JPH02205643A - 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 retaining high conductivity by forming it with the compsn. contg. each prescribed amt. of Ni, Sn, Zn and P and the balance Cu with inevitable impurities. CONSTITUTION:The high strength copper alloy for a lead frame is composed of the compsn. contg. 1.2 to 2.8% Ni, 1.0 to 5.0% Sn, 0.3 to 1.3% Zn, 0.03 to 0.3% P and the balance Cu with inevitable impurities. By the copper alloy, sufficient work hardening can be shown, so that strength equal to that of high Ni alloy can be retained as well as about 66% working ratio. Furthermore, interface peeling resistance in soldering can perfectly be prevented without influencing highly on the lowering of the dielectric constant by suitably adding Zn to the alloy. In this way, the alloy is suitable for working a lead frame into copper alloy.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a high-strength copper alloy useful for lead frames, and in particular to a high-strength copper alloy that has excellent solder interface peeling resistance and can maintain high electrical conductivity. It concerns strength steel alloys.

[Conventional technology l Conventionally, 42 alloy (Fe-42%Ni) and Kovar, which have a low coefficient of thermal expansion and good adhesiveness and sealing properties with semiconductor elements and sealing materials, have been used as lead frame materials for semiconductor devices. (
High nickel alloys such as Fe-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 high nickel alloy has a tensile strength of 65 h.
Good gf/cur2, but conductivity is 3% rA
Thermal conductivity, which is extremely low at around cs and exhibits properties almost parallel to ordinary electrical conductivity, cannot be said to be sufficient.

Therefore, there has been a growing trend to use copper alloys, which have excellent electrical conductivity and thermal conductivity, as lead frame materials in place of the high nickel alloys.

In addition to the above-mentioned characteristics that are generally required for lead frame materials for semiconductor devices, in addition to the above-mentioned excellent electrical conductivity and thermal conductivity, there are also characteristics that are required for reliability during mounting and incorporation into devices. The essential conditions are that the material has sufficient strength to withstand external forces, and that soldering has excellent properties since soldering involves a process.

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.

[Problems to be Solved by the Invention] In lead frames, outer leads are often soldered to attach them to a substrate.

'In lead frame materials using copper alloys to which alloying elements are added as described above to improve Wtrf,
After soldering, a phenomenon in which brittle peeling occurs over time at the soldered interface may be observed, which poses a serious problem from the viewpoint of reliability. The formation of such a brittle layer is thought to be caused by the diffusion of Cu as the material and the Sn component and additive elements in the solder. ε in the Cu-3n system at the interface of
It has been confirmed that highly brittle intermetallic compounds such as phase or η phase are formed by diffusion.

Furthermore, a migration layer of additive elements is diffused and formed at the interface (especially noticeable for Fe, P, and Si).
It has also been revealed that these are the cause of the brittle peeling.

Although the reason for this is unknown, it has been found that adding Zn is very effective in preventing the occurrence of such solder interface peeling.

Table 1 shows that 20 was added to the copper alloy in the indicated amounts of various elements in the various amounts indicated in the table, and 5n-4
After plating the 0% PB solder without plating, heat it at 150℃ for the time shown in the table, and then heat it at 0.25R for 9
This figure shows the results of microscopic observation of the presence or absence of peeling at the interface when the film was bent by 0° and then bent back.

In Table 1, ○ indicates no interfacial peeling, and X indicates interface 1.
The cases in which 11AI occurred are shown respectively.

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.

On the other hand, in order to increase the strength of copper-based alloys by adding alloying elements, it is preferable to add precipitation-hardening elements that have relatively little effect on electrical conductivity. Cu-Nr-sr alloys have already been proposed as copper alloys.

However, in order to obtain strength comparable to the above-mentioned high nickel alloy, it is necessary to add both Ni and Si at considerably high concentrations. In this case, as can be seen from Table 1 above, 8
The higher the concentration of 1, the higher the concentration of zn to prevent interfacial peeling.
It is necessary to greatly increase the amount of addition of , which has a large effect on the decrease in conductivity, making it undesirable as a lead frame material for semiconductor devices that consumes a large amount of power.

