PCB Multi-Solder Assembly for Temperature-Sensitive Components
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The conventional printed circuit board (PCB) assembly process using a single solder paste alloy exposes all components to high reflow temperatures, potentially damaging temperature-sensitive components and requiring extensive qualification validation for each component type, while also limiting the use of Low Temperature Solder (LTS) paste due to compatibility and volume control issues.
Innovation Solution
Implementing a multi-solder board assembly process that uses multiple solders with different reflow temperatures, allowing each set of electronic components to be attached at temperatures compatible with their specific temperature tolerance, without reflowing previously attached components, thereby reducing thermal warpage and maintaining the reliability of higher temperature-tolerant components.
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 warpage and unreliable solder joints
Solution Approach 1:
The patent segments the board assembly process into multiple reflow steps, each dedicated to specific component types with different temperature requirements. High-temperature components ( GPUs, memory modules) are attached in a first reflow step at 235-260°C, while temperature-sensitive components (CPU packages) are attached in a second reflow step at lower temperatures (150-190°C). This segmentation allows each component type to be processed at its optimal temperature without exposing it to damaging high temperatures.
Solution Approach 2:
The patent applies different solder paste compositions to different locations on the PCB based on the temperature requirements of the components being attached. SAC 305 solder paste is applied to pads for high-temperature components, while LTS solder paste is applied to pads for temperature-sensitive components. This local differentiation ensures that each component receives the appropriate solder material matched to its thermal tolerance.
2Reliability
If Low Temperature Solder (LTS) paste is used for all components, then temperature-sensitive components can be assembled at lower temperatures, but extensive qualification validation is required for each component type and solder paste volume control becomes difficult
Solution Approach 1:
The patent uses LTS solder paste locally only where temperature-sensitive components are located, rather than applying it universally across the entire board. This selective application eliminates the need for comprehensive qualification validation of LTS with all component types, as LTS is only used with components that require low-temperature processing. It also simplifies volume control since LTS paste is applied only to specific pads rather than requiring different volumes for different component types.
3Reliability
If multiple solders with different reflow temperatures are used, then each component can be attached at its optimal temperature, but the assembly process becomes more complex with multiple reflow steps
Solution Approach 1:
The patent divides the assembly process into distinct sequential steps, with each step targeting specific component types. The first reflow step attaches high-temperature components using SAC 305 solder, and the second reflow step attaches temperature-sensitive components using LTS solder. This segmentation organizes the complexity into manageable, well-defined phases rather than attempting to process all components simultaneously.
Solution Approach 2:
The patent performs preliminary actions by pre-applying the appropriate solder paste to each pad location before component placement. SAC 305 paste is applied to pads for high-temperature components, and LTS paste is applied to pads for temperature-sensitive components. This preliminary differentiation of solder types before the multi-step reflow process simplifies the overall assembly by having everything prepared and positioned correctly from the start.
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 successful assembly of temperature-sensitive components at lower temperatures without affecting the quality and reliability of higher temperature-tolerant components, optimizing attachment reliability and reducing thermal warpage, while allowing the continued use of conventional higher melting point solders for other components.
Implementation Method 1
heating the first solder to a first temperature to reflow the first solder; allowing the reflowed first solder to cool to form one or more first solder joints attaching the electrical contacts of the first electronic component to the first electrical contacts of the PCB
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; allowing the reflowed second solder to cool to form one or more second solder joints attaching the electrical contacts of the second electronic component to the second electrical contacts of the PCB
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.