JPH0437138A - Formation of bump by wire bump - Google Patents

Abstract

PURPOSE:To prevent occurrences of scatter in heights of bumps and avoid some of remainders of tail which causes defective connection at the cutting part of a bump and then, form the bump which is compact and is stable in shape by making junctions of the pointed end of a metallic fine line with electrodes or the like by pressing while loading ultrasonic waves and further, cutting the junctions and the fine line. CONSTITUTION:In a method for forming a bump 6 which is provided between electrodes 2 that are formed on a semiconductor element 1 and an inner lead and further, connects both electrodes and the inner lead, the pointed end 3a of a fine line 3 is junctioned with the electrodes or the inner lead by pressing a part that is located along the longitudinal direction of the fine line 3 in the pointed end 3a of the metallic fine line 3 while loading ultrasonic waves. Then, junctions mentioned above and the fine line 3 are cut in such a way that, for example, the metallic fine line 3 made of Al, an alloy of Al, Cu, an alloy of Cu, Au, an alloy of Au or the like is inserted slantwise into the tool 4 of a wedge bonder and the pointed end of the fine line is located at a pressed face 5 that is formed at the lower face of the tool 4 and the pointed end 3a of the fine line 3 is junctioned with each electrode 2 by lowering the tool 4.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a wire bump that is provided between an electrode formed on a semiconductor element and an inner lead to form a bump that connects the two in wireless bonding. The present invention relates to a bump forming method according to the present invention.

"Conventional Technology" In recent years, with the increasing number of IC chips, thin metal wires have been used as a method for connecting IC chips to lead frames, replacing the wire bonding method that had been used up until now due to economic efficiency and connection reliability requirements. Wireless bonding methods that do not use

In this wireless bonding method, the chip (
It is necessary to form bumps (metal protrusions) on the electrodes or inner leads of semiconductor devices (semiconductor elements), and conventionally known methods for forming these bumps include drilling, cleaning, and etching.

This involves depositing a metal film as a barrier metal on the electrodes of the chip, forming a plating pattern using photoresist after this deposition, and using the metal film as one electrode.
Bumps are formed within the pattern by electrolytic plating.

Then, the unnecessary photoresist is removed and a new photoresist is applied over the hump to form a pattern for etching the barrier metal. Then, using this renost pattern as a mask, all exposed barrier metal on the chip is removed by etching, and finally the resist pattern is removed to form bumps.

However, in the above method, the processing steps such as plating and etching are complicated, so there are problems such as low yields and expensive equipment for these processings, resulting in high bump formation costs. Ta.

Therefore, as a bump forming method that solves the above problem, a method called a transfer bump method has been proposed. This involves aligning the bumps on the bump-forming substrate and the leads, applying heat and pressure to transfer the bumps to the lead side, and then transferring the bumps on the board and the ρ electrodes on the chip. The bump and the electrode A (electrode) are bonded together by aligning, applying pressure, and heating. This method does not require complicated processing steps such as plating and etching, so it is possible to reduce the bump formation cost to some extent. However, as chips become more multipolar and the distance between the electrodes becomes narrower, there are problems in that the above alignment becomes difficult and the yield decreases.

Therefore, a method called a pole bump method has been proposed as a bump forming method that solves the above problem. In this method, a pole is formed at the tip of a thin wire made of Au or Au alloy using an electric torch, and the pole is crimped to the l electrode of the heated chip while applying ultrasonic waves. The bump is formed by gripping the portion with a clamper and tearing it off from the pole. This method takes more time to manufacture than the transfer bump method described above, but it does not require much time, such as alignment of the bumps on the bump forming substrate and the leads, alignment of the bumps on the transferred leads and the AQ electrodes on the chip, etc. There is no need to carry out this process, which has the advantage of high yield.

"Problems to be Solved by the Invention" However, the pole bump method has the following problems.

In other words, ■The bump is formed by crimping the pole formed at the tip of the wire to the electrode and then tearing off the wire, so the height of the bump may vary depending on the size of the pole, the pressure during crimping, etc. In addition to this, a tail remains at the cut portion of the bump, which is the main cause of poor connection.

