Induction Heater Counterflow Design for Convective Rework
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Solution Overview
Problem
Existing convective rework systems for electronic components, particularly those using resistance coil heating elements, are inefficient, costly, and difficult to control, leading to excessive heat generation, premature failure, and slow throughput due to high thermal mass and inefficient heat transfer.
Innovation Solution
An induction heater system with a nickel-plated copper coil and a ferromagnetic stainless steel wool core, utilizing an LC resonant Royer oscillator circuit, which efficiently heats fluid through a counterflow heat exchanger design, allowing for precise temperature control and reduced thermal mass, thereby minimizing errant heat and extending component and system lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If resistance coil heating elements are used to heat fluid for convective soldering, then heating capability is provided, but heat transfer efficiency is poor and excessive power is consumed
Solution Approach 1:
The patent replaces resistance coil heating (electrical heating through resistive elements) with induction heating (electromagnetic induction through an induction coil and ferromagnetic core). This substitution fundamentally changes the heating mechanism from direct electrical resistance heating to electromagnetic induction heating, which directly induces eddy currents in the ferromagnetic core, generating heat more efficiently and transferring it to the fluid with superior heat transfer coefficients.
Solution Approach 2:
The patent changes the physical parameters of the heating system by introducing a ferromagnetic stainless steel wool core with high surface area and enhanced magnetic properties. This core material has superior thermal and electrical conductivity characteristics compared to traditional resistance coils, enabling more efficient energy conversion and heat transfer to the fluid passing through the heater assembly.
2Strength
If resistance coil heating elements with high thermal mass construction are used, then structural robustness is achieved, but temperature control precision and response time deteriorate
Solution Approach 1:
The patent fundamentally changes the thermal mass parameter by using a ferromagnetic core structure that achieves the required structural robustness through magnetic material properties rather than thermal mass. The ferromagnetic stainless steel wool core provides structural integrity while maintaining low thermal mass, enabling rapid temperature response and precise control without the inertia associated with traditional high-mass resistance coil constructions.
3Reliability
If resistance coil heaters are made robust and well-insulated to withstand errant heating, then reliability under heavy use is improved, but physical size and complexity increase
Solution Approach 1:
The patent replaces the resistance coil heating system with an induction heating system that inherently generates less errant heat. The induction coil heats the ferromagnetic core directly through electromagnetic induction, and the fluid passing through the core is efficiently heated with minimal heat loss to surrounding components. This eliminates the need for extensive thermal insulation and robust heat-resistant constructions, reducing overall system complexity and size while maintaining reliability.
4Power
If resistance coil heating elements are used, then heating function is provided, but heating speed and throughput are slow due to high thermal mass
Solution Approach 1:
The patent replaces resistance coil heating with induction heating, which directly induces eddy currents in the ferromagnetic core, generating heat rapidly and efficiently. This substitution eliminates the thermal inertia of resistance coils and their high thermal mass construction, enabling much faster heating rates and improved throughput for convective soldering operations.
Solution Approach 2:
The patent changes the thermal mass parameter by using a ferromagnetic core structure that achieves required structural properties without excessive mass. The ferromagnetic stainless steel wool core provides the necessary structural robustness while maintaining low thermal mass, enabling rapid temperature response and fast heating speeds that directly improve productivity and throughput.
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 induction heater system provides superior heat transfer efficiency, faster heating and cooling, reduced power consumption, and increased reliability, enabling precise process control and improved throughput while minimizing heat-related issues in adjacent systems, thus enhancing the overall performance and longevity of the rework system.
Implementation Method 1
An induction heater consists of an induction coil (typically made of copper or copper alloy and nickel plated for protection against oxidation) around a ferromagnetic core (typically made of stainless steel wool or similar material)
Implementation Method 2
a ferromagnetic stainless steel wool core, utilizing an LC resonant Royer oscillator circuit, which efficiently heats fluid
Implementation Method 3
heated all the solder interconnections ('solder joints') simultaneously with a heated fluid (typically air or nitrogen) to some point above solder melt temperature
Data Source
AI summary
An induction heater having inner and outer chamber cylinders connected in an air tight manner to a base and cover with an inner chamber being formed within the inner chamber cylinder and an outer chamber being formed between the inner and outer chamber cylinders, a heat exchange core disposed in the inner chamber, and an induction heater coil disposed in the outer chamber extending around the inner chamber cylinder. A flow path is provided from a cool air inlet in the base, along the outer chamber, into the inner chamber and through the inner chamber and core to a heated air outlet in the base in a counterflow direction relative to the flow along the outer chamber. The heater is especially well suited for use in convective soldering and rework apparatus.