Investigation on the Reliability of Chips onto the Flex Substrate with a Non-Conductive Paste for Flex Substrates Pretreated by Argon Plasma

Ar plasma was expected to enhance the reliability of chips onto the flex substrate using nonconductive paste (NCP). Flexible substrates have pretreated by argon plasma before chips onto the flex substrate. The NCP deposited on the flexible substrate after the flexible substrate was treated by argon plasma, and then a chip was flipped-bonded to the flexible substrate. A specimen of the chip onto the flexible substrate using NCP was cured completely, the specimen experienced to the tests on HTS and PCT, and all the tested parameters were followed the specifications stated in JEDEC. For the specimen experienced to the reliability tests, a shear test was using to detect the joining strength and the SEM was conducted to verify the changes on the break mode. For the flexible substrate both pretreated with and without Ar plasma, the shear strength varied faintly when the specimen experienced to various periods of HTS. After the shear test, the main break occurred at joining interface of Au bumps and chips as a result of the thermal stress was upraised on joining interface of the Au bump and the chip when the specimen experienced to 1000 h of HTS. The NCP remaining well adhered to the flexible substrate, indicating Ar plasma is effective in improving the reliability of HTS. A shear strength reduced seriously for the tested period of PCT increased when the flexible substrate both pretreated with or without Ar plasma. A crack was found at the vertical and horizontal joining interfaces between the NCP and chips for specimens experienced to PCT, and the crack sustained growth for tested periods extending to 336 h, finally the poor reliability of PCT was made. The NCP was unable to resist the moisture at the test conditions of the elevated temperature and the high pressure, and then lost its adhesive strength, a poor shear strength of the specimen was thus made. However, the NCP remaining well adhered to a flexible substrate pretreated by argon plasma, indicating the joining performance between the NCP and the flexible substrate remaining good after the PCT. It proves that argon plasma is a worthy way to enhance the binding performance of the NCP and the flexible substrate during the reliability tests of HTS and PCT.