Reflow Soldering with Local Heating for Mixed Thermal Mass PCBs
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Solution Overview
Problem
Conventional reflow soldering methods face challenges in effectively soldering a mix of very small and large components due to thermal mass mismatch, leading to issues such as overheating, inadequate flux activation, and suboptimal solder joint formation, which are not adequately addressed by current convection ovens.
Innovation Solution
A reflow soldering method utilizing a heating control system with a cover or shield to reduce heat transfer to smaller components and a secondary heater to increase heat transfer to larger components, allowing for tailored heating profiles based on thermal mass, ensuring proper solder joint formation without damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the oven temperature is increased to heat large thermal mass components adequately, then the heating of large components is improved, but small components are overheated and damaged
Solution Approach 1:
The patent applies local quality by providing different heating conditions to different regions of the circuit board. Heating zones are configured with different temperature profiles - higher temperatures for regions with large thermal mass components and lower temperatures for regions with small components. This allows each component to receive appropriate heating without causing damage to temperature-sensitive components.
Solution Approach 2:
The heating system is segmented into multiple independent heating zones, each capable of operating at different temperature levels. This segmentation allows the oven to simultaneously maintain different temperature profiles in different areas, resolving the contradiction between heating large components and protecting small components.
2Duration of action of moving object
If the heating time is extended to ensure proper flux activation for small components, then solder wetting is improved, but the time above liquidus exceeds the maximum limit for large components
Solution Approach 1:
Different dwell times above liquidus temperature are applied to different heating zones based on component requirements. Small components receive extended heating time for proper flux activation, while large components are maintained at appropriate temperatures without excessive exposure time, ensuring both achieve optimal solder joint quality within their respective time requirements.
3Stability of the object's composition
If the fan speed is increased to improve heat transfer uniformity, then temperature distribution is improved, but components may move due to excessive air flow
Solution Approach 1:
The fan speed is dynamically adjusted based on the specific heating requirements of different zones and components. The system optimizes air flow velocity to achieve uniform heat transfer while maintaining conditions that prevent component displacement, balancing heat transfer efficiency with component stability.
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 ensures that both small and large components are soldered effectively, forming strong mechanical and electrical connections while preventing overheating, thereby improving the reliability and quality of solder joints in electronic circuit boards.
Implementation Method 1
forming a first solder joint between the first component and the substrate by heating the first component and the substrate
Implementation Method 2
forming a second solder joint between the second component and the substrate using the heater
Implementation Method 3
the soldering paste refluxes (i.e. is heated to a melting or reflux temperature) in a heating area and then cools in a cooling area to form solder joints
Data Source
AI summary
According to an aspect of the invention there is provided a reflow soldering method for manufacturing an electronic circuit board including a first component and a second component, wherein the first component has a first thermal mass, the second component has a second thermal mass and wherein the second thermal mass is different to the first thermal mass. The reflow soldering method includes: applying a solder paste to a substrate to be soldered; applying the first component to the substrate; applying the second component to the substrate; providing a heating control means proximal to one or both of the first component and the second component; forming a first solder joint between the first component and the substrate by heating the first component and the substrate; and forming a second solder joint between the second component and the substrate using the heater.