JPS6033312B2 - semiconductor equipment - Google Patents

Abstract

PURPOSE:To improve, in semiconductor device having elements arranged on a lead frame, the bonding strength between the brazing material and semiconductor element, by disposing a nickel-plating layer and a phosphorus-containing plating layer on the portions of the lead frame where the elements are to be mounted. CONSTITUTION:A bright electro-plating layr 3b of nickel and a nickel plating layer 13b containing phosphorus are formed on the surface of a substrate 3a. A brazing material 16 is press-contacted against the plating layer 13b and is then molten. A semiconductor element 4 is mounted on the molten brazing material 16. Since the standard oxide-forming energy of phosphorus contained by the nickel-phsphorus alloy plating layer is lower than those of the brazing material and the lead frame, the nickel plating on the brazing material and lead frame are activated to provide a stronger bonding between the brazing material and the semiconductor element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a high-output semiconductor device having an improved structure for a bottom portion of a lead frame on which a semiconductor element is disposed.

An example of a high-output semiconductor device is the one shown in a perspective view in FIG. 1 that uses a lead frame and is sealed with resin.

In the figure, la, lb, and lc are all leads, 2 is a resin sealing body, and 3 is an element mounting base portion that also serves as a heat sink. Next, FIG. 2 shows a top view of the relationship between the above-mentioned pedestal mounting base and the semiconductor element disposed thereon. That is, in the figure, reference numeral 4 denotes a semiconductor element, and an electrode on one main surface of the semiconductor element is in contact with the element mounting platform 3, and this element mounting platform is further connected to one lead lb. Note that 5a and 5c lead out the remaining electrodes of the semiconductor element to leads la and lc, respectively, using bonding wires. The connection between the semiconductor element 4 and the element mounting platform 3 is generally shown in FIG. 3, which is a cross-sectional view of the part. A bright nickel plating layer 3b is provided on the surface, and a semiconductor element is bonded to this layer at one electrode using a brazing material such as solder. 6 in the figure indicates a wax layer. (2) The above-mentioned joining is performed by automatic assembly using a machine, but there are problems with oxidation of the bright nickel-plated metal frame and oxidation of the surface of the wax. There were drawbacks such as a significant increase in the amount of inert gas or reducing gas used. Moreover, since the nickel oxide in the deaf frame cannot be sufficiently reduced by the above method, the third method is
As shown in the figure, the semiconductor element may be tilted, the brazing material directly under the element may not fit well with the nickel plating layer of the IJ card frame, and voids 7, 7', etc. may occur, causing the brazing material to become uniform. There was no flow and product reliability was not perfect. In order to improve the above-mentioned conventional drawbacks, this invention has the following points:
To provide a semiconductor device having a structure that does not cause oxidation of a nickel plating layer and a surface of a brazing material for soldering a semiconductor element to at least the element mounting base part of a lead frame.

A semiconductor device according to the present invention is provided with a bright nickel plating layer and a phosphorus-containing nickel plating layer laminated thereon on at least the element mounting base of a lead frame made of copper or copper alloy, and the phosphorus-containing nickel plating layer is laminated thereon. Another feature is that the semiconductor element is placed in the base layer.

Next, the present invention will be explained in detail with reference to the drawings regarding the differences from the conventional semiconductor device according to one embodiment.

FIG. 4 shows a cross-sectional view of a part of the surface of a part of the element mounting base of the lead frame. In the figure, reference numeral 13 denotes an element mounting base that also serves as a heat sink, and the substrate 3a is made of copper or copper alloy.
A bright nickel plating layer 3b with a thickness of 3 layers is deposited on the surface, and a nickel plating layer 1 containing phosphorus is further laminated.
An electrolytic nickel phosphorus alloy plating layer 3b is deposited to a thickness of 0.2 mounds. After a brazing material 16 such as lead or tin is pressure-welded to the alloy plating layer, the brazing material 16 is melted and the semiconductor element 4 is mounted. The standard free energy for the formation of oxides of phosphorus contained in the above nickel-phosphorus alloy plating layer is 0.
"Metal Handbook": Edited by the Japan Institute of Metals, (Maruzen)) is 2500 (all units are Kcal/mol), which is approximately 1130.
30,000 and about 118, which is smaller than the brazing filler metals normally used in semiconductor devices, such as tin and lead, and the nickel used in lead frame plating, that is, at 25qC (all units are in Kcal/mol). Tin: about 1110, Lead: about 1100, Nickel: about 1106
At 30,000 Tin: approx. 1106, Lead: approx. 180
, Nickel: Approximately 195%, very easily oxidized.

