BS 62739-3:2017 pdf download – Test method for erosion of wave soldering equipment using molten lead- free solder alloy Part 3: Selection guidance of erosion test methods
Surface processing is classified as surface diffusion type which is forming a surface processlayer by’diffusing nitrogen (for example) into material and coating type which is forming acoating layer on the surface of the mater material. Examples of each type are given below.
a) Surface diffusion type: nitrogen supersaturated solid solution diffusion treatment, diffusionpenetration nitriding, gas nitriding, nitrocarburizing, plasma nitriding
b) Coating type: fine ceramic coating by chemical densified process,CrN coating by a
Physical Vapor Deposition (PVD) method,and alumina coating by thermal spray.
NOTE The erosion mechanism of the test is explained in Annex c.
6 common items for each test method
6.1Specimen preparation
The specimens shall be prepared as indicated below.
a) Basically,specimen shaping shall be carried out by punching,using a press machine.
However, for high hardness materials such as titan and cast iron which are not suitable forpunching, shaving shall be used.
b)Specimen edge burrs, etc.,which are produced during specimen shaping and may cause
erosion,shall be removed by chamfering and such;
c) if necessary, surface processing shall be done after processes a) and b).
d) Care shall be taken to handle the specimen after fabrication, so as not to contaminate thespecimen by oil, or other contaminants,since this could affect the test result.
6.2Solder alloy
Unless otherwise specified,Sn96,5Ag3Cu,5 solder alloy specified in lEC 61190-1-3 shall beused. If Sn purity is too high, erosion occurs after a short time and inaccurate results may bethe consequence.
6.3Accelerated stress conditions6.3.1Test temperature
The test temperature is specified as 350 °C ± 3 C in IEC 62739-1 and 450 °C ± 3 C inIEC 62739-2.These test temperatures are determined so as to clearly identify the non-erosionarea which is used for the baseline of the erosion depth by the focal depth method and todifferentiate metal material and surface processing employed by erosion the depth on thespecimen.A sufficient test duration for metal material shall be pre-set, suitable for each metalmaterial and surface processing (see Annex A).
NOTE The thermal acceleration factor for erosion is explained in Annex D.6.
3.2Rotation speed
The speed difference between molten solder alloy and the specimen by rotating the specimenis assuming the molten solder flow speed in the wave soldering equipment.A rotation speedof 100 r/min ± 3 rlmin is specified for all test methods. lf the rotation speed is slower than thespecified value,then the molten solder flow speed is lower than the speed in the actualproduction process. Thus, this condition is not recognized as an acceleration factor of themolten solder flow speed in the actual production process. lf the rotation speed is higher thanthe specified value, then the molten solder begins to rotate and the relative speed differencebetween the molten solder and the specimen becomes minimal. This condition is also not recognized as an acceleration factor of the molten solder flow speed in the actual production process.
NOTE An example of a test result is shown in Figure A.3.
6.3.3 Bending stress to the specimen If it takes too long during the rotation test at 450 °C, further acceleration is needed. During the rotation test at 450 °C with 2 mm bending specified in IEC 62739-2, the specimen is subjected to bending stress as additional acceleration. 1 mm bending stress is not enough to accelerate occurrence of erosion (see Clause A.2). Bending stress exceeding 2 mm gives permanent deformation of the specimen, thus the erosion depth measurement by the focal depth method becomes difficult.
6.4 Dross
6.4.1 Dross generation and removal interval
The higher the test temperature and the higher the rotation speed, the more dross is generated due to the promoted oxidation of molten solder. Compared to the amount of dross produced by the rotation test at 350 °C the rotation test at 450 °C, generates more dross. However, by removing dross every 1 6 h, both tests can be run without problems such as firing and overflowing.BS 62739-3 pdf download.