Research On The Yield Improvement Of ICS Module

For the semiconductor devices final test, the manufactory have to run the testflows at different temperature include cold, hot and room to make sure all modules ofthe devices can work well at the full temperature range as mentioned in datasheet.And after a new device safe launched to manufactory, if no unit from huge loadingfailed at room test, manutactory can eliminate the room test from the safe launchflows to get the manufactory test capacity improvement, but at least the cold test andthe hot test were necessary for the semiconductor products test, especially for thedevices which will be used for automotive.The study object of this paper is about ICS (Internal Clock Source) module ofFreescale HCS08SG32/16series.SG32/16devices under2final test insertions at both cold and hot, and alwayshad the ICS test low yield issue at the2ndfinal test insertion (hot test). As a specialfunction, Freescale S08series have an ICS trim register which can modify thefrequency of ICS module output by write different value into it. This paper studied thecorrelation between the ICS output frequence, test temperature and the trim value ofICS trim regiester to understand the root cause of the low yield. Base on the study,product engineer get an idea to make the test yield improvement and keep stable: Atthe1stfinal test insertion (cold test), test program will verify multi ICS trim value andall of them should make the unit pass the1stfinal test insertion, and at the2ndfinal testinsertion (hot test), the test program will select the one which can make sure the unitpass the2ndinsertion test, so the final trim value can support the unit pass both the1stand the2ndtest insertion. The final trim value will be record into the flash forcustomer reference and it can make sure the ICS module works well at the fulltemperature range.The new test method had been released to manufactory and lots of SG32/16units had been tested with the new method, the result is positive. The new test methodhad also been fanned out to SG8/4devices and EL32/16devices, all the devicesshowed the new test method can get about3%yield improvement. The new testmethod had reduced a lot of unwanted loss, and save lots of cost for Freescale.