Method and stencil for extruding material on a substrate

Abstract

A stencil for use in fabricating semiconductor devices is disclosed that has an aperture having a first portion extending from a first side thereof and a second portion extending from a second side thereof to minimize the shear stress between the material extruded therethrough and the stencil. The stencil allows for material to be extruded through the top of the stencil to the surface of the substrate and not contact the wall of the second portion of the aperture of the stencil. Since the material only contacts a small area of the first portion of the aperture near the top of the stencil, the material remains on the substrate and not in the aperture of the stencil.

1 . A method for attaching a device to a substrate comprising the steps of: 
 forming a plurality of substantially vertical attaching elements on the substrate;    aligning the device with the plurality of substantially vertical attaching elements; and    securing the device to the substrate via the plurality of substantially vertical attaching elements.    
   
   
       2 . The method according to  claim 1  wherein the forming step comprises the steps of: 
 applying a stencil to a surface of the substrate;    extruding a material through at least one aperture formed in the stencil; and    removing the stencil and leaving the material in a substantially vertical column.    
   
   
       3 . The method according to  claim 2  wherein the extruding step further comprises the steps of: 
 applying the material to the surface; and    wiping the material across the surface to force the material through the at least one aperture.    
   
   
       4 . The method according to  claim 2  wherein the material has a viscosity range between 30K-310K centipoise.  
   
   
       5 . The method according to  claim 2  wherein the material has a viscosity of approximately 70K centipoise.  
   
   
       6 . The method according to  claim 2  wherein the material has a thixotropic index ranging between 1.7-3.2.  
   
   
       7 . The method according to  claim 2  wherein the material has a thixotropic index of approximately 2.5.  
   
   
       8 . The method according to  claim 2  wherein the aperture has a range of cross-sectional area from 0.1 to 10 times of the cross-sectional area of a second portion of the aperture to the cross-sectional area of a first portion of the aperture.  
   
   
       9 . The method according to  claim 2  wherein the stencil has a thickness ranging from 0.1 to 10 times the diameter of a first portion of the aperture.  
   
   
       10 . The method according to  claim 2  wherein the stencil has a thickness twice that of the first portion of the aperture.  
   
   
       11 . The method according to  claim 2  wherein the stencil is made of stainless steel.  
   
   
       12 . The method according to  claim 2  wherein the stencil is made of rigid plastic.  
   
   
       13 . The method according to  claim 2  wherein the aperture further includes at least one shoulder between a first portion of the aperture and a second portion of the aperture, the at least one shoulder being sloped towards the second portion of the aperture.  
   
   
       14 . The method according to  claim 2  wherein the aperture has a first portion and a second portion, the first portion having a smaller cross-sectional area than the cross-sectional area of the second portion, the second portion opening forming a cross-sectional area having a side wherein the material does not contact the side thereof.