■Since the bump is formed by crimping the pole to the electrode, the bump may extend laterally and protrude from the electrode due to the pressure when the pole is crimped. Especially when the distance between the electrodes becomes narrow, this protrusion may cause Adjacent electrodes may interfere with each other.

When forming a bump on the ρ electrode, the tip is
Au
Intermetallic compounds are excessively produced between the pap and the Aρ electrodes, and Kirkendall voids are likely to occur, which poses a problem in the reliability of the joint.

This invention aims to solve the above problems.

[Means for Solving the Problems] In order to achieve the above object, the method for forming bumps using wire bumps according to claim 1 of the present invention provides a method for forming bumps using wire bumps in accordance with claim 1 of the present invention. The tip of the thin wire is joined to the electrode or inner lead by pressing the longitudinal portion of the thin wire while applying ultrasonic waves, and then this joined portion and the thin wire are cut. .

In the bump forming method according to claim 2, the tip of the thin metal wire is pressed against the electrode or inner lead of the semiconductor element by applying ultrasonic waves to the tip of the thin wire along the longitudinal direction of the thin wire. The part is joined to the electrode or inner lead, and further, the separation is performed by pressing a part separated from the first joint part to the proximal end of the thin wire by a predetermined distance to the electrode or inner lead while applying ultrasonic waves. The method is characterized in that the second joint portion is joined to the inner lead, and then this second joint portion and the thin wire are cut.

In the bump forming method according to claim 3, in the bump forming method according to claim 1 or 2, the thin wire material is AQl, 1 alloy, C
It is made of one of u, Cu alloy, and AuqAu alloy.

"Function" In the bump forming method using a wire bump according to claim 1 of the present invention, a portion of the tip of a thin metal wire along the longitudinal direction is pressed onto the electrode or the inner lead while applying ultrasonic waves. Since the bumps are formed by cutting this joint and the thin wire, the height of the bumps may vary, and tails remain at the cut portions of the bumps, which is the main cause of connection failures. In addition, bumps that are small and stable in shape are formed.

Further, in the bump forming method using wire bumps according to claim 2, in addition to the effect of claim 1, the first joint portion and the second joint portion
By appropriately adjusting the distance to the joint, the length of the bump can be freely adjusted.

Furthermore, in the method of claim 1 or 2, if the material of the thin wire is Aff or Aρ gold alloy, no intermetallic compound will be formed between the bump and the electrode, and Kirkendall voids will not occur.

"Example" Hereinafter, an example of the bump forming method using wire bumps of the present invention will be described.

(Embodiment corresponding to claim 1) In FIG. 1, the symbol l indicates a Si chip (semiconductor element). A large number of electrodes 2 and
・is formed. These electrodes 2 are made of an AI2 alloy containing about 1% by weight of Si in AC or AQ, and each electrode 2 is connected to an inner lead (not shown) via a bump. It has become.

Bumps for connection with inner leads are formed on the electrode 2 in the following manner.

That is, A, (1%'AQ alloy, CuSCu alloy, A
Thin wire made of metal such as u, Au alloy (diameter = about 30μπ)
3 is inserted obliquely into the tool 4 of the wedge bonder, and the tip of the thin wire is positioned on the pressing surface 5 formed on the lower surface of the tool 4.

Next, the tool 4 is lowered, and as shown in FIG.
The tip portion 3a of the thin wire 3 is joined to the electrode 2 by applying ultrasonic waves to the thin wire 3 via the tool 4 using an ultrasonic vibration source (not shown) provided in the thin wire 3.

Thereafter, as shown in FIG. 3, the tool 4 is raised and
By holding and pulling the thin wire 3 with a clapper (not shown), the thin wire 3 and the joint portion (tip portion) 3a are cut. As a result, bumps 6 are formed on the electrodes 2.

Then, the bumps 6 are formed on all the electrodes 2 by repeating the above steps on the electrodes 2 one after another.

