JPH0331450A - Fe-ni-co alloy for lead frame - Google Patents

Abstract

PURPOSE:To obtain the Fe-Ni-Co alloy for a lead frame showing the low thermal expansion coefficient similar to that of an Si element and having good adhesion with a sealing resin by forming it from the compsn. contg. each prescribed amt. of Ni, Co, Mn, Si, Be Cu and the balance Fe with inevitable impurities. CONSTITUTION:The above Fe-Ni-Co alloy has the compsn. constituted of 26 to 34% Ni, 8 to 20% Co, <=1.0% Mn, <=0.5% Si, 0.01 to 0.05% Be, <=5.0% Cu and the balance Fe with inevitable impurities. In the above alloy, by adding a small amt. of Be to an alloy of a low expansion coefficient contg. each prescribed amt. of Fe, Ni, Co, Mn, Si and Cu, a BeO layer is formed on the surface of stock, and the BeO layer improves the adhesion with a sealing resin. Furthermore, a small amt. is enough for the amt. of Be to be added to the above alloy, the alloy is essentially constituted of the one having a low expansion coefficient. Thus, the thermal expansion coefficient suitable for a lead frame material can be secured.

Description

Detailed Description of the Invention "Industrial Field of Application" The present invention provides F
Regarding the e-N i-G o alloy, by adding a specific amount of Be to an alloy containing specific amounts of Fe, Ni, Go, Mn, Si, and Cu, it was made to have a low coefficient of thermal expansion and excellent resin adhesion. It is something.

"Conventional Technology" In recent years, the development of highly integrated large-scale integrated circuits (LSI) and very large-scale integrated circuits (VLSI) has become active. Silicon elements are becoming larger and generating more heat.

Therefore, if the difference in coefficient of thermal expansion between the silicon element and the lead frame is large, there is a risk that the silicon element will be subject to thermal stress due to the expansion and contraction of the lead frame due to the heat generated by electricity, and may break or crack. So L
In lead frame materials for SI and VLSI, it is particularly necessary to bring the coefficient of thermal expansion close to that of silicon elements.

For this reason, lead frame materials have traditionally been made of 42% Fe-Ni alloy with a low thermal expansion coefficient for the purpose of relieving thermal stress acting on silicon elements, etc.
A 1loy (42% Ni-Fe) (Unexamined Japanese Patent Publication No. 1983-
119156 etc.), copal (29%Ni-17%
Go-Fe), and low expansion Kovar (29%Ni-
13%Co-Fe) (Japanese Patent Application Laid-open No. 198741/1983) is known.

“Problems to be solved by inventions” However, recently, with the increase in the size of IC5LSIs,
With the miniaturization of packaging, in surface mount type lead frames and lead frames with large chip sizes, cracks can occur between the sealing resin and the lead frame due to heat history during the assembly process, and these cracks can occur. Problems such as causing malfunction of ICs and LSIs have been occurring.

The present invention has been made to solve the above problems,
Fe-Ni for lead frames, which exhibits a low coefficient of thermal expansion close to that of silicon elements and also has good adhesion to sealing resin.
-Co alloy.

"Means for Solving the Problems" In order to solve the problems described above, the present invention provides Ni 26 to
34% Co 8-20% Mn 1.0% or less Si 0.5% or less Be 0.01-0.05% Cu 5.0% or less Balance Fe and unavoidable impurities.

"Operation" By adding a small amount of Be to a low expansion coefficient alloy containing predetermined amounts of re, Ni, Go, Mn, Si, and Cu, a Be0 layer is generated on the material surface, and this Be0 layer acts as a sealing resin. Improves adhesion. In addition, since only a small amount of Be is added to the Fe-NiCo alloy, the main component of the alloy is an alloy with a low coefficient of expansion, thus ensuring a coefficient of thermal expansion suitable for use as a material for lead frames. be done.

The present invention will be explained in more detail below.

In the alloy of the present invention, Ni (nickel) is 26 to 3
4%, Co (cobalt) 8-20%, Be (beryllium) 0. O1~0.05%, Si (silicon) 0.5%
% or less, Mn (vngan) 1.0% or less, Cu (copper)
Contains 5.0% or less. In these compositions,
The contents of Ni, Co, Mn, and Si are determined in the high-strength, low-expansion Fe-N 1-Co alloy and its manufacturing method, which the present inventors have previously applied for in Japanese Patent Application No. 63-315647. It corresponds to the composition of the alloy described. In addition, in the alloy of the present invention, as unavoidable impurities, C (carbon) is 0.1% or less, S (sulfur) is 0.1% or less.
1% or less, Al (aluminum) 0.1% or less, Mg (
Magnesium) 0.1% or less, Ca (calcium) 0.
There is no problem even if it contains 1% or less.

In the above composition, if the Ni content is set to a value other than 26 to 34%, or the Co content is set to a value other than 8 to 20%,
This is not preferable because it becomes impossible to obtain a coefficient of thermal expansion that matches the coefficient of thermal expansion of the silicon element, etc. to which the lead frame material is applied. Furthermore, if the Be content is less than 0.01%, a BeO oxide film will not be formed and the adhesion with the sealing resin will become insufficient, which is not preferable. Note that when the Be content is 0.
If it exceeds 0.05%, no further adhesion improvement effect is produced, and addition of expensive e increases costs unnecessarily, so the amount of Be added is preferably 0.05% or less. Furthermore,
Si is used as a deoxidizing agent, but if the m content exceeds 0.5%, it will cause the alloy to become brittle, which is disadvantageous.Also, Mn improves forgeability and is used as a deoxidizing agent, but if the m content exceeds 1. If it exceeds .0%, it is not preferable because it deteriorates bendability.

Further, if the Cu content exceeds 5.0%, the thermal expansion becomes too large, which is inappropriate.

An example of a method for manufacturing an alloy having the above composition will be described below.

To manufacture the alloy, first, raw materials are blended to have the composition as described above, and then vacuum melting is performed in an atmosphere of Ar gas or the like to avoid contamination with impurities to obtain an ingot having the composition as described above.

Next, this ingot is forged at 1200 to 1400°C, rolled to a desired shape, for example, a desired plate thickness, preferably at a processing rate of 70% or less, and 5oo-t.
The annealing treatment carried out at too much degree Celsius is repeatedly performed. Then, during the final rolling process, the processing rate is preferably set to about 50% or less, and after the final rolling process, for the purpose of strain relief annealing, 300 to 70%
Heat treatment is performed in a temperature range of 0° C., preferably for up to 5 hours, to obtain a plate material of desired thickness.

The alloy manufactured as described above is mainly composed of a Fe-N1-Co alloy with a low coefficient of thermal expansion, and a small amount of Be is added to it, so it has a coefficient of thermal expansion close to that of a silicon element, and has a lead Suitable as frame material. In addition, a Be0 layer is generated on the surface of the material due to the effect of added Be, and this Be0 layer improves the adhesion with the resin material. This has the effect of improving the adhesion of ICs and LSIs and preventing malfunctions of ICs and LSIs.

"Example" Each raw material was blended so as to have the composition shown in Table 1 below, and each blend was melted in a vacuum atmosphere of 80 Torr containing Ar gas to create an ingot. Hot forging at ℃, followed by rolling at a processing rate of 70% or less and 800~
The annealing process of heating to 1100°C and then slow cooling was repeated, the final rolling process was performed at a processing rate of 50% or less to complete the rolling process, and then the aging process of heating to 600°C for 1 minute was performed to prepare samples No. A lead frame-shaped test piece of No. 6 was obtained.

Average coefficient of thermal expansion of each test piece (30-300°C, μ/μ.

・°C) was measured, and the results are shown in Table 2.

Table 1 Table 2 As shown in Table 2, alloy sample N of the present invention.

Samples No. 2 to No. 6 have the same low coefficient of thermal expansion as sample Not, which is a conventional alloy known as a low expansion alloy.

Further, a resin adhesion evaluation test was conducted on alloy samples No. 1 to No. 6 obtained as described above.

In the resin adhesion evaluation test, the inventive product and comparative product were tested at 100%
QF P (Q
After processing by attaching elements and wiring, it was packaged and sealed with low stress resin. Next, the package is subjected to moisture absorption treatment (0 to 32% in an environment of 85℃ and 80% humidity).
solder immersion treatment (2) followed by solder dipping treatment (2).
3 times for 10 seconds in a 40°C solder bath)
After that, internal cracks were observed using an ultrasonic flaw detector.

FIG. 1 shows a schematic cross-sectional structure of the lead frame used in the test, where l is the lead frame, 2 is the IC chip, 3 is the pad part of the lead frame on which the IC chip 2 is installed, 4 is the lead wire, 5 indicates a crack that occurred in the resin portion surrounding the lead frame l. The internal crack is a phenomenon in which moisture penetrates due to poor adhesion between the resin and the lead frame l, and a crack 5 enters the sealing resin around the corner of the pad part 3 of the lead frame on which the IC chip 2 is mounted. If this crack 5 enters the sealing resin, the lead wire 4 sealed together with the sealing resin may be disconnected.

The fruits whose internal cracks were observed using the ultrasonic flaw detection device are shown in Table 3 below. In Table 3, the O mark indicates that no internal crack occurred, and the X mark indicates that an internal crack occurred.

As is clear from Table 3, sample No. of the invention product
For Nos. 3 to 6, in the case of moisture absorption treatment for 4 hours or less,
It was found that no cracks were observed. Also, B
Sample No. 4, 5.6 of the product of the present invention with an increased amount of e
In this case, the generation of cracks could be better suppressed by increasing the amount of Be added. Furthermore, in sample No. 2, a comparative product in which the addition m of Be was set to o, oos%, cracks were observed after 4 hours of moisture absorption treatment, similar to the conventional sample No. 1, and the amount of Be added was It shows that there are few. In addition, sample No. with the addition amount of Be 0.01%
In Sample No. 3, no cracks were observed even after 4 hours of moisture absorption treatment. Therefore, it has become clear that the amount of Be added must be 00O1% or more.

"Effects of the Invention" As explained above, according to the present invention, Fe, Ni and C
By adding a small amount of Be to a low expansion coefficient alloy containing predetermined amounts of O, Mn, Si, and Cu, it maintains a thermal expansion coefficient close to that of silicon elements and has better resin adhesion than conventional alloys. Alloys can be provided.

Therefore, according to the present invention, it is possible to provide a lead frame material that is superior to the conventional material. Further, since the alloy of the present invention is expensive, only a small amount of e is added, so it can be obtained at low cost.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing how an IC chip and a lead frame are attached. ! ...Lead frame, 2...IC chip, do part,
4...Lead wire, 5...Crack. 3...Para

Claims (1)

[Claims] Ni: 26-34% (weight %, the same applies hereinafter) Co: 8-20% Mn: 1.0% or less Si: 0.5% or less Be: 0.01-0.05% Cu: 5.0% or less The remainder contains Fe and unavoidable impurities A Fe-Ni-Co alloy for lead frames having the following composition.