Other Surface Finishes

Clothing - man-made fibres such as rayon and nylon, dyes, waterproofing and other surface finishing chemicals. 

Further work could be carried out in order to extend the durability of the antimicrobial property by using different cross-linking agents. The fabric can be functionally enhanced by applying other surface finishes, such as to improve the handle of the fabric. The durability aspect of the antimicrobial finish can be studied over larger number of washes than those conducted during this study. The fabric can also be functionally enhanced by applying other types of finishes. 

Electrochemical variations of several other surface finishing methods are used to a limited extent and these will be considered in this section. 

Other surface finishes include reflowed tin-lead, electrolytic nickel/electrolytic gold, antitarnish and reflux, electroless palladium, electroless gold, direct immersion gold, and solid solder deposit. 

Other surface finish-delated defects Immersion silver (Imm-Ag) sometimes exhibits hn-ear arrays of microvoids at the intermetalhc interface which detracts from solder joint strength. Electroless nickel/immersion gold (ENIG) sometimes results in brittle fracture if the plating chemistries are not maintained properly. 

Contact Lands. The PWB is much like any other board. It has lands to accommodate electrical interconnect of the LGA socket to the board. The lands correspond in size and shape to socket requirements. Most often, the LGA lands on the PWB are electrolytic nickel covered by electrolytic gold. Hardened gold is often used for added contact durability and reliability. Other surface finishes can also be used, but should be tested for reliable and long-lasting contact. 

Surface Finishes. Tin-lead solder alloys (e.g., 63/37) are the most popular alloy used for surface finishes on PCBs. Other surface finishes are rapidly finding their way onto the PCBs. IPC-6012 lists more than 20 different surface finishes that are now in use for PCBs. Lead-free alloys are also appearing on PCBs. It is important to understand that the composition and type of the surface finish influence solderability. The procurement documentation must state specifications for surface finish. Methods available for analyzing the alloy composition on the plated PCB include wet analysis, atomic absorption, and x-ray fluorescence (XRF). XRF is popular because of the ease of obtaining the alloy composition and thickness nondestructively. 

There are a number of other surface finishes used in the industry, such as Electroless Nickel Electroless Palladium Immersion Gold (NiPdAu), Immersion Silver, Immersion Gold, Immersion Tin, OSP and Electrolytic Nickel Gold. There are reliability and process trade offs with each surface finish. That is why it is recommended that strain/strain rate characterization and thermal cycling be performed for each set of surface finish before it is selected for the specific end-use conditions in which it will be used. The industry test methods used to evaluate different surface finishes are outlined in detail in the next chapter. 

This formula is another variation on the Affinity Laws. Monsieur s Darcy and VVeisbach were hydraulic civil engineers in France in the mid 1850s (some 50 years before Mr. H VV). They based their formulas on friction losses of water moving in open canals. They applied other friction coefficients from some private experimentation, and developed their formulas for friction losses in closed aqueduct tubes. Through the years, their coefficients have evolved to incorporate the concepts of laminar and turbulent flow, variations in viscosity, temperature, and even piping with non uniform (rough) internal. surface finishes. With. so many variables and coefficients, the D/W formula only became practical and popular after the invention of the electronic calculator. The D/W forntula is extensive and eomplicated, compared to the empirieal estimations of Mr. H W. 

Because of the above properties, together with other features such as the ability to mould to close dimensional tolerances, low warpage, low shrinkage, low moisture absorption and good surface finish, polycarbonate-ABS alloys have become widely used in the automotive industry, for electrical applications and for housings of domestic and business equipment. 

Other requirements. These could include electrical insulation properties, including resistance to tracking and arcing, transparency, frictional properties, surface finish, scuff resistance and specific gravity. 

There is a frequent dememd for materials suitable for housings for computer, domestic, electrical and automotive equipment. In these applications toughness, excellent surface finish, surface durability, reasonable rigidity, dimensional stability, good weathering behaviour and low water absorption are common requirements. In these applications ABS is frequently considered first but its limited deflection temperature and heat aging resistance may lead to other... 

Synthetic resins are extensively used, e.g., in surface finishes, in the fabrication and repair of boat and motor vehicle bodies, in the manufacture of laminated boards, for electrical components, in pattern making and in paints and varnishes. Non-rubber adhesives made from fish glues and from cotton derivatives (e.g. cellulose acetate) tend not to be sensitizing but, depending upon composition and the manner of use, many other types may pose significant dermatitic and fume hazards. 

---