Electroplating trends

There has been a continual increase in size and complexity of PCBs with a concurrent reduction in conductor and hole dimensions. Conductors can be less than 250 p.m wide some boards have conductors less than 75 pm wide. Multilayer boards greater than 2.5 mm thick having hole sizes less than 250 pm are being produced. This trend may, however, eventually cause the demise of the subtractive process. It is difficult to etch such fine lines using 35-pm copper foils, though foils as thin as 5 pm are now available. It is also difficult to electroplate holes having high aspect ratio. These factors may shift production to the semiadditive or fully additive processes. 

Snyder, D. D., Landau, U. and Sard, R., Electroplating engineering and waste recycle new developmentsf and trends, Proc. Electrochemical Society (USA), 83-12, Pennington (1983)... 

In a computer hard drive, the data are stored on one or more rigid disks coated with magnetic materials. The magnetic film is coated on a planar NiP substrate. NiP film is typically electroplated on an aluminum disk. Before the coating process, the NiP must be planarized. The planarization process is similar to oxide ILD CMP except that the material is a metal. The slurry chemistry is similar to copper or tungsten CMP except that the end point is to form a perfectly planar substrate. Hydrogen peroxide can be used as an oxidizer in NiP CMP as stated in the patent by Jia and coworkers [14,15]. As shown in Fig. 7.5, the removal rate for NiP film follows the same trend as for copper. At higher concentration, the removal rate decreases because of the formation of a native protective NiO film [12]. 

In conventional additive-based electroplating, competitive adsorption for surface sites occurs coincident with substrate immersion and the onset of metal deposition. Additive adsorbate coverage evolves with metal deposition and is often accompanied, to some extent, by incorporation into the growing solid with associated influence on the microstructure and resulting physical properties. The adsorbates can have an accelerating or inhibitory effect on the metal deposition process. Inhibition manifests as an increase in electrode polarization with additive concentration while accelerating or depolarizing additives exhibit the opposite trend. Recent use of... 

Snyder, D. D., U. Landau, and R. Sard, eds. Electroplating Engineering and Waste Recycle—New Developments and Trends. 

The heavy metals are still commonly precipitated with caustic soda and the solids then allowed to settle, although the modern trend is towards direct electrolytic metal recovery from the effluent (see Chapter 11). The control units for the electroplating baths operate at a current between 100 and 10 000 A and a voltage of-8 to-12 V. 

Of the many modern developments in electroplating technology, several trends may be highlighted. 

Volume conductivity measurements indicate that the composition of the electroplated substrates is of prime importance with an increase in resistivity covering 5-6 orders of magnitude. The conductive adhesives have volume resistivities in the range of 6.5 X 10 -1.6 X 10 " fi cm but the values measured for the joined assembhes extend from 9 X 10 " to 1 X 10 fi cm. The general trend observed with all adhesives is that the increase in resistivity is related to the ease of oxidation of the plated substrates, in particular when nickel and aluminium are compared to noble metal plating. Other studies support these results indicating that the best silver-filled adhesives have a volume resistivity of 5 X 10 fl cm approaching the value of solders, typically 2 X 10 fi cm. The contact resistance at the interfaces with the metallic conductors is, however, more important than the bulk conductivity [155-157]. 

Electroplated contact materials for connectors and relays, Y. Okinaka, in New Trends in Electwchemical Technology, Vol.3, Microelectronic Packaging, eds. M. Datta, T. Osaka, and J.W. Schultze, CRC Press, Boca Raton, FL, 2005. 

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