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Q: What is the recommended process for curing my specific polyimide?
A: The process is easy with the right equipment. First lets define a polyimide...
Polyimides are high temperature engineering polymers utilized by semiconductor manufacturers for their excellent mechanical, thermal and electrical properties. Polyimides are usually applied in liquid form and then soft-baked to set the film. After the polyimide has been imaged and developed, it is ready to be thermally cured. The cure cycle activates the desired properties of the polyimide. While temperatures may change depending on the particular polyimide, the techniques developed to achieve an ideal film are universal. Now, let me go into detail on what the curing process for polyimide is doing. First, the polyimide needs to be cured in an oxygen-free environment. During the cure process oxygen will interfere with the cross- linking of the polyimide and result in a weak film. Our YES-450PB Series of tools first purge oxygen from the system through a series of vacuum pumpdowns and nitrogen backfills. Then a controlled temperature ramp commences, which provides an ideal process for curing almost any polyimide. I prefer slightly lower ramp rates when running processes which decreases stress in the film of polyimide. Many cure recipes include "Holding" a process at a temperature around 200°C for an indefinite amount of time allows the solvent in the film to evaporate. Since the YES-450PB tools cure at a reduced pressure, the solvent is being drawn out of the film from the beginning of the process. Therefore the hold step isn't necessary, especially if the ramp is slowed down slightly.
After the solvent has been removed from the film, the next step is to fully imidize the polyimide. This is the conversion of the film from polyamic acid to polyimide. The ramp continues, usually until the film reaches the glass transition temperature. The temperature will be held at 300-400°C for 30-60 minutes depending on the polyimide. The product is then cooled to allow for safe removal from the system. The cooling rate can be much faster than the heating rate because the characteristics of the film are set.
This is a standard application for the YES-450PB. The system can be programmed to follow the manufacturer's recommended cure cycle exactly or however it is appropriate for the application. For instance, when YES ran a bond pad re-routing using multiple layers of polyimide as the dielectric, after the first layer, we could not exceed the glass transition temperature of the polyimide on subsequent layers. Consequently, Layer 1 was cured to 400°C, Layer 2 was cured to 360°C and Layer 3 was cured to 350°C.
Yield Engineering Systems can work with your engineers to determine which tool within the YES- 450PB Series will work best for what you are trying to achieve.
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