Space Transforming LGA Interposers for High I/O Density
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Solution Overview
Problem
Current MCM and LGA interposer technologies face limitations in achieving high I/O densities due to practical pitch limits, primarily governed by economic and manufacturing requirements, which restrict the ability to increase I/O contacts without increasing the MCM package size or decreasing the pitch of contacts on the PCB or node card.
Innovation Solution
The use of a space transforming LGA interposer with variable pitch connectors and fan-out wiring to provide direct electrical connections between fine pitch I/O contacts on a chip module and coarse pitch contacts on a circuit board, allowing for increased I/O interconnections without expanding the chip module footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional LGA interposer with uniform pitch is used, then manufacturing is simpler, but I/O density is limited by pitch constraints
Solution Approach 1:
The interposer is divided into multiple regions with different pitch characteristics. A first region has a first pitch suitable for fine-pitch I/O contacts, while a second region has a second pitch suitable for coarse-pitch I/O contacts. This segmentation allows each region to be optimized for its specific function, increasing overall I/O density without requiring the entire interