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Underfill Misalignment Predictor (Download .zip or .tar.gz

This code is designed for cases where one wants to determine the upper and lower pad displacements across a flip-chip geometry solder joint (standoff height and misalignment) given known normal and shear forces on the joint. This is particularly relevant to study of misalignment for a flip-chip that supported only by the solder joint(s), such as during reflow of a flip-chip on a board. Those interested a code where the standoff height and misalignment are considered known and the equilibrium normal and shear forces are calculated should follow this link.

This page is a description of a down-loadable Surface Evolver code including .fe files and .cmd files. The code was developed to compare experimental and simulated flip-chip displacements. The novelty of the code is the ability to predict both normal and lateral displacements. Below are some images of experimental cross sections and simulated flip-chip solder joints. Experimental work was carried out with varying solder volume, pad sizes and weights to obtain a range of vector misalignments. Fitting of simulation to experimental results gave optimized values for the contact angle and surface tension of the solder which were consistent with measured and literature values.


Users of this code are requested to separately cite the paper describing implementation of this code (D. Josell, W.E. Wallace, J.A. Warren, D. Wheeler and A.C. Powell IV, "Misaligned flip-chip solder joints: prediction and experimental determination of force-displacement curves", to appear in Journal of Electronic Packaging) and this website address in publications containing results from code based substantially on this code. Users are also asked to note the website address (only) in presentations.

Experimental cross-sectioned joint

Experimental cross-sectioned solder joint

Simulated joint

Simulated solder joint showing offset
The code includes a group of evolver files which predict the lateral and normal displacements given a vector force. In most cases this code will need to be modified to model specific problems. Most of the modifications with respect to geometry and initial conditions will occur at the beginning of the file force.fe Included in underfill.tar.gz are the following files:

bracketx.cmd         fixonconstraint.cmd  forcez.cmd           iterate.cmd          report.cmd
bracketz.cmd         force.fe             goon1.cmd            minimumz.cmd         pev
evolve1-md.cmd   forceb.fe            goon2.cmd            onpad.cmd
evolve1.cmd          forcex.cmd           iter.cmd             param.cmd

To run an example test case type:

evolver force.fe

and then at the evolver command prompt type:


This will find the displacements for a particular vector force.
To see the results use the following commands:

printf "%g %g %g %g %g %g %g %g %g %g\n",facet_count,hgt,total_energy,xoff,ac_xoff,tilt,prop_off_pad_2,prop_off_pad_1,gamma,theta_out1  | "cat >> tilt.dat";
printf "{%g,%g},",tilt,xoff  | "cat >> m.dat";

Look in tilt.dat and you will see the x-offset (xoff) and stand-off height (hgt) for a given tilt angle (tilt).
The vector force is given from the equations on lines 29&30 in force.fe.

Also included is a shell script (pev) for running sequential evolver processes. This can be used to
plot force displacement curves.

If you have any problems using this code please email me

Download the code as a .zip or as a .tar.gz

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Date created: July 19, 2001
Last updated: July 19, 2001