Metal Finishing Guide Book


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enhanced by the presence of halogen ions. The concentration of these organic additives must also be closely controlled in order to attain the desired deposition properties and surface morphology. In most instances, the recommended working temperature for the sulfuric acid plating solution does not exceed about 27��C, and more typically, plating is carried out at room temperature. Because these copper plating electrolytes are designed for use at room temperature, they are not generally suited for plating through-holes at elevated temperatures. On many occasions, the brighteners undergo chemical changes at elevated temperatures and are no longer effective for copper plating. In other instances, the levelers used in combination with the wetter/suppressor additives in the solution present issues leading to the deposition of dull, rough layers, especially inside the through-holes. The thermal characteristics of the copper layer deposited at elevated temperatures are adversely affected and reliabiliFigure 1: Thickness of copper plated on the surface and in the throughty performance hole. decreases. Failure occurs during the soldering operation that follows plating.Over the past few years, printed circuit board fabrication has dramatically increased in geographic areas with hot climates. In order to maintain the desired temperature in these areas, chillers or other cooling Figure 2: HT 100 microdistribution on 1.6 mm measured at 24��C.. methods are generally needed. Thus, it is desirable to simplify the process in these warmer areas to eliminate the need for chillers or other cooling methods while still obtaining a desired plating deposit. A new direct-current process for plating smooth, bright, Figure 3: HT 100 microdistribution on 1.6 mm measured at 35��C. and planar copper layers at temperatures up to 40��C (104��F) is described in this article. The method outlined herein yields excellent microdistribution. The organic brightener used assists in reducing the surface-to-hole thickness ratio, as well as improving the ductility and tensile strength of the copper deposit. Furthermore, the thermal characteristics of the deposited copper are excellent. 289

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