JPS6341215B2 - - Google Patents

Abstract

A method of wire-bonding comprises a first step (Fig. 3) of bonding the wire to a selected one of the electrodes of a semiconductor chip on a ceramic package and to a lead to be connected to the selected electrode. During this, the distance Dal from the highest starting position or home position A of an ultrasonic wedge bonding tool to the selected electrode and the corresponding distance Dfm to the corresponding lead are measured and stored. When bonding the remaining electrodes and leads, the speed and range of each movement of the tool is based on the measured distances to provide a desired motion of the tool (Fig. 4(a)). In particular, the tool is moved slowly into contact with the electrode or lead, as shown at C, only in ranges +/- DELTA alpha and +/- DELTA beta about the determined distances Dal and Dfm. With this method, it is possible to increase the speed of the bonding process because the times T1' and T2' for which the tool is moving slowly are less than the times T1 and T2 which would otherwise be taken. The quantities DELTA alpha and DELTA beta are based upon statistical determinations of the accuracy of manufacture of the components. A wire-bonder for performing this method is also disclosed and includes a memory store for controlling the rotational speeds and angles of a cam for effecting the requisite tool movements. <IMAGE>

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wire bonding method, and in particular, an object of the present invention is to speed up the vertical movement of a wedge (terminal for bonding) in ultrasonic wire bonding technology, and to increase the bonding speed. It is something to do.

In general, the ultrasonic wire bonding method uses ultrasonic energy to pressurize and vibrate a bonding wire against a bonded object while exposing the mutually fresh surfaces to perform solid phase bonding by plastic deformation. Therefore, if the bonding wire is deformed, such as crushed, before wire bonding, it will not be possible to bond with good bonding properties. It is necessary to bring them into contact and then perform bonding using ultrasonic vibration of the wedge.

For this reason, in the conventional ultrasonic wire bonding method, the vertical movement of the wedge during wire bonding is as shown in Figures 1a to 1b, in which the bonding wire is slowly lowered when the wedge approaches the object to be wire bonded. The wedge is lowered at a low speed so that the wire does not deform when it comes into contact with the object to be bonded.

In addition, in FIG. 1b showing the vertical movement profile of the wedge, A to D in the figure show the modes of the vertical movement speed of the wedge, where A shows the wedge in a normal position, B shows the wedge in a high-speed descending speed state, C indicates that the wedge is in a low-speed descending speed state, and D indicates that the wedge is in a high-speed rising speed state. Further, each point indicated by a to k indicates a point where the operating speed of the wedge changes.

However, in the conventional ultrasonic wire bonding method, the lowering operation of the wedge requires a long time, which is an obstacle to increasing the speed of bonding.

In the case of a ceramic package as the object to be bonded, this is due to variations in the precision of the ceramic and leads, variations in the depth of embedding of pellets in the bonding material, and variations in the depth of embedding of leads in glass. The variation in the latter is large, especially as much as ±0.3mm, and the bonding height between each bonded object differs greatly due to variation in component precision, so the variation in height becomes noticeable, and it is necessary to absorb this variation. As much time as possible (T ₁ in Figure 1,
T ₂ ), this is due to the fact that the wedge must continue to descend at a low speed.

As a countermeasure to this problem, it is possible to increase the lowering speed of the wedge or shorten the period of low-speed lowering, but in this case, the high-speed lowering of the wedge may cause the bonding wire to come into contact with the pellet or lead that is the object to be bonded. Such countermeasures naturally have their limits, as they lead to a loss of bonding properties and deteriorate bonding properties.

For this reason, it is necessary to take up a large amount of time for the wedge to fall during the vertical movement of the wedge, and this time becomes large, which becomes a hindrance to increasing the bonding speed.

On the other hand, the vertical movement mechanism of the wedge in conventional ultrasonic wire bonders moves the bonding arm to which the wedge is attached in one direction using a cam having a cam diagram that allows the wedge to move as shown in Figure 1. The wedge is moved up and down while rotating.

Therefore, in such a conventional wedge vertical movement mechanism, the width and speed of the vertical movement of the wedge are determined by the cam diagram and the rotation speed of the cam. To change the aspect, it is necessary to replace the cam with a cam of a different specification that has a corresponding cam diagram. Therefore, there is a drawback that the movement of the wedge cannot be easily changed and various types of bonding cannot be performed using one bonder.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wire bonding method that solves the problems caused by the conventional wire bonding method and allows high-speed wire bonding.

