Hi mukesh, can you tell more details about yor process parameter? in general, if the temperature of tmah bath is more then silicic acid will dissolve faster in tmah solution. Also it depends on silicic acid contents. for us 40 gms/ltr silicic acid takes approx. 3 hours to get dissolved in 5%TMAH solution at 85 deg celcius. i.e around 250 ml of 5% TMAH and 10 gms of silicic acid. we had experienced similar kind of problem what you are facing now. it may be due to shelf life of either TMAH or silicic acid. repeat ur experiments by changing either tmah or silicic acid. if you still find problem, feel free to contact mde.. --ravi shankar.