JPH09198917A - Gold alloy thin wire for semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gold alloy thin wire whose deformation in sealing with resin is reduced, can manage well with improved construction with a narrower pitch and a longer span, and is suitable for high-density mounting on a circuit board. SOLUTION: A gold alloy thin wire contains 0.015-1.0wt.% Cu, 0.0002-0.02wt.% Ca, and gold and associated impurities inevitable as the remainder. To this, one or more of Pt, Pd, In is added in a total amount of 0.002-3.0 in wt.%. To the obtained mixture, one or more of Y, La, Ce is added in a total amount of 0.0003-0.03 in wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gold alloy thin wire for a semiconductor element used for bonding to electrically connect an electrode on a semiconductor element and an external lead.

[0002]

2. Description of the Related Art At present, a wire bonding method is mainly used for electrical connection between a circuit wiring electrode on a semiconductor element and an external lead. Recently, as semiconductors have become highly integrated and multifunctional, and the demands for smaller and thinner IC chips have also increased, there has been an increasing need for higher density semiconductor packaging. In order to increase the number of terminals and increase the number of pins, the inner lead portion recedes with respect to the silicon chip, so that the wire joining interval (span) tends to be long. When the span is a long span of 5 mm or more, it is necessary to strictly control the loop shape such as ensuring linearity and reducing variations. Further, with the increase in the number of pins, there is a demand for a narrower pitch in which the electrode spacing is reduced, a minimum pitch between wires of 100 μm or less is desired, and a thin wire is also desired. In order to achieve such a large number of pins and a narrow pitch, improvement of a bonding device, development of a wire excellent in looping property, and the like are being advanced.

[0003]

In the high density packaging of semiconductors, when the span becomes a long span of 5 mm or more, in order to cope with the increase in the number of pins of the wire and the narrow pitch, contact between adjacent wires, The most important issue is to suppress the occurrence of defects due to contact between the wire and the chip or inner lead portion. In the long span, various looping controls are performed to secure the loop height and prevent sagging, but there is a high probability that loop bending will occur during bonding. Further, when the wire is deformed and flows at the time of sealing with the highly viscous epoxy resin, the longer the span, the larger the flow amount, and thus the poor contact between the adjacent wires is likely to occur.

The wire tends to be thinned to realize a narrow pitch, and as expected from the fact that the strength decreases with the square of the wire diameter, the wire bends during loop formation and the resin flow of the wire. Will become even more serious. In order to reduce the pitch, it is necessary to reduce the ball diameter, and it becomes difficult to secure the bondability of the ball portion.
The effect of element addition in gold alloy thin wires has been investigated in consideration of thinning, bondability, and the like.
No. 109587 shows that Cu element is effective as an additional element, but in order to obtain a sufficient effect, 1
A content of up to 5% by weight is required, and at a high concentration, there is a concern that the shape of the ball portion will be defective and the ball portion will be cured. Also, regarding the addition of a predetermined amount of Cu element into a gold wire, the method described in JP-A-2-
As disclosed in Japanese Patent Publication No. 215140, the present invention relates to the effect of suppressing the compound growth at the Au / Al junction.

An object of the present invention is to provide a gold alloy fine wire for a semiconductor element, which is suitable for high density mounting and which is capable of reducing wire deformation at the time of resin encapsulation and corresponding to a narrow pitch and a fine wire.

[0006]

In view of the above points, the inventors of the present invention investigated the characteristics required as a wire suitable for high-density packaging, and found that the wire was formed especially during loop formation and during resin flow. We obtained the view that reducing deformation is the biggest technical issue. Furthermore, when the relationship between the addition of elements in the gold alloy thin wire and the loop linearity and resin flowability was studied, it was found for the first time that the combined addition of Cu and Ca was useful for suppressing the flowability. Further, as will be described later, addition of Pt, Pd, and In elements increases the strength of the heat-affected zone in the vicinity of the ball.
It has been found that the flow resistance during resin encapsulation is further improved by adding La and Ce.

