Metal fusion bonding – Process – With condition responsive – program – or timing control
Patent
1988-10-05
1990-05-15
Godici, Nicholas P.
Metal fusion bonding
Process
With condition responsive, program, or timing control
228179, 228 45, 228 9, 228103, B23K 2000, B23K 3100
Patent
active
049250833
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In microelectronics, bonding generally refers to the interconnection of components by glueing or welding as distinguished from conventional soldering in which the connections are made by means of solder (mostly a tin-lead-alloy). A distinction is made between chip (die) bonding methods for mounting a component on a supporting substrate and wire bonding methods for connecting the component leads to the substrate or for connecting the contact pads of component and substrate by means of fine wires. The present invention deals with the last-mentioned method, in particular with ball bonding, as it is called. The various steps of ball bonding are as follows: therewith and including a flame-scarfed bond ball from an upwardly retracted starting position to a first bonding location; and/or ultrasonic assistance; defined bonding pressure and/or ultrasonic assistance; position, breaking the bond wire by subjecting it to a pulling force by means of a clamp engaging the bond wire, and subsequent upward retraction of the bond capillary to the starting position; and
In view of the progressively increasing miniaturization of components and thus of the bonding or contact pads the size of the ball must be correspondingly reduced so as to prevent short-circuits between adjacent bonding or contact pads. Moreover, there is a demand for the mentioned "mini-balls" to be accurately dimensioned. These two prerequisites cannot readily be satisfied with the described conventional method. This is due to the fact that with conventional ball bonding the following phenomena are not taken into account: the unloaded state after welding to the second bonding pad due to internal stresses.
Due to the fact that the specified phenomena are not taken into account, a highly undefined tail length and a correspondingly undefined ball size are obtained with conventional ball bonding.
SUMMARY OF THE INVENTION
Accordingly, the present invention is based on the object of providing a ball bonding method of the specified kind and an apparatus for performing said method, by means of which the ball size can be accurately controlled, especially also in case of so-called mini-balls.
The specified object is solved in a surprisingly simple way by a method and apparatus wherein a voltage is impressed between a clamp for raising the wire and the second pad to provide a measure that the clamp is raised to break the wire. In accordance with another feature of the invention, after the wire breaks, it is moved down to reference abutment, which may be a flame scarfing device, and then raised a set distance to establish a predetermined spacing from the flame-scarfing device.
In addition to solving the specified object, the methods according to the present invention additionally provide further information. When an electrical connection between the wire clamp and the bonding pad or lead frame cannot be made as soon as the wire clamp is in wire clamping position, there is no tail connection to the second bonding pad or the bond wire has already broken without the wire clamp becoming active. In this case the bonding apparatus is preferably deenergized, and the failure is investigated and eliminated whereupon the bonding apparatus is reset.
In the method including a predetermined lowering of the bond head, if contact between the free end of the bond wire and the flame-scarfing means still cannot be detected after the predetermined basis, the tail length is too short to form a sufficiently dimensioned ball. In this case also the bonding apparatus is preferably deenergized, the failure is investigated and eliminated, whereupon the bonding apparatus is reset.
Thus, the methods in accordance with the present invention permit additional failure signals which cannot be obtained when operating in accordance with the conventional methods.
Other features of the method including moving the clamp and wire in steps and counting the steps moved in breaking the wire. After the wire breaks, the counting of the steps is reset to zero.
BRIEF DESCRIPTION
REFERENCES:
patent: 3863827 (1975-02-01), Foulke et al.
patent: 3941486 (1976-03-01), Tyler
patent: 4109846 (1978-08-01), Pennings et al.
patent: 4213556 (1980-07-01), Persson et al.
patent: 4555052 (1985-11-01), Kurtz et al.
patent: 4586642 (1986-05-01), Driebelbis et al.
Birgel Walter
Farassat Farhad
Emhart Deutschland GmbH
Godici Nicholas P.
Heinrich Samuel M.
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