PCB Assembly Using Multiple Solders for Temperature-Sensitive Components
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Solution Overview
Problem
Conventional board assembly processes using a single solder paste alloy, such as SAC 305, can damage temperature-sensitive components due to high reflow temperatures, and require full qualification validation for each component type when using Low Temperature Solder (LTS) paste, which complicates solder paste volume control.
Innovation Solution
Implementing a multi-solder board assembly process that uses different solder types with varying reflow temperatures to attach components, allowing for temperature-sensitive components to be assembled at lower temperatures without reflowing higher-temperature solder joints, thereby optimizing reliability and minimizing thermal warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single high-temperature solder paste (SAC 305) is used for all components, then all components can be attached using a common reflow process, but temperature-sensitive components are damaged due to excessive reflow temperatures
Solution Approach 1:
The patent divides the board assembly process into multiple reflow steps, each using different solder paste alloys with different melting points. Temperature-sensitive components are attached in a first reflow step using LTS solder paste at lower temperatures, while temperature-tolerant components are attached in a second reflow step using SAC 305 solder paste at higher temperatures. This segmentation allows each component type to be processed at its optimal temperature range.
Solution Approach 2:
The patent applies different solder paste alloys to different locations on the PCB based on the thermal sensitivity of the components being attached. LTS solder paste is applied to locations with temperature-sensitive components, while SAC 305 solder paste is applied to locations with temperature-tolerant components. This local differentiation ensures each component receives the appropriate thermal treatment.
2Reliability
If LTS solder paste is used for all components to avoid high temperatures, then temperature-sensitive components are protected, but full qualification validation is required for each component type and solder paste volume control becomes complex
Solution Approach 1:
The patent segments the component population into two groups based on thermal sensitivity: temperature-sensitive components processed with LTS solder paste, and temperature-tolerant components processed with SAC 305 solder paste. This segmentation eliminates the need for full qualification validation of LTS solder for all component types, as only the temperature-sensitive subset requires LTS processing.
Solution Approach 2:
The patent changes the solder paste alloy parameter (melting point temperature) based on component thermal sensitivity. By using SAC 305 solder paste for temperature-tolerant components, the process leverages existing qualifications and simplifies validation requirements, while still protecting temperature-sensitive components with LTS solder paste.
3Reliability
If multiple solder types are used for different components, then temperature-sensitive components can be assembled at lower temperatures, but the assembly process becomes more complex with multiple reflow steps
Solution Approach 1:
The patent performs preliminary action by pre-heating the PCB and components before applying solder paste in each reflow step. This preliminary heating reduces thermal shock and ensures uniform temperature distribution, simplifying the overall process control despite multiple reflow steps.
Solution Approach 2:
The patent systematically changes the temperature parameter between reflow steps, with the first reflow step operating at a lower temperature range for LTS solder and the second reflow step operating at a higher temperature range for SAC 305 solder. This parameter differentiation is managed through a controlled reflow profile that transitions between temperature zones.
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 enables the assembly of temperature-sensitive components at lower temperatures without affecting the quality and reliability of higher-temperature-tolerant components, enhancing overall PCB reliability and reducing thermal warpage risks.
Implementation Method 1
heating the first solder to a first temperature to reflow the first solder
Implementation Method 2
heating the second solder to a second temperature that is lower than the first temperature to reflow the second solder without reflowing the first solder joints
Data Source
AI summary
Board assembly processes are disclosed that may be implemented using multiple different electrically conductive solder types to assemble or attach different electronic components to a printed circuit board (PCB). For example, multiple different electronic components may be attached to a common PCB using a multiple-step assembly process that may be performed at different solder reflow temperatures and/or which may incorporate multiple different solder types having different respective minimum reflow temperatures (i.e., melting point temperatures). The disclosed processes may be implementing using a variety of different forms of solder, such as solder paste form, wire solder form, ingot solder form, etc.