That is, the gist of the present invention is as follows. (1) Cu is contained in the range of 0.015 to 1.0% by weight, Ca is contained in the range of 0.0002 to 0.02% by weight, and the balance is composed of gold and its unavoidable impurities. Fine wire for semiconductor devices. (2) Cu is contained in the range of 0.015 to 1.0% by weight, Ca is contained in the range of 0.0002 to 0.02% by weight, and one or two kinds of Pt, Pd and In are further contained. A gold alloy fine wire for a semiconductor device, characterized by containing the above in a total amount of 0.002 to 3.0% by weight, and the balance being gold and its unavoidable impurities.

(3) 0.015 to 1.0% by weight of Cu
In the range of 0.0002 to 0.0
It is contained in the range of 2% by weight, and further contains one or more of Y, La, and Ce in a total amount of 0.0003 to 0.03% by weight.
A gold alloy thin wire for a semiconductor device, characterized in that it is contained in the range of 10 and the balance consists of gold and its unavoidable impurities. (4) Cu in an amount of 0.015 to 1.0% by weight and Ca in an amount of 0.0002 to 0.02% by weight, and one or more of Pt, Pd, and In. In the range of 0.002 to 3.0% by weight in total, and one or more of Y, La, and Ce in 0.0 in total.
A gold alloy fine wire for a semiconductor device, characterized in that it is contained in the range of 003 to 0.03% by weight, and the balance comprises gold and its unavoidable impurities.

[0009]

The structure of the present invention relating to the gold alloy thin wire for semiconductor device will be further described below. To evaluate loop linearity and flowability during resin encapsulation, bonding is performed using a metal thin wire, the amount of deformation in the loop shape is measured, and the bonded sample is resin-encapsulated. It is necessary to measure the flow rate of The loop deformation or the flowability during resin encapsulation depends largely on the setting conditions or experimental conditions of the bonding equipment or resin encapsulation equipment, the type of encapsulation resin, etc. It is difficult to extract and evaluate only.

Therefore, with respect to the loop linearity and the flowability at the time of resin sealing, the mechanical properties of the thin metal wire were examined for correlation with tensile strength, elastic modulus, yield strength and the like. It was confirmed that the higher the loop linearity, the more the loop linearity was improved and the flowability during resin sealing was suppressed. Although it is necessary to take into account characteristic values such as elastic modulus, yield strength, and bending elasticity for rigorous analysis, tensile strength that can be easily measured as a method for evaluating the suitability of thin metal wires for narrow pitches and thinning. Will be adopted.

In order to increase the tensile strength of the gold alloy fine wire, it is effective to add Cu element and Ca element together. Although Cu alone increases the strength at room temperature, its effect is small. The addition of Cu alone did not satisfy the characteristics for high-density mounting. On the other hand, although it has been confirmed that the strength increases with the addition of Ca, an increase in the addition amount causes a defective shape at the time of forming the ball portion due to the oxidation of the Ca element. The upper limit of the addition amount is determined by the ball-forming property, and it is difficult to achieve sufficient strength for thinning by adding Ca alone.

Table 1 shows the effect of tensile strength due to the addition of Cu and Ca. After continuously annealing a wire having a wire diameter of 24 μm in a horizontal furnace, a tensile test of the wire was performed to show the breaking strength. In general-purpose metal thin wires for semiconductor devices, the breaking elongation is mainly in the range of 3 to 5%, so the annealing temperature was selected so that the elongation would be about 4%. It can be seen that the breaking strength is remarkably increased from about 30% to about 60% when both of them are contained at the same time as compared with the addition of an appropriate amount of Cu element or the addition of an appropriate amount of Ca element. From the viewpoint of the flow resistance of a thin metal wire in a long span with a wire length of about 5 mm, the tensile strength is 14
If it is at least gf, the result is that the flow can be reduced to such an extent that it does not pose a practical problem, and the combined addition of Cu and Ca in Table 1 satisfies the condition.

[0013] Although there are some unclear points about the mechanism of characteristic development by these elements, Cu element and Ca element interact with each other to cause precipitation or a compound phase in Au, whereby mechanical characteristics are improved. Seems to be improving.