Another object of the present invention is to provide a wire bonding method in which the vertical movement of the wedge can be easily changed, various types of bonding can be performed with one bonder, and which can be automated. In order to achieve this purpose, the wire bonding method of the present invention deals with a plurality of electrodes of an element pellet and their electrodes, which have variations in height due to the downward movement of the bonding terminal that changes from high-speed operation to low-speed operation. In a wire bonding method in which a plurality of external conductive leads are connected with wires in consideration of variations in the height positions of a plurality of electrodes of the element pellet, during the connection,
detecting the height of the electrode by detecting that the terminal lands on the electrode of the element pellet;
Based on the detected height of the electrode and the variation in the height position of the plurality of electrodes of the element pellet,
determining a transition timing from high-speed operation to low-speed operation in the downward movement of the terminal such that the terminal changes from high-speed operation to low-speed operation at a position higher than the height of the detected electrode; The present invention is characterized in that bonding is performed by controlling a driving means for moving the terminal up and down so as to switch from high-speed operation to low-speed operation at the switching time. Hereinafter, the present invention will be specifically explained in detail using an ultrasonic wire bonding method which is a preferred embodiment of the present invention.

Figures 2a to 2b are views showing a dual-in-line type ceramic package which is an example of the object to be bonded. be. In the figure, 2
1 is a ceramic package body, 22 is a semiconductor element pellet provided with 1c, and the surface thereof is
There are 14 pad electrodes 22a to 22n, which are die-bonded to the ceramic package body 21 using a bonding material 23. 24a-2
4n is the 14 pad electrodes 2 in the pellet 22
These are leads corresponding to 2a to 22n, and are attached to the ceramic package body 21 by a low melting point glass 25.

The ultrasonic wire bonding method according to the present invention for wire bonding to this type of wire bonded object will be explained step by step.

(1) Vertical movement of the wedge set with a margin for the low-speed lowering time T ₁ and T ₂ of the wedge (see Figure 3)
Accordingly, the pad electrode 2 of the semiconductor pellet 22
2a and the lead 24a corresponding to the pad electrode 22a are interconnected with an aluminum wire serving as a bonding wire. In this case, the reason why a margin is provided for the low speed lowering times T ₁ and T ₂ of the wedge is that the positions of the pad electrode 22a and the lead 24a are not clearly known at this point.

In this case, the distance Dal from the initial position a of the wedge to the position l of the pad electrode 22a (distance until the wedge descends and lands on the pad electrode 22a) is measured;
After wire bonding, the distance Dfm from the raised positions e and f of the wedge to the position m of the lead 24a (the distance from which the wedge descends until it lands on the lead 24a) is measured.

(2) Individual pad electrodes 22a, 22b,......,
22n mutual height position variation value ±Δα
and individual leads 24a, 24b, ......, 2
The value ±Δβ of the mutual height position variation of 4n is selected as the positional variation to be suppressed within one bonding target body based on the component accuracy and assembly accuracy of the bonding target body. Then, the low-speed operating range when the wedge descends relative to the pad electrode is defined as the area of ±Δα centered on the Dal position, with the height of the wedge as the range of low-speed operating when the wedge descends relative to the lead. The height of the wedge is defined as an area of ±Δβ centered on the position of Dfm, and the vertical motion profile of the wedge is determined based on this definition. This profile is illustrated in FIG. 4a.

(3) Move the wedge according to the vertical movement profile of the wedge as shown in Figure 4a,
The pad electrodes 22b and the leads 24b are wire-bonded with an aluminum wire, and then the pad electrodes 22c, 22
d, ......, 22n and the corresponding lead 2
4c, 24d, .
FIG. 4b is a diagram showing the vertical movement profile of the wedge in wire bonding as described above.

(4) Next, when wire bonding is performed on each wire-bonded body in sequence, the steps (1) to (3) described above are performed.
This will be done through the following procedures.

