BGA Substrate Pad Structure for Solder Coplanarity and Joint Strength
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Solution Overview
Problem
The reliability of solder joints in ball grid array (BGA) packaged chips is compromised due to fatigue cracking, especially at the chip's corners, which is exacerbated by inconsistent solder ball heights and irregular shapes, leading to poor soldering and increased management complexity.
Innovation Solution
A substrate design with strategically positioned hollow-out regions and metal layers, allowing for controlled solder spreading and uniform coplanarity, utilizing a barrier layer and integrated metal structures to enhance solder joint reliability without additional manufacturing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the pad size is enlarged to increase soldering area, then solder joint strength is improved, but solder ball coplanarity cannot be ensured and soldering quality deteriorates
Solution Approach 1:
The pad structure is segmented into two distinct parts: a first pad area for receiving solder balls with standardized dimensions to ensure coplanarity, and a second pad area extending from the first pad to provide additional soldering area. This segmentation allows each part to fulfill its specific function independently, resolving the contradiction between strength and precision.
Solution Approach 2:
The pad structure transitions from a two-dimensional planar design to a three-dimensional stepped configuration. The first pad and second pad are arranged at different heights or positions, creating a multi-level structure that provides both standardized solder ball reception and extended soldering area without compromising coplanarity of the solder balls on the first pad.
2Reliability
If adjacent pads with same attribute are used at four corners to increase soldering area, then solder joint reliability is improved, but device complexity and management difficulty increase
Solution Approach 1:
The invention applies different pad configurations to different locations: the first pad with standardized dimensions is used for solder ball placement where precision is critical, while the second pad with extended area is used specifically at corner locations where additional strength is needed. This localized differentiation optimizes reliability without uniformly increasing complexity across the entire device.
Data Source
AI summary
A substrate includes: a base body and a barrier layer disposed on a surface of the base body, where a first metal layer and a plurality of second metal layers arranged in an array are disposed between the base body and the barrier layer, and the first metal layer is disposed near at least a part of the second metal layers on an outer side of the array. A first hollow-out region is provided at a position that is of the barrier layer and that is opposite to the first metal layer, and at least a part of the first metal layer is exposed in the first hollow-out region. A second hollow-out region is provided at a position that is of the barrier layer and that is opposite to each second metal layer, at least a part of the second metal layer is exposed in the second hollow-out region.