Composite Printed Wiring Board Bonding for Reflow Heat Resistance
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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 from the frame, which hampers the mounting of electronic components.
Innovation Solution
A composite printed wiring board design featuring bonding layers made of high melting point metals and low melting point metals, formed through mutual diffusion, which prevents melting during solder reflow heating, ensuring stable bonding and efficient heat dissipation.
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 printed wiring boards can be stacked with electronic components, 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 (metal with melting point higher than reflow heating temperature). This parameter change allows the bonding material to withstand reflow heating temperatures without melting, resolving the contradiction between ease of manufacture and reliability during reflow heating
Solution Approach 2:
The invention uses composite bonding layers comprising multiple metals including a first metal (melting point ≥1000℃), second metal, and third metal. This composite material structure provides both high temperature resistance and adequate bonding strength, enabling printed wiring boards to be stacked and subsequently undergo reflow heating without separation
2Reliability
If the melting point of the bonding material is increased to prevent melting during reflow heating, then bonding reliability is improved, but the bonding strength may be reduced due to reduced ductility at high temperatures
Solution Approach 1:
The bonding layer uses a composite material system with multiple metals having different properties. The first metal (melting point ≥1000℃) provides high temperature resistance, while the second and third metals contribute to bonding strength and ductility. This composite approach resolves the contradiction by combining materials that individually have limiting properties but together provide both high temperature stability and adequate bonding strength
Solution Approach 2:
Different regions of the bonding layer have different metal compositions optimized for different functions. The bonding layer is designed with specific metal distributions to provide high temperature resistance where needed while maintaining bonding strength at the interfaces, resolving the contradiction between reliability and strength
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
The solution allows for reliable reflow heating of electronic components without separating the printed wiring boards, enhancing the bonding strength and heat dissipation capabilities of the composite printed wiring board.
Implementation Method 1
bonding layers which bond the first printed wiring board and the second printed wiring board to the intermediate member, contain high melting point metal and low melting point metal
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A composite printed wiring board (1) that allows for reflow heating for mounting electronic components using solder includes a first printed wiring board (2), an intermediate member (4), a second printed wiring board (3), and a bonding layer (5, 6). The intermediate member (4) is stacked on the first printed wiring board (2). The intermediate member (4) has a cavity (7). The second printed wiring board (3) is stacked on a surface on the opposite side to a surface opposed to the first printed wiring board (2) in the intermediate member (4). The bonding layer (5,6) is arranged at a bonding section between the first printed wiring board (2) and the intermediate member (4) and at a bonding section between the second printed wiring board (3) and the intermediate member (4). The bonding layer (5, 6) contains high melting point metal and low melting point metal. The melting point of the bonding layer (5,6) is higher than the melting point of the low melting point metal.