As is clear from the above, in the ultrasonic wire bonding method according to the present invention, the low-speed lowering time of the wedge (T ₁ ', T ₂ ' in Fig. 4) is short, so that the vertical movement of the wedge is short. The time required is extremely short and high-speed bonding is possible. The reference position for the wedge to be lowered is determined in advance for each object to be bonded.
This is because Dal and Dfm are measured in advance, and based on these measurements, the range of low-speed descending motion when descending relative to the pad electrode and lead of the wedge is determined. In addition, the values ±Δα and ±Δβ selected as wedge height variations are based on the component accuracy and assembly accuracy of each bonding target, so the bonding between each bonding target is This is because the height variation is eliminated and the value is small.

That is, in the ultrasonic wire bonding method according to the present invention, as shown in _FIG . 22b, 22c, ......, 2
2n and the corresponding leads 24b, 24c,...
_{The time} required for wire bonding with _. be. On the other hand, the time required for wire bonding to one bonded object using the conventional method is nt ₁ . Therefore,
In the present invention, compared to the conventional method, the time required to wire bond one bonded object is nt ₁ - {t ₁ + (n-1) t ₂ } = (n-1) (t ₁ −
t ₂ ) and, as mentioned above, T ₁
+T ₂ ≫T ₁ ′+T ₂ ′, so t ₁ ≫t ₂ ,
The present invention can significantly shorten the wire bonding time, making it possible to perform high-speed wire bonding.

Next, the ultrasonic wire bonder according to the present invention will be explained.

FIG. 5 is a schematic view showing an ultrasonic wire bonder for carrying out the wire bonding method of the present invention, and in particular is a view showing the vertical movement mechanism of the wedge. In the figure, 1 is a wedge that is a bonding terminal, and an aluminum wire 2 that is a bonding wire is led to the tip of the wedge. Reference numeral 3 denotes a horn to which an ultrasonic vibrator is connected, which is moved up and down by the rotation of a cam 5 through a horn support 4, thereby moving the wedge up and down.

6 is a drive motor that rotates the cam 5. 7
is an XY table for moving the wedge back and forth, right and left, 8 is a body to be bonded, and 9 is a support base for supporting the body 8 to be bonded.

10 is a wedge landing detector, and a horn support 4
The wedge 1 is electrically connected to a lever 11 which is electrically insulated from the bonding target 8. When the wedge 1 descends and comes into contact with the bonded object 8, the lever 11 separates from the grounded cam and the lever voltage increases. It is possible to detect the state when the bonding object 8 lands (contacts) on the bonding target body 8.

The cam 5 has a cam diagram as shown in FIG. 7, and the relationship between rotation angle and cam lift is linear.

Further, this wire bonder is equipped with a control mechanism section as shown in FIG. This control mechanism section is
It is capable of controlling the vertical movement speed and amount of movement of the wedge, and includes a motor 6, a rotary encoder (for detecting the rotation angle) 12 and a tachometer generator (for detecting the rotation speed) 13, which are directly connected to the motor 6. It has a mechanical circuit and an electric circuit for controlling it, that is, a memory circuit 14 capable of storing rotation angle command data, a rotation angle determination circuit 15, a speed control circuit 16, a motor driver circuit 17, and when bonding wedges, etc. The main element is a timer 18 that can be stopped as appropriate.

Therefore, if the vertical movement speed and movement amount of the wedge 1 corresponding to the rotation angle of the control cam 5 are stored in the memory 14, this control mechanism section will control the motor 6 according to the command from the memory 14. , and correspondingly rotates the cam 5 to move the wedge 1 up and down at a desired high-speed descending speed, low-speed descending speed, and rising speed, and to stop the operation of the wedge 1 through a timer 18. It is.

The operation of this type of ultrasonic wire bonder will be explained step by step with respect to the manner in which wire bonding is performed on the objects to be bonded shown in FIGS. 2a to 2b.

(1) By vertically moving the wedge 1 (see Fig. 3), which is set with a margin for the low-speed lowering times T ₁ and T ₂ of the wedge 1, the pad electrode 22a of the semiconductor pellet 22 and its pad electrode 22a are matched. The aluminum wires 2 interconnect the leads 24a. In this case, the low speed lowering time T ₁ of wedge 1,
At this point, allowing T ₂ a margin is as follows:
This is because the positions of the pad electrode 22a and the lead 24a are not clearly known.

During this wire bonding, the wedge landing detector 10 detects that the wedge 1 descends and contacts the pad electrode 22a, and the output of the rotary encoder 12 at this time is stored in the memory 14 inside the control section. Similarly, the wedge landing detector 10 detects that the wedge 1 has descended and made contact with the lead 22a, and the output of the rotary encoder 12 at this time is stored in the memory 14 inside the control section.