Such a bump 6 is formed by pressing the longitudinal portion of the tip 3a of the thin wire 3 against the electrode 2, so unlike the conventional ball bump method, there may be variations in the height of the bump or There is almost no tail left at the cut end, which is the main cause of connection failure.

In addition, since it is possible to form a bump that is smaller than the conventional ball bump method and has a stable shape, the bump 6 does not protrude from the electrode and short-circuit with the adjacent electrode 6. This is effective for semiconductor devices where the space between .6 and 6 is narrow (about 50 μl).

Furthermore, since the bumps 6 can be formed at room temperature,
High reliability of joints when held at high temperatures.

In addition, when AQ thin wire is used as the thin wire for forming the bump 6, intermetallic compounds are not generated between the bump 6 and the AQ electrode, and Kirkendall voids are not generated, so the reliability of the joint is improved. is even higher.

In addition, in the above embodiment, the bump 6 was formed on the electrode 2, but
The inner lead may be formed using a method similar to that described above.

(Embodiment corresponding to claim 2) In FIG. 4, reference numeral 8 indicates an inner lead. These inner leads 8 are made of an alloy containing 1% by weight of Si in AC.
are connected to electrodes formed on the semiconductor element via bumps, respectively.

Bumps for connection with electrodes are formed on the inner lead 8 in the following manner.

That is, as shown in FIG. 5, AC, AQ gold alloy Cu
; Thin wire made of metal such as Cu alloy, Au, Au alloy (diameter:
(approximately 30 μm) 3 is inserted obliquely into the tool 4 of the wedge bonder, and the tip of the thin wire is positioned on the pressing surface 5 formed on the lower surface of the tool 4.

Next, as shown in FIG. 6, the tool 4 is lowered and the pressing surface 5 presses the longitudinal portion of the tip 3a of the thin wire 3 against the upper surface of the tip of the inner lead 8 at room temperature. The tip portion 3a of the thin wire 3 is joined to the inner lead 8 by applying ultrasonic waves to the thin wire 3 via the tool 4 using an ultrasonic vibration source (not shown) provided in the thin wire 3.

This portion will be referred to as a first joint portion 9.

Next, the tool 4 is once raised and moved to the proximal end side of the inner lead 8 by a predetermined distance, and then
As shown in FIG. 7, from the first joint portion 9 to the thin wire 3
The spaced apart portion 3b is joined to the inner lead 8 by pressing the spaced apart portion 3b spaced a predetermined distance away from the base end side of the inner lead 8 while applying ultrasonic waves in the same manner as described above. This portion will be referred to as the second joint portion IO.

Thereafter, as shown in FIG. 8, the tool 4 is raised again, and the thin wire 3 is clamped and pulled by a clamper (not shown), thereby cutting the thin wire 3 and the second joint lO. As a result, bumps 11 are formed on the electrode 2.

By repeating the above steps one after another on the inner leads 8, bumps 11 are formed on all the inner leads as shown in FIG.

Such a bump 11 is formed by pressing the longitudinal portion of the tip of the thin wire 3 against the inner lead 8, so unlike the conventional pole bump method, there may be variations in the height of the bump or There is almost no tail remaining at the cut portion, which is the main cause of connection failure.

Further, since the bumps 11 are formed on the inner leads 8 along the longitudinal direction, the bumps 11 are formed on the inner leads 11.
It does not protrude from the first joint part 9 and the second joint part 9.
The length of the bump II can be freely adjusted by appropriately adjusting the distance to the junction lO.

Furthermore, since the bumps I+ can be formed at room temperature, when forming the bumps 11, the inner leads 8 will not be affected by thermal strain and will not be misaligned. It is possible to reliably connect to the electrodes of the element via the bumps 11.

In addition, as a thin wire for forming the bump 11, +1
Or, when using AQ alloy thin wire, intermetallic compounds will not be generated between hump 1 and inner lead 8, or bump 11 and Aff electrode, and Kirkendall voids will not occur at the joint. Even more reliable.

