Lead Pin Bonding Surface Geometry for Reflow Soldering
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Solution Overview
Problem
Flat type lead pins experience inclination failures during reflow soldering due to insufficient solder distribution around the connection head portion, leading to inadequate correction of their inclined state.
Innovation Solution
A lead pin design featuring a connection head portion with a flat central surface, a convex surface shaped like a ring with radius R, and a concave or inclined surface, ensuring adequate solder distribution and correction of inclination during reflow soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat type lead pin is used, then the manufacturing process is simple and the structure is easy to manufacture, but the solder distribution around the connection head portion is insufficient, causing inclination failure during reflow soldering
Solution Approach 1:
The bonding surface is designed with different local geometries: a flat surface in the center and a convex surface at the periphery. This local differentiation allows the central flat area to provide stable bonding while the peripheral convex area accumulates solder, ensuring adequate solder distribution without complicating the overall manufacturing process
Solution Approach 2:
A convex surface with a specific radius of curvature is introduced at the periphery of the bonding surface. This curvature creates a natural solder accumulation zone during reflow soldering, allowing solder to be retained in sufficient quantities around the connection head portion, thereby preventing inclination failure while maintaining manufacturing simplicity
2Reliability
If the bonding surface is made entirely convex like a sphere, then solder distribution is improved and inclination can be corrected, but the bonding strength is reduced and solder may overflow beyond the outermost edge
Solution Approach 1:
The bonding surface combines a flat central region for strong, stable bonding with a peripheral convex region for solder accumulation. This local differentiation ensures that the central flat area maintains adequate bonding strength while the peripheral convex area provides the necessary solder distribution to prevent inclination failure
Solution Approach 2:
Instead of making the entire bonding surface convex, only the peripheral portion is made convex while the center remains flat. This partial application of convexity provides sufficient solder accumulation to correct inclination without causing excessive solder overflow or reducing overall bonding strength
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively corrects the inclination of lead pins to within permissible limits, preventing failure and improving the bonding process by maintaining solder within the bonding surface, thus enhancing the yield and appearance of the wiring substrate.
Implementation Method 1
a convex surface which is provided like a ring shape to an outside of the flat surface and rounded by a radius R like a convex shape
Implementation Method 2
an inclining surface which is provided like a ring shape to an outside of the convex surface and whose height is lowered toward an outside gradually
Implementation Method 3
when the semiconductor chip is reflow soldered to the upper side of the wiring substrate, to the lower side of which the lead pins are fixed by the solder layer, simultaneously the solder layer fixing the lead pins is reflown again by the heating process
Data Source
AI summary
A lead pin includes a shaft portion, a connection head portion provided to a top end side of the shaft portion, and having a diameter which is larger than a diameter of the shaft portion, wherein the connection head portion includes a bonding surface on an opposite side to the shaft portion side, and the bonding surface includes a flat surface provided in a center part, a convex surface which is provided like a ring shape to an outside of the flat surface and rounded by a radius R like a convex shape, and a concave surface which is provided like a ring shape to an outside of the convex surface and rounded by a radius R like a concave shape.