| 摘要 |
<p>PURPOSE:To improve solderability by coating an outer lead with a Pb alloy containing not less than 60 wt. % Pb in 1.5mum or more and an Sn alloy containing not less than 40 wt. % Sn in thickness of 1mum or more in succession. CONSTITUTION:The upper section of a base body 1 is coated with an A layer 2 consisting of Pb or a Pb alloy containing not less than 60 wt. % Pb in thickness of 1.5mum or more and the upper section of the A layer 2 with a B layer 3 composed of Sn or an Sn alloy containing not less than 40 wt. % Sn in thickness of 1mum or more before mounting as shown in the figure (a), an Sn section in the A layer 2 reacts with Cu in the base body 1 to form a Cu.Sn compound layer 4 such as Cu6Sn5, Cu3Sn, etc., as shown in the figure (b) by heating at the time of mounting, and a residual Pb section covers the upper section of the Cu.Sn compound layer 4 as a Pb-rich layer 5. The Pb-rich layer 5 is made up of an alpha phase including Pb or a minute quantity of Sn, and functions as a barrier inhibiting the diffusion of Cu. The B layer 3 shapes the reacting layer 6 of the A layer and the B layer on a boundary with the Pb-rich layer 5, and partial Sn forms a compound with Cu, but the effect of these formation has no effect on the surface, thus holding excellent solder wettability.</p> |