In the above embodiment, the bumps 6 are formed on the inner leads 8, but they may be formed on the electrodes of the semiconductor element using a method similar to that described above.

(Experiment example) Next, an experimental example will be given to clarify the effects of this invention.

Bumps were formed on electrodes or inner leads of a semiconductor element using the method of claim 1 or 2 above. Table 1 shows the size and material of the electrodes of the semiconductor element, the pitch between adjacent electrodes, the material and size of the inner lead, and the diameter of the wire (thin wire) used to form the bump. Note that the one-point method shown in Table 1 refers to the method of claim 1, and the two-point method refers to the method of claim 2.

Table 2 also shows the material of the wire, the formation conditions when forming bumps, the output of the ultrasonic wave, the oscillation time of the ultrasonic wave, the load when pressing the wire against the electrode or inner lead, and the electrode and inner lead. The conditions for inner lead bonding, which connects these through bumps, include the output of ultrasonic waves, the oscillation time of ultrasonic waves, and the load when pressing the bumps against the electrodes or inner leads. Note that the bump formation conditions for the electrode and inner lead were the same.

Furthermore, as a comparative example, bumps were formed on the Aρ electrode by a conventional ball bump method. The bump formation conditions are as follows.

Wire: Au-1% Pd, 20 μmφ, ball diameter 260 μ11, ultrasonic output +701W.

Ultrasonic oscillation time: 15m5ec, load: 609, temperature: 250℃, semiconductor element size: 10ix101xxlO, 4ix
(t), ρ electrode size: 110 (C) XIIO (w
)Xl-1,5(t) μm.

Pitch of AQ electrode = 140 μm, material of A12 electrode: Al2-1 wt% Sis, and bump Nos. 1 to 24 formed by the method of this invention.
and Bump No. formed by the method of the above comparative example.
, 25 were evaluated. The results are shown in Table 3. In this table, each bump is 100 for each number.
The average value of the bump height for each No. and the absolute value of the difference between the height of the bump that deviates most from this average value and the average value are shown.

Regarding the evaluation of the lead tension test, as shown in Fig. 1θ, a fishhook-shaped hook 16 is provided at the tip of a small tension gauge 15, and this hook 16 is used to connect the inner lead 8.
and measure the shear mode and shear force. Then, when the shearing mode is appropriate and the shearing force is equal to or higher than a predetermined set value, the test is judged as a pass, and in other cases, the test is judged as a fail.

Here, the appropriate shearing mode is a key in which breakage occurs midway between the leads, for example, in Figures 11 to 11]
This is the mode shown in Figure 3. On the other hand, inappropriate shearing modes are the modes shown in Figures 4 and 15,
Figure 14 is likely to occur when the bonding conditions are inappropriate or the bump or lead is contaminated, and Figure 15 shows the cause of bump formation due to poor bonding between bump 6 (11) and electrode 2. Occurs in some cases. In addition, when performing the above-mentioned measurement, the semiconductor element 1 is fixed on the glass plate I8 with the double-sided adhesive tape 17.

Furthermore, regarding high-temperature storage evaluation, electrodes and leads were bonded via bumps for 50 minutes at a temperature of 250°C.
After being stored for 0 hours, the bonding strength was measured and the pass rate was examined.

Regarding the evaluation of noyotes, the number of bumps that protruded from the electrode of the semiconductor element to the adjacent electrode among the formed bumps was expressed as a ratio to the total number of bumps (1000).

As is clear from Table 3 below, the bumps formed by the method of the present invention are superior to the bumps formed by the conventional ball bump method in all evaluation items.

“Effects of the Invention” As explained above, the claims of this invention! The method for forming bumps using wire bumps described above provides the following effects.

■A bump is formed by pressing the tip of a thin metal wire along the length of the thin wire onto the electrode or inner lead while applying ultrasonic waves, and cutting the bonded portion and the thin wire. Therefore, unlike the conventional ball bump method, there is almost no variation in the height of the bumps, and there is almost no tail left at the cut portion of the bumps, which is the main cause of connection failures.

