JPH02161737A - Wire bonding method - Google Patents

Abstract

PURPOSE:To eliminate causes of failures such as short-circuiting by arranging a chip and the surface to be bonded of an outer lead on the vertical upper part of a tool so as to face vertically downward. CONSTITUTION:A tool 1 moves at the lower position of a pad 4, and, at the position, moves vertically upward; a ball 6, of a wire 7 chip, which is previously formed by electric discharge fusion is made to abut against a pad 4 and subjected to thermocompression bonding by heating. After the tool 1 has descended to a specified position, a clamper 5 is closed; the tool 1 descends lower and cuts a wire 7 at the part where the strength is decreased by the thermocompression bonding on the lead 3. After the above bonding process is ended, discharge is carried out between a discharge electrode 8 and a wire 7, thereby, fusing the wire 7 tip and forming the ball 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in wire bonding methods for semiconductor devices.

[Conventional technology]

2. Description of the Related Art Conventionally, wire bonding for connecting pads of a chip of a semiconductor device, such as an IC, and external leads (hereinafter referred to as leads) has been performed by a thermocompression bonding method shown in FIG.

Figure 3 shows the wire bonding process in order from (a) to (
As shown up to g), the tool 1, which is a connection tool during this process, is placed vertically above, and the IC chip 2 and external leads 3 are placed vertically below.

In the figure, 5 is a clamper, 7 is a wire, and 6 is a pole at the tip of the wire 7.

First, the tool l is moved above the position of the pad 4 as shown in the same figure (
a)) At that position, descend vertically and press the pole 6 at the tip of the wire 7, which has been formed in advance by electric discharge melting, against the pad 4, heat it, and bond it by thermocompression (FIG. 2(b)).
).

Then, the tool l rises vertically upward ((C) in the same figure)
, Next, after the tool 1 has moved laterally above the position of the wire 3 (FIG. 3(d)), the tool 1 is lowered and the wire 7 is moved upward.
Press the tip of the lead 3 against the lead 3, heat it, and bond it by thermocompression (
Figure (e)).

Then, after the tool l rises to a certain position, the clamper 5 closes, and the tool 1 rises higher than that, thereby cutting the wire 7 at the part of the wire whose strength has decreased due to thermocompression bonding on the lead 3. (Figure (f)).

With step 1- above, the bonding work is completed, and for the next bonding work, a discharge is generated between the discharge electrode 8 and the wire 7, and the tip of the wire 7 is melted to form the pole 6 (as shown in the same figure). g)).

-L'y! The so-called loop shape, which is the shape of the wire 7 that is connected using the conventional wire bonding method, is
As shown in FIG. 4, when forming the ball 6 of the wire 7 directly in the pad 4, the recrystallized and hardened portion A and the lead 3
Cured by thermocompression with L 1. It is divided into a part 0, which is supported by a part 0, and a part B, which is supported between a part A and a part D.

In this loop shape - [, from the IC chip 2 to the wire 7
The height H below a certain level causes a short circuit, which affects the quality and is considered to be a particular problem.

As for height H, if part A of the straight part is maintained vertically, the minimum allowable height is determined by design-L, and the cause of the short circuit can be eliminated.

However, in reality, when the tool 1 is moving from the pad 4 to the lead 3, if a load is applied to the part A that pulls it in the direction of the lead 3, then the part A will move to the lead 3 as shown in FIG. Fall to the side.

A sufficient height H cannot be obtained.

Incidentally, the movement of the tool 1 in the wire bonding work is carried out by a so-called tracing movement by the rotation of a cam, and is carried out along a trajectory shown by an arrow in FIG. here,
After moving the tool l to a high position a directly above the pad 4, in the process of moving it to a position directly above the pad 4.

In order to weaken the load applied to the above-mentioned portion A in the direction of the lead 3, the angle θ between the portion B of the wire 7 to be paid out and the wire 7 inside the tool 1 is set to be large. This will cause tool 1
The frictional force acting between the wire 7 and the wire 7 is reduced, and no strong load is applied to the portion A.

Due to such a circuitous path of the tool 1, the wire 7 is unwound to a length greater than necessary, and its own weight causes it to hang downward as shown in FIG. As Tool 1 descends, Tool! The wire 7 existing between the tip of the lead 3 and the band 40 is reduced by being retracted, but even when it reaches the bonding position on the lead 3 side, the wire 7 that is excessively drawn out is sufficiently absorbed. I can't do it. Therefore, Bad 4 and Riichi 13
The total wire length used during the bonding period will be slightly in excess of the required minimum total wire length. Due to this excess wire 7, the actual loop shape is changed in the lead as shown in FIG. It had a sagging shape.

[Problems that Hatsu+1 is trying to solve] In the conventional wire bonding method, the total wire length from band 4 to lead 3 is the shortest length J, and the length T is longer than the required minimum length, as if J were connected in two series. There is.

Therefore, as shown in FIG.
．． However, as the number of pins in IC increases, problems arise as the width of the lead 3 becomes narrower.

FIG. 9 is a plan view showing a state where the IC chip 2 is wire-bonded. In this example, since the IC chip 2 is placed at a position that is different from the layer 3,
It is possible to obtain the support area C portion of the area. However, as shown in the back view of FIG. 1θ, when a deviation of Δy occurs when the IC chip 2 is die-bonded, the wire is deviated from the direction of the lead 3 and becomes oblique. At this time, since the width of the layer 3 is narrower, the wire 7 is connected to one route 3.
The support area must be the 01 part, which is shorter than the normal C part, to prevent it from twisting. As a result, the loop shape formed by the excess wire 7 with no support area becomes a curved curl shape as shown in the plan view of FIG. As shown in the figure, it becomes a sagging shape that hangs down from the bottom of the dome 3. Therefore, there was a drawback that it would cause defects such as short circuits.

