Plated copper electroplating process

The first commercial boards usiag electroless plating for connection between the sides were made by Motorola ia 1953 (41). An unclad plastic board was coated with electroless silver, a reverse resist appHed, and copper electroplated to the required circuit thickness. The resist and excess silver were removed. This semi-additive process is stiU used, with copper replacing the silver. 

You have learned that electroplating is a process in which a metal is deposited, or plated, onto the cathode of an electrolytic cell. In this investigation, you will huild an electrolytic cell and electrolyze a copper(II) sulfate solution to plate copper onto the cathode. You will use Faraday s law to relate the mass of metal deposited to the quantity of electricity used. 

The heavy metals used in printed circuit electroless plating (copper and nickel) are in chelated form (chemically "tied-up" in an organic matrix). The plating baths are more unstable than electroplating baths, thereby resulting in more frequent "dumping". As a result, waste treatment requirements in printed circuit manufacturing operations present special problems and opportunities for membrane separation processes. 

Figure 21-5 Electroplating with copper. The anode is made of pure copper, which dissolves during the electroplating process. This replenishes the Cu ions that are removed from the solution as Cu plates out on the cathode.

Electroplating on plastics n. Articles of almost any of the common plastics can be plated by conventional processes used on metals after their surfaces have been rendered conductive by precipitation of silver or other conductor. A layer of copper is usually applied first, followed by a final plating of gold, silver, chromium, or nickel. Acrylonitrile-butadiene-styrene resins have been most widely used for electroplated articles. Others in commercial use for the process include cellulose acetate, some grades of polypropylene, polysulfones, polycarbonate, polyphenylene oxide, nylons, and rigid PVC. 

A method used to ensure the complete filling of vias is electroless plating of nickel. Electroless plating is a process to plate metal without electrical current involved. As a result, it eliminates the seed layer needed in electroplating. To plate nickel on copper, the copper surface must first be activated in a palladium chloride solution. This activation treatment allows palladium to bond to copper at certain sites so that the subsequent nickel plating can nucleate. 

Copper can be electroplated onto the substrate in two techniques. In the first process, as shown in Figure 8.25a, an adhesion or seed layer is deposited on the ceramic. This adhesion layer can be thin film, either sputtered or evaporated, thick film, or refractory metallization. A sputtered or evaporated gold layer is deposited on top of the seed layer for thin-film metallization. Copper is then electroplated to the required thickness. This is followed by electroplated nickel and an optional gold electroplate. Figure 8.26 shows the buildup of plated copper metallization. 

Parallel Plate Electrowinning Systems. The purpose of parallel plating, in a central system, is to recover copper as a 99.9 percent pure metal sheet (for resale) and to reduce the copper concentration in the liquid being recirculated to 1.0 g/l,or less.The efficiency of the reaction drops significantly below 1.0 g of copper per liter, as observed by the generation of heat in the bath by the electroplating process. 

The negative resist pattern is used to selectively build up the circuit by copper electroplating. When the required conductor thickness (typically 17 or 35 pm) is reached, it is plated with tin, tin-lead or gold as a positive resist. Removal of the resist is followed by rapid etching of the electroless copper layer. The remainder of the process is similar to that for subtractive methods. In the "folly additive method, the full conductor thickness may be built up in a single, long (24 h) electroless deposition stage. 

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