JPH02205642A - High strength copper alloy for lead frame - Google Patents

Abstract

PURPOSE:To obtain the high strength copper alloy for a lead frame having particularly excellent interface peeling resistance in soldering and strength- improving properties by work hardening by forming it with the compsn. contg. each prescribed amt. of Ni, Sn, Zn, Si and P and the balance Cu with inevitable impurities. CONSTITUTION:The high strength copper alloy for a lead frame is formed with the compsn. contg. 1.0 to 5.0% Ni, 0.5 to 2.5% Sn, 3.3 to 7.0% Zn, 0.2 to 1.0% Si, 0.03 to 0.3% P and the balance Cu with inevitable impurities. By the copper alloy, work hardening can be shown in addition to precipitation hardening and, as the result, strength superior to the one of high Ni alloy can be retained. Furthermore, interface peeling resistance in soldering can perfectly be prevented by suitably adding Zn to the copper alloy. Thus, the copper alloy is suitable for making a lead frame into copper alloy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-strength copper alloy useful for lead frames, which has particularly excellent solder interface peeling resistance and strength improvement properties through work hardening. It concerns high-strength copper alloys.

[Prior Art] Conventionally, 42 alloy (Fe-42%Ni) and Kovar, which have a low coefficient of thermal expansion and good adhesion and sealing properties with semiconductor elements and sealing materials, have been used as lead frame materials for semiconductor devices. (F
High nickel alloys such as e-29%Ni-17%Co) have been mainly used.

However, recently, the degree of integration of semiconductor devices has been increasing, and the number of devices with high power consumption has increased, and the demand for lead frame materials with good electrical conductivity and thermal conductivity has further increased.

The above high nickel alloy has a tensile strength of 65 kg.
r/ms", but the electrical conductivity is extremely low at about 3% lAC3, and cannot be said to be sufficient even in terms of thermal conductivity, which exhibits properties almost parallel to normal electrical conductivity.

Therefore, there is a growing trend to use copper alloys as lead frame materials, which have excellent electrical conductivity and thermal conductivity, instead of the high nickel alloys mentioned above. In addition to the above-mentioned excellent electrical and thermal conductivity, it also has the characteristics of being strong enough to withstand external forces applied during mounting and assembly into equipment, etc. in terms of reliability, and the ability to solder. Since soldering involves a process, it is considered an essential condition that soldering has excellent characteristics.

Even if an ordinary copper-based material is used as a lead frame material, it is insufficient in terms of strength, and some kind of strength improvement measure is required. There are two general methods for increasing the strength of metal materials: adding alloying elements and increasing the degree of cold working, and such measures have also been taken for lead frame materials.

[Problem to be Solved by the Invention J] In the case of copper alloys, the addition of certain alloying elements can make them precipitation-hardening alloys whose strength can be increased by heat treatment. However, relying on precipitation hardening may not provide sufficient strength, and in such cases it is necessary to add solid solution hardening alloying elements and also use hardening through cold working. be.

Further, in lead frames, outer leads are often soldered to a substrate.

In lead frame materials that use copper alloys to which alloying elements have been added to improve strength, after the above soldering, brittle peeling may occur over time at the soldered interface. , from the viewpoint of reliability, there is a large gap. The formation of such a brittle layer is thought to occur due to the diffusion of Cu as a material, the sn component in the solder, and additive elements, and
According to the findings by the y1 microanalyzer, there is an ε phase or η phase in the Cu-3n system at the interface between the copper alloy and the solder.
It has been confirmed that intermetallic compounds with high brittleness such as phases are formed by diffusion. Furthermore, it has been revealed that a migration layer of additive elements is diffused and formed at the interface (this is particularly noticeable in Fe, P, and Si), and that this causes the brittle peeling.

It is an object of the present invention to solve the problems of the prior art as described above, to improve the strength of copper-based alloys by applying extensive cold working, and to significantly improve the peelability at the soldering interface. The present invention aims to provide a novel high-strength copper alloy for lead frames.

[Means for Solving the Problems] The present invention provides Ni1.0 to 5.0% and Sn0.5 to 2.5%.
%, Zn3.3-7.0%, Si 0. 2-1.0
%, P0.003 to 0.3%, and the balance is Cu and unavoidable impurities.

``Effect I An alloy in which Ni and Si are added to Cu in the above range forms a precipitation-hardening alloy, which can be precipitation-hardened by heat treatment to improve strength.

However, when seeking sufficiently high strength, it is not appropriate to rely solely on precipitation hardening, and it is necessary to add solid solution hardening elements to improve the strength based on work hardening.

