PCB Pad Layout for Uniform Bump Height on Large BGA Substrates
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Solution Overview
Problem
The increasing demand for high-density, large-area flip-chip BGA substrates in applications like electric vehicles and servers poses challenges in maintaining consistent bump height due to the larger substrate sizes, which complicates the manufacturing process and increases the risk of defects.
Innovation Solution
A printed circuit board design that includes an insulating layer, an interconnection layer with metal pads, and a solder resist layer with openings, where the outermost openings form a rectangular region divided into cells, with specific ratios of metal pad areas within each cell maintained within a narrow range, ensuring uniformity and flatness of the bump region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If substrate size is increased to meet demand for large-area flip-chip BGA substrates, then the substrate can accommodate more bumps and higher density designs, but it becomes more difficult to secure constant bump height and maintain flatness
Solution Approach 1:
The patent applies local quality by dividing the large substrate into multiple cells with different area ratios of metal pads to cell areas. Each cell has a controlled area ratio (Pmax - Pmin ≤ 20%), creating local uniformity in the bump region. This local control of metal pad distribution compensates for the overall substrate size increase, maintaining consistent bump heights across the entire large substrate area.
2Quantity of substance
If substrate size is increased, then more bumps can be mounted, but the manufacturing process becomes more complex and difficult to control
Solution Approach 1:
The patent segments the large substrate into multiple cells, each with controlled metal pad area ratios. This segmentation transforms the complex problem of controlling bump heights across a large substrate into simpler, independent cell-level controls. The manufacturing process becomes more manageable by focusing on maintaining area ratio consistency within each cell rather than controlling every individual bump across the entire substrate.
3Quantity of substance
If substrate size is increased, then higher density designs are achieved, but the risk of defects increases
Solution Approach 1:
By enforcing local uniformity through controlled area ratios in each cell (Pmax - Pmin ≤ 20%), the patent reduces variability in the bump region properties. This local quality control prevents defects that arise from excessive variation in bump heights and metal pad distributions, thereby maintaining reliability even as bump density increases across the large substrate.
Data Source
AI summary
A printed circuit board includes an insulating layer; an interconnection layer disposed on the insulating layer, and including a plurality of metal pads for mounting a semiconductor chip thereon; and a solder resist layer disposed on the insulating layer and covering the interconnection layer, the solder resist layer having a plurality of openings respectively exposing at least a portion of at least one of the plurality of metal pads. A rectangular region created by substantially connecting outer edges of outermost openings among the plurality of openings in a straight line is substantially equally divided into a plurality of cells, and a ratio of areas of the metal pads disposed in each cell to an area of each cell is calculated, and when a maximum value thereof is PMax and a minimum value thereof is PMin, (PMax−PMin)*100≤20.