Journal of SMT Article

ULTRASONIC GOLD TO GOLD FLIP CHIP INTERCONNECT PROCESS USING LOW COST SUBSTRATES

Authors: Philip Couts and M. Kawahara
Company: TDK Corporation of America - Factory Automation Di
Date Published: 7/1/2007   Volume: 20-3

Abstract: Ultrasonic gold to gold interconnect (GGI) process provides a no lead, no flux, high throughput process solution, for precision small die attach. Gold to gold interconnect provides superior bond strength reliability and excellent electrical high frequency performance.

The ultrasonic GGI process has been used primarily for small die measuring 5 µm square with up to 30 bumps2. By expanding the machine capability to include a 100 Newton load force head and higher ultrasonic power capability, die with up to 100 bumps can be ultrasonically bonded.

Ultrasonic flip chip GGI is a high precision die attach process with mounting accuracy of +/- 8 µm to bond dies with gold stud bump diameters down to 40 µm. Ultrasonic bonding can be used for thin die attach with a minimum thickness of 80 µm. This is important to reduce the height profile of packaged devices. GGI flip chip process allows the bottom die surface to be array gold stud bumped. This process provides device package form factor size reduction of 50%~70% compared with perimeter gold wire bonding process.

Ultrasonic GGI bonding minimizes the stress to the die using low power ultrasonic energy and a heated bond table temperature of less than 150°C for die attach. Software control features include ultrasonic monitoring and bond tool monitoring that allows individual die verification of impedance of each die bond.

New low cost organic substrate materials and embedded passive component low temperature co-fired ceramic (LTCC) substrates can take advantage of the low temperature individual bonding capability of ultrasonic die bonders. The range of applications has been expanded from SAW filters and LED’s and can now include higher integrated CSP products used in sensor, medical, and mobile device packaging.

Flip chip ultrasonic GGI die attach provides a monolithic metal to metal interconnect method for precision small die bonding. Flip chip interconnect methods using metal and contact bonding methods are shown in (Figure 1)2.

Ultrasonic fl ip chip GGI process is a variant of gold wire bonding process (Figure 2). In ultrasonic GGI fl ip chip bonding, traditional wire bonds are replaced with gold stud bumps. Replacing the wire with stud bumps reduces the form factor of the device package. The die attach process is done using a ultrasonic flip chip die bonder where die mounting and bonding process occurs in a compact 1.69 meter2 equipment foot print. Ultrasonic GGI die bonding provides excellent productivity since die bonding process time is less than 500 msec.

Ultrasonic GGI individually bonds each die with high precision with a mounting accuracy +/- 8 µm.

High reliability flip chip ultrasonic GGI process is used for bump diameters of 40 µm and bump pitches to 60 µm in high volume production.



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