Overview

This part of IEC 62739 describes the selection methodology of an appropriate evaluating test method for the erosion of the metal materials without or with surface processing intended to be used for lead-free wave soldering equipment as a solder bath and other components which are in contact with the molten solder. In the erosion test for materials without surface treatment, the temperature of the molten solder, the rotation speed and so on are specified as test conditions. These conditions are determined by a preliminary erosion test and the erosion and slag generation are observed during the test. When a solid metal is immersed in molten metal or is in contact with molten metal, it generally dissolves in the molten metal as soon as wetting occurs, that is, erosion occurs even at a temperature below the melting point of the solid metal. At a soldering temperature of around 250 °C, for example, a metal such as copper (Cu), nickel (Ni) and gold (Au) dissolves in the molten solder within a short period. The erosion of metallic materials without surface treatment that are used in wave soldering equipment is understood as the phenomenon of metal dissolution. For the erosion test of materials without surface treatment, the temperature of the molten solder specified in IEC 62739-1 is 350 °C +/- 3 °C. It is difficult to carry out erosion testing of materials with surface treatment at this temperature. If the erosion test of an existing material with surface treatment is carried out at 350 °C, erosion may not occur even after 1 000 hours. Therefore, the promotion of erosion generation, for example by thermal or mechanical stress, is necessary for an efficient evaluation. In materials with surface treatment by atomic diffusion, such as nitriding, erosion occurs in the following steps: - the surface of the nitrided layer becomes detached and the nitrided layer is wetted with molten solder. - tin (Sn) diffuses into the nitrided layer and a Sn diffusion layer is formed; at the same time, the metal compound of the base material diffuses into the molten solder and melts. An Fe-Sn compound forms in the boundary layer between the molten solder and the Sn diffusion layer (original nitrided layer). - the Sn diffusion layer spreads over the entire nitrided layer. - a tin-rich (low chromium) area is formed in the boundary layer between the Sn diffusion layer and the base material. - the tin-rich area grows into the base material and erosion begins below the Sn diffusion layer (original nitriding layer). - the Sn diffusion layer (original nitriding layer) located between the tin-rich area and the molten solder is destroyed and erosion progresses. The responsible committee is DKE/K 682 "Aufbau- und Verbindungstechnik für elektronische Baugruppen" ("Packaging and interconnection technology for electronic assemblies") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 682 - Aufbau- und Verbindungstechnik für elektronische Baugruppen