JPH0631486A - Production of composite solder ingot - Google Patents

Abstract

PURPOSE:To uniformly disperse the respective particles of the powder to be added into molten solder in the solder in the process for production of the solder ingot in order to produce the composite solder contg. the powder of the m.p. higher than the m.p. of the solder. CONSTITUTION:The films of metals (Cu, Ni, Au, Ag) which are easily wettable with the solder are formed on the surfaces of the respective particles a1, a1... of the powder (a) consisting of the materials (Cu, Ni, Mo, W, ceramics, alumina, glass, BN, etc.) having the m. p. higher than the m. p. of the solder. These particles are kneaded with a flux (b) and are then put into the solder (c) which consists of PbSn, PbAgSn, etc., and are melted by heating. The base material (d') obtd. by stirring the molten solder (c') to uniformly disperse the respective particles al, la... therein is packed into a mold K and is solidified by cooling, by which the composite solder ingot (d) having the uniform density of the particles a1 of the powder (a) is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connecting material used for connecting electronic parts in a power transistor or the like, more specifically,
The present invention relates to a method for manufacturing a solder ingot for molding a composite solder used for fixing a semiconductor chip to a substrate or the like.

[0002]

2. Description of the Related Art Conventionally, as a connecting material used for fixing a semiconductor chip on a substrate, a solder body made of a known solder material into a predetermined shape is made of a material having a melting point higher than that of the solder. A composite solder in which powder is mixed in a scattered manner is known.

When this composite solder is heated and melted in an appropriate amount placed on the substrate C, the thickness (height) of the solder melted by each particle of the powder is kept constant and set on the solder. The semiconductor chip is fixed horizontally on the substrate.

As described above, in order to connect the semiconductor chip horizontally on the substrate, that is, to keep the thickness (height) constant after melting the solder, a predetermined heat cycle strength is maintained at the connecting portion, and the temperature is kept constant. This is useful in preventing peeling of the semiconductor chip and poor conduction due to changes.

In order to produce the above-mentioned composite solder, as shown in FIG. 5, powder 200 of a material having a melting point higher than that of solder is put in molten solder 100, stirred, and then cooled and solidified. Then, a method of manufacturing a solder ingot and molding a tape-shaped or pellet-shaped product from the ingot is used.

[0006]

However, according to the above conventional method, when the powder 200 is put into the molten solder 100 and stirred, the particles 201, 201 ... Unable to disperse evenly in 100 (Fig. 5
(See (b)), particles are unevenly distributed in the obtained ingot.

When the semiconductor chip X is fixed on the substrate Y using the composite solder 300 manufactured from such an ingot, as shown in FIG. 6, the solder is thick and the density is low in the portion where the density of the particles 201 is high. It becomes thin at the part. Therefore, a predetermined heat cycle strength cannot be obtained in a portion where the solder is thin, and there is a defect that peeling of the semiconductor chip X or defective conduction occurs due to temperature change.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object thereof is to mix in a solder ingot for producing a composite solder containing a powder having a melting point higher than that of the solder. It is an object of the present invention to provide a method capable of uniformly dispersing each particle of powder to be melted in molten solder.

[0009]

In order to achieve the above-mentioned object, a method for manufacturing a composite solder ingot according to the present invention comprises:
On the surface of powder particles made of a material having a melting point higher than that of the solder, a film of a metal that is easily wettable with the solder is formed, and this is kneaded with flux into molten solder, and the molten solder is stirred to The method is characterized in that after the particles are dispersed, they are cooled and solidified.

[0010]

According to the manufacturing method of the present invention, the flux prevents the formation of an oxide film on the surface of the metal film while forming a metal film which is easily wetted by the solder on the surface of the powder particle. Therefore, the ease of transfer of the powder particles in the molten solder is dramatically improved, and if the powder is put in the molten solder and stirred, each particle is uniformly dispersed, and the particle density in the obtained ingot is Homogenize.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the manufacturing method of the present invention will be described below with reference to FIG. FIG. 1A shows a powder a made of a material having a melting point higher than that of solder, for example, powders of Cu, Ni, Mo, W, ceramics, alumina, glass, BN and the like.

(First step: FIG. 1 (b)) The above powder a
Is a metal that easily wets with solder (Ni, Cu, Au, Ag, etc.)
By immersing it in a solution containing the ions of and plating by well-known electroplating and electroless plating,
The metal (Ni, Cu, Au,
A film of Ag or the like) is formed.

(Second step ... FIG. 1 (c)) By kneading the particles a1, a1 ... Having the metal film formed on the surface together with the flux b, and subjecting the particles a1, a1.
Prevents the oxide film from being formed on the surface of the metal film. The particles a1 thus obtained have a metal film that is easily wettable with solder on the surface, and the flux film prevents the formation of an oxide film on the surface of the metal film. Ease of use is dramatically improved.

