In the production of printed circuit boards for the electronics industry, a 0.29

Question

In the production of printed circuit boards for the electronics industry, a 0.295 mm layer of copper is laminated onto an insulating plastic board. Next a circuit pattern made of a chemically resistant polymer is printed on the board. The unwanted copper is removed by chemical etching and the protective polymer is finally removed by solvents. One etching reaction is

Cu(NH3)4Cl2(aq) + 4NH3(aq) + Cu(s) ? 2Cu(NH3)4Cl(aq)

A plant needs to manufacture 10700 printed circuit boards, each 8.40cm x 12.5cm in area. An average of 83.0% of the copper is removed from each board (density of copper=8.96g/cm3.) What mass of Cu(NH3)4Cl2 reagent is required?

Explanation / Answer

Each board has a volume of 8.4 cm x 12.5 cm x 0.0295 cm = 3.0975 cm3

Density of copper = 8.96 g/cm3, so each board has a mass of 8.96 g/cm3 x 3.0975 cm3

= 27.75 g Cu

If we must remove 80% of this, 0.80 x 27.75 g Cu = 22.2 g Cu must be reacted on each board.

10,000 x22.2 = 2.2 x 10^5 g of Cu must be reacted for the 10,000 boards.



2.2*10^5*237.9/63.55 of Cu(NH3)4Cl2

= 8.24x 10^5 g of Cu(NH3)4Cl2

and
8.24x 10^5 g *68/237.9 of NH3
=2.355 x 105 g NH3

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