Split BGA Pad for Multi-Chip Module Testing
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Solution Overview
Problem
Multi-chip modules (MCMs) face high yield loss due to the inability to test individual components before attaching high-value components, resulting in the loss of both the MCM and the high-value components if the module fails.
Innovation Solution
The implementation of split Ball Grid Array (BGA) pads on MCMs, which allow for the testing of attached low-value components before attaching high-value components, by separating the pad into sections connected by wires to different groups of pads, enabling separate testing and reducing the risk of losing high-value components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all components are attached before testing the MCM, then the module can be tested as a complete unit, but high-value components are lost when the module fails due to inability to test individual components beforehand
Solution Approach 1:
The BGA pad structure is segmented into multiple sections, where each section can be electrically connected to different groups of pads. This allows individual components to be tested separately before final assembly, preventing loss of high-value components when lower-value components fail testing.
Solution Approach 2:
Testing of individual components is performed preliminarily before final module assembly by utilizing the segmented pad structure. The first component is tested using the first section of the split pad before the second component is attached, enabling early detection of defects without committing high-value components to a potentially faulty assembly.
2Loss of substance
If individual components are tested before attachment, then high-value components can be preserved, but the testing process becomes more complex and time-consuming
Solution Approach 1:
The segmented BGA pad structure serves multiple functions: it enables individual component testing during assembly, allows electrical connection to different pad groups, and facilitates selective rework. This multi-functionality is achieved through the split pad design where each section can be independently utilized for testing purposes.
Solution Approach 2:
The testing process utilizes the existing pad structure and wiring layers of the MCM itself, rather than requiring external testing equipment or additional test structures. The split pad configuration allows the module to test its own components during the assembly process, simplifying the overall testing infrastructure needed.
3Ease of manufacture
If a single continuous pad is used for BGA connection, then the structure is simple and manufacturing is easier, but testing of individual components before final assembly is not possible
Solution Approach 1:
The continuous BGA pad is divided into multiple sections separated by gaps, with each section connectable to different pad groups through wiring layers. This segmentation enables individual component testing while maintaining a relatively simple manufacturing process that builds upon conventional BGA pad fabrication techniques.
Solution Approach 2:
The pad structure transitions from a two-dimensional continuous surface to a segmented configuration utilizing the third dimension through wiring layers. The gaps between pad sections are bridged by wires in upper wiring layers, creating a three-dimensional electrical connection architecture that enables testing functionality without significantly complicating the manufacturing process.
Data Source
AI summary
A multi-chip module, and method of fabricating the multi-chip module. The multi-chip module includes: a substrate containing multiple wiring layers, each wiring layer having first pads on a top surface of the substrate and second pads on a bottom surface of the substrate, wherein the second pads include split pad and a conventional pad; a first solder ball in direct physical contact with a contiguous bottom surface of the conventional pad and connected to a next level of packaging under the conventional pad, wherein the first solder ball has a first height; and a second solder ball in direct physical contact with first and second sections of the split pad separated by a gap, wherein the second solder ball has a second height that is sufficiently less than the first height such that the second solder ball is not connected to the next level of packaging.