Flashlamp Solder Reflow for Thermally Fragile Surface-Mount Components
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Solution Overview
Problem
Current methods for connecting surface-mount electronic components to circuit boards, such as reflow soldering, face challenges including high temperature requirements, lengthy processing times, mechanical and electrical robustness issues, and precision alignment problems, particularly with small components and non-uniform heating sources.
Innovation Solution
A system using a flashlamp to apply multiple light pulses to the solder, with adaptive adjustment of pulse duty cycle based on measured temperature and radiant exposure, allowing precise control of thermal processing to reflow solder without heating the entire circuit board, ensuring uniform and efficient connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reflow soldering is used to connect surface-mount electronic components, then good electrical and mechanical connections are achieved, but high temperature (about 217°C for SAC-305) is required which may damage thermally fragile components
Solution Approach 1:
The patent applies selective laser heating to reflow solder paste only at specific joint locations rather than heating the entire circuit board uniformly. This localized approach allows the solder to reflow at lower temperatures while protecting thermally fragile components from excessive heat exposure
Solution Approach 2:
The reflow process is segmented into multiple discrete laser pulses applied to individual solder joints rather than a continuous bulk heating process. This enables precise control of thermal energy delivery to each joint independently, achieving reliable connections without requiring high overall board temperature
2Reliability
If reflow soldering is used, then solder paste is properly reflowed, but lengthy processing time (about 10 minutes) is required due to controlled thermal profile
Solution Approach 1:
The patent uses periodic laser pulses to deliver thermal energy to solder joints in a controlled sequence. Multiple pulses are applied at specific intervals to accumulate the necessary thermal energy for reflow, achieving reliable solder connections in seconds rather than minutes
Solution Approach 2:
The laser process rapidly delivers concentrated thermal energy to each solder joint, skipping through multiple joints in sequence. This rushes through the heating process that would otherwise require slow, controlled thermal diffusion across the entire board, reducing processing time from 10 minutes to seconds
3Power
If laser process is used for selective solder reflow, then precise power delivery and rapid processing (about one second) are achieved, but the inherently serial nature increases total time for circuits with many solder joints
Solution Approach 1:
The patent transitions from serial one-dimensional processing to parallel two-dimensional processing by using a scanning laser system that can simultaneously address multiple solder joints arranged in a grid pattern on the circuit board. This dimensional change allows multiple joints to be processed concurrently, dramatically increasing productivity
4Stability of the object's composition
If reflow oven convection heating is used, then solder paste is heated uniformly, but aerodynamic shear from air flow may cause small electronic components to blow off or become misaligned
Solution Approach 1:
The patent extracts the harmful aerodynamic shear force from the heating process by replacing convection-based heating with direct laser heating. This removes the air flow that causes small components to blow off or misalign, while still achieving the necessary thermal energy delivery to the solder paste
Solution Approach 2:
Instead of uniform convection heating that requires high air flow velocities, the patent applies localized laser heating directly to each solder joint. This eliminates the need for high-velocity air flow that causes aerodynamic shear, while still achieving effective heating through direct optical-to-thermal energy conversion at the target location
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 method enables rapid, precise, and uniform thermal processing of solder, reducing thermal stress on components and circuit boards, improving mechanical and electrical robustness of connections while accommodating thermally fragile materials and small components.
Implementation Method 1
Multiple light pulses from the flashlamp are applied to the electronic component, substrate and solder until the solder reflows
Implementation Method 2
a solid-state laser can be directed on solder joints or electronic components to heat them and reflow the solder
Data Source
AI summary
A method for connecting an electronic component to a circuit board is disclosed. Initially, a substrate and an electronic component having solder located between them are placed under a flashlamp. Multiple light pulses from the flashlamp are applied to the electronic component, substrate and solder until the solder reflows. During the application of the light pulses, the power of one of the light pulses from the flashlamp and the temperature of the electronic component are measured, the measured power is converted to radiant exposure, and in response to the measured temperature of the electronic component, the duty cycle of a next light pulse is adjusted adaptively according to the radiant exposure of the one light pulse.