JP2001127076A - Alloy member for die bonding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloy member for die bonding containing no Pb which can bond a large semiconductor element. SOLUTION: The alloy member for die bonding comprises a basic material of pure Al plate of 0.05-0.5 mm thick or 42 alloy material provided, on the opposite sides thereof, with a bonding alloy layer of 0.05-0.1 mm thick. An alloy having liquid phase line temperature of 400 deg.C or below and solid phase line temperature of 280 deg.C or above containing no Pb, or an alloy having volumetric ratio of liquid phase at 280 deg.C equal to or lower than 15% is employed in the bonding alloy layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alloy member used for die bonding of a semiconductor device.

[0002]

2. Description of the Related Art Solder is used in die bonding of semiconductor devices such as power transistors. Solder for this purpose: 1) A semiconductor element can be joined to a lead frame at a temperature of about 400 ° C. or less. 2) The bonding state between the semiconductor element and the lead frame is ensured at a temperature of about 280 ° C. or lower so that no inconvenience occurs in the process after die bonding. 3) The bondability does not deteriorate in the environment in which the manufactured semiconductor device is used. Therefore, Pb-based solder typified by Pb-5% Sn has been used.

In recent years, there has been an increasing movement to restrict the use of Pb in consideration of environmental pollution. In response to such a movement, there is a demand for a solder containing no Pb in the field of solder for die bonding of semiconductor elements.

[0004] However, there has not been found any alloy containing no Pb that completely satisfies the above-mentioned required characteristics.

For example, Au— having a eutectic temperature of 280 ° C.
The 20% Sn eutectic alloy satisfies the above-mentioned required characteristics when the semiconductor element is small, but has a problem that the semiconductor element is cracked when joining a large semiconductor element due to high alloy hardness. As described above, there are several kinds of alloys that satisfy the condition of the melting point but have high hardness and cannot be used in a large semiconductor element.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to
An object of the present invention is to provide an alloy member for die bonding that does not contain b and that can join a large semiconductor element.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, an alloy member for die bonding according to the present invention has a thickness of 0.0%.
A pure Al plate or a 42 alloy material having a thickness of 5 to 0.5 mm is used as a base material, and a bonding alloy layer having a thickness of 0.005 to 0.1 mm is provided on both surfaces thereof.

Further, the bonding metal layer may be 400
Use a Pb-free alloy having a liquidus temperature of 280 ° C. or less and a solid phase temperature of 280 ° C. or more or a Pb-free alloy having a liquid phase volume ratio at 280 ° C. of 15% or less. ing.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the configuration of the present invention will be described below.

When a large semiconductor element is joined, the semiconductor element is cracked because the semiconductor elements (eg, Si elements) constituting the semiconductor device, the lead frame, and the solder alloy have different coefficients of thermal expansion. This is because a difference occurs in the amount of shrinkage of each member during cooling and a stress is generated. In the case of conventionally used Pb-based solder, the solder is plastically deformed to relieve this stress, thereby preventing the semiconductor element from breaking.

According to the present invention, a solder layer having a low ability to relieve stress by itself is used as a pure Al plate or a 42 alloy (Fe-4).
By forming it on both sides of a substrate made of a (2% Ni alloy) plate, the problem of stress generated due to a difference in thermal expansion coefficient is solved, and cracking of the semiconductor element is prevented.

In the present invention, the pure Al plate material is plastically deformed similarly to the Pb-based solder to reduce stress.
On the other hand, the 42 alloy plate has a coefficient of thermal expansion and high strength close to those of the Si element, thereby preventing the occurrence of stress inside the Si element.

The reason why the respective plate thicknesses are set to 0.05 to 0.5 mm is that if the plate thickness is 0.05 mm or less, the plate thickness is too thin, and the above-mentioned stress relaxation effect and stress prevention effect are insufficient. On the other hand, even if the plate thickness exceeds 0.5 mm, there is no problem in terms of relaxation of stress, but this causes a problem in assembling the semiconductor element. This pure Al
By providing a bonding alloy layer on the surface of the plate or 42 alloy plate, bonding of the semiconductor element and prevention of cracking of the semiconductor element can be achieved at the same time.

The thickness of the surface alloy layer is 0.005 to 0.1 m
The reason for setting m is that if the thickness is less than 0.005 mm, the alloy layer is too thin to bond the semiconductor element uniformly, and if it exceeds 0.1 mm, the semiconductor element cracks due to the influence of the alloy layer itself. That is because

It is necessary for the joining alloy to satisfy each of the characteristics 1) to 3) described in the prior art. That is, it has a liquidus temperature of 400 ° C. or less so that the element can be bonded at a temperature of about 400 ° C. or less, and has a liquidus temperature of 2 ° C.
Has a solidus temperature of 80 ° C or higher, or 280 ° C
It is necessary to use an alloy in which the volume ratio of the liquid phase is 15% or less. Even if the solidus temperature is lower than 280 ° C. and a part of the bonding alloy becomes a liquid phase at 280 ° C., if the volume ratio of the liquid phase is 15% or less, the bonding state between the semiconductor element and the lead frame is not increased. Secured.

