JPS61147539A - Manufacture of semiconductor rectifier - Google Patents

Abstract

PURPOSE:To readily automate manufacturing steps by disposing solders of different melting points between a metal electrode and semiconductor substrate, individually heating them, and executing scribing step. CONSTITUTION:Laminated parts of a high melting point solder tablet 2 and a rectifier 3 are maintained at approx. 360 deg.C in a wide portion 5 of a metal electrode 1, and engaged with a heater 6 disposed in atmosphere of H2:N2=1:9. When the high melting point solder is melted, scribing step is executed to remove air bubbles contained in the solder layer, and the smoothness of the wide portion 5 is compensated. After the solder layer is cooled, other metal electrode 1 by low malting point solder and the rectifier 3 are secured. Then, laminated reversely to the case of high melting point solder, heated and scribing step is similarly executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor rectifier suitable for use in a vehicle, and in particular is installed in a generator for a vehicle.

[Technical background of the invention]

Semiconductor rectifiers for vehicles are normally assembled as a device with, for example, a three-phase bridge circuit, and attached to an alternator mounted on the vehicle. However, the characteristics required of semiconductor rectifiers are Products with excellent thermal fatigue properties (TPT) are being prized so that they can be used under various conditions, and low-cost products are also being demanded due to economic factors.

By the way, in this type of semiconductor rectifier, there is a type in which a semiconductor substrate is fixed between a pair of metal electrodes with solder, but the method for this is to place it in a guide jig (4) as shown in Figure 4. A semiconductor rectifying element (3) was stacked between the pair of metal electrodes (1) with solder (2) interposed therebetween, and this integrated structure was passed through a hydrogen furnace.

[Problems with background technology]

As mentioned above, since it is attached to the alternator mounted on the vehicle, the dimensions of the metal electrode (1) must meet certain standards, depending on the vehicle model, and the outer diameter of the mechanical conductor rectifying element must also be economical. Due to such restrictions, it is necessary to use a rectifying element as small as possible, and therefore a semiconductor rectifying element having a smaller diameter than the metal electrode (1) is used. In this case, the solder (2) and the semiconductor rectifier (3) cannot be guided by the jig (4), and therefore both parts move during heating in the hydrogen furnace, causing the molten solder layers to collide. This caused a solder bridge failure.

Furthermore, since a hydrogen furnace is used, a so-called scrub process cannot be employed, and the wettability of the solder layer is poor, resulting in frequent occurrence of solder voids.

This manufacturing method requires an extremely large number of jigs and is difficult to automate. That is, in addition to requiring human labor to supply components to the jig and to remove mounted components from the jig, automation requires considerable equipment costs.

[Purpose of the invention]

The present invention overcomes the above-mentioned difficulties and provides a simple method for manufacturing semiconductor rectifying elements that is particularly easy to automate.

[Summary of the invention]

In fixing a semiconductor rectifying element with a pair of metal electrodes, the present invention has confirmed the fact that the low melting point solder layer and the high melting point solder layer do not bridge even if they are heated and scrubbed separately using solders with different melting points. Completed on the basis of In selecting these solders, it is necessary that the metal ff1l be soldered to the ornetator at a higher melting point than the soldering temperature.

[Embodiments of the invention]

The embodiment will be described in detail with reference to FIGS. 1 to 3.
Components common to the figures are given the same numbers, and FIG. 1 shows a longitudinal sectional view of a semiconductor rectifier to which the present invention is applied. The illustrated semiconductor rectifying element (3) is a so-called button diode in which boron is diffused into an N-type silicon semiconductor substrate to form a P+ layer, and its PN junction end is exposed on the side of the semiconductor substrate. The sides of this button diode are treated with so-called positive bevel processing to improve withstand voltage. As specific methods thereof, chemical etching methods, dry awning processing, etc. are well known.

On the other hand, the metal electrode (1) with a T-shaped cross section is made of Cu, and a Ni plating film is formed on the surface, but its dimensions must meet certain values depending on the vehicle model due to the requirements of the vehicle. be.

