Composite Printed Wiring Board With Diffusion Bonding for Reflow
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Solution Overview
Problem
The existing composite printed wiring boards face issues with solder balls melting during reflow heating, leading to separation of printed wiring boards from the frame, which hampers the mounting of electronic components.
Innovation Solution
A composite printed wiring board design featuring a first printed wiring board, an intermediate member with a cavity, and a second printed wiring board, bonded using a mutual diffusion bonding layer containing high and low melting point metals, where the bonding layers have a melting point higher than the low melting point metal, allowing for reflow heating without melting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If solder balls are used to bond printed wiring boards to the frame, then the bonding process is simple and effective, but the solder balls may be melted by reflow heating, causing separation of the printed wiring boards from the frame
Solution Approach 1:
The bonding material's melting point parameter is changed from low (solder balls) to high (mutual diffusion bonding layer with melting point higher than low melting point metal), enabling the bonding to withstand reflow heating temperatures without melting or separation
Solution Approach 2:
The bonding layer is formed as a composite structure containing both high melting point metal and low melting point metal, where the high melting point metal provides thermal stability during reflow heating while the low melting point metal enables bonding at lower temperatures, creating a multi-functional bonding material
2Productivity
If printed wiring boards are stacked using solder balls, then the assembly process is straightforward, but additional reflow heating for mounting electronic components causes melting of solder balls and separation of boards
Solution Approach 1:
The mutual diffusion bonding layer is formed in advance before the reflow heating process for mounting electronic components. This preliminary bonding with high melting point characteristics ensures that the printed wiring boards remain firmly bonded to the frame during subsequent reflow heating operations, preventing separation while maintaining assembly efficiency
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 design enables reliable reflow heating for mounting electronic components while preventing the disintegration of the bonding layers, ensuring stable bonding and efficient heat dissipation through the cavity.
Implementation Method 1
a mutual diffusion bonding layer is arranged at a bonding section between the first printed wiring board and the intermediate member and at a bonding section between the second printed wiring board and the intermediate member. The bonding layer contains high melting point metal and low melting point metal.
Implementation Method 2
The melting point of the bonding layer is higher than the melting point of the low melting point metal
Data Source
AI summary
A composite printed wiring board that allows for reflow heating for mounting electronic components using solder includes a first printed wiring board, an intermediate member, a second printed wiring board, and a bonding layer. The intermediate member is stacked on the first printed wiring board. The intermediate member has a cavity. The second printed wiring board is stacked on a surface on the opposite side to a surface opposed to the first printed wiring board in the intermediate member. The bonding layer is arranged at a bonding section between the first printed wiring board and the intermediate member and at a bonding section between the second printed wiring board and the intermediate member. The bonding layer contains high melting point metal and low melting point metal. The melting point of the bonding layer is higher than the melting point of the low melting point metal.