The present paper reviews some fundamental aspects related to the understanding of the high rate anodic dissolution processes and their influence on thin film patterning by electrochemical micromachining. The role of convective mass transport and current distribution on the surface finish and shape evolution is discussed. Several examples of the applications of maskless and through-mask electrochemical micromachining are presented.

Shape evolution during through-mask electrochemical micromachining was investigated to study the problem of island formation caused by loss of electrical contact. A mathematical model was developed to predict shape evolution. Laplace's equation for potential was solved using the boundary element method to determine current distribution at the anode. The current distribution was combined with a moving boundary algorithm to predict the shape of the evolving cavity. The influence of the photoresist artwork dimensions on current distribution at the surface of an evolving feature was investigated. The island formation problem was identified as most likely to occur with a combination of low aspect ratio and low film thickness ratio. Elimination of the island formation problem is discussed.

A mathematical model to predict shape evolution during through‐mask electrochemical micromachining (EMM) has been developed. Boundary element method has been used to solve the Laplace equation for electric potential with appropriate boundary conditions that describe the metal dissolution process under ohmic control. The influence of mask wall angle on shape of the evolving cavity, current distribution within the cavity and etch factor have been determined. For mask wall angles less than 90°, the etch factor increased due to the shadowing effect of the mask, whereas the etch factor decreased for mask wall angles greater than 90°. The influence of mask wall angle has been found to diminish with increasing metal film thickness.

Electrochemical fabrication of PbSn C4s (controlled collapse chip connection) offers significant cost, reliability, and environmental advantages over the currently employed evaporation technology. A continuous seed layer is required for through-mask electrodeposition of the solder alloy. This layer becomes the ball limiting metallurgy (BLM) for the solder pad after etching. The seed layer metallurgy and the BLM etching are crucial to obtaining mechanically robust C4s. In the present study, the issues related to the selection of seed layer metallurgy, uniformity of plating and etching, and mechanical integrity of C4s have been investigated. The resul~s demonstrate the feasibility of electrochemically fabricating highly reliable PbSn (97/3) C4 structures with a high degree of dimensional uniformity on a variety of wafer sizes ranging up to 200 ram.