Composite Magnetic Sheet Resin Decomposition Control
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Solution Overview
Problem
Composite magnetic sheets expand during the reflow process due to the decomposition of viscosity improvers, leading to separation from circuit boards and poor circuit board quality, especially when the pore ratio is high or even at low ratios during the reflow process.
Innovation Solution
The composite magnetic sheet is formed using a magnetic slurry with a first resin that is hardly decomposed at reflow temperatures and a second resin that is significantly decomposed, with heat-treatment performed at a temperature equal to or higher than the reflow temperature to reduce gas generation and expansion, incorporating a forming method that includes mixing soft magnetic powder with these resins and heat-treating the slurry to create a binder that is stable during reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pore ratio is reduced to 2.5% or less, then the separation from circuit board is prevented, but the composite magnetic sheet still expands during reflow process
Solution Approach 1:
The patent changes the thermal decomposition parameters of the binder resin by selecting a resin with a specific decomposition temperature range (200-400°C) that matches the reflow process temperature. This parameter matching ensures the resin decomposes at the right time to prevent gas generation during reflow, thereby maintaining dimensional stability while preserving bond strength.
Solution Approach 2:
The patent utilizes the phase transition (decomposition) of the binder resin at a controlled temperature range. By selecting a resin that decomposes between 200-400°C, the harmful gas generation is timed to occur before or during the reflow process, converting a potentially harmful phase transition into a beneficial effect that prevents expansion while maintaining structural integrity.
2Stability of the object's composition
If the heat-treatment temperature is increased to reduce gas generation, then the decomposition of viscosity improver is reduced, but the binder resin may be damaged
Solution Approach 1:
The patent optimizes the heat-treatment temperature parameter to a specific range (200-400°C) that balances two competing requirements: high enough to decompose the viscosity improver and reduce gas generation, but not so high as to damage the binder resin. This precise parameter control resolves the contradiction between reducing gas generation and preserving binder strength.
3Reliability
If the reflow temperature is increased for lead-free soldering, then the soldering quality is improved, but the composite magnetic sheet expands due to resin decomposition
Solution Approach 1:
The patent converts the harmful effect of resin decomposition (gas generation causing expansion) into a beneficial effect by carefully selecting a resin whose decomposition temperature matches the reflow process temperature. The decomposition that would normally cause harm is instead timed to occur in a controlled manner, preventing gas entrapment and expansion while allowing high-temperature lead-free soldering to proceed successfully.
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
This approach significantly reduces the expansion of the composite magnetic sheet during the reflow process, ensuring a stable bond with the circuit board and maintaining the sheet's integrity and magnetic properties.
Implementation Method 1
the decomposition of the viscosity improver during the reflow process generates gas in the composite magnetic sheet
Implementation Method 2
The obtained intermediate body was heat-treated so that a composite magnetic sheet was obtained
Data Source
AI summary
A forming method of a composite magnetic sheet. The forming method comprises a preparing step, a forming step and a heat-treating step. In the preparing step, magnetic slurry is prepared by mixing at least a soft magnetic powder having a flat shape, a first resin having a solid component and a second resin having a solid component, weight loss of the solid component of the first resin being 4.0% or less at 220° C., weight loss of the solid component of the second resin being 5.0% or more at 220° C. In the forming step, the magnetic slurry is formed into an intermediate body having a sheet-like shape. In the heat-treating step, the intermediate body is heat-treated at a heat-treatment temperature between 220° C. and 400° C. (both inclusive).