Tombstone Example for the Surface Evolver

tombstone A chip is said to "tombstone" when uneven melting of solder pulls the chip from a horizontal to a vertical position. This set of Surface Evolver datafiles models a rectangular chip wetted by liquid solder at one end. The ultimate goal is to calculate the forces and torques on the chip in an arbitrary position. The datafiles start very simple and build in complexity. The list of datafiles is given below, with brief descriptions. Each datafile has its own page, elaborating on added features. The complete set of datafiles can be downloaded as (DOS format) or tombdata.tar (UNIX format).

NOTE:These models require Evolver version 2.11 (March 1, 1999) or higher to run. One of the benefits of writing my own software is that if it needs features, I can add them. Some of the datafiles could run on old versions with a little editing, but some definitely need the new features.

It is assumed that you are familiar with the operation of the Surface Evolver at least to the level of the basic Evolver Tutorial examples cube.fe, cat.fe, and mound.fe.

The chip has a nonwettable region (pink) and a wettable region (red). The liquid solder surface is yellow. The rectangular solder pad on the circuit board is green. Physical parameters that will need to be specified in the datafiles are the chip and pad dimensions, chip and pad contact angles for the solder, the density of the solder, and the surface tension of the liquid solder. All of these need to be given in one consistent system of units, such as cgs or MKS. We will use cgs here.

The general sequence of steps in modelling something like this is

There are a number of general themes in the sequence of models:

The Datafiles:

The sequence of datafiles starts simple and adds features. The sequence is not strictly linear; the main sequence keeps the contact surface on the chip explicitly represented by facets, and a sideline replaces those facets with edge integrals. Each datafile link here opens a commentary page, from which one can also open the datafile in a separate browser window. The idea is to be able to look at the commentary and datafile simultaneously. The datafiles themselves also contain a little commentary. You are also urged to have the Evolver running and run the models as they are discussed.
This page last modified 3/1/1999.
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