Sn is added as an element that can be work hardened and subjected to solid solution treatment, but if the content is less than 0.5%, the effect is insufficient, and if it exceeds 2.5%, the conductivity will decrease. The decrease becomes large, which is not preferable.

Regarding the Ni content, if it is less than 1.0%, the high strength effect will be low, and if it is more than 5.0%, the workability will deteriorate and the electrical conductivity will decrease, which is not preferable.

Regarding the Si content, if the Si content is 0.2% or less, the strength improvement effect will be small, and if it is 1.0% or more, the
As can be seen from the table, it is necessary to increase the amount of zn added to prevent the interface tl1M, which is undesirable because the conductivity decreases as a result.

zn, although the details of the reason are still unknown,
As will be explained in detail later, it is very effective in preventing interfacial peeling during soldering of copper alloys.

However, if this content is less than 3.3%, the effect of preventing peeling at the solder interface will be insufficient due to the relationship with the addition of Si, which is effective for precipitation hardening, which is undesirable, and if it is more than 7.0%, the electrical conductivity will decrease significantly. It's just as undesirable.

P is added as a deoxidizing agent to prevent Zn, which is effective in preventing interfacial peeling, from being consumed in deoxidizing, resulting in a reduction in the original interfacial peeling preventing effect. However, if the P content is less than 0.003%, the deoxidizing effect will be small (Zn consumption will be large, and if it is more than 0.3%, the processability will deteriorate, which is undesirable). .

[Example J The present invention will be described below with reference to Examples.

Table 1 shows the results of adding Zn in various amounts shown in the table to a copper alloy containing various elements in the amounts shown.
After plating the dots on the 0% PB solder, heat it at 150℃ for the time shown in the table, and then heat it at 0.25R for 9
Use a microscope to check if there is peeling at the interface when you bend it by 0° and then bend it back! This shows the result of +1.

In Table 1, O indicates the case where interfacial peeling did not occur, and X indicates the case where interfacial peeling occurred.

As can be seen from Table 1, the addition of Zn makes it possible to accurately prevent peeling at the soldering interface, although the effect varies depending on the added element. The reason why Zn has the effect of preventing interfacial peeling is as follows.
As mentioned above, there are still many details that are unclear, but when the content of Sl and P increases, the effect is inhibited #J! The flesh is clearly visible. Therefore, even if their effectiveness is known, it is not desirable to add too much Sl or P.

550mm' x0. 25Rm' (7) After forming a plate, it was heat treated at 500°C for 1 minute.

Next, from the above plate material, 15 mm x 0.25 + u + 'X 5
A 0 m' test piece was cut out and evaluated for releasability at the soldering interface.

Each test piece was plated in a sn-40%pb soldering medium kept at 250°C, heated in the atmosphere for 150'C x 100 hours, and then heated at 0.25R for 9
The film was bent by 0°, then bent back, and the presence or absence of peeling at the interface was observed and evaluated using a 100x microscope.

Table 2 shows the evaluation results.

Example A copper alloy having the composition shown in Table 2 was semi-continuously cast in a water-cooled mold, hot rolled at 850°C,
It was made into a plate of x10mm'. This was annealed and cold rolled repeatedly to form a plate of '
The alloys according to the present invention, which are cold-rolled at 6%, show a high tensile strength of 69krf/+m'' or more due to the addition of precipitation hardening and work hardening, and are superior to the high nickel alloys mentioned above. It can be seen that it can maintain superior strength.

Moreover, as shown in Table 2, the alloy of the present invention can completely prevent the occurrence of solder interface peeling by containing Zn in a predetermined amount or more.

On the other hand, in the comparative examples that do not contain Zn, interfacial peeling occurs in all cases. In addition, in those with a high Sl content, interface #I separation occurs despite the addition of 2.5% or 3.0% Zn, and the strength is increased by increasing the Si content. It can be seen that if an attempt is made to increase the size, there is no effect unless ZnK is also added in an amount of 3.3% or more.

[Effects of the Invention] As described above, according to the copper alloy of the present invention, work hardening is observed in addition to precipitation hardening, and as a result, strength superior to that of high nickel alloys can be maintained, and Zn is appropriately added. By doing so, it is possible to completely prevent delamination at the soldering interface, and this is of great significance as it allows us to appropriately respond to copper alloying of lead frames.

Agent: Patent Attorney Fujio Sato

Claims (1)

[Claims] (1) Ni 1.0-5.0%, Sn 0.5-2.5%,
A high-strength copper alloy for lead frames containing 3.3 to 7.0% Zn, 0.2 to 1.0% Si, and 0.003 to 0.3% P, with the balance being Cu and unavoidable impurities.