In other words, it has a reducing effect on the oxides of the soldering filler metal and the soldering material, and moreover, this oxide of phosphorus sublimates at a temperature of about 35,000 ℃, which is the semiconductor element mounting temperature (``Chemistry Handbook Basic Machine Edition 1'': (Maruzen)), the other effects of phosphorus on the brazing material (mechanical properties, etc.) are almost eliminated by raising the temperature at which the semiconductor element is mounted on the lead frame to a higher temperature. Therefore, the nickel plating on the brazing metal and lead frame has a very beautiful metallic luster and is activated.
Alternatively, the compatibility between the brazing material and the semiconductor element, that is, the adhesion strength is significantly improved. In addition, the thickness of the nickel plating layer containing phosphorus is necessary to the extent that the bonding properties of bright nickel plating are not lost, and in experiments, the above effect of phosphorus is satisfied within the range of several hundred amps to several thousand amps. The results showed that the bonding properties were also good.
Next, for forming the above-mentioned nickel plating layer containing phosphorus, it is preferable to include 10% of phosphorus in the plating solution as an example, but the present invention is not limited to this, and it is effective to include phosphorus in the plating solution. Although the phosphorous-containing nickel plating layer alone has sufficient ability to reduce the oxides of the brazing material, the surface of the plating layer is matte, and it is called a bright nickel plating layer or a "bright nickel plating layer." Compared to a laminated layer of ``nickel plated layer containing phosphorus'', the exposed surface of the plated layer discolors significantly when heated, and even if the thickness of the plated layer is changed, the bonding property is extremely poor compared to a glossy plated layer. It was found that due to the inferior quality, the assembly process was slow and the reliability of the product was also incomplete. Therefore, the "bright nickel plating layer" and "nickel plating layer containing phosphorus" of the present application
According to the laminated layer, the following remarkable advantages are recognized.

'1} Because the brazing material blends well with the frame surface and the backside of the semiconductor element, the brazing material flows stably and evenly over the entire backside of the semiconductor element, greatly improving product reliability. . One example of an important reliability test is a thermal fatigue test, the results of which are shown in FIGS. 5 and 6, respectively, in comparison with conventional tests. In each figure, the vertical axis shows the thermal resistance value (Rth) in units (℃/W), and the horizontal axis shows the number of thermal fatigue test cycles (Cyc.). (Before the exam) Distribution and 10
FIG. 6 shows the 000-cycle distribution for a semiconductor device according to an embodiment of the present invention in accordance with the representation shown in FIG. Comparing both figures, the semiconductor device according to one embodiment of the present invention is stable, with no significant increase in thermal resistance after 10,000 cycles of the thermal fatigue test. '21 Because the work margin in the automatic assembly process has been expanded, the yield has improved by 15 to 20% compared to the case of only a bright nickel plating layer. {3' Conventionally, when mounting a semiconductor device on an IJ-board frame, a long scrubbing time (approximately 0.5 to 1 second) was required to improve the adhesive strength, but the surface of the brazing material and lead frame Since it is activated and blends in very well, the scrubbing time can be reduced to 1/4 to 1/4 degrees, and the index has been significantly improved.

This has made it possible to automate this process.
'4' The amount of inert gas or reducing gas used is also very small, and the structure of automatic assembly machines does not require as much attention as before.

The present invention as described above uses a lead frame equipped with a phosphorous-containing nickel plating layer laminated on a semiconductor substrate via a bright electrolytic nickel plating layer, thereby eliminating oxides of brazing materials such as solder. It is reduced to improve compatibility with lead frames, brazing filler metals, and semiconductor elements.
The brazing material was made to flow uniformly as desired over the entire main surface (back surface) on the side where the semiconductor element was disposed.

This has further ensured the reliability of the product.
In addition, in the above-mentioned element arrangement part, an electroless nickel plating layer containing several percent of phosphorus may be provided instead of the electrolytic nickel-phosphorus alloy plating.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the semiconductor device, FIG. 2 is a top view of the semiconductor device mount, FIG. 3 is a cross-sectional view of a part of FIG. 2, and FIG.
The figure is a cross-sectional view of a part of the mounting part of a semiconductor device according to an embodiment of the present invention, FIG. 5 is a conventional one, and FIG. 6 is an embodiment of the present invention. FIG. Note that the same reference numerals in the figures indicate the same or corresponding parts, respectively. la to lc...Semiconductor device leads, 2...Resin sealing body, 3, 13...Element placement platform floor that also serves as a heat sink, 3a, 13a.・・・・・・
・Base material of element placement base floor, 3b... Bright nickel plating layer, 13b... Nickel plating layer containing phosphorus, 4... Semiconductor element, 6 , 16... Brazing layer (brazing material). Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A bright nickel plating layer and a phosphorus-containing nickel layer laminated thereon are provided on at least the element mounting base of a lead frame made of copper or copper alloy, and a semiconductor element is soldered to this phosphorus-containing nickel plating layer. A semiconductor device characterized by: