Metal fusion bonding – Means to apply vibratory solid-state bonding energy to work
Reexamination Certificate
2000-02-23
2001-08-28
Dunn, Tom (Department: 1725)
Metal fusion bonding
Means to apply vibratory solid-state bonding energy to work
C228S008000, C073S579000, C073S581000
Reexamination Certificate
active
06279810
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a piezoelectric sensor for measuring bonding parameters, such as impact force, ultrasonic amplitude and bonding time, in the bonding of components within integrated circuits. The invention also extends to ultrasonic bonding apparatus incorporating such a sensor.
BACKGROUND OF THE INVENTION
In the manufacture of microelectronics products and integrated circuits bonding is a mechanical process that also produces an electrical interconnection between two components (for example between an integrated circuit component and the printed circuit board) by means of a metallic bonding wire (for example aluminium, gold or copper). The bonding process generally involves two stages. In the first stage an ultrasonic bonding apparatus touches down on the contact pad and pre-deforms the bonding wire. Then, in a second sage, a burst of ultrasonic energy is applied by the bonding apparatus. In this second stage the bonding apparatus is vibrated and begins with the tool to move together with the wire and removes an unbondable oxide layer (if any) on the surface. Then the wire is caused to deform after an absorption of ultrasonic energy and pressure and a metallurgical bond is formed at the wire-pad interface.
In both these stages there are parameters tat must be monitored. In the first stage the force of impact and the subsequent force applied to the wire needs to measured and monitored for bond quality assurance purposes. In the second stage, the amplitude of the ultrasonic burst and its duration (known as bonding time) both have a significant effect on bond quality and must therefore also be monitored. An optimized range of these bonding parameters which can guarantee the required quality is usually determined for each different type of bonding machine. To ensure that the parameters remain within this range, however, they must be constantly monitored.
PRIOR ART
U.S. Pat. No. 4,854,494 describes a method for monitoring the bonding parameters by using a piezoelectric sensor that is attached to an ultrasonic concentrator to measure the ultrasonic amplitude, and by using wire strain gauges to monitor the bonding force. In this design, however, two separate sensors are required for monitoring the bonding parameters.
U.S. Pat. No. 4,040,885 describes an apparatus for nondestuctively monitoring the bonding quality of an ultrasonic bonding system by comparing the vibration amplitude of the bonding tool in a freely vibrating (ie no load) condition and during the bonding operation.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a simple apparatus for measuring the bonding parameters and which can be formed as an integral part of the ultrasonic bonding apparatus so that it can readily be transported from one bonding apparatus to another.
According to the present invention there is provided a sensor for measuring bonding parameters in an ultrasonic bonding operation, said sensor comprising piezoelectric material located adjacent an ultrasonic transducer of an ultrasonic bonding apparatus, said sensor having a first output for sensing at least one first bonding parameter, and a second output for sensing at least one second bonding parameter.
By this men a single sensor can be provided which may be used to measure a number of bonding parameters at the same time. Furthermore by locating the sensor adjacent the ultrasonic transducer, the sensor may be formed integrally with the bonding apparatus such that it may be moved with the bonding apparatus from one bonding machine to another. In addition, by providing different signal outputs for different parameters, the outputs may be optimised in their signal response for the different parameters being measured.
In a preferred embodiment of the invention the first output is for sensing impact force, and the second output is for sensing ultrasonic amplitude and bonding rime. Preferably the first output comprises a pair of electrodes oriented in a direction parallel to the direction of the applied impact force which is along the direction of motion of the bonding tool, and wherein the second output comprises a pair of electrodes oriented transversely to the direction of the applied impact force.
The electrodes may be applied to a single piece of piezoelectric material This piece of piezoelectric material may be generally annular in shape and the electrodes may be disposed about the piezoelectric material at 90° intervals. However, other shapes for the piezoelectric material, for example square or rectangular, may also be possible.
Preferably signal processing means are provided for processing the signals output from the fist and second outputs, the processing means comprising means for separating the two signals. The signal processing means may comprise a low pass filter for the signal output from the first signal output, and a high pass filter and a harmonic filter means for the signal output from the second signal output. The signal processing means may also comprise signal amplifying means.
It will also be understood that the present invention also extends to bonding apparatus incorporating such a sensor, and accordingly therefore viewed from another broad aspect the present invention provides ultrasonic bonding apparatus comprising, an ultrasonic transducer and an ultrasonic concentrator, said apparatus flier including a sensor comprising piezoelectric material located adjacent said transducer, said sensor having a first output for sensing at least one first bonding parameter, and a is second output for sensing at least one second bonding parameter.
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Chan-Wong Lai Wa
Cheung Yiu Ming
Chiu Siu San
Or Siu Wing
ASM Assembly Automation LTD
Burns Doane Swecker & Mathis L.L.P.
Dunn Tom
Johnson Jonathan
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