[0014]

[Table 1]

The reason why the addition amounts of Cu and Ca are set in the above range is that the above effect is small when Cu is less than 0.015% by weight or Ca is less than 0.0002% by weight. On the other hand, if Ca is more than 0.02% by weight, defects such as shrinkage cavities are formed at the tip of the ball or the sphericity is deteriorated. If Cu is contained more than 1.0% by weight,
Since the working strength during wire drawing increases remarkably, the wire drawing die is abraded at the time of wire production, and the wire bending of the wire drawing material is likely to occur. Although this measure can be dealt with by performing intermediate annealing several times, the process is complicated.

Since the strength of a thin wire is proportional to the square of the wire diameter,
The thinner the wire diameter, the higher the strength of the thin wire is required to reduce the resin flow. The current mainstream wire diameter is 25-30μ
It is difficult to use a fine wire of m for a narrow pitch mounting of 80 μm or less. It is effective to use a fine wire containing Cu and Ca, which has improved strength, and has a wire diameter of 25 μm or less, which is thinner than the conventional material. In particular, it is desired to increase the strength by 20% or more with respect to 25 μm, and when the wire diameter is 23 μm or less, it is desired that the effect of increasing the strength by the combined addition of Cu and Ca is high.

Since the inner lead portions of the lead frame are thin for mounting at a narrow pitch, problems due to vibration during transportation tend to occur. From the viewpoint of vibration resistance, it is desirable that the strength of the neck part directly above the ball is high,
It is necessary to suppress the coarsening of recrystallized grains due to the influence of heat.
In addition to the addition of Cu and Ca described above, Pt, P
By containing one or more of d and In,
Crystals in the neck portion become finer and the strength of the neck portion increases. The effect of suppressing the recrystallization behavior is insufficient only by adding the element group of In, Pt, and Pd, and the effect of increasing the strength of the neck portion is enhanced by the synergistic effect of the inclusion of Cu and Ca. Here, the addition of Pt, Pd, and In is 0.00
If it is less than 2% by weight, the above effect is small, while 3.0% by weight.
Above this, the ball portion becomes flat and the sphericity decreases,
It is difficult to form small balls for a narrow pitch connection, and the balls are hardened, which causes damage to the silicon chips during bonding.

In the resin sealing step, the wire is deformed by injecting a highly viscous thermosetting resin at a high speed into the molding die heated to the range of 150 to 200 ° C.
The mechanical characteristics of the wire, especially the high temperature characteristics, dominate the resin flowability of the wire. 1 for Y, La, Ce
If one or more kinds are contained in the range of 0.0003 to 0.03% by weight, the high temperature strength of the wire is increased. However, the addition of Y, La, and Ce alone does not significantly improve the mechanical properties at room temperature, so that it is necessary to use Cu and Ca together. The total content of Y, La, and Ce is set to the above range because when it is less than 0.0003% by weight, sufficient high temperature characteristics cannot be obtained, and when it exceeds 0.03% by weight, shrinkage cavities at the time of ball formation are formed. This is because generation or deterioration of sphericity becomes a problem.

[0019]

EXAMPLES Examples will be described below. Using electrolytic gold having a gold purity of about 99.995% by weight or more, Table 2 and Table 3
(Continued from Table 2), Table 4 and Table 5 (Continued from Table 4) Gold alloys having the chemical composition shown in Table 4 are melt-cast in a melting furnace, and the ingot is subjected to rolling and drawing to obtain gold having a final wire diameter of 24 μm. After forming the alloy thin wire, continuous annealing was performed in the atmosphere to adjust the elongation.

Using a high-speed automatic bonder used for wire bonding, the gold alloy ball produced at the tip of the wire by arc discharge was observed with a scanning electron microscope. Those in which good bonding to the electrode on the semiconductor element, such as those in which the occurrence of the above is not observed, are indicated by Δ, and those in which good bonding is indicated by ○.

