Curved Surface Mount Contact Pad Geometry for High-Density PCBs
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Solution Overview
Problem
It is challenging to place surface mount contact pads of sufficient size close to via contact pads surrounding power and ground pins or pads in high-density Pin Grid Array (PGA) and Ball Grid Array (BGA) packages, as altering the geometry of the contact pads reduces their surface area, thereby decreasing the noise decoupling capability of components like decoupling capacitors.
Innovation Solution
The design features surface mount contact pads with curved edges adjacently opposite via contact pads and a linear edge opposite another surface mount contact pad, maximizing the surface area while maintaining specified minimum distances, resulting in a substantially octagonal shape that allows for close location to via contact pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If surface mount contact pads are placed close to via contact pads to reduce spacing, then the distance between contact pads is reduced, but the surface area of contact pads decreases
Solution Approach 1:
The contact pads use curved edges instead of straight edges, creating a rounded or octagonal shape that allows the pads to be positioned closer together while maintaining sufficient surface area. The curvature enables the pads to nestle closer to via contact pads without linear edges creating excessive spacing requirements.
Solution Approach 2:
Different edges of the contact pad have different geometries: edges adjacent to via contact pads are curved to maximize proximity, while the edge opposite another contact pad may be linear. This localized differentiation optimizes both spacing and surface area for each specific orientation.
2Area of stationary object
If surface mount contact pads are made larger to increase surface area, then the noise decoupling capability is improved, but the proximity to via contact pads is reduced
Solution Approach 1:
Curved edges allow the contact pad to extend closer to via contact pads while maintaining a larger overall surface area compared to straight-edged pads of the same spacing. The curvature enables more efficient use of the available space between vias.
Solution Approach 2:
The curved geometry changes the dimensional distribution of the contact pad, allowing it to achieve greater surface area within the constrained spacing by utilizing circular/curved perimeter rather than linear edges, effectively optimizing area within the given boundary.
3Ease of manufacture
If conventional straight-edged contact pads are used, then the manufacturing is simpler, but the surface area is reduced when placed close to via contact pads
Solution Approach 1:
The curved edges can be implemented using standard PCB manufacturing processes such as electroplating or laser cutting, making the complexity increase minimal. The manufacturing process remains relatively simple while achieving significantly improved surface area utilization.
Data Source
AI summary
A circuit board has a first side and a second side opposite thereto. The board includes vias extending through the substrate from the first side to the second side, and via contact pads on the second side, each of which surrounds a corresponding via. The board includes a pair of surface mount contact pads on the second side. Each surface mount contact pad has a surface area and edges, each of which can have a shape to maximize the surface area while maintaining predetermined minimum separation distances. Each edge except one or more edges that are opposite another surface mount contact pad have a curved shape, and each edge opposite another surface mount contact pad have a linear shape. Curved edges adjacently opposite corresponding via contact pads can have curved shapes can have concave shapes, and curved edges not adjacently opposite via contact pads can have convex shapes.