Conductive polymer film bonding technique

DETAILED DESCRIPTION Referring to FIG.
1, a portion of a substrate is shown at 11 with an array of contact pads 12 formed e.
g.
by standard printed circuit techniques.
The device chip or assembly 13 carries an array of bumps 14 which may be gold bumps or solder bumps as are standard in the art.
The ACF film is shown at 15 with conductive particles at 16.
In a typical interconnection process, e.
g.
flip chip on glass (FCOG), the glass substrate is of the order of 1-3 mm thick and the bonding areas 12 are portions of a metallization pattern, e.
g.
indium tin oxide, or aluminum.
The pitch of these pads in current technology is of the order of 50-200 .
mu.
m and the spacing between pads may be 20-50 .
mu.
m.
The bumps 14 in this illustration are gold bumps with dimensions corresponding to the contact pad array of the substrate in the x-y plane, and with a height (z-dimension) of typically 15-30 .
mu.
m.
The device package is square or rectangular with sides measuring typically in the 2-50 mm range.
Standard ACF materials are typically epoxies, and the conductive particles are typically gold-plated epoxy resin particles.
The films are generally 10-40 .
mu.
m thick and the conductive particles have an average diameter of 3-10 .
mu.
m.
The bonding operation is conventional and involves the application of heat to the surfaces being bonded, while pressing the surfaces together.
As suggested earlier the ACF bonding temperatures are typically above 200 degrees C.
She pressure depends upon the ACF material and usually is above 0.
5 tons per square inch of bump area, typically about 5 tons per square inch of bump area.
As seen in FIG.
2, after the bonding process has occurred, with the component assembly 13 and the substrate 11 thermocompressively bonded, the desired layer of conductive particles is depleted between the bumps 14 and pads 12 due to the migration of conductive particles out of the gap region due to the applied bonding force.
Under typical thermocompression conditions the polymer matrix which contains the conductive particles softens significantly, enough that fluid dynamics allows rapid migration of the conductive particles in the polymer but not enough that the pressure in the polymer is completely hydrostatic