Flip-Chip Alignment Force

This code is designed for cases where one wants to determine the equilibrium forces on a flip-chip geometry solder joint given fixed normal and shear displacements such as might be relevant where the chip is part of an assembly that imposes location. Those interested in a code where the normal and shear forces on the solder joint are considered known and the equilibrium displacements (standoff and misalignment) are calculated should follow this link.

This file sets up a column of liquid solder between two wetting patches of different radius, and calculates the capillary force between them.

The pads are oriented normal to the z-axis, so gravity works (volume can be computed using the standard z*zhat integrand plus a content integrand around the top trace). Circular pads are used for now, but this can be changed, though it's not easy.

Running this file is a breeze. Just set your parameters, hit the "submit" button, save the generated file as yourname.fe, and then in the same directory, type

evolver yourname

and at the next prompt, type

evolve

and it will do all of the iteration, mesh refinement, etc. for you automatically. If at the end the scale is very small, so that it just does one iteration per cycle, then you may use

keepon

to give the system a "push" and move toward equilibrium.

The beauty of Evolver codes is that actual application is limited only by the user's imagination. We therefore encourage the user to use this code in whatever way it is helpful. The original driving force for writing this particular evolver solution was the issue of self-allignment of flip chip assemblies with underfill/solder bumps applied at the wafer level. This code, which calculates the capillary forces associated with the liquid solder joint between two (potentially misalligned) pads given their relative positions, addresses the simplified geometry existing without the underfill. Another code written for the underfill project can be found here.

This code was written by Adam C. Powell, IV while employed at the Materials Science and Engineering Laboratory at the National Institute of Standards, with partial support from the Advanced Techology Program.

Share and enjoy!

Bottom pad radius, mm:
Top pad radius, mm:
Spacing between pads, mm:
Volume = pi r1^2 hgt * this:
X offset of top pad, mm:
Y offset of top pad, mm:
Wetting angle on bottom pad:
Wetting angle on top pad:
Wetting angle on bottom outside pad:
Wetting angle on top outside pad:
Surface tension (kg/s^2):
Density (kg/mm^3):