This metal electrode (1) has a wide part (5) formed thereon, and its end face is made perfectly flat, but its smoothness is not perfect and there are parts with a maximum slope of about 2 degrees. ing.

Next, the semiconductor rectifying element (3) is attached to this metal electrode (1).
The solder used is pb-In.
-Ag was applied. As a high melting point solder, the In content is 5
%, Ag 2.5%, Ba1. Pb, low melting point solder was In 15%, Ag 2.5%, Ba 1.
Pb is used, and the former has a melting point of about 302°C, and the latter has a melting point of about 280°C.

Note that this solder is formed into a tablet shape.

As shown in Figure 2, the wide part (5) of the metal electrode (1)
A laminated component in which a high melting point solder tablet (2) and a rectifying element (3) were stacked on top of each other was maintained at approximately 360°C, and H2: N2 = 1.
: It is locked to the heating part (6) placed in the atmosphere of 9.

When the high melting point solder is melted, a scrubbing process is performed to remove air bubbles contained in the solder layer, and the wide part (5) is removed.
compensate for the smoothness of After cooling, this solder layer fixes the semiconductor rectifying element (3) to another metal electrode (1) using low melting point solder. In this case, a tablet of low melting point solder (2) and a wide part (5) of another metal electrode (1) are laminated in this order on the semiconductor rectifying element (3) fixed to the high melting point half H3 (2), This laminated component is held in a heating part (6) heated to about 320°C, but the atmosphere is I+2: N2=-
1:9, and the same scrubbing process as in the case of using the high melting point solder is performed when the low melting point solder is melted, to obtain exactly the same effect.

Next, as shown in FIG. 1, silicone resin (7) is filled in the space between the wide parts (5) of the opposing metal electrodes to encap the beveled surface of the semiconductor rectifier (3). . Further, an epoxy resin (8) is transfer-molded onto the metal electrode (1) (1) integrated with the semiconductor rectifier (3) to complete a semiconductor rectifier (9).

〔Effect of the invention〕

In this way, the semiconductor rectifier device in which the semiconductor rectifier element of the metal electrode is fixed with solder having a different melting point and is further subjected to a scrubbing process has a solder bridge failure rate of about 1/10, compared to the conventional 1 to 2%. .1% or less. Furthermore,
Instead of conventional heating in a hydrogen furnace, heating in a forming gas atmosphere was used, making it possible to perform a so-called scrub process. As a result, it was possible to suppress voids generated between the solder layer, the metal electrode adjacent thereto, and the semiconductor rectifying element. In order to judge the wettability of the solder layer, the area of generated voids expressed as a percentage of the area of the solder layer is 1 to 10% in the conventional method, but 2% or less in the present invention. Met. Moreover, as described previously, the wide part (5) of the metal electrode (1)
) is not perfect and has a maximum inclination of about 2°, but the molten solder layer compensates for this by the scrubbing process and a substantially smooth surface is obtained, improving thermal fatigue properties. Furthermore, since the heating step is performed in a forming gas atmosphere, it is safer than conventional methods that use a hydrogen atmosphere.

The conventional method requires many jigs and about five people for the hydrogen furnace and assembly, but the present invention not only allows automation but also requires about one person.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor rectifier according to the present invention, FIGS. 2 and 3 are cross-sectional views showing a soldered state of a semiconductor rectifier element and a metal electrode according to the present invention, and FIG. 4 is a jig. FIG. 3 is a longitudinal cross-sectional view of the conventional method during assembly. ■---Metal electrode 2--1 Solder 3-m-Semiconductor rectifier 4-m-Jig 5-11 Wide part 6--1 Heating part 7-m-Silicon resin 8-11 Epoxy resin, once -m- semiconductor rectifier

Claims (1)

[Claims] When a semiconductor substrate with a bond formed therein is fixed between a pair of metal electrodes that are longer and have a substantially flat surface, solder with a different melting point is placed between the metal electrode and the semiconductor substrate to separate them. 1. A method for manufacturing a semiconductor rectifying device, which comprises heating the device to a temperature of 100.degree. C. and performing a scrubbing step.