JPH0331449A - Fe-ni alloy for lead frame - Google Patents

Abstract

PURPOSE:To obtain the Fe-Ni 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 alloy has the compsn. constituted of 30 to 50% Ni, <=2.0% Co, <=1% Mn, <=0.5% Si, 0.01 to 0.05% Be, <=5.0% Cu and the balance Fe with inevitable impurities. In the above Fe-Ni 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, since a small amt. is enough for the amt. of Be to be added, the alloy is essentially constituted of the one having a low thermal expansion coefficient. Thus, the thermal expansion coefficient suitable for a lead frame material can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention is directed to F
Regarding e-Ni alloy, Fe, Ni, CO, Mn and S
By adding a specific amount of Be to an alloy containing specific amounts of i and Cu, it has a low coefficient of thermal expansion and excellent resin adhesion.

"Conventional technology" In recent years, the development of highly integrated large-scale integrated circuits (LSI) and very large-scale integrated circuits (very large-scale integrated circuits) has become active. 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.S.
For lead frame materials such as I and VLSI,
In particular, it is necessary to bring the coefficient of thermal expansion close to that of the silicon element.

For this reason, lead frame materials have traditionally been made of 4-Fe-Ni alloy, which has a low coefficient of thermal expansion and is intended to alleviate the thermal stress that acts on silicon elements.
2 A 1loy (42% Ni-Fe) (Unexamined Japanese Patent Publication No. 5
5-119156 etc.), Kovar (29%N+-1
7% Co-Fe) and low expansion Kovar (29% N
i-13%G o-F e) (Japanese Unexamined Patent Publication No. 1987-19874
No. 1) is known.

``Problems to be solved by inventions'' However, recently, I0. As LSIs and other devices become larger,
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.
The purpose is to provide alloys.

"Means for Solving the Problems" In order to solve the problems described above, the present invention solves the problems described above.
55% Go 2.0% or less Mn 1% or less Si 0.5% or less Be 0.01-0.05% Cu 5.0% or less the balance Fe and unavoidable impurities.

"Operation" By adding a small amount of Be to a low expansion coefficient alloy containing predetermined amounts of Fe, Ni, Go, Mn, Si, and Cu, a Be0 layer is generated on the surface of the material, 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-Ni alloy, the main component of the alloy is an alloy with a low coefficient of expansion, and therefore has a low coefficient of thermal expansion suitable as a material for lead frames. is ensured.

The present invention will be explained in more detail below.

In the alloy of the present invention, Ni (nickel) is 30 to 5
5%, Go (cobalt) 2.0% or less, Be (beryllium) 0.01-0.05%, Si (silicon) 0.
5% or less, Mn (manganese) at 1% or less, and Cu (copper) at 5.0% or less. In these compositions, N
The contents of i, CO, Mn, and Si are described in the high-strength, low-expansion Fe-Ni alloy and its manufacturing method, which the present inventors have previously applied for in Japanese Patent Application No. 63-315646. It corresponds to the composition of the alloy.

In addition, in the alloy of the present invention, unavoidable impurities include C (carbon) 0.1% or less, S (sulfur) 0.1% or less, Al (aluminum) 0.1% or less, Mg (magnesium) 0.1% or less. % or less, and may contain Ca (calcium) 0.1% or less.

In the above composition, if the Ni content is other than 30 to 55%, it is undesirable because the lead frame material will not have a thermal expansion coefficient that is compatible with the thermal expansion coefficient of the silicon element, etc. to which it is applied. If the content exceeds 2.0%, the coefficient of thermal expansion becomes too large, which is not preferable. Also,
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 if the Be content exceeds 0.05%, it will be expensive and the addition of e will unnecessarily increase the cost.
The amount of e added is preferably 0.05% or less. Furthermore, Si is used as a deoxidizing agent, but if the content exceeds 0.5%, it causes the alloy to become brittle, which is inconvenient.Also, Mn improves forgeability and is used as a deoxidizing agent, but the content exceeds 0.5%. is 1
, 0% 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, and then rolled to a desired shape, for example, a desired thickness, preferably at a processing rate of 70% or less, and
The annealing treatment performed at 100°C is preferably set to about 50% or less, and after the final rolling, for the purpose of strain relief annealing, 300°C
Heat treatment is preferably performed within a temperature range of ~700°C for 5 hours to obtain a plate material with a desired thickness.

The alloy manufactured as described above is Fe-Ni-C.

Since the material is mainly made of a low thermal expansion coefficient alloy with a small amount of Be added, it has a thermal expansion coefficient close to that of a silicon element, and is suitable as a lead frame material. Also,
Due to the effect of added Be, a Be0 layer is formed on the surface of the material, and this Be0 layer improves the adhesion with the resin material.
When a lead frame is constructed and sealed with resin, the adhesion between the sealing resin and the lead frame is improved, and there is an effect of 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 strain relief process of heating to 600°C for 1 minute was performed to obtain sample No. 1. -6 lead frame-shaped test pieces were 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.

As shown in Table 1, Table 2, and Table 2, alloy samples No. 2 to No. 6 of the present invention
has an equivalent low coefficient of thermal expansion compared to sample No. 1, a conventional alloy known as a low expansion alloy.

Further, a resin adhesion evaluation test was conducted on the 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 the schematic cross-sectional structure of the lead frame used in the test, where l is the lead frame, 2 is the tC 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 results of observing internal cracks 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
3 to No. 6, in the case of moisture absorption treatment for 8 hours or less,
It was found that no cracks were observed. Also, B
In sample No. 5.6 of the product of the present invention in which the added amount of e was increased, the occurrence of cracks could be suppressed until 16 hours of moisture absorption treatment. Furthermore, sample No. 2 of the comparative product in which the added amount of Be was set to 0.008% is different from that of the conventional product sample No.
Similar to 1, cracks were observed after 4 hours of moisture absorption treatment.
This shows that the amount of Be added is small. Further, in sample No. 3 in which the amount of Be added was 0.01%, no cracks were observed even after 8 hours of moisture absorption treatment. Therefore, it has become clear that the amount of Be added must be 0.01% 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 conventional materials. 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. l...Lead frame, 2...IC chip, 3...
・Pad part, 4...Lead wire, 5...Crack.

Claims (1)

[Claims] Ni 30-55% (weight%, same below) Co2.0% or less Mn 1% or less Si0.5% or less Be0.01~0.05% Cu5.0% or less Balance: Fe and inevitable impurities An Fe-Ni alloy for lead frames having the composition.