CS218541B1 - Method of plating electrodes - Google Patents

Abstract

The subject of the invention is a method of plating expansion electrodes of power semiconductor elements, the essence of which is that an Ag alloy with a maximum addition of 5% Ge is plated onto an untreated surface — the surface of the basic material of the expansion electrode, chemically cleaned, for example, by etching — in an inert or reducing atmosphere, or in a vacuum, at a defined temperature regime with a temperature increase gradient of maximum 60 °C/min, a dwell time at a temperature of 820 to 920 °C of at least 10 minutes and a temperature decrease gradient of 20 to 50 °C/min.

Description

The present invention relates to a process for metallizing diode electrodes used in the manufacture of power semiconductor devices such as diodes and thyristors.

In order to obtain the desired properties of the diode electrode, particularly with respect to providing suitable properties for the attachment of the Si plate, respectively. to ensure minimum contact resistance values with other parts of the case, the surface is metallized. The methods of applying the metallic layer are chosen with respect to the subsequent processing technology.

The electroplating process usually requires the formation of a multi-layer coating system (Ni, Ag, Au, etc.) in order to avoid dissolution of the metallic solder layer in the solder used. The deposited layers usually require heat treatment at higher temperatures to perfectly anchor them to the surface of the raw diode electrode. The disadvantage is that in the case of thicker layers, there is a risk of peeling due to internal stresses during the heat treatment.

By vapor deposition of the contact layers on the expansion electrode, it is used only marginally, due to the problems of selecting a suitable solder and adjusting the soldering technology, not necessarily being equipped with suitable equipment.

Said methods of depositing a metal layer are characterized by either a limitation of the subsequent soldering technology, high labor intensity or the complexity of the equipment used. Connection technology using a Si wafer with PN junctions to electrode expansion based solders of Pb, Ag with a melting point of about 300 ^C C requires sufficient force plating to prevent its full odlegování used to solder, thus reducing the mechanical strength of the joint. These requirements are usually met by the technological method of cladding Ag or Au foils of different thickness.

These requirements are met by a method of metallizing the diode electrodes for semiconductor devices according to the invention, which consists in that the untreated surface of the electrode base material, chemically cleaned by etching, for example, is alloyed with Ag alloy with an additive of max. 60 ° C / min, a residence time of 820 to 920 ° C for at least 10 min and a temperature gradient of 20 to 50 ° C / min.

The metallization method according to the invention guarantees the required properties of the diode electrode not only for perfect connection of the Si plate with PN junction soldering by Pb, Sn-based solders, but also ensures perfect and stable contact to the individual housing parts. The labor of such prepared electrodes is lower compared to other production methods.

Exemplary embodiment

The uncoated Mo disk electrode, adjusted to mechanical dimensions by mechanical operations, is degreased and cleaned in an ordinary chemical manner by etching in an acid or alkaline bath. AgGe3 alloy plating wheels are degreased and etched cleaned. The components prepared in this way are assembled in a graphite preparation in such a way that the AgGe3 alloy wheel is always placed on the upper and lower surface of the electrode to be metallized. The clad alloy assembly, metal electrode, clad alloy is loaded with a suitable weight . This assembly placed in the graphite preparation is subjected to a heat treatment with a defined mode. - with a temperature rise gradient of 60 ° C / min, a residence time of 890 ° C for 15 minutes and a temperature gradient of 25 ° C / min.

Claims (1)

Method of metallization of diodes of power semiconductor elements, characterized in that an alloy of Ag with an additive of max. 60 ° C / min, a dwell time of 820 to 920 ° C for at least 10 minutes and a temperature drop of 20 to 50 ° C / min.