Development of photosensitive solder resist with high reliability for semiconductor package

Printed circuit boards are becoming denser as the electronic products have been reduced in size and improved in performance. Excellent reliability for High Accelerated Stress Test(HAST) resistance, crack resistance, and higher resolution are critical requirements for solder resist to be formed at the outermost layer of the printed circuit board, especially for the solder resist for substrate for the ball grid array packages. Increased demands for higher density package substrates drives finer line and space(L/S) from narrower pad pitch, and thinner layers, and requirements for solder resist is getting more critical. We have successfully established technology to enhance HAST reliability through reduction of chlorine ion impurities to improve anti-hydrolysis properties. This new technology significantly improves ion migration resistance resulting in a higher HAST reliability even with a thinner solder resist film. For crack resistance, a simulation has been designed to analyze the mechanism of cracking as well as a target of physical properties of the solder resist possessing superior crack resistance. Outstanding crack resistance was successfully achieved in the thermal shock test(TST), with the solder resist using the new technology based on the results from our simulation. As for the resolution, we optimized exposure wavelength and the refractive index of the material and successfully demonstrated good resolution in accordance with the design size.