Therefore, for lead frame materials with strong demands for maintaining electrical conductivity, sl is not added, and instead of relying on precipitation hardening for the strength of the copper alloy, it relies mainly on solid solution hardening, and the necessary Zn content is reduced. It is desirable to be able to reduce the amount added.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, to improve the strength of copper-based alloys mainly through cold working, and to greatly improve the peelability at the soldering interface, as well as to improve conductivity. It is an object of the present invention to provide a new high-strength copper alloy for lead frames that can maintain a suitable ratio.

[Means for Solving the Problems] The present invention provides Ni 1.2 to 2.8% and Sn 1.0 to 5%.
0%, Zn0.3-1.3%, Po, 003-0.3%
, and the remainder consists of Cu and unavoidable impurities.

[Effect] When Sn is added in the above range, it forms a solid solution by heating and rapidly cooling, and the strength improvement effect by work hardening is large.Therefore, there is no difference in strength compared to the case where Si is added and precipitation hardened. Not only can the strength be obtained, but also the amount of Zn added can be reduced since there is no addition of Sl, and the possibility of a large decrease in electrical conductivity is avoided.

However, if the Ni content is less than 1.2%, the high strength effect will be low, and if it is more than 2.8%, the electrical conductivity will decrease, which is not preferable.

Regarding the sn content, if it is less than 1.0%, the effect of improving the strength will be small, and if it is more than 5.0%, the electrical conductivity will decrease significantly, which is not preferable.

As explained above, zn is very effective in preventing interfacial peeling during soldering of copper alloys.

However, if the content is less than 0.3%, the effect of preventing peeling at the solder interface will be insufficient, which is not preferable, and if it is more than 1.3%, the electrical conductivity will tend to decrease, which is also not preferable.

P is added as an acid agent to prevent Zn, which is effective in preventing interfacial peeling, from being consumed for deoxidation, 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 and the consumption of Zn will be large, and if it is more than 0.3%, the decrease in 1 conductivity, which deteriorates workability, will be large, which is not preferable.

〔Example] The present invention will be described below with reference to solid line examples.

The doves were plated in a 40% Pb solder bath, heated at 150°C x too many hours in the atmosphere, and then heated to 0.
．． It was bent 90 degrees at 25R, then bent back, and the presence or absence of peeling at the interface was observed and evaluated using a 100x W4 microscope.

Table 2 shows the evaluation results.

Example A copper alloy having the composition shown in Table 2 was semi-continuously cast using a water-cooled mold, hot-rolled at 850°C, and heated to 550°C.
The board was made of X10mm. This was annealed and cold rolled repeatedly to make a 550w' x Q, 75+m+' plate, and then
Heat treatment was performed at 00°C for 30 minutes. Thereafter, it was cold rolled at a workability of 66% to form a 550w'xO, 25m' plate.

Next, 15mm' X 0, 25am from the above plate material
A test piece of 'X50am' was cut out and evaluated for releasability at the soldering interface.

Each g+ specimen was held at 250°C.
Table All alloys according to the present invention have a tensile strength of 62k.
It shows a high value of tr/ram2 or more, indicating that it can maintain strength comparable to that of the high nickel alloys described above.

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.

[Effects of the Invention] As described above, the copper alloy according to the present invention exhibits sufficient work hardening, resulting in a workability of about 66% and a strength comparable to that of high nickel alloys. In addition, by appropriately adding Zn, it is possible to completely prevent delamination at the soldering interface without significantly reducing conductivity. The significance of being able to respond appropriately to copper alloying of the frame is significant.

Agent: Patent Attorney Fujio Sato

Claims (1)

[Claims] (1) Ni 1.2-2.8%, Sn 1.0-5.0%,
A high-strength copper alloy for lead frames containing 0.3 to 1.3% of Zn and 0.003 to 0.3% of P, with the remainder being Cu and unavoidable impurities.