Screen Printing Grade Polyimide Paste for Alpha-Particle Protection

Polyimide coatings are becoming an important means of providing large-scale memory devices with protection against alpha-particle induced soft error. Efforts to develop a cost-effective method of application have led to the introduction of screen-printable polyimide materials. Conventional polyimide formulations are not suitable for screen printing because their filler particles fire larger than 4 um, which results in more than one pinhole per square centimeter. In addition, the N-methyl-pyrrolidone (NMP) solvent in the formulations breaks down silicone applicators and polyvinyl alcohol (PVA) screen emulsion and evaporates so fast that pot life of the formulations is limited to 2 h. Research has led to the development of new manufacturing techniques to produce smaller sized filler particles to eliminate pinholes as well as a new solvent system that extends the useful pot life of the material.