Examples of such alloys include: a) 1 to 7% by weight of Al (hereinafter simply referred to as%), represented by Zn-4% Al-3% Mg-3% Ga alloy;
Alloy containing 0.5 to 6%, and further containing 1 to 10% of Ga, with the balance being Zn and unavoidable impurities. b) Ge represented by a Zn-6% Al-5% Ge alloy
Alloy containing 2 to 9% of Al, 2 to 9% of Al, and the balance of Zn and unavoidable impurities. c) Sn is 5 to 2 typified by a Zn-15% Sn alloy.
Zn alloy containing 5%, with the balance being Zn and unavoidable impurities. d) S represented by Zn-15% Sn-5% Ge alloy
containing 5 to 25% of n, and further containing 0.1 to 7% of Ge,
The balance is a Zn alloy composed of Zn and unavoidable impurities. e) Sn is 18 to 18% typified by an Au-20% Sn alloy.
Au containing 27%, with the balance being Au and unavoidable impurities
alloy. f) Ge is 11 to 11 as represented by an Au-12% Ge alloy.
A containing 13%, with the balance being Au and unavoidable impurities
u alloy. g) Si, represented by Au-6% SiGe alloy,
Au alloy containing 5 to 6.5%, with the balance being Au and unavoidable impurities. and so on.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Zn, Al having a purity of 99.9 to 99.99%,
Using Mg, Ga, Ge, Sn, Au, and Si, Zn alloys and Au alloys having the compositions shown in Table 1 were melted in an atmosphere melting furnace.

[0018]

[Table 1]

The obtained alloy was melted in a graphite crucible in an electric furnace to prepare alloy baths having the respective compositions. The temperature of the alloy bath is calculated from the liquidus temperature of each alloy to the liquidus temperature + 50
Set between ° C. 99.9% commercially available with various thicknesses
A sample having a width of 10 mm was prepared from an Al plate and a 42 alloy plate, a commercially available flux for stainless steel was applied, and then immersed in an alloy bath to form a bonding alloy layer on the surface. The desired alloy layer thickness was obtained by adjusting the temperature of the alloy bath and further performing cold rolling on the sample after forming the alloy layer.
A 4 mm square die bonding sample was cut out from the plate material obtained as described above.

The evaluation of the obtained sample was performed as follows.

Regarding the die bonding property, a solder die bonder (EDB-200 manufactured by Dage) was used.
5 mm of Au deposited on the back surface as a semiconductor element on a 1 mm thick Cu alloy lead frame plated with g
It was investigated whether a dummy chip having a thickness of 0.2 mm square can be joined. A case where chips were normally bonded was evaluated as good, and a case where bonding was defective or chip cracks occurred was evaluated as poor. Furthermore, in the case where normal bonding was possible, the lowest die bonding temperature at which bonding was possible was examined.

Whether or not the wire bonding as the next assembly process is normally performed is determined by using a commercially available gold wire and a ball bonder (FB-118 manufactured by KAIJO) and depositing Al on the chip that has been subjected to the previous die bonding. This was investigated by conducting a wire bonding test between the surface and the Ag-plated surface on the lead frame. The wire bonding test was performed at a stage temperature of 250 ° C., and the case where the wires were joined was evaluated as good, and the case where the wires were not joined was evaluated as poor.

Regarding the bonding reliability, after performing die bonding, an epoxy resin (EME-630 manufactured by Sumitomo Bakelite Co., Ltd.) was used with a transfer mold type molding machine.
270 ° C. for each of the samples molded
Heat test of holding for 0 second, temperature cycle test of -50 ° C / 150 ° C 1000 cycles, temperature 80 ° C, humidity 80% 10
Conduct a constant temperature and humidity test of holding for 00 hours to check whether the package appearance has cracks or seepage of the solder material, and whether there is any crack at the chip or solder joint interface in the observation after opening the resin. investigated. A case where cracking of a package, a chip, or a bonding interface was generated or a seepage of a solder material was observed was evaluated as bad, and a case where no exudation was observed was evaluated as good.

Table 2 shows the results of the above evaluation. As is clear from Table 2, the use of the clad material according to the present invention enables die bonding at a temperature of about 300 to 400 ° C. without occurrence of chip cracks, and has no problem in bonding reliability and the like. .

[0025]

[Table 2]

[0026]

As is clear from the above, the present invention can provide a Pb-free die bonding alloy member suitable for use in assembling electronic components and the like.

Claims (3)

[Claims] 1. A pure Al plate or a 42 alloy material having a thickness of 0.05 to 0.5 mm is used as a base material.
An alloy member for die bonding, comprising a bonding alloy layer having a thickness of 0.1 mm. 2. The bonding alloy layer having a liquidus temperature of 400 ° C. or less and a Pb-free alloy having a solidus temperature of 280 ° C. or more. The alloy member for die bonding according to the above. 3. The bonding alloy layer has a liquidus temperature of 400 ° C. or less, and is made of an alloy containing no Pb and having a liquid phase volume ratio at 280 ° C. of 15% or less. The die bonding alloy member according to claim 1.