Solid Electrolytic Capacitor Protective Film for Reflow Crack Relief
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Solution Overview
Problem
Solid electrolytic capacitors face deterioration of the solid electrolyte layer due to cracks formed between the solid electrolyte and cathode layers during temperature changes, particularly during reflow soldering, and moisture ingress through cracks in the sealing resin.
Innovation Solution
A solid electrolytic capacitor design featuring a porous sintered body, an anode wire, a dielectric layer, a solid electrolyte layer, a cathode layer, and a protective film with a glass transition point of 180° C. or lower, which softens during reflow soldering to relieve stress and fill cracks, preventing moisture ingress and thus suppressing solid electrolyte layer deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the protective film has a high glass transition point to maintain structural stability, then the film maintains its shape and strength, but the film cannot soften during reflow soldering to relieve stress and prevent crack formation
Solution Approach 1:
The protective film uses a polymer material with a glass transition point of 180°C or lower, which changes its physical properties at different temperatures. During reflow soldering, the film softens to relieve stress and prevent crack formation, while at operating temperatures it maintains sufficient mechanical strength and stability.
Solution Approach 2:
The protective film transitions from a rigid state at room temperature to a flexible, soft state during reflow soldering. This dynamic property allows the film to adapt to thermal expansion and stress changes, preventing crack formation between the solid electrolyte layer and cathode layer.
2Volume of moving object
If the sealing resin is made thin to reduce size, then the capacitor compactness improves, but the sealing resin cracks during reflow soldering allowing moisture ingress
Solution Approach 1:
The protective film acts as an intermediary layer between the cathode layer and the external environment. It provides an additional barrier against moisture ingress and reinforces the sealing structure, allowing the sealing resin to be thinner while maintaining overall sealing integrity during reflow soldering.
3Reliability
If the pores of the porous sintered body contain moisture to improve ionic conductivity, then the capacitor performance improves, but the moisture expands during reflow soldering causing cracks in the sealing resin
Solution Approach 1:
The protective film is applied beforehand to cushion and absorb the expansion pressure of moisture in the porous sintered body during reflow soldering. This prevents the moisture expansion from causing cracks in the sealing resin, allowing the capacitor to maintain both performance and structural integrity.
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 protective film effectively suppresses crack formation between the solid electrolyte and cathode layers and inhibits moisture entry, thereby preventing solid electrolyte layer deterioration and maintaining capacitor performance.
Implementation Method 1
the protective film has a glass transition point of 180° C. or lower... the protective film softens during reflow soldering, thus relieving stress that forms a crack between the solid electrolyte layer and the cathode layer
Implementation Method 2
the softened protective film can flow into the crack and fill the cracked portion
Data Source
AI summary
A solid electrolytic capacitor includes: a porous sintered body made of a valve metal; an anode wire that has a portion extending inside the porous sintered body, and that protrudes from the porous sintered body; a dielectric layer formed on the porous sintered body; a solid electrolyte layer formed on the dielectric layer; a cathode layer formed on the solid electrolyte layer; and a protective film having at least a portion formed on the cathode layer. The protective film has a glass transition point of 180° C. or lower.