Copper foil Resistivity

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

SemiadditiveMethod. The semiadditive method was developed to reduce copper waste. Thin 5.0 lm (4.5 mg/cm ) copper foil laminates are used, or the whole surface may be plated with a thin layer of electroless copper. Hole forming, catalysis, and electroless copper plating are done as for subtractive circuitry. A strippable reverse—resist coating is then appHed. Copper is electroplated to 35 p.m or more, followed by tin or tin—lead plating to serve as an etch resist. The resist is removed, and the whole board is etched. The original thin copper layer is quickly removed to leave the desired circuit. This method wastes less than 10% of the copper. 

Copper To 1500 Properties depend on other construction materials and form of copper used. Packing made of copper foil over asbestos core resists steam and alkalies to lOOO F. Packing of braided copper tinsel resists water, steam, and gases to 1500 F. 

The combination of low optical absorbance and high electrical conductivity has attracted a lot of interest for transparent conductor applications. When coupled with its flexibility, it is widely seen as a possible replacement for indium-doped tin oxide (ITO), which has a sheet resistance of 100 Q/cm at 90 % transparency. By growing graphene on copper foils, sheet resistances of 125 Q/cm at 97.4% transparency have been achieved [19]. This has been improved by combining four layers with doping of the graphene, giving resistance of 30 Q/cm at 90% transparency, all done on 30-inch roll-to-roll production scale. 

Shin, Oxidation resistance of iron and copper foils coated with reduced graphene oxide multilayers, Acs Nano, vol. 6, pp. 7763-7769, 2012. 

Solvent resistant laminates for printed circuits were manufactured by coating of copper foil with a solution of PPO, BPA/DC, bis(4-maleimidophenyl) ether and Zn octoate in toluene the coated foil was laminated with PPO-impregnated glass fabric [47]. Similar result was achieved by the modification of PPO with polyfunctional cyanates or maleimides, liquid polybutadiene and a polymerization catalyst [48], A solvent and heat resistant composition for printed circuits consists of copoly [(2,6-dimethylphenylene)-(2,3,6-trimethylphenylene)]oxide, maleic anhydride grafted poly-1,2-butadiene, bis(4-maleimidophenyl)methane, BPA/DC and toluene. BPA/DC prepolymer may be used instead of the monomer [49]. 

The copper foil is subsequently covered with a photoresist layer that is patterned by lithography techniques to produce the desired circuitry. Areas of exposed, cross-linked resist protect the copper that is to remain on the board as circuitry. The unprotected copper that is not needed for the circuitry is etched away, usually with ferric chloride solution. At this point, the printed board must have the following characteristics the substrate has to be structurally sound (no delamination), and the copper conductor patterns have to adhere well to the substrate in addition, the assembly should have good dimensional stability, and it has to show good solderability (ability to withstand short exposures to liquid solder at temperatures around 250 C or higher) to allow for the connection of components and devices to the circuitry. 

The tremendous growth of the electronics and computer industry has also given a boost to phenolic resin sales. Printed circuits are manufactured by bonding copper foil to a laminated phenolic base, printing the area representing the circuit with acid-resisting ink, and then etching away the remainder of the foil. The dimensional stability, acid resistance, and excellent electricals make phenolics a necessity in the application. 

Retain adhesion while the circuit is flexed Wet and bond well to both the polymer film and the copper foil Have low moisture absorption Have good dielectric properties Have low or no-flow characteristics Be thermally resistant to solder-reflow temperatures... 

New cyanoacrylate compounds exhibit good adhesion to various plastics and elastomeric surfaces, such as Mylar, copper foil, and vinyl films. These products show better impact resistance and good flexibility compared to standard cyanoacrylates, good resistance to cracking under flexing or bending, and a longer open time than that of standard products. 

The majority of base materials for circuit boards are combinations of a copper foil with a laminate, where the laminate itself consists of a carrier material and a resin. Thus properties of the base material such as mechanical strength, dimensional stability, and processi-bility are determined primarily by the carrier material. On the other hand, the resin materials are responsible for the thermomechanical and electrical properties as well as for its resistance against chemicals and moisture. Frequently used carrier materials are based on glass and carbon fibers, papers, and polyamide, whereas the majority of the laminating resins are thermosets such as epoxies, phenolics, cyanates, bismaleimide triazine (BT) resins, maleimides, and various combinations of these [13]. 

