Flux-less Solder Bonding with Temporary Organic Retainer
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Solution Overview
Problem
Conventional bonding techniques face challenges in maintaining positional accuracy between bonded members, particularly when using flux-less solder bonding, which can lead to positional displacement issues due to the lack of retaining force between substrates, especially in small-scale solder bump structures.
Innovation Solution
A bonding structure manufacturing method that employs a temporary non-reducing organic agent with different boiling points to provide retaining force between substrates, allowing for flux-less solder bonding while preventing positional displacement by evaporating the agent before or during the soldering process, thereby eliminating the need for cleaning treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If flux-less solder bonding is used to eliminate cleaning treatment, then manufacturing complexity is reduced, but positional displacement between substrates occurs due to lack of retaining force
Solution Approach 1:
A non-reducing organic agent is applied to the substrate surface before solder bonding to provide temporary retaining force (stack force) that prevents positional displacement. This preliminary action allows flux-less bonding without positioning errors, and the organic agent is subsequently evaporated during heating, eliminating the need for cleaning treatment.
Solution Approach 2:
A non-reducing organic agent serves as an intermediary substance between substrates during bonding. It provides temporary retaining force to maintain positional accuracy, then evaporates during the heating process, leaving no residue that requires cleaning. This mediator resolves both the positioning and cleaning issues.
2Reliability
If conventional flux is used to prevent oxide film, then solder bonding quality is improved, but flux residue causes insulation failure and requires cleaning treatment
Solution Approach 1:
The patent changes the chemical properties of the organic agent from reducing (flux) to non-reducing. This parameter change allows the agent to provide retaining force without creating harmful residues that cause insulation failure, thereby improving reliability while eliminating the need for cleaning treatment.
Solution Approach 2:
The non-reducing organic agent undergoes phase transition from liquid to vapor during the heating process. This phase transition allows the agent to evaporate completely after providing retaining force, eliminating flux residue and the associated harmful effects without requiring cleaning treatment.
3Area of stationary object
If solder bump size is reduced to increase density, then area utilization is improved, but flux removal becomes difficult and residue increases
Solution Approach 1:
By changing the organic agent from reducing to non-reducing type, the patent enables easy removal through evaporation rather than requiring mechanical or chemical cleaning processes. This parameter change makes flux removal straightforward even when solder bump size is reduced and pitch is minimized, thereby improving ease of manufacture.
4Reliability
If multiple cleaning treatments are applied to remove flux residue, then insulation reliability is improved, but manufacturing complexity and time increase
Solution Approach 1:
The non-reducing organic agent undergoes phase transition from liquid to vapor during the heating process, automatically removing itself without requiring separate cleaning steps. This eliminates multiple cleaning treatments while maintaining insulation reliability, thereby improving productivity by reducing manufacturing cycle time.
Solution Approach 2:
The patent extracts the harmful reducing properties from the organic agent, using only the retaining force function. The non-reducing organic agent provides stack force during bonding, then evaporates cleanly without leaving residue, eliminating the need for subsequent cleaning treatments and reducing manufacturing complexity.
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 method effectively alleviates positional displacement between bonded members during solder bonding, ensuring accurate positioning and preventing insulation failures and voids in the underfill resin, even with small-scale solder bumps, without the need for flux or cleaning treatments.
Implementation Method 1
an evaporation step for evaporating the organic agent by heat application before or after the bonding step or over the bonding step
Implementation Method 2
a bonding step for melting the heat-melting material, thereby bonding the plurality of bonded members with the heat-melting material interposed therebetween
Data Source
Figure 1
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AI summary
A soldering method capable of alleviating positional displacement between substrates even though a step of removing flux can be omitted is provided. A temporary bonding agent 55 is applied onto multiple substrates 50a, 50b, and a heater 33 heats the substrates while the substrates are temporarily bonded with the temporary bonding agent 55 interposed therebetween, and before the solder 54 is melted or while the solder 54 is melted, the temporary bonding agent 55 is evaporated, and the substrates 50a, 50b are bonded with solder with the melted solder 54 interposed therebetween.