浸せきはんだ付におけるぬれ不良部の発生について 電子部品はんだ付部の信頼性に関する研究 Ｉ

Abstract

The local non-wetted Area occurred on the surface of copper specimen dipped in molten eutectic solder bath was measured as functions of the surface contamination of specimen, the immersion time, depth, rate etc. of specimen and the activity of used flux, by using a commercial type meniscograph tester and a profile projector.The results obtained were as follows;1) The oxide film on specimen greatly influenced the occrrence of non-wetted parts. Before dipping, when the specimen was heated at 150°C within 10 min in air, the ratio of non-wetted area to the soldered area of specimen was below a few percent.2) The ratio of non-wetted area was depended on the immersion depth of specimen. When the depth equals a equilibrium height of negative meniscus by non-wetting liquid, or is below, the ratio was fairly small. This case was named as I type wetting process. However, when the depth is over the equilirbium height, the ratio increased with increasing of the depth, because the flux painted on specimen was removed by the hydrostatic pressure of molten solder. This case was named as II type wettig process.3) The equilibrium height of negative meniscus was 3.6 mm for copper plate of infinite width and eutectic solder at 230°C. From this value, the radius of curvature at the height was calculated as 1.8 mm. Moreover, the equilirbium height of negative meniscus for a lead wire of 0.8 mm dia. was measured as 1.6 mm. In this case, the radii of curvature on two liquid surfaces which intersect perpendicularly at the height of negative meniscus were calculated as 1.8 mm and 3.2 mm respectively.4) For a lead wire of 0.8 mm dia., the immersion depth of 2-2.5 mm standeadized by JIS C 5033 belongs to II type wetting process in our experiment.