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Boundary conditions for 2 bonded wafers - membrane load
Posted Jan 7, 2011, 4:42 p.m. EST 3 Replies
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Hi everybody,
when my 2 wafers get cooled down from 400°C to room temperature, they look like this: (attached pics). The graph shows the edge at lower left. This means, that the wafer's sidewalls move upstairs during cooling down.
Fixed point for this study was (0,0,0) - the corner at the lower center of the symmetric model.
Now the membrane on top of the second wafer should get stressed. I can't use a fixed constraint for the bottom of the lower wafer since his edges are lifted up. So again I use (0,0,0) as fixed point for boundary condition. But this only works as long as the remaining lower edges reach z=0 (they move downstairs due to membrane load) . As from now I need further boundaries that fix the corners at the bottom at z=0. Otherwise these corners would move to z<0 which stands for lifting up the center of the lower wafer. That won't happen in reality!
So I need boundaries for the lower corners, that only get effective if their z-coordinate gets z<=0. Is it possible to implement this in Comsol?
Next question concerns membrane load. I want to avoid a point load in the centre of the membrane since this is not a realistic case. In a bend test a stamp would transfer a defined force into the membrane. Don't know how to model this in Comsol. Any suggestions?
Thanks a lot!
Chris
when my 2 wafers get cooled down from 400°C to room temperature, they look like this: (attached pics). The graph shows the edge at lower left. This means, that the wafer's sidewalls move upstairs during cooling down.
Fixed point for this study was (0,0,0) - the corner at the lower center of the symmetric model.
Now the membrane on top of the second wafer should get stressed. I can't use a fixed constraint for the bottom of the lower wafer since his edges are lifted up. So again I use (0,0,0) as fixed point for boundary condition. But this only works as long as the remaining lower edges reach z=0 (they move downstairs due to membrane load) . As from now I need further boundaries that fix the corners at the bottom at z=0. Otherwise these corners would move to z<0 which stands for lifting up the center of the lower wafer. That won't happen in reality!
So I need boundaries for the lower corners, that only get effective if their z-coordinate gets z<=0. Is it possible to implement this in Comsol?
Next question concerns membrane load. I want to avoid a point load in the centre of the membrane since this is not a realistic case. In a bend test a stamp would transfer a defined force into the membrane. Don't know how to model this in Comsol. Any suggestions?
Thanks a lot!
Chris
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3 Replies Last Post Jan 10, 2011, 3:51 a.m. EST
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Posted:
1 decade ago
Hi
if you apply a pressure on the top, I believe you need a contact type BC on the bottom , still restraining your central point in x,y to avoid lateral slipping. or use a small x,y spring constant to avoid a hard point
if you havent used contact before, try a couple of simple exercices, and check the KB + the forum more to learn there
--
Good luck
Ivar
if you apply a pressure on the top, I believe you need a contact type BC on the bottom , still restraining your central point in x,y to avoid lateral slipping. or use a small x,y spring constant to avoid a hard point
if you havent used contact before, try a couple of simple exercices, and check the KB + the forum more to learn there
--
Good luck
Ivar
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Posted:
1 decade ago
Hi,
found a very nice example for contact boundaries, called "Cylinder Roller Contact". That will be very helpful!
Still there is my question concerning "conditional" BCs. Is it possible to let some BCs only get active, if special parameters (for instance when a structure is reaching a certain coordinate due to deformation) are fulfilled?
Best regards
Chris
found a very nice example for contact boundaries, called "Cylinder Roller Contact". That will be very helpful!
Still there is my question concerning "conditional" BCs. Is it possible to let some BCs only get active, if special parameters (for instance when a structure is reaching a certain coordinate due to deformation) are fulfilled?
Best regards
Chris
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Posted:
1 decade ago
Hi
you can write equations that contain boleans, but note tha the solvers might well have convergion problems, s make these transitions smooth and at least derivable once, if not twice
--
Good luck
Ivar
you can write equations that contain boleans, but note tha the solvers might well have convergion problems, s make these transitions smooth and at least derivable once, if not twice
--
Good luck
Ivar