Question

Copper is an excellent electrical conductor widely used in making electric circuits. In producing a printed circuit board for the electronics industry, a layer of copper is laminated on a plastic board. A circuit pattern is then printed on the board using a chemically resistant polymer. The board is then exposed to a chemical bath that reacts with the exposed copper, leaving the desired copper circuit, which has been protected by the overlaying polymer. Finally, a solvent removes the polymer. One reaction used to remove the exposed copper from the circuit board is \(\mathrm{Cu}(\mathrm{s})+\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}(a q)+4 \mathrm{NH}_{3}(a q) \longrightarrow\) \(2 \mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}(a q)\) A plant needs to produce 5000 circuit boards, each with a surface area measuring \(2.0\) in. \(\times 3.0\) in. The boards are covered with a \(0.65-\mathrm{mm}\) layer of copper. In subsequent processing, \(85 \%\) of the copper is removed. Copper has a density of \(8.96 \mathrm{~g} / \mathrm{cm}^{3}\). Calculate the masses of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\) \(\mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) needed to produce the circuit boards, assuming that the reaction used gives a \(97 \%\) yield.

Short answer

To produce 5000 circuit boards, the mass of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\) needed is \(7.33 \times 10^{2} \mathrm{g}\) and the mass of \(\mathrm{NH}_{3}\) needed is \(4.93 \times 10^{2} \mathrm{g}\), accounting for a 97% reaction yield.

Step-by-step solution

Calculate the total surface area of one circuit board

The surface area of one circuit board is given by the product of its length and width: Surface area = length × width Surface area = 2.0 in × 3.0 in

Convert the surface area to cubic centimeters

Now let's convert the surface area to cm², using the conversion factor of 2.54 cm = 1 inch Surface area = 2.0 in × 3.0 in × (2.54 cm/in)² Surface area = 15.2906 cm²

Calculate the volume of copper removed from one circuit board

We are given that 85% of the copper is removed and the thickness of the copper layer is 0.65 mm. Volume of copper removed = Surface area × Thickness of copper layer × 85% Volume of copper removed = 15.2906 cm² × 0.065 cm × 0.85

Calculate the mass of copper removed from one circuit board

We can use the density (d) of copper to find the mass (m) of copper removed, using the formula: m = d × V m = (8.96 g/cm³) × (15.2906 cm² × 0.065 cm × 0.85)

Calculate the mass of copper removed from 5000 circuit boards

Now let's find the total mass of copper removed from 5000 circuit boards. Total mass = mass removed from 1 board × 5000

Use stoichiometry to calculate the masses of Cu(NH3)4Cl2 and NH3 needed

From the balanced chemical equation: \(\mathrm{Cu}(\mathrm{s})+\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}(a q)+4 \mathrm{NH}_{3}(a q) \longrightarrow 2 \mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}(a q)\) It can be seen that 1 mol of \(\mathrm{Cu}\) reacts with 1 mol of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\) and 4 mols of \(\mathrm{NH}_{3}\). Now, let's use the molar masses of the species to find the masses of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) needed.

Calculate the theoretical masses of Cu(NH3)4Cl2 and NH3 needed

To calculate the theoretical masses, we will use the stoichiometry along with the molar masses of each species.

Account for the 97% yield of the reaction

Since the reaction has a yield of 97%, the actual mass of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) needed will be more than the theoretical mass. Calculate the actual mass as follows: Actual mass = Theoretical mass ÷ Yield Finally, we will have the masses of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) needed to produce the 5000 circuit boards.

Key concepts

Copper Removal

Copper removal is a critical step in creating circuit boards. It ensures that only desired copper patterns remain. This procedure involves a chemical reaction that dissolves copper, leaving it unattached from the rest of the board, exposed by the printed polymer pattern. The copper's chemical resistance allows it to hold up against solvents but not against the etching solution. This solution forms a soluble complex with the copper, removing it effectively.
Copper is a highly conductive metal that needs precise handling to maintain circuit design integrity.

• The layers of copper on circuit boards are generally very thin but also a bit dense.
• When we remove copper, calculations must account for the intended engineering outputs, such as how much copper remains and its placement.
• After exposure to the etching solution, polymer overlays are dissolved, revealing the remaining copper pattern.

Understanding these concepts for copper removal helps maintain design consistency in electronics without compromising board functionality.

Stoichiometry Calculation

In chemical reactions, stoichiometry is essential for determining the amount of reactants needed. This is based on balanced equations similar to a recipe, ensuring products are created with precision.
In the case of copper removal from circuit boards, the goal is to accurately measure how much \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\mathrm{Cl}_{2}\) and ammonia \(\mathrm{NH}_{3}\) are needed.

• The balanced reaction shows that 1 mole of \(\mathrm{Cu}(\mathrm{s})\) requires 1 mole of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\) and 4 moles of \(\mathrm{NH}_{3}\).
• Stoichiometry helps calculate how these amounts change when scaling up to larger quantities, like 5000 circuit boards.
• Consider reaction yields: In practice, not all reactants convert into products, so the actual quantities needed must account for efficiency, in this case, a 97% yield.

Proper stoichiometric calculations ensure reactants are available in adequate amounts, optimizing both resource use and production efficiency.

Chemical Engineering

Chemical engineering combines principles of chemistry, physics, and math to develop processes for transforming raw materials into valuable products. In electronics manufacturing, chemical engineering expertise is critical. The creation of circuit boards demands careful chemical interactions to form precise electrical paths.
These procedures require controlled environments where properties like density and thickness directly influence outcomes.

• Circuit board fabrication is an example of application in chemical engineering, highlighting process optimization and resource management.
• Engineers design and operate the chemical bath for copper removal, balancing reactant concentration and exposure time to achieve desired results efficiently.
• They also consider environmental and economic impacts, reducing waste and improving reaction yields.

Overall, chemical engineering drives advancements in technology, where precision and efficiency bring innovative electronic solutions to life. This meticulous approach ensures the development of high-quality, reliable devices.