(Third step ... FIG. 1 (d), (e)) Each particle
Powder a having a metal film on the surface of a1, a1 ... And having its surface subjected to flux treatment is put together with flux b in molten solder c'and stirred to put each particle a1, a1 ... In molten solder c '. Base material for ingot molding d ′
To get The molten solder c ′ is obtained by heating the solder c made of a known material such as PbSn or PbAgSn so as to be in a semi-molten state.

(Fourth step ... FIG. 1 (f), (g)) The base material d'obtained in the above step is poured into an appropriate mold K and cooled,
Let it solidify. After the solidification, the ingot d is taken out from the mold K to obtain the ingot d in which the particle density of the powder a in the solder c is uniform.

As shown in FIG. 2, the composite solder ingot d obtained as described above has a step of producing a base material of an appropriate shape by a well-known molding method such as extrusion molding, and further rolling the base material. After that, it is formed into a product (composite solder). This composite solder is produced in a desired shape such as a pellet shape or a ribbon shape shown in FIG. 3A, a tape shape shown in FIG. 3B, or a pellet shape or a wire shape not shown,
In the solder body 1 made of the solder c, each particle a of the powder a
1, a1 ... are evenly dispersed.

A case in which the semiconductor chip X is fixed on the substrate Y by using the pellet-shaped composite solder A thus obtained will be described with reference to FIG.

First, the tip portion of the solder body 1 in the composite solder A produced as described above is brought close to the board Y (see FIG. 4).
(A)) Then, by heating and melting the portion, an appropriate amount of molten solder 1'is placed on the board Y (Fig. 4 (b) to (c)).
). At this time, each particle a of the powder a contained in the solder body 1
, 1, a1 ... Are uniformly dispersed in the molten solder 1 ′ without being locally unevenly distributed.

When the semiconductor chip X is set on the molten solder 1'in this state, the particles a1, a1 ... In the solder 1'are horizontally aligned and the thickness (height) of the molten solder 1'is increased. ) Is held constant, and the semiconductor chip is fixed horizontally on the substrate (Fig. 4 (d)).

Therefore, in the state where the semiconductor chip X is connected to the substrate Y, a thin portion is not partially formed in the connecting portion, that is, the composite solder after solidification, and the predetermined thermal cycle strength is exerted over the entire connecting portion. Can be obtained. Therefore, it is possible to provide a highly reliable semiconductor device Z in which there is no risk of peeling of the semiconductor chip X or defective conduction due to temperature change.

The composite solder is not limited to the shape described above. For example, the external shape of the composite solder may be, for example, formed into a sheet shape and cut into a chip shape having a desired size at the time of use, or previously molded into a chip shape. Is optional.

In the above description, the bonding material for fixing the semiconductor chip X on the substrate Y has been described, but the composite solder according to the present invention is not limited to this and can be used for connecting various electronic components. The size and shape of the solder body and powder are appropriately changed according to the size of the two members to be connected.

1, 4 and 5, the particles a1, a1 ... Of the powder a are shown in an enlarged manner for the sake of convenience. Actually, the diameters 20 μ, 50 μ and 100 μ as shown in FIGS. Needless to say, it is a very small thing.

[0024]

According to the manufacturing method of the present invention, particles of powder having a higher melting point than solder can be uniformly dispersed in the molten solder to form a composite solder ingot having a uniform particle density,
The particle density in the composite solder produced from the ingot can be made uniform. When this composite solder is heated and melted to connect electronic parts, each particle of the powder is evenly distributed between the two members to be connected, and the thickness (height) of the solder is maintained evenly. It is possible to more reliably prevent the thermal cycle strength from being lowered later.

Therefore, when providing a highly reliable semiconductor device having a predetermined heat cycle strength, it is extremely useful for manufacturing a solder ingot for obtaining a composite solder which is indispensable for manufacturing the semiconductor device.

[Brief description of drawings]

FIG. 1 is a simplified diagram showing an embodiment of a solder ingot manufacturing method according to the present invention.

FIG. 2 is a block diagram showing a process of producing a composite solder using the solder ingot obtained by the method of the present invention.

FIG. 3 is a perspective view of a composite solder made from the solder ingot obtained by the present invention.

FIG. 4 is a cross-sectional view illustrating a method of using the composite solder according to FIG.

FIG. 5 is a simplified diagram showing a conventional method for manufacturing a composite solder ingot.

FIG. 6 is a cross-sectional view showing a usage state of a composite solder manufactured from an ingot obtained by a conventional method.

[Explanation of symbols]

a: powder a1: particles b:
Flux c: Solder d: Ingot A: Composite solder 1: Solder body X: Semiconductor chip Y: Substrate Z:
Semiconductor device

Claims (1)

[Claims] 1. A metal film that is easily wettable with solder is formed on each particle surface of powder made of a material having a melting point higher than that of solder,
Manufacturing of an ingot for composite solder, which is prepared by kneading these particles together with flux in molten solder, stirring the molten solder to disperse the particles, and then cooling and solidifying. Method.