■Also, since it is possible to form smaller bumps than the conventional ball bump method, the bumps do not protrude from the electrodes and short-circuit with adjacent electrodes.
This is effective in semiconductor devices where the distance between adjacent electrodes is narrow (approximately 50 μm).

■Furthermore, since bumps can be formed at room temperature,
High reliability of joints when held at high temperatures.

■In addition, bumps can be formed at room temperature, so
When forming bumps on the inner leads, the inner leads are not misaligned due to thermal strain, so the inner leads can be reliably connected to the electrodes of the semiconductor element via the bumps. .

■In addition, if a thin wire made of Hachirō or AQ alloy is used to form the bump, the bump and Affl
Since intermetallic compounds and Kirkendall voids do not occur between the K electrodes, the reliability of the joint is even higher.

Further, according to the bump forming method using wire bumps according to the second aspect, the following effects are achieved in addition to the effects of the method according to the first aspect.

A portion of the tip of a thin metal wire along the length of the thin wire is pressed onto the electrode or inner lead while applying ultrasonic waves to the electrode or the inner lead, and then a predetermined portion is attached to the proximal end of the thin wire from this first bonded portion. The separated parts separated by a distance were joined by pressing the electrode or inner lead while applying ultrasonic waves, and then the second joint part and the thin wire were cut to form a bump, so that the first joint part By appropriately adjusting the distance between the bump and the second bonding portion, the length of the bump can be freely adjusted, and the bump can be applied to various semiconductor devices.

[Brief explanation of drawings]

FIGS. 1 to 9 are for explaining the method of forming a bump using a wire bump according to the present invention. 1 to 3 are for explaining the method of claim 1, in which FIG. 1 is a side view of the main part of a semiconductor element, and FIG. 2 is a main part showing a state in which thin wires are bonded to electrodes. FIG. 3 is a side view of a main part of a semiconductor device in which bumps are formed on electrodes, FIGS. 4 to 9 are for explaining the method of claim 2, and FIG. Plan view of main parts of inner lead, 5th
Figure 6 is a side view showing the state in which the first joint part is joined to the inner lead, Figure 7 is a side view showing the state in which the second joint part is joined to the inner lead, and Figure 8 is a side view showing the state in which the second joint part is joined to the inner lead. FIG. 9 is a side view showing a main part of the inner lead on which bumps are formed, and FIG. 9 is a plan view thereof. Figures 10 to 15 are for explaining the strained tensile test in the experimental example, Figure 10 is a side view for explaining the tensile test method, and Figures 11 to 13 are for explaining appropriate shear modes, respectively. FIGS. 14 and 15 are side views showing inappropriate shear modes, respectively. 1... Semiconductor element, 2... Electrode, 3...
・・・Thin line, 6, 11... Bump, 8...
...Inner lead, 9...First joint part, 10
...Second joint.

Claims (3)

[Claims] (1) A method of forming a bump that is provided between an electrode formed on a semiconductor element and an inner lead to connect the two, the bump being provided at the tip of a thin metal wire on the electrode or inner lead. The tip of the thin wire is joined to the electrode or the inner lead by pressing the longitudinal portion of the thin wire while applying ultrasonic waves, and then the joined portion and the thin wire are cut. Bump formation method using wire bumps. (2) A method of forming a bump that is provided between an electrode formed on a semiconductor element and an inner lead to connect the two, the bump being provided at the tip of a thin metal wire on the electrode or inner lead. By pressing the longitudinal portion of the thin wire while applying ultrasonic waves, the tip of the thin wire is joined to the electrode or inner lead, and further, the first
A spaced part spaced a predetermined distance from the joint part to the base end side of the thin wire is pressed against the electrode or inner lead while applying ultrasonic waves to join the spaced part to the electrode or inner lead, and then the second A method for forming a bump using a wire bump, the method comprising cutting the joint and the thin wire. (3) The material of the thin wire is Al, Al alloy, Cu, Cu alloy,
3. The method for forming a bump using a wire bump according to claim 1, wherein the wire bump is made of either Au or an Au alloy.