Method and device for controlling the generation of ultrasonic wire bonds
A method for generating a wire bond between a wire and an electrical contact member is provided. The method comprising the steps of: pressing a first surface of a portion of the wire against a second surface of the electrical contact member with a first force while vibrating the portion of the wire along the second surface in order to generate a bond; measuring the time dependent vibration amplitude of the portion of the wire at a number of discrete time steps during the generation of the bond; measuring the time dependent deformation of said portion of the wire due to said applied first force and said vibration at a number of discrete time steps during the generation of the bond; and generating a time dependent first signal from at least said vibration amplitude and said deformation at a number of discrete time steps during the generation of the bond that is a direct measure of the stability of the bond at the respective time step.
1. Method for generating a bond between a wire and an electrical contact member, comprising the steps of:
pressing a first surface of a portion of the wire against a second surface of the electrical contact member with a first force while vibrating the portion of the wire along the second surface in order to generate a bond,
determining the time dependent vibration amplitude of the portion of the wire during the generation of the bond,
determining the time dependent deformation of said portion of the wire due to said applied first force and said vibration during the generation of the bond, and
generating a time dependent first signal using at least said amplitude and said deformation during the generation of the bond that represents a minimal force that has to be applied to the bond along or across the second surface in order to physically break the bond at a considered time during generation of the bond, wherein an optimal first signal is determined before the generation of the bond, wherein the optimal first signal defines an optimal bond during generation of said optimal bond and at least one control parameter is adjusted during generation of the bond depending on the difference measured between said optimal first signal and said first signal during generation of the bond.
2. Method according to claim 1 , wherein the at least one control parameter is adjusted so as to decrease the absolute value of the difference between the optimal first signal and the measured first signal during generation of the bond.
3. Method according to claim 2 , wherein the control parameter is adjusted such that a minimum required first signal that is needed in order to form an optimal bond is achieved during generation of the bond.
4. Method according to claim 1 , wherein the at least one control parameter is one of:
a vibrational energy per unit time,
a norm and/or direction of the first force.
5. Method according to claim 1 , wherein, the time dependent first signal represents the minimal shear force that has to be applied to the bond in order to physically break the bond at a considered time during generation of the bond.
6. Method according to claim 1 the optimal first signal represents the minimal shear force that has to be applied to an optimal bond in order to physically break the optimal bond at a certain time during generation of said optimal bond.
7. Method according to claim 1 , wherein the vibration amplitude of the portion of the wire is determined by measuring the corresponding vibration amplitude of a tool that is used for generating said vibration of said portion of the wire.
8. Method according to claim 7 , wherein the vibration amplitude of the vibration of the tool is measured by means of a laser.
9. Method according to claim 7 , wherein the vibration amplitude of the tool is measured under a predefined angle with respect to the direction of the first force.
10. Method according to claim 9 , wherein the deformation of the portion of the wire is extracted from the vibration amplitude of the tool.
11. Method according to claim 7 , wherein, the vibration amplitude of the tool is determined by means of one of an inductive sensor, an acceleration sensor, and a force sensor.
12. Method according to claim 1 , wherein the generated bond is marked in case the difference between the optimal first signal and the first signal measured during generation of said bond surpasses a predefined value during generation of the bond, in order to automatically detect said marked bond among a group of generated bonds.
13. Method according to claim 12 , wherein generated bonds are examined, wherein marked bonds are detected and repaired.
14. Method according to claim 2 , wherein a frictional energy dissipated per unit time due to the interaction between the first surface of the portion of the wire and the second surface of the electrical contact member is measured during generation of the bond for controlling the at least one control parameter.
15. Method according to claim 2 , wherein a time dependent deformation energy for achieving the deformation of the portion of the wire is measured during generation of said bond for controlling the at least one control parameter during generation of the bond.
16. Method according to claim 1 , wherein a frictional energy dissipated per unit time due to the interaction between the wire and the second surface of the electrical contact member is measured during generation of said bond for determining a temperature dependent parameter characterizing the temperature dependency of the bond forming process.
17. Method according to claim 16 , wherein the parameter is one of a flow stress of the wire, a flow stress of the electrical contact member, an interatomic connection of the wire, and an interatomic connection of the electrical contact member.
18. Method according to claim 2 , wherein a second force being exerted by the tool via the portion of the wire on the second surface of the electrical contact member, wherein the second force is directed along the second surface, is measured during generation of the bond for controlling the at least one control parameter during generation of the bond.
19. A method according to claim 1 , wherein said minimal force is the minimal sheer force that has to be applied to the bond along or across the second surface in order to physically break the bond at a considered time during generation of the bond.