Elliptical Peripheral Pads for Semiconductor Package Alignment
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Solution Overview
Problem
Manufacturing errors in semiconductor packages can lead to displacement issues between substrates, causing solder balls to move over the edge of the solder resist layer, resulting in insufficient solderability and reduced connection reliability due to differences in diagonal sizes between substrates.
Innovation Solution
The design of a wiring substrate with elliptical connection pads on the periphery and circular pads at the center, where the major axis of the elliptical pads extends towards the center, ensures proper alignment and mounting of solder balls even with displacement, preventing solder ball movement onto the edges and maintaining consistent solder area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If substrates are manufactured with standard circular pads, then manufacturing process is simple, but displacement causes solder balls to move off the pad edges resulting in poor solderability
Solution Approach 1:
The pad shape is changed from circular to elliptical specifically at peripheral substrates where displacement occurs, while central substrates maintain circular pads. This local differentiation addresses the solderability issue at critical locations without unnecessarily complicating the entire substrate design.
Solution Approach 2:
Elliptical pads introduce asymmetric geometry with the major axis oriented toward the block center, creating an asymmetric tolerance buffer that compensates for displacement. The asymmetric shape provides larger coverage area in the displacement direction while maintaining manufacturing feasibility.
2Adaptability or versatility
If diagonal size difference between substrates increases, then manufacturing flexibility improves, but displacement amount increases causing solder balls to move off pad edges
Solution Approach 1:
The pad shape parameter is changed from circular to elliptical at peripheral locations, and the major axis length is oriented toward the block center. This parameter modification creates a larger effective pad area in the displacement direction, compensating for alignment precision loss due to diagonal size differences.
3Manufacturing precision
If solder ball placement area is reduced due to displacement, then manufacturing tolerance is easier to achieve, but connection reliability decreases
Solution Approach 1:
The elliptical pad shape with major axis toward the block center pre-establishes a larger coverage area that acts as a cushion against displacement. This beforehand cushioning ensures that even with manufacturing tolerances, the solder ball remains within the effective pad area, maintaining connection reliability.
Data Source
AI summary
A wiring substrate includes a block with substrates laid out in an array. The block includes corners and a plan view center. Each substrate includes a substrate body. Pads are formed on the substrate body. Each pad includes a pad surface. The pads of the substrates include first pads, which are the pads of one of the substrates located in at least one of the corners of the block. The pad surface of each of the first pads includes a first axis extending from the first pad toward the plan view center of the block. The pad surface of each of the first pads has a first length along the corresponding first axis and a second length along a second axis, which is orthogonal to the first axis. The first length is longer than the second length.