TSMC Leads the Industry in Recycling Electronic-Grade Copper Materials
TSMC aggressively promotes all kinds of green activities with the aim of becoming "the executor of green power," and incorporates "circular economy" into TSMC's long-term strategies and sustainable development goals. To put circular economy into real practice, the company has done extensive work in recycling copper waste liquid. In 2016, TSMC cooperated with contractors to build in-house recycling facilities to replace outsourcing of copper sulfate treatment. In 2017, the company further cooperated with raw material suppliers to replace supplier's copper materials with TSMC's regenerated copper tubes, which were processed into electronic-grade electroplating copper. In 2018, TSMC was the first in the industry to successfully return regenerated electronic-grade electroplating copper to the semiconductor fabrication process for further use.
Tubular Electrolytic Reduction Tank Increases Copper Recycling Efficiency
To increase copper recycling efficiency, TSMC chose to utilize tubular electrolytic reduction equipment. This closed electrolytic reduction tank enables electrolytes to be stirred at a high speed, overcoming the problem of Mass Transfer at low ion concentration. When operated at high current density (higher than 600 A/m2), the tank can decrease electrode surface area significantly, and effectively recycle and regenerate to lower the metal concentration. In addition, the anode and cathode are designed in a tubular shape, which produces better uniformity for the electrolytic recycled metal. After inserting a separable cathode plate, copper can be extracted by crane. Compared to general electrolytic reduction equipment using planks, this method reduces operation time.
Dosage Adjusted in Manufacturing Process to Improve Copper Tube Quality
In the waste copper sulfate regeneration process, agent dosages have significant influence on copper tube quality. To ensure an agent makes a homogeneous mixture with copper sulfate, the TSMC Green Manufacturing group made a thorough analysis and decided to directly add a leveling agent, polyethylene glycol, or PEG, into the last pair of electrodes. The circulating motor operates for an hour before the electrolysis system is activated, allowing the leveler to homogeneously react with each pair of electrodes.
Treeing is showed in the form of soft fine grains which can be easily wiped out, and is less susceptible to large dendrite formation. Bridge short circuits can almost be completely prevented.
Treeing emerges as large solid dendrites which cannot be removed. A copper tube needs to be drawn out earlier to avoid consistent short circuits.
Treeing is in the shape of spiral stripes, and the recirculated bath starts to bubble, leading its water level gauge to make misjudgments. Excessive dosages will also affect plating efficiency.
Fulfilling Circular Economy to Recreate New Value from Waste
In 2016, TSMC successfully converted 445 metric tons of copper sulfate waste previously outsourced for treatment into 9.7 metric tons of recycled copper tubes. In 2017, the company continued to reduce 1,942 metric tons of copper sulfate waste, and converted it into 42 metric tons of recycled copper tubes. Among them, 6.7 metric tons were made into electronic-grade anode copper and returned back to TSMC for coating process in 2018. In the future, TSMC's Green Manufacturing team will continue to expand the scope of process verification, taking a big step toward circular economy.