Copper etching

Most priated circuit board (PCB) production uses the subtractive process (41). In the simplest version, a thin copper foil is laminated to a nonconductor, holes are fabricated, and the unwanted copper etched off. These siagle-sided boards do not require plating. Known as ptint-and-etch, this version is used for the most simple priated circuit boards. 

F. Y. Zhang, A. K. Prasad, and S. G. Advani. Investigation of a copper etching technique to fabricate metallic gas diffusion media. Journal of Micromechanics and Microengineering 16 (2006) N23-N27. 

Fig. 4. Profllometer results illustrating the difference of copper etching in the presence or not of titanium nitride, after 1.5 h in 0.1% HF + FNH, at pH = 7.

Additive (or "pattern plating") methods are becoming increasingly popular, for they generate less waste and require lower manufacturing costs (Brush 1983). In additive methods, metal is deposited only in the holes and on the circuit locations, so there is less waste of copper. Also, the copper etching step is eliminated. The additive method does have drawbacks, however. Additive processes require use of solvent processable instead of aqueous processable photoresists. In addition, waste streams contain heavily complexed copper. 

Cupric chloride (CuClj) ia a strong etch employed for producing circuit patterns on the board. The etchant loses its effectiveness as copper etched from the board reduces the CuClj to cuprous chloride (CuCl). The spent etchant can be regenerated, however, by oxidizing the CuCl, using direct chlorination (DHS 1987). 

Fig. n.3 AFM image of copper etched for 20 s at 10 V in a Type III eutectic of 1 choline chloride 2 ethylene glycol (right side of image masked during experiment). 

Copper has emerged as the leading contender for back-end-of-line metallization for advanced integrated circuits. Lack of a viable copper etch process and depth-of-focus limitations of advanced lithography leads to the chemical-mechanical polishing (CMP) of Damascene structures as the preferred method by which copper-based metallization is formed. CMP is the only known feasible method by which copper metallization can be patterned to the requisite, feature size and global planarity. 

The etch rates of oxides in DHF vary dramatically with their chemical composition and deposition conditions. Ideally, it would be possible to control the oxide etch rate by the concentration of DHF, and the copper etch rate with a second, independent variable. Figure 2 shows the results of cleaning metallic copper deposited on hydrophobic silicon from a copper-spiked HF solution [2]. SC-2 solutions with varying HCl and HjOj flows and a total flow of 1,760 ml/min were dispensed in the nitrogen-purged environment of a spray acid processor. The concentration of HCl had little effect on the total Cu removed as measrrred by TXRF. 

Ferric nitrate (50%) (cone, copper etching solution) 144 No effect ... 

Alternatives to Chlorine Gas in Circuit Board Manufacturing Photocircuits Corporation, in Glen Cove, NY, manufactures printed circuit boards for use in computers, cars, phones, and many other products. The facility formerly used chlorine gas in the copper etching process used to make circuit boards, but switched to sodium chlorate. This change reduced hazards to employees and eliminated an off-site vulnerability zone that encompassed 21,000 people. 

Mandler D, Bard AJ (1989) Scanning electrochemical microscopy - the application of the feedback mode for high-resolution copper etching. J Electrochem Soc 136(10) 3143-3144. doi 10.1149/ 1.2096416... 

Figure 12.28 Principles of copper etching by the SECM in the feedback mode.

Dyconex DYCOre Copper etching Etched copper bumps... 

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