8.7 Vertical Structure LEDs
173
should not be contacted with acidic substances to avoid the generation of highly toxic
cyanide acid.
Acidic sulfuric acid copper plating solution has good leveling and specular brightness, low cost, no volatile highly toxic gas, and relatively easy disposal of waste
liquid. Such a solution is widely used. The acid sulfuric copper plating solution has
two types of ordinary plating liquid and bright plating liquid. The bright plating
solution is obtained by adding some brightener to the ordinary plating solution.
The common plating solution is composed of a salt of copper sulfate, sulfuric acid,
a hydroxycarboxylic acid, and a chloride ion. At the cathode, the divalent copper
ions are reduced to copper atoms accompanied by a hydrogen reduction reaction.
When the anode copper atoms are dissolved into divalent copper ions, the anode is
passivated, and oxygen is also precipitated.
Cu
2+
+ 2e = Cu
(8.9)
Cu − 2e = Cu
2+
(8.10)
The sulphuric acid copper plating solution is extremely efficient, close to 100%.
The chance of hydrogen ion discharge on the cathode is small. On the anode, if the
sulfuric acid content in the plating solution is low and the anode current density is
large, the anode will be passivated and oxygen will be released.
Copper sulfate is the main salt for providing copper ions, and the content is 150–
200 g/L. The low concentration will lower the upper limit of the cathode current
density and the brightness of the coating. When the concentration is high, it will be
easily crystallized. The role of sulfuric acid is mainly to prevent copper salt hydrolysis, reduce copper powder, improve the conductivity of the plating solution and
cathodic polarization. This also improves the dispensability and anodic solubility of
the electrolyte. Sulfuric acid is generally controlled at 50–70 g/L. Excessive sulfuric
acid concentration will reduce the solubility of copper sulfate. Therefore, when the
sulfuric acid content is increased, the content of copper sulfate must be reduced. If
the sulfuric acid content is too low, copper sulfate is easily hydrolyzed into insoluble
copper oxide, which is deposited on the cathode to cause a loose coating. Sulfuric
bright copper plating are mostly combined brighteners which can be divided into
main brightener according to their role, leveling agent, and brightener carrier. These
three substances can be used together to obtain good results. Chloride ions in the
solution not only brighten coating, but also reduce the internal stress generated after
adding other brightening agent, generally in an amount of 0.02–0.08 g/L. If the
content is low, the plating level is poor and the brightness is low. Furthermore, the
internal stress is large and the bright streaks are easily generated. In severe cases, the
plating layer is rough. If the content is high, the plating layer is not very bright.
Copper plating conditions require strict control. Increasing the temperature of
the plating during electroplating can increase the current density, thereby improving
the brightness and leveling of the plating layer. The toughness is also good. The
temperature control of acid bright copper plating is related to the brightener used.
173
should not be contacted with acidic substances to avoid the generation of highly toxic
cyanide acid.
Acidic sulfuric acid copper plating solution has good leveling and specular brightness, low cost, no volatile highly toxic gas, and relatively easy disposal of waste
liquid. Such a solution is widely used. The acid sulfuric copper plating solution has
two types of ordinary plating liquid and bright plating liquid. The bright plating
solution is obtained by adding some brightener to the ordinary plating solution.
The common plating solution is composed of a salt of copper sulfate, sulfuric acid,
a hydroxycarboxylic acid, and a chloride ion. At the cathode, the divalent copper
ions are reduced to copper atoms accompanied by a hydrogen reduction reaction.
When the anode copper atoms are dissolved into divalent copper ions, the anode is
passivated, and oxygen is also precipitated.
Cu
2+
+ 2e = Cu
(8.9)
Cu − 2e = Cu
2+
(8.10)
The sulphuric acid copper plating solution is extremely efficient, close to 100%.
The chance of hydrogen ion discharge on the cathode is small. On the anode, if the
sulfuric acid content in the plating solution is low and the anode current density is
large, the anode will be passivated and oxygen will be released.
Copper sulfate is the main salt for providing copper ions, and the content is 150–
200 g/L. The low concentration will lower the upper limit of the cathode current
density and the brightness of the coating. When the concentration is high, it will be
easily crystallized. The role of sulfuric acid is mainly to prevent copper salt hydrolysis, reduce copper powder, improve the conductivity of the plating solution and
cathodic polarization. This also improves the dispensability and anodic solubility of
the electrolyte. Sulfuric acid is generally controlled at 50–70 g/L. Excessive sulfuric
acid concentration will reduce the solubility of copper sulfate. Therefore, when the
sulfuric acid content is increased, the content of copper sulfate must be reduced. If
the sulfuric acid content is too low, copper sulfate is easily hydrolyzed into insoluble
copper oxide, which is deposited on the cathode to cause a loose coating. Sulfuric
bright copper plating are mostly combined brighteners which can be divided into
main brightener according to their role, leveling agent, and brightener carrier. These
three substances can be used together to obtain good results. Chloride ions in the
solution not only brighten coating, but also reduce the internal stress generated after
adding other brightening agent, generally in an amount of 0.02–0.08 g/L. If the
content is low, the plating level is poor and the brightness is low. Furthermore, the
internal stress is large and the bright streaks are easily generated. In severe cases, the
plating layer is rough. If the content is high, the plating layer is not very bright.
Copper plating conditions require strict control. Increasing the temperature of
the plating during electroplating can increase the current density, thereby improving
the brightness and leveling of the plating layer. The toughness is also good. The
temperature control of acid bright copper plating is related to the brightener used.