Crystec Technology Trading GmbH

Applications and Chemistry

Polyimides are high-temperature resistant polymers with excellent mechanical, thermal and electrical properties. Applications in microelectronics include buffer layers, passivation layers, bonding layers and dielectric interlayers. Polyimides are typically applied as liquids and then cured in a furnace. During this step the polyimide acquires the desired properties. For most applications the polyimide can be patterned lithographically.

Most customers use polyimide as an adhesion promoter for the encapsulant and as a buffer layer to reduce rejects during IC packaging and to prevent later temperature-related failures. Polyimide coatings can also help avoid problems when IC packaging is carried out in a different factory than the one where they were produced.

The polyimide layer reduces stress in the silicon caused by encapsulation and prevents edge cracking. The polyimide must be cured under very uniform temperature conditions to avoid cracking in the polyimide and color non-uniformities. A uniform color is important for the pattern recognition systems used in packaging technology. Low oxygen levels are necessary to achieve bright material and good adhesion.

Types of Polyimide

There are essentially three types of polyimide:

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  Non-photosensitive polyimide
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  Photosensitive, ionic polyimide
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  Photosensitive, ester-type polyimide

CLH Polyimie oven

Non-photosensitive material is relatively inexpensive and easy to handle. Decomposition products that occur during the thermal treatment are liquid and do not form permanent solid residues for a short time. For this type of polyimide our clean furnace type CLH can be used. A special version exists for polyimide curing.

Process Simplification

Ester-bound types are more stable than ionic polyimide types and have a longer storage life. Viscosity is less dependent on aging and the achievable contrast between exposed and unexposed material is higher. The solubility of the unexposed material is higher.   JTEKT Thermo Systems has extensive experience in curing photosensitive polyimide. Together with Asahi a new vertical furnace concept was developed specifically for this process, and more than 100 vertical furnaces for this application have now been sold. Photosensitive polyimides, and especially those of the ester type which show the best properties, unfortunately form very stubborn deposits on the furnace walls that are very difficult to remove. In cooperation with one of the largest manufacturers of photosensitive polyimides, Asahi Chemicals, Japan, JTEKT Thermo Systems developed a special vertical furnace model. Special LGO Heating elements ensure excellent temperature control and thus high temperature uniformity in the low temperature range (350°C - 400°C) normally used for this curing process. Furthermore, JTEKT Thermo Systems installs special quartz parts in this furnace for this process which prevent the deposition of by-products. An effective exhaust system is also necessary.

The furnace is maintenance-free and the outstanding characteristics of this furnace are best demonstrated by our long reference list of satisfied customers. There is now another vertical furnace model that combines the processes of polyimide curing and hydrogen annealing.