Copper Plate Surface Machining for Silver Paste Bonding
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Solution Overview
Problem
Conventional methods for bonding electronic parts, such as semiconductor chips, on copper plates or copper-plated plates using silver paste fail to maintain a good bonding state under heat cycles, resulting in a high number of bonding defects.
Innovation Solution
The method involves surface machining the copper plate to achieve a surface roughness of 0.4 µm or more, applying a silver paste, and sintering the silver to form a bonding layer, with the copper plate being annealed to reduce hardness to less than 40 Vickers hardness before paste application, ensuring a strong and durable bond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a copper plate or copper-plated plate is used as a metal plate to bond electronic parts with a silver paste bonding agent, then the bonding process can be simplified, but the bonding state deteriorates with heat cycles resulting in a high number of bonding defects
Solution Approach 1:
The copper plate surface is pre-machined to a specific roughness (0.4 μm or more) before applying the silver paste bonding agent. This preliminary surface preparation creates anchor points and increases the effective bonding area, allowing the bonding process to proceed simply while ensuring the bonding state can withstand subsequent heat cycles without developing defects
Solution Approach 2:
The surface roughness parameter of the copper plate is specifically controlled to be 0.4 μm or more. This parameter change optimizes the interaction between the copper substrate and silver paste, enabling simple bonding processes to achieve reliable, defect-free bonds that maintain integrity under thermal stress
2Strength
If the surface roughness of the copper plate is increased to improve bonding, then the bonding strength improves, but the surface machining complexity increases
Solution Approach 1:
The surface roughness is optimized to a specific threshold (0.4 μm or more) that provides sufficient bonding strength without requiring excessive machining complexity. This parameter optimization achieves the balance between bonding strength and machining simplicity by identifying the minimum effective roughness level needed for reliable silver paste bonding
3Reliability
If the copper plate hardness is reduced through annealing to improve bonding, then the bonding state improves, but the mechanical strength of the copper plate decreases
Solution Approach 1:
The copper plate is annealed to reduce hardness specifically in the bonding region, creating a local soft zone that facilitates good bonding state with silver paste. The rest of the copper plate maintains its original mechanical strength, achieving local optimization of bonding properties without compromising overall structural integrity
Solution Approach 2:
The copper plate undergoes preliminary annealing treatment before the bonding process to reduce its hardness and improve bonding characteristics. This pre-treatment ensures that the bonding occurs under optimal material conditions while the bulk material retains sufficient mechanical strength for the application
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 results in an electronic part mounting substrate with excellent thermal shock resistance and minimal bonding defects, maintaining a good bonding state even after repeated heat cycles.
Implementation Method 1
the copper plate or copper-plated plate having the one side, which is surface-machined to have the surface roughness of 0.4 μm or more, is annealed to have a Vickers hardness Hv of not greater than 40
Implementation Method 2
sintering silver in the silver paste to form a silver bonding layer to bond the electronic part to the surface-machined side of the copper plate or copper-plated plate
Data Source
Figure 1~2
AI summary
In a method for producing an electronic part mounting substrate wherein an electronic part 14 is mounted on one major surface (a surface to which the electronic part 14 is to be bonded) of the metal plate 10 of copper, or aluminum or the aluminum alloy (when a plating film 20 of copper is formed on the surface), the one major surface of the metal plate 10 (or the surface of the plating film 20 of copper) is surface-machined to be coarsened so as to have a surface roughness of not less than 0.4 µm, and then, a silver paste is applied on the surface-machined major surface (or the surface-machined surface of the plating film 20 of copper) to arrange the electronic part 14 thereon to sinter silver in the silver paste to form a silver bonding layer 12 to bond the electronic part 14 to the one major surface of the metal plate 10 (or the surface of the plating film 20 of copper) with the silver bonding layer 12.