In view of the above circumstances, an object of the present invention is to provide a wire bonding method that prevents the wire 7 from curling or sagging and eliminates causes of defects such as short circuits.

[Means to solve the problem]

In the present invention, the tip of the tool, which is a wiring tool, is arranged vertically upward, and the tool is arranged vertically upward so that the surfaces to be bonded of the IC chip and the external leads face vertically downward. I try to do bonding.

[Effect]

In the wire bonding method, the vertical relationship between the IC chip and the leads relative to the tool is reversed to prevent the wire from curling or sagging, thereby eliminating causes of defects such as short circuits.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of the operation of the wire bonding method according to the first embodiment of the present invention.

As is clear from the figure, tool l, which is a wiring tool, is
The tip is arranged so as to face vertically upward, and
The IC chip 2 and the external leads 3 are arranged vertically above the tool 1 so that the surfaces to be bonded face vertically downward.

Next, the operation will be explained, and the bonding sequence is as follows according to the conventional bonding method.

First, the tool l moves below the position of the pad 4 as shown in the same figure (
a)) At that position, the pole 6 at the tip of the wire 7, which has been formed in advance by electric discharge melting, is raised vertically upward and pressed against the pad 4, heated, and bonded by thermocompression (FIG. 2(b)).
).

Then, tool 1 descends vertically ((C) in the same figure)
, Next, after the tool 1 moves laterally below the position of the wire 3 (FIG. 1(d)), the tool 1 is raised and the wire 7
Press the tip of the lead 3 against the lead 3, heat it, and bond it by thermocompression (
Figure (e)).

Then, after the tool 1 is lowered to a certain position 4, the clamper 5 is closed, and the tool 1 is further lowered to a lower level, thereby cutting the wire 7 at the part of the wire whose strength has decreased due to thermocompression bonding on the lead 3. ((f) in the same figure).

With this, the bonding work is completed. For the first bonding work, a discharge is generated between the discharge electrode 8 and the wire 7, and the tip of the wire 7 is melted to form the pole 6 (see (g) in the same figure). ).

However, unlike traditional wire bonding methods,
Since the chip 2 and the external leads 3 are placed vertically above and the tool 1 is placed vertically below, the wire 7 is unwound excessively during the connection process from the pad 4 to the lead 3. Even if there is no area on 3 to support this excess wire 7, the excess wire 7
Since the wire 7 is pulled downward as shown by the arrow in FIG. 1 due to its own weight, the tension acting on the recrystallized hardened portion of the wire becomes weaker, as shown in position a in FIG. 6.
<There is no need to provide a large 1llf distance from the pad 4. Therefore, excessive wire 7 does not hang down from the surface of the lead 3 or curl between the pad 4 and the lead 3.

FIG. 2 is an explanatory diagram of the operation of the wire bonding method according to the second embodiment of the present invention. In this embodiment, since the pad 4 is not located at the edge of the chip, the distance from the pad 4 to the layer 3 is long.

In this second embodiment, an operation of closing the clamper 5 that moves up and down with the tool 1 while the tool 1 is rising to the lead 3 is added to the first embodiment.

Then, as shown in FIG. 2(C), if the clamper 5 is kept closed until the thermocompression bonding on the lead 3 side is completed, the total wire length to be wired will be the height at which the clamper 5 is closed. A predetermined excess can be made according to the following. The wire 7, which has exceeded the predetermined amount, is pulled downward, as shown in the figure (
Even if the distance from the edge of the IC chip 2 to the pad 4 becomes long as shown in d), if the distance is determined appropriately, the I
A sufficient distance H between the C chip 2 and the wire 7 can be obtained.

〔Effect of the invention〕

As explained above, in the wire bonding method of the present invention, the tip of the tool is arranged vertically upward, and the tool is arranged vertically upward so that the bonding surfaces of the IC chip and external leads face vertically downward. During the bonding process in which the wire is placed and bonded, the wire is constantly pulled downward by its own weight, and the tension acting on the recrystallized hardened portion at the tip of the wire is reduced. I can finish it. Therefore, there is an excellent effect that the wire does not become curled or sagging, and causes of defects such as short circuits can be eliminated.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the operation of the wire bonding method according to the first embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the wire bonding method according to the second embodiment of the present invention, and FIG. Diagram for explaining operation, Figure 4 is a plan view showing the loop shape after bonding, Figure 5 is a plan view showing the defective loop shape after bonding, and Figures 6 and 7 are tool trajectories according to the conventional wire bonding method. Fig. 8 is a front view of the loop shape obtained by the conventional wire bonding method, Fig. 9 is a plan view of the loop shape, Fig. 1θ is a plan view showing the curled state of the loop, and Fig. 11 shows the sagging state. FIG. l...Tool, 2...IC chip. 3...Lead. 4...Pad. 5... Clamper. 6...Paul. 7...Wire, 8...Discharge electrode. Patent applicant Susumu Uchihara (dl Figure 2 (b)) Patent attorney representing NEC Corporation

Claims (1)

[Claims] Bonding is performed by arranging the tip of a tool that is a wiring tool so as to face vertically upward, and arranging the tool vertically above so that the surfaces to be bonded between the IC chip and the external leads face vertically downward. Characteristic wire bonding method.