Via Pad Structure With Keyhole Solder Mask To Reduce Wicking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional via and pad structures in circuit assemblies suffer from solder wicking issues, leading to unreliable solder joints and misalignment of components due to capillary action, which can be exacerbated by gold plating and require precise alignment of solder masks, while attempts to mitigate these issues often increase trace inductance and degrade performance at high frequencies.
Innovation Solution
The substrate incorporates a via and pad structure with a conductive pad extending beyond the terminal sides of components, surrounded by a keyhole-shaped solder mask that reduces solder formation at the terminal end and features a chemically compatible plating finish to minimize wicking, along with a method to calculate the optimal extension of the conductive pad to prevent solder wicking and ensure reliable solder joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the inner diameter of the solder mask is decreased to reduce solder wicking, then solder wicking is reduced, but the solder mask must be precisely aligned to avoid covering the via hole and trapping contaminants causing corrosion
Solution Approach 1:
The solder mask opening is designed with an asymmetric keyhole shape that has a larger opening area on one side and a smaller opening area on the other side. This asymmetric geometry allows the solder mask to effectively prevent solder wicking into the via hole while maintaining adequate alignment tolerance, resolving the contradiction between reducing solder wicking and maintaining manufacturing precision requirements
2Reliability
If gold plating is applied to the plated via to decrease corrosion, then corrosion resistance is improved, but solder wicking increases due to increased wettability
Solution Approach 1:
The solder mask opening employs a non-uniform keyhole shape with different opening areas at different locations. The larger opening area is positioned away from the via hole while the smaller opening area is closer to the via hole, creating local quality variations that allow adequate solder flow to the pad while preventing solder wicking into the via hole, thus resolving the contradiction between corrosion resistance and solder wicking prevention
3Object-affected harmful factors
If the conductive pad is moved further from the via hole to reduce solder wicking, then solder wicking is reduced, but trace inductance increases and performance at high frequencies degrades
Solution Approach 1:
The solder mask opening is segmented into distinct regions with different opening areas - a larger opening area providing adequate solder access to the conductive pad and a smaller opening area near the via hole that prevents solder wicking. This segmentation allows the conductive pad to remain close to the via hole for low inductance while the solder mask geometry prevents solder from wicking into the via hole
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 configuration achieves high component density with reliable solder joints on terminal sides, reducing solder wicking and maintaining low trace inductance, thus enhancing the reliability and performance of circuit assemblies at high frequencies.
Implementation Method 1
The small amount of solder remaining will form an unreliable solder joint 31 at the terminal end 37 of the component 33. This problem is referred to as solder wicking.
Data Source
AI summary
This invention relates to a substrate with via and pad structure(s) to reduce solder wicking. Each via and pad structure connects a component to conductive layers associated with the substrate. The substrate includes one or more plated vias, solder mask(s) surrounding the plated vias, and a conductive pad with a conductive trace connected to each plated via. The conductive pad extends beyond the terminal sides to increase solder formation and the solder mask reduces solder formation at the terminal end of the component. The via and pad structure is suitable for a variety of components and high component density. The invention also provides a computer implemented method for calculating the maximum distance of a conductive pad extending beyond the terminal side of a component.