Electroplating, etching prior

Figure 12.2 presents the optical view of the polished cross-section of A1 layers made at —20 mAcm-2 on a mild steel substrate without performing in situ etching prior to the electroplating. An interstice between the substrate and the electroplated layer is seen due to a thin oxide layer which forms after the last pre-treatment step. 

Plastic surfaces may be etched, prior to electroplating, by Cr(vi) in order to improve adhesion. 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

Prior to the introduction of Cu electroplating, the primary method used to form a multilevel structure of interconnections in integrated circuit applications was A1 and Al-alloy metallization.49 Localized porous-type anodization was developed in the 1970s to obtain planar interconnection metallization for multilevel large-scale integration (LSI) 26,46,50 For example, Schwartz and Platter showed that the subtractive etching for A1 interconnects could be substituted... 

Methane sulfonic acid (MSA) is a relatively expensive acid used to strip (remove) solder (tin/lead) and copper metals. This acid is also used to condition metal surfaces prior to fluo-borate free-solder electroplating when applying a final etch resist of solder onto multilayer printed circuit boards. By continuously recirculating the acid bath through a diffusion dialysis unit, a 95 percent reduction of chemical purchases (required by the process steps indicated in the first paragraph of this section) may result, producing less than a six-month return on the initial capital investment (ROI).Typically, 80 to 90 percent of the acid is recovered with 70 to 90 percent of the metals removed in an equal volume of dilute acid. 

Controlled surface roughening in order to promote adhesion of a coating via more direct chemical bonding, as in the mild etching of metals prior to electroplating or anodizing (Chapter 8). 

Copper is etched at further stages in the manufacture of printed circuit boards including, after resist application (1) removal of electroless and electroplated deposits before pattern plating with copper (2) prior to electroplating gold onto edge contacts and (3) final etching of all unwanted copper to leave the desired circuit pattern. 

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