Soldering Structure with Acute Contact Angles
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Solution Overview
Problem
Conventional electronic component soldering methods face challenges in achieving high connection reliability at low cost and high productivity due to increased production costs, joint reliability issues, high electric resistance, and limitations in applying to complex substrates like multilayered or double-sided mounting substrates, where high bonding loads are required.
Innovation Solution
The method involves applying a thermosetting resin containing solder particles onto a rigid substrate, heating a flexible substrate to melt the solder particles, and pressing it onto the substrate under a controlled pressure to form a columnar solder part with acute contact angles, surrounded by a resin part that bonds the components, thereby securing reliable connections with reduced material costs and processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder precoating method is used to connect terminal to circuit electrode, then electrical conduction is achieved, but production cost increases due to additional step of forming solder part
Solution Approach 1:
The circuit electrode is pre-coated with solder material before the flexible substrate is attached. This preliminary action ensures that when the flexible substrate is pressed against the rigid substrate, the pre-formed solder part immediately melts and bonds the terminal to the circuit electrode, eliminating the need for separate soldering steps and reducing production costs
Solution Approach 2:
The invention changes the physical state of solder material from solid to liquid by controlling temperature parameters. The solder coating on the circuit electrode is heated to melting point during the press-heating process, enabling the solder to flow and form reliable electrical connections between the terminal and circuit electrode
2Area of stationary object
If narrow-pitching circuit electrodes are used to reduce device size, then device compactness is improved, but bridge formation occurs readily during soldering reducing joint reliability
Solution Approach 1:
The invention applies different properties to different parts of the soldering system: the solder material has low melting point for easy flow into narrow spaces, while the rigid substrate provides high thermal conductivity for localized heating control. This local quality differentiation enables reliable soldering of narrow-pitch electrodes without bridge formation
Solution Approach 2:
The invention uses controlled pressure application during the press-heating process to ensure uniform distribution of melted solder material between narrow-pitch electrodes. The hydraulic pressure ensures that solder flows evenly without excessive accumulation that could cause bridging, while still achieving reliable electrical connections
3Reliability
If ACF method with conductive particles is used for connection, then electrical conduction is achieved, but electric resistance is high at connection part
Solution Approach 1:
The invention replaces the mechanical contact of conductive particles in ACF with a metallurgical bonding system using melted solder. Instead of relying on particle-to-particle contact through the resin matrix, the solder material creates direct metallic bonds between the terminal and circuit electrode, achieving significantly lower electric resistance
Solution Approach 2:
The invention uses a composite approach by combining solder material with the rigid substrate coating. The solder-coated electrode structure creates a metallurgical composite that provides both mechanical strength and excellent electrical conductivity, overcoming the high resistance issue of pure particle-based ACF connections
4Reliability
If high bonding load is applied to bring conductive particles into contact, then connection is achieved, but application to multilayered or double-sided mounting substrates is limited
Solution Approach 1:
The circuit electrode is pre-coated with solder material before mounting, creating a ready-to-bond surface. This preliminary preparation eliminates the need for high bonding loads during assembly, as the solder material flows easily when heated, enabling connection of complex substrates like multilayered or double-sided mounting boards that cannot withstand high pressure
Solution Approach 2:
The invention changes the bonding mechanism from mechanical pressure-dependent (ACF) to temperature-dependent (solder melting). By controlling temperature parameters rather than applying high mechanical loads, the method becomes applicable to a wider range of substrate types including multilayered and double-sided mounting substrates that have limited pressure tolerance
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 ensures high connection reliability with low electric resistance and reduced production costs, enabling application to various electronic components, including those with complex substrates, without the need for high-pressure bonding, thus enhancing productivity and cost-effectiveness.
Implementation Method 1
the solder particles put between the circuit electrode and the terminal melt by thermocompression bonding thereby to solder the circuit electrode and the terminal to each other
Implementation Method 2
the flexible substrate is heat-bonded to the solid substrate, whereby the circuit electrode and the terminal are brought into contact with each other with the conductive particles between them, and the thermosetting resin thermosets
Data Source
AI summary
In an electronic component soldering method of connecting a terminal provided on a flexible substrate to an electrode of a rigid substrate, after solder-mixed resin in which solder particles are mixed in thermosetting resin has been applied onto the rigid substrate so as to cover the electrode, the flexible substrate is put on the rigid substrate and heat-pressed, whereby there are formed a resin part that bonds the both substrates by thermosetting of the thermosetting resin, and a solder part which is surrounded by the resin part and has narrowed parts in which the peripheral surface is narrowed inward in the vicinity of the terminal surface and in the vicinity of the electrode surface. Hereby, the solder parts are soldered to the electrodes and the terminal at acute contact angles so that the production of shape-discontinuities which lowers fatigue strength can be eliminated.