To evaluate the strength of the neck portion after loop formation, the lead frame and the semiconductor element to be measured are fixed by a jig, and then the central portion of the gold alloy thin wire after bonding is pulled to determine the tensile strength at the time of breaking the thin wire. The average value of 100 pull strengths was determined. The wire bending is observed by observing the wire bonded so that the bonding distance (span) at both ends of the wire is 4.5 mm from the upper direction substantially perpendicular to the semiconductor element, and the straight line connecting the wire both ends bonding part and the wire The distance of the perpendicular to the portion with the largest bend is shown by the average value of 80 pieces measured using a projector.

Regarding the measurement of the wire flow after resin encapsulation, after the lead frame on which the semiconductor element bonded so as to obtain a wire span of 4.5 mm is mounted is encapsulated with an epoxy resin using a molding device, , X-ray projection of the inside of the semiconductor element sealed with resin using a soft X-ray inspection device, the flow amount of the maximum wire flow portion was measured by the same procedure as the above-mentioned wire bending, and the average value was calculated. The value (percentage) divided by the wire span length was defined as the wire flow after sealing.

In Comparative Examples 1 to 4 of Tables 4 and 5, the wire flow at the time of resin sealing shows a high value of 5% or more, and there is a high possibility that defects will occur due to contact between adjacent wires. The wire bend is also 20 μm or more, which is a concern as a variation in loop shape. On the other hand, Examples 1 to 6 in Tables 2 and 3 relate to the gold alloy thin wire according to claim 1 of the present invention, and contain Cu in an amount of 0.015 to 1.0% by weight, Further, it has been confirmed that by containing Ca in the range of 0.0002 to 0.02% by weight, the resin flow is particularly reduced, and addition of an appropriate amount suppresses the amount to 4% or less. In Comparative Example 5 shown in Tables 4 and 5, the Cu content is more than 1.0% by weight, the wire drawing strength is high, the wear of the die is concerned, and the wire bending during wire drawing becomes remarkable, Intermediate annealing was required three times in the manufacturing process.

Examples 7 to 11 in Tables 2 and 3 relate to the fine gold alloy wire according to claim 2, and the pull strength is 7 gf.
It has been confirmed that the strength of the neck portion is improved because the fracture is always right above the ball portion. Further, it was confirmed that Examples 12 to 15 similarly relate to the gold alloy fine wire according to claim 3, and the resin flow is suppressed to a low value of 3% or less. Similarly, Examples 16 and 17 relate to the fine gold alloy wire according to claim 4, the pull strength is increased to about 8 gf, and it is confirmed that the resin flow is suppressed to a low value of 2.6% or less. Was done.

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

The fine gold alloy wire for semiconductor device of the present invention can reduce the wire bending at the time of bonding and the wire flow at the time of resin sealing, and can be applied to high density mounting of semiconductors, especially narrow pitch connection.

Claims (4)

[Claims] 1. Containing Cu in the range of 0.015 to 1.0% by weight and Ca in the range of 0.0002 to 0.02% by weight, with the balance being gold and its unavoidable impurities. A gold alloy thin wire for a semiconductor element, which is characterized by: 2. Cu is contained in the range of 0.015 to 1.0% by weight, Ca is contained in the range of 0.0002 to 0.02% by weight, and one or more of Pt, Pd and In, or A gold alloy thin wire for a semiconductor device, comprising two or more kinds in a total amount of 0.002 to 3.0% by weight, and the balance being gold and unavoidable impurities thereof. 3. Cu in an amount of 0.015 to 1.0% by weight, Ca in an amount of 0.0002 to 0.02% by weight, and one or more of Y, La, and Ce. A gold alloy thin wire for a semiconductor device, comprising two or more kinds in a total amount of 0.0003 to 0.03% by weight, and the balance being gold and its unavoidable impurities. 4. Cu in an amount of 0.015 to 1.0% by weight and Ca in an amount of 0.0002 to 0.02% by weight, and one or two of Pt, Pd and In. At least 0.002 to 3.0% by weight, and at least one of Y, La, and Ce at least 0.003 to 0.03% by weight. The balance is made of gold and its unavoidable impurities, and a fine gold alloy wire for semiconductor devices.