PCB Solder Paste Offset and Resist Region Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In the manufacturing of printed circuit boards, voids in solder junctions occur due to gasification of solvents and activators in solder paste, leading to reduced joining reliability, especially in miniaturized semiconductor packages like LGA, where the gap between the package and the board is small, causing insulation resistance issues and potential short circuits.
Innovation Solution
A method involving a printed wiring board with specific regions - a first region covered with solder resist, a second region uncovered, and a third region adjacent to the second region uncovered as well - where solder paste is supplied to extend over the second and third regions, allowing molten solder to move and fill the junction without separation, thereby reducing voids and accumulating flux residues in the third region to maintain insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder paste is supplied to extend over the electrode pad and solder resist, then the solder can fill the junction and reduce voids, but the solder may separate and move between electrode pads causing short circuits
Solution Approach 1:
The patent applies local quality by creating distinct regions with different properties: the first region has solder resist for insulation, the second region has electrode pad for soldering, and the third region is an intermediate zone. This spatial differentiation allows solder to move freely in the third region without causing short circuits, while maintaining proper solder joints in the second region.
Solution Approach 2:
The patent segments the electrode pad area into three distinct regions: (1) a first region covered with solder resist, (2) a second region that is the electrode pad itself, and (3) a third region adjacent to the second region. This segmentation controls solder flow paths and prevents unwanted electrical connections between adjacent pads.
2Volume of moving object
If the gap between semiconductor package and printed wiring board is reduced for miniaturization, then the package size is reduced, but void formation in solder junction increases
Solution Approach 1:
The patent addresses the void formation problem by extending the solution from the vertical dimension (gap reduction) to the horizontal dimension (solder paste placement). By positioning solder paste in the third region offset from the electrode pad center, the patent creates a horizontal solder flow path that forces gas escape during reflow, compensating for the reduced vertical gap space.
3Reliability
If solder paste is supplied offset from the electrode pad, then gas can be forced out and voids reduced, but the solder may not adequately fill the electrode pad junction
Solution Approach 1:
The third region acts as an intermediary zone between the solder paste supply position and the electrode pad. This intermediate region allows solder to accumulate and then flow toward the electrode pad during reflow, ensuring both void reduction through forced gas escape and complete junction filling.
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 effectively reduces voids in solder junctions, enhances joining reliability, and maintains high insulation resistance by allowing molten solder to fill the junction and containing flux residues, addressing the challenges of miniaturization and small gaps in semiconductor packages.
Implementation Method 1
heating the solder paste to be molten
Implementation Method 2
causing the molten solder to move from the third region toward the second region
Implementation Method 3
when the flux in the solder paste 8 removes a surface oxide film of the electrode pad 4, gas is generated
Data Source
AI summary
A method of manufacturing a printed circuit board includes: supplying solder paste so as to be offset from an electrode pad of a printed wiring board; flowing the solder paste during melting; and forming a region that is not covered with solder resist on the outer peripheral region adjacent to the electrode pad of the printed wiring board to which solder paste is supplied, thereby increasing a gap between a semiconductor package and the printed wiring board to prevent separation of the solder.