SV: [mems-talk] Re: su8 cracking

[eowin rohan]

Hi all, 
  I guess that Oygm observation is true in general, because if SU-8 is over-exposed you get a more compact or more cross-linked and so less permeable polymer, so it´s much more difficult that it get swollen due to developer, and cross-linked is more uniform, there are less tensile stress. When there are a under-exposure, the external su-8 layer is well cross-linked but not the layers down, so these last can adsorb solvent and give craks...
   
  There are something that I don´t understand, you say that there are some cracks but they disspear after hard-bake... sound strange, because the cross-linking make Su-8 not softening or meltable by increasing the temperature... but if it works... it works.
  Do you have some problem with bubbles?
   
  Eowin
  
oygm <sonic_1217 at hotmail.com> skrev:
  
Today I tried exposure dose 400mJ/cm2. This time most of the cracks disappeared with 120s developing. And the feature looks very nice. After 140c 60s hard bake, all cracks disappeared. Hence I believe Kevin gets the point, under-exposure leads to the cracks in my case!