools to be applied to metal cleaning. Through the years, abrasives, soaps, compounded alkaline materials, and solvents have been used to remove soils From metals. Trichlorethylene Solvent degreasing has had a wide reception in industry since its introduction in 1930. The DETREX SONICLEAN PROCESS combines sound energy and trichlorethylene solvent degreasing for metal cleaning. This is accomplished by immersing specially treated barium titanate transducers in chlorinated solvents, producing cleaning results previously unobtainable. Crossrod, conveyorized equipment incorporating constant distillation and filtration of the solvent in the ultrasonic chamber and providing a final vapor rinse and drying is now in use in industrial plants producing as many as 8,000 parts per hour.

Ultrasonics is one of the newest tools to be applied to metal cleaning. Through the years abrasives, soaps, compounded alkaline materials, and solvents have been used to remove soils from metals. Trichlorethylene Solvent degreasing has had a wide reception in industry since its introduction in 1930. The Detrex Soniclean process combines sound energy and trichlorethylene solvent degreasing for metal cleaning. This is accomplished by immersing especially treated barium titanate transducers in chlorinated solvents producing cleaning results previously unobtainable. Crossrod, conveyorized equipment incorporating constant distillation and filtration of the solvent in the sonics chamber and providing a final vapor rinse and drying is now producing as many as 8000 parts per hour in industrial plants.

Some differences between wool grease obtained by the solvent extraction of raw wool and wool grease recovered centrifugally from emulsion scour liquors are described. Refining problems arising from the peculiar properties of solvent wool grease are outlined, and some suitable refining methods are suggested.