Tombstone Example tomb-A for the Surface Evolver

[Click for the tomb-A.fe datafile in a second window.]

This is the simplest model in the tombstone series. It shows just the chip and the pad, without any solder. The chip is horizontal and some distance above the pad (as placed on solid solder blocks before the solder is melted). The surfaces shown here are actually just for the convenience of the viewer; they will not be used at all in energy or force calculations.

Oblique view.	View down x-axis.	View down negative y-axis.	View down z-axis.

The wire frame diagram shows the vertices and edges of the datafile. The numbering may look strange, but that is because when I first set up the tombstone file, I did pure solder first, then added the pad and chip displays. I removed the solder for this datafile, hence the high numbers. This view has the z+ face on top, the x+ face in front, and the y- face on the left. The orientation of the edges is shown by the edge numbers being toward the heads of the edges. (The labeled wire frame pictures are made by

  set facet color clear; show edge where original > 1 

Notable features:

• The solder pad on the circuit board (green) is at z = 0. The chip is a distance THeight above the pad, horizontal with its long axis above the x-axis, its wettable (red) end towards positive x.
• In this file, the front end of the chip is over the center of the pad. The position of the chip is given by three parameters (x0,y0,z0) for the coordinates of the center of the lower front edge. The parser does not interpret x0 as the 0th coordinate since coordinate numbers start at 1 (one of the things version 2.11 is needed for to work right).
• All the chip planes shown here are defined as level-set constraints using the positioning parameters, so the chip may be moved at runtime.
• I refer to the chip faces as x+ for the face with outward normal (1,0,0), y+ with outward normal (0,1,0), etc., when the chip is in its initial position. These labels will remain fixed even when the chip is rotated in later datafiles.
• The element numbering has gaps in it, due to the history of these datafiles, and to leave room for inserting additional elements. The elements get renumbered consecutively when the datafile is loaded. To keep the same numbering, start the Evolver with the -i option.
• The edges and faces are given the "no_refine" attribute, since there is no point in wasting computer resources refining perfectly flat rectangular regions.
• The surface tension is set to 0 on all faces of the chip and pad since we are not using these in the energy calculation.
• Not much you can do with this file at runtime, except look at it. You can practice "picking" elements with the right mouse button (on systems that support picking). You can move the chip around by changing x0, y0, and z0, such as:

   Enter command: z0 := .0015; recalc 

  The recalc is necessary because changing the value of the variable z0 by itself does not change everything that depends on it, such as the coordinates of vertices on constraints. Note that changing the height this way does not raise the vertices in the middles of the vertical faces. To uniformly raise all vertices, one could define these:

  new_z0 := z0
  change_z0 := { dz := new_z0 - z0; z0 := new_z0;
                 set vertex z z+dz where z > 0;
                 recalc;
               }
  

  Now you can raise the chip uniformly by doing

   Enter command: new_z0 := .0015; change_z0
  

  Note that change_z0 sets z0 before modifying vertex coordinates. That is because changing a vertex coordinate also automatically projects the vertex to its constraints, which should have the new z0.