Solder Drawing Lands with Slits for Bridge Prevention
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Solution Overview
Problem
The challenge in mounting four-way lead flat package ICs on printed circuit boards with narrow pitches using lead-free solder is the occurrence of soldering bridges and residues, which is exacerbated by the poor soldering reliability of lead-free solder compared to lead-containing eutectic solder.
Innovation Solution
The solution involves a printed circuit board design with front and rear soldering land groups and solder drawing lands in neighboring areas or trailing areas, where each solder drawing land has a slit parallel to adjacent solder drawing lands, facilitating the use of a jet-flow type soldering bath for soldering and removing solder bridges by dissipating surface and interfacial tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder is used for environmental reasons, then environmental compliance is improved, but soldering reliability deteriorates due to poor wetting and increased soldering bridges
Solution Approach 1:
The patent introduces a specific solder land configuration with drawing lands and slits as an intermediary structure between the solder and the IC leads. This configuration mediates the soldering process by controlling solder flow and preventing bridges, thereby enabling reliable lead-free soldering despite the inherently poor wetting characteristics of lead-free solder
Solution Approach 2:
The patent changes the geometric parameters of the solder lands by introducing drawing lands with specific slit configurations. This parameter change modifies the soldering process characteristics, creating controlled flow paths that compensate for the poor wetting of lead-free solder and prevent soldering bridges
2Quantity of substance
If the pitch of IC leads is narrowed to increase component density, then mounting density is improved, but manufacturing precision deteriorates due to difficulty in maintaining accurate soldering
Solution Approach 1:
The patent applies local quality by creating specific solder drawing lands with slit configurations in particular locations between the IC leads. This localized structural modification provides precise control over solder flow in the critical areas between narrow-pitch leads, enabling accurate soldering despite the reduced spacing
Solution Approach 2:
The patent segments the solder land area into distinct regions including drawing lands with slits positioned between the IC leads. This segmentation creates controlled zones that guide solder flow independently for each lead pair, maintaining precision even when the overall pitch is narrowed
3Device complexity
If conventional solder land configurations are used without slits, then device complexity is reduced, but soldering quality deteriorates due to occurrence of soldering bridges and residues
Solution Approach 1:
The patent segments the solder land structure by introducing slits that divide the drawing lands into distinct sections. This segmentation creates controlled flow paths for solder, preventing uncontrolled bridging while maintaining a relatively simple overall structure that can be manufactured with standard processes
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 effectively prevents soldering bridges and residues, improving work efficiency and allowing for the use of lead-free solder, which is environmentally preferable, while maintaining high-quality soldering without manual correction.
Implementation Method 1
a step of first solder jet-flowing for soldering lead portions of the four-way lead flat package IC mounted on the printed circuit board using a jet-flow type soldering bath
Implementation Method 2
a step of second solder jet flowing for removing soldering bridges formed between the lead portions of the four-way lead flat package IC during the first solder jet-flowing step, by the solder drawing lands having the slits
Implementation Method 3
dissipating surface and interfacial tension
Data Source
AI summary
A four-way lead flat package IC-mount printed circuit board, carrying a four-way lead flat package IC and having front soldering land groups placed in front of the four way lead flat package IC and rear soldering land groups placed in the rear of the four-way lead flat package IC, has solder drawing lands, in a neighboring area, between the front soldering land groups and the rear soldering land groups adjacent to the front soldering land groups, and/or a trailing area of the rear soldering land groups. The solder drawing lands are formed with slits substantially parallel to the lines of soldering lands of the front soldering land groups or the rear soldering land groups placed in front of the solder drawing lands. These result in an advantageous effect of enabling the prevention of the occurrence of soldering bridges and soldering residues in the front soldering land groups or the rear soldering land groups.