This information is obtained by measuring the distance Dal until the wedge descends and lands on the pad electrode 22a, and after wire bonding to the pad electrode 22a, the wedge 1 in the stopped state descends again and lands on the lead 24a. Distance to Dfm
This corresponds to measuring .

(2) Individual pad electrodes 22a, 22b,......,
22n mutual height position variation value ±Δα
and individual leads 24a, 24b, ......, 2
The value ±Δβ of the variation in the mutual height positions of 4n is selected based on the component precision and assembly precision of the object to be bonded. Then, the low-speed operation range when wedge 1 descends relative to the pad electrode is set to the wedge height, and ±
The low-speed operation range when wedge 1 descends relative to the lead is defined as the area of ±Δβ with the wedge height as the center, and the range of wedge 1 based on this specification is A vertical motion profile is determined and stored in the memory circuit of the control section. This profile is illustrated in FIG. 4a.

(3) When the memory circuit outputs a signal according to the wedge vertical movement profile described above, the motor 6
rotates accordingly. By this operation, the wedge 1 is moved up and down, and the pad electrodes 22b, 22c, ..., 22n and the leads 24b, 24c, ..., 24 corresponding to the electrodes are sequentially moved up and down.
By wire bonding n with an aluminum wire, wire bonding of one ceramic package, that is, one body to be wire bonded, is completed.

(4) Next, when wire bonding is performed on each wire-bonded body in sequence, the steps (1) to (3) described above are performed.
Perform the following operations.

As is clear from the above, the ultrasonic wire bonder for carrying out the present invention has the following features.

(1) The vertical motion of the wedge can be easily changed by the wedge vertical motion profile stored in the memory circuit.

(2) Since the vertical movement of the wedge requires only the exchange of information stored in the memory circuit, and therefore can be easily changed, various types of bonding can be performed with one bonder.

(3) Wire bonding can be performed in accordance with the wire bonding method according to the present invention, and the wire bonding operation can be automated.

(4) Since wire bonding can be performed in accordance with the wire bonding method according to the present invention, high-speed wire bonding can be performed.

The present invention is not limited to the ultrasonic wire bonding method, but can also be applied to wire bonding methods such as thermocompression bonding.

[Brief explanation of the drawing]

Figures 1a to 1b are diagrams showing the vertical movement profile of the wedge in the conventional ultrasonic wire bonding method, and Figures 2a to 2b are diagrams showing a ceramic package, which is a type of object to be bonded.
is a plan view, figure b is a vertical cross-sectional view taken along arrow AA' in figure a,
3 to 4 a to 4 b are diagrams showing vertical movement profiles of the wedge according to the present invention, and FIGS. 5 to 6
The figure is a schematic diagram showing an ultrasonic wire bonder according to the present invention, and FIG. 7 is a cam diagram of a cam according to the present invention. 1... Wedge, 2... Aluminum wire, 3...
...Horn support, 5...Cam, 6...Motor, 7
... XY table, 8 ... Bonded body, 9
... Support stand, 10 ... Wedge landing detector, 11
...Lever, 12 ...Rotary encoder, 13
...Tachometer generator, 14...Memory circuit, 1
5...Rotation angle determination circuit, 16...High speed control circuit, 17...Motor driver circuit, 18...Timer.

Claims (1)

[Claims] 1. Due to the descending movement of the bonding terminal that changes from high-speed operation to low-speed operation, the plurality of electrodes of the element pellet with variations in height position and the plurality of external conductive leads corresponding to the electrodes are connected to the plurality of electrodes of the element pellet. In the wire bonding method, which takes into account the variation in the height position of the electrode, the height of the electrode is determined by detecting that the terminal lands on the electrode of the element pellet during the connection. and the terminal changes from high-speed operation to low-speed operation at a position higher than the detected height of the electrode based on the height of the detected electrode and the variation in the height position of the plurality of electrodes of the element pellet. determining a transition timing from high-speed operation to low-speed operation in the lowering operation of the terminal so as to switch;
A wire bonding method characterized in that bonding is performed by controlling a driving means for moving the terminal up and down so that the terminal changes from high-speed operation to low-speed operation at the switching time determined as described above.