Electrodeposited Copper Recrystallization Mechanics in High Density Circuit Stackups
Thermal cycles in high density stackups drive copper recrystallization, causing grain growth and vacancy coalescence that trigger microvia interface failures.
Polyalkylene Glycol
Chemical Compound
Synthetic polymer consisting of repeating ethylene oxide and propylene oxide units used as a suppressor in copper electroplating baths. Polyalkylene glycol molecules adsorb onto the cathode surface to form a thin barrier that regulates the rate of copper ion reduction. This suppression is essential for achieving a uniform plating thickness across the diverse topography of a circuit board.
The compound is soluble in water and functions effectively in the acidic environment of a typical sulfate plating solution.
Deposition Control
The adsorption of polyalkylene glycol onto the copper surface increases the overpotential required for plating to occur. This effect is most pronounced at the openings of microvias and the edges of traces where the diffusion of copper ions is most rapid. By slowing down the deposition in these areas, the polymer allows for more uniform growth in the bottom of deep features.
This ensures that the via fills from the bottom up rather than closing at the top and trapping a void. The molecular weight of the polymer determines how strongly it binds to the surface and how easily it can be displaced by other additives like accelerators.
Thermal Sensitivity
The effectiveness of the suppressor depends on the temperature of the plating bath. If the electrolyte becomes too hot, the polymer may lose its affinity for the copper surface and fail to provide adequate control.