Iwasaki and Todoroki [92] use a response surface technique to process the electrical resistance measurements. A large number of cross-ply and quasi-isotropic specimens were tested such that statistical data processing could be applied. Copper-foil electrodes mounted on one side of the CFRP specimens during prepreg layup were co-cured with the specimen (Figure 16.39). Impact-induced matrix cracking and delaminations were detected. Probability of location estimation and error bands were computed [92]. The extension of this method to woven CFRP composites is described in Hirano and Todoroki [93]. 

Polymer substrates were also metallized by evaporation. Prior to metal deposition, the specimens were cleaned in a 2 % aqueous detergent, rinsed and dried. A resistively-heated conical tungsten basket containing 99.99+ % purity copper foil served as the metal source. Typically 100-200 nm of metal was deposited in an Edwards E306A coating system. The chamber was evacuated to 2 x 10 4 Pa and held for at least 1 h prior to metal deposition in order to properly degas the substrates. Complete details of the evaporation procedure have been given previously... 

Blends of PAEK and PEI can offer increased Tg, good chemical resistance at the lower PEI levels and reduced cost relative to pure PAEK. In particular PEI can be used to build the heat distortion temperature (HDT) of PAEK. Such blends find uses where PAEK-like performance is required in combination with an improved HDT. There are also applications in which the PEI is used above its Tg as a melt adhesive. For example, laminates of copper foil and PEEK/ PEI blend films can be produced in which the copper adheres to the hot, amorphous blend which subsequently crystallises to produce a chemical and solder-resistant structure. Mitsubishi has produced flexible printed circuit boards based on this concept [9]. 

Single-sided boards (SSBs) have circuitry on only one side of the board and are often referred to as print-and-etch boards because the etch resist is usually printed on by screen-printing techniques and the conductor pattern is them formed by chemically etching the exposed, and unwanted, copper foil. 

The primary conductive material used in printed circuits is copper foil. However, the trend toward circuit densification has brought about recent developments in copper foil technology as well. In addition, copper foils subsequently plated with other metal alloys are employed to manufacture printed circuits with resistive components buried within a multilayer structure. 

The electrodeposited copper foils described above account for most of the conductive foils used in rigid printed circuits. However, modified versions of these foils are sometimes used in niche applications. These modified versions include double-treated copper foil and resistive foils. 

Subtractive plating is a method of forming traces and other conductive patterns on a PCB by first covering a sheet of laminate with a continuous sheet of copper foil. A layer of etch resist is applied such that it covers the copper pattern that is desired.The panel with protective coating is passed through an etcher that removes (subtracts) the unwanted copper, leaving behind the desired patterns. This is the dominant, almost only, method in common usage in the printed circuit industry today. 

Voltage and Ground Plane Resistance. The sheet resistance of sohd copper voltage and ground planes is relatively low for most copper foil thicknesses. For 35-pm-thick copper foil, the dc (solid) sheet resistance is less than 1 niH/sq.The dc resistance of copper foil is shown in Eq. (15.2). The (solid) sheet resistance for selected copper foils is shown in Table 15.3. Due to the almost infinite number of possible variations in the size, placement, and shape of perforated mesh planes, the following data are presented for informational and comparative pin-poses only. 

TABLE 15.3 Solid Area Copper Foil Sheet Resistance... 

Photoprint. Photoprint involves a supplier coating a thin, resistive layer on a copper-foil sheet and selling this to either a laminate suppher or directly to the board fabrication shop. The fabricator uses two imaging and etching steps the first to image the copper conductors on the layer, and the second to size individual resistors by using a second, different etchant solution, specifically for the resistor composition. Typically, alkaUne etchants are used in step one, and acidic etchants are used in step two. 

Etch an opening in the copper foil that will serve as the resist mask. 

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