Fwd: [mems-talk] Re: Metal Paste for Screen Printing

[Tom Rust]

Im not sure what you mean by interface problems. Most of these films are 
MADE for interface to silicon wafers, but each with different 
properties. For example, the Dupont PV202 silver paste is designed to 
make a low R contact with silicon, but not appreciably penetrate any 
oxide or nitride insulators. The PV147 silver paste is similar, but will 
penetrate thin oxide or nitride insulators, but not penetrate any 
appreciable depth into the silicon. The aluminum pastes generally will 
penetrate insulators AND some depth into the silicon - buit that is a 
property any aluminum will exhibit when heated to melting point 
temperatures. These all need to be fired with a peak temp at least 675C.
The low temp pastes, such as epoxy and thermoplastics, are generally not 
used for silicon interfaces, but I have used the epoxy on bare silicon - 
you just have to be aware that there will be a thin oxide barrier which 
can often be broken down with an initial small voltage pulse. Often used 
as a simple interface for thermal silicon heaters, where modest currents 
are needed anyway.
In general the fired pastes are better and lower R.

KSRC Murthy wrote:

>We have found that these thick film pastes are not compatible with silicon
>wafers. We tried to print and fire these materials on silicon wafers (On
>silicon surface, poly-silicon surface as well as Oxide surface)and we landed up
>with severe interface problems.
>
>Dr.Murthy KSRC