Electrolytic Capacitor Terminal Structure for Reflow Mounting Reliability
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Solution Overview
Problem
Existing electrolytic capacitors face issues with lead terminal separation from outer packaging resin during reflow treatment and insufficient connection strength between the terminal and printed circuit boards, leading to potential mounting failures.
Innovation Solution
The electrolytic capacitor design includes a lead terminal with a terminal portion partially exposed and two anchor portions that extend into the outer packaging resin, featuring inclined surfaces to enhance terminal strength and connection reliability, preventing separation and facilitating strong solder fillet formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the terminal portion is embedded in outer packaging resin, then terminal strength should be improved, but the terminal portion may separate from the outer packaging resin due to expansion during reflow treatment
Solution Approach 1:
The lead terminal is divided into distinct functional portions: an embedded portion that anchors into the outer packaging resin for strength, and an exposed terminal portion for electrical connection. This segmentation allows each portion to optimize its function without compromising the other, preventing separation while maintaining terminal strength.
Solution Approach 2:
The lead terminal is pre-formed with a specific geometry including an embedded portion designed to anchor into the resin before the molding process. This preliminary configuration ensures proper embedding and prevents separation during subsequent reflow treatment, addressing the reliability issue before it occurs.
2Strength
If the terminal portion is designed for strong soldering connection, then connection strength should be improved, but mounting failures may occur due to resin burrs between terminal tips
Solution Approach 1:
The design extracts the problematic resin burrs from the critical mounting area by positioning the terminal tips to protrude slightly from the bottom surface. This ensures that resin burrs remaining between tips during molding do not interfere with soldering, preventing mounting failures while maintaining connection strength.
Solution Approach 2:
The terminal structure employs different geometries at different locations: the embedded portion has a configuration optimized for resin anchoring, while the terminal tips have a specific protrusion design optimized for soldering. This local differentiation allows each area to perform its function optimally without compromising the other.
Data Source
AI summary
An electrolytic capacitor includes a capacitor element having a bottom surface and an upper surface, an anode lead terminal, and outer packaging resin. The electrode lead terminal includes a terminal portion and two anchor portions. The terminal portion has a principal surface exposed from the bottom surface, and has an end side along a longitudinal direction of the anode lead. Each of the two anchor portions includes an upright portion that rises from an end side of the terminal portion toward the upper surface. The upright portion has a first region exposed from the bottom surface in a vicinity of a boundary with the end side, the first region has an inclined surface continuous with the principal surface of the terminal portion, and the inclined surface is inclined to form an obtuse angle with the principal surface of the terminal portion.