Metal Finishing Guide Book

2012-2013

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Table IX. Electroless Palladium Bath Palladium chloride 10 g/L Rochelle salt 19 g/L Ethylenediamine 25.6 g/L Cool solution to 20��C (68��F) and then add: Sodium hypophosphite 4.1 g/L pH (adjusted with HCl) 8.5 g/L Temperature 68-73��C(155-165��F) (PdCl2) immersion for subsequent deposition of the electroless copper. Many proprietary activators are available in which these solutions can be used separately or together at room temperature. Palladium drag into the electroless copper bath can cause solution decomposition instantly. The pH of an electroless copper bath will influence the brightness of the copper deposit. Usually a value above 12.0 is preferred. A dark deposit may indicate low bath alkalinity and contain cuprous oxide. The plating rate is equally influenced by pH. In formaldehyde-reduced baths a value of 12.0-13.0 is generally best. Stability of the bath and pH are critical. A high pH value (14.0) results in poor solution stability and reduces the bath life. Below 9.5, solution stability is good; however, deposition slows or ceases. The principal components of the electroless copper bath (copper, formaldehyde, and caustic) must be kept within specification through replenishment. Other bath chemical components will remain within recommended ranges. Complexing agents and stabilizer levels occasionally need independent control. Other key operating parameters include temperature, air agitation, filtration, and circulation. Various common reducing agents have been suggested, however, the best known reducing agent for electroless copper baths is formaldehyde. The complexing agent (i.e., Rochelle salt) serves to complex the copper ion to prevent solution precipitation and has an effect on deposition rates as well as the quality of the deposit. These conventional baths are stable, have plating rates of 1-5 ��m or 0.04-0.2 mil/hr, and operate in an alkaline solution (pH 10.0-13.0). An example of a formaldehyde-reduced electroless copper bath is provided in Table VII. Recent formulations allow for alkanol amines such as quadrol-reduced baths. These high build [>10 ��m/hr >0.4 mil/hr)] or heavy deposition baths operate at a lower pH without the use of formaldehyde. High build baths generally are more expensive and exhibit less stability but do not have harmful formaldehyde vapors given off during subsequent solution make up, heating, and deposition. These baths can deposit enough low stress copper to eliminate the need for an electrolytic flash. Quadrol is totally miscible with water and thus is resistant to Table X. Electroless Cobalt Bath Cobalt chloride 30 g/L Sodium hypophosphite 20 g/L Sodium citrate 35 g/L Ammonium chloride 50 g/L pH Temperature 9.5 95��C (203��F) 461

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