Plated copper electroless process

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. 

It is interesting to conclude this section with an example that, in a sense, brings the chapter full circle. The metallization of plastic materials used as metal substitutes is a process with actual and future commercial potential. Usually, plastics are plated after appropriate sensitization by an electroless process which involves reduction of metal ions (e.g. Ni2+, Cu2+) by chemical rather than electrical means.19 There seems no reason why the reducing agent should not be incorporated in the polymer and Murray and his collaborators101 have demonstrated that copper, silver, cobalt and nickel may each be electrodeposited on to films of [poly-Ru(bipy)2(4-vinylpyridine)2]2+ coated on to platinum electrodes. The metal reductions are mediated by the Ru1 and Ru° states of the polymer. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

Later, McPherson (39) demonstrated that the Inclusion of a CTBN/liquid epoxy adduct enhanced both the flexibility and adhesion of a dimer acid flexibllized epoxy/brominated epoxy mixture when cured with a combination of chlorendic and nadic-methyl anhydrides. With an epoxy-glass laminate as substrate, such mixtures were coated at 0.5-2.0 mils thickness, cured, sensitized and copper plated (1.5 mils) by an electroless process. 90 peel testing (2 inches/mln. rate, 25 C) gave 14.0 pli peel force where 5.0 pli is considered normal. 

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. 

The electroless plated copper process is capable of making through-hole vias in the ceramic. The via walls may be metallized or the entire via filled. The minimum size of through-ceramic vias is a fxmction of the laser used for machining. 

Panel is metallized by usual copper reduction process (consisting of catalyzing and electroless copper plating or by direct metalhzation process). 

Plated Copper Technology. The various methods of plating copper to a ceramic all begin with the formation of a conductive film on the surface. This film may be vacuum deposited by thin-fihn methods, screen printed by thick-film processes, or deposited with the aid of a catalyst. A layer of electroless copper may be plated over the conductive surface, followed by a layer of electrolytic copper to increase the thickness. 

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

Electroless copper solutions underwent similar development during the same period (10). Early printed circuit boards used mechanically attached eyelets to provide electrical conductivity between the copper sheathing laminated on two sides of a plastic board. Electroless copper plating provided a less expensive, better conductive path, allowing much greater numbers and smaller sizes of holes. Later, electroless coppers even replaced the laminated bulk copper sheathing in the semiadditive and additive processes (see Copper). 

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