Multiaxial magnetic field-enabled underfilling
A method and corresponding system for employing fluid vorticity to drive an underfilling process with a magnetic particle-loaded curing resin is disclosed. An applied multiaxial magnetic field drives the magnetic particles, and thus the curing resin, throughout the gap between a die and corresponding carrier chip. A magnetic field generator, for example, a set of triaxial Helmholtz coils, may be driven with different frequencies and phases along each axis, and may further include a DC component along one or more axes. To further minimize voids, the die and carrier chip may be placed in a vacuum oven to assist in removing any air pockets.
1 . A method comprising the steps of:
providing a carrier chip;
providing one or more die;
electrically interconnecting each of the one or more die to the carrier chip;
preparing a curing resin by loading the curing resin with magnetic particles, thereby creating a magnetic particle-loaded curing resin;
applying the magnetic particle-loaded curing resin along at least one edge of at least one of the one or more die;
subjecting the one or more die and the carrier chip to a vacuum to remove at least a portion of air trapped in a space between the one or more die and the carrier chip; and
subjecting the one or more die and the carrier chip to a multiaxial magnetic field to drive distribution of the magnetic particle-loaded curing resin throughout the space between the one or more die and the carrier chip.
2 . The method of claim 1 , wherein the step of preparing a curing resin includes at least one of:
sonication to reduce the number of magnetic particle clumps; or
vortex mixing process to disperse the magnetic particles within the curing resin.
3 . The method of claim 1 , wherein the magnetic particles include one or more magnetically soft materials.
4 . The method of claim 1 , wherein the magnetic particles include at least one of iron, nickel, iron oxide, or stainless steel.
5 . The method of claim 1 , wherein a size of the magnetic particles is less than or equal to approximately 33% of a size of a gap between the carrier chip and the one or more die.
6 . The method of claim 1 , wherein the magnetic particles comprise between approximately 5 vol. % and 20 vol. % of the magnetic particle-loaded curing resin.
7 . The method of claim 1 , wherein a first portion of the magnetic particles have a first size, and a second portion of the magnetic particles have a second size, the second size being approximately 10% or less of the first size.
8 . The method of claim 1 , wherein the step of preparing a curing resin further includes loading the curing resin with nonmagnetic particles.
9 . The method of claim 8 , wherein the nonmagnetic particles are adapted to cause a coefficient of thermal expansion of the magnetic particle-loaded curing resin to more closely match a coefficient of thermal expansion of the carrier chip or the one or more die.
10 . The method of claim 8 , wherein at least one of:
a size of the nonmagnetic particles is less than or equal to approximately 33% of a size of a gap between the carrier chip and the one or more die; or
the nonmagnetic particles comprise between approximately 20 vol. % and 30 vol. % of the magnetic particle-loaded curing resin.
11 . The method of claim 1 , wherein the step of applying the magnetic particle-loaded curing resin includes applying the magnetic particle-loaded curing resin along at least a portion of all sides of each of the one or more die.
12 . The method of claim 1 , wherein the step of subjecting the one or more die and the carrier chip to a vacuum employs a vacuum oven.
13 . The method of claim 1 , wherein the step of subjecting the one or more die and the carrier chip to a vacuum further includes subjecting the one or more die and the carrier chip to a thermal process.
14 . The method of claim 1 , wherein the multiaxial magnetic field includes three orthogonal magnetic field components.
15 . The method of claim 14 ,
wherein a first and a second of the three orthogonal magnetic field components each includes a respective AC magnetic field component; and
wherein a third of the three orthogonal magnetic field components includes a DC magnetic field component.
16 . The method of claim 14 ,
wherein a first, a second, and a third of the three orthogonal magnetic field components each includes a respective AC magnetic field component; and
wherein the third of the three orthogonal magnetic field components further includes a DC magnetic field component.
17 . The method of claim 14 , wherein a phase angle exists between a first and a second of the three orthogonal magnetic field components.
18 . The method of claim 14 , wherein a ratio of a frequency of a first of the three orthogonal magnetic field components and a frequency of a second of the three orthogonal magnetic field components is a rational number greater than 1.
19 . The method of claim 14 , wherein a ratio of a frequency of a first of the three orthogonal magnetic field components and a frequency of a second of the three orthogonal magnetic field components is within 3% a rational number greater than 1.
20 . The method of claim 1 , wherein a frequency of each magnetic field component of the multiaxial magnetic field is less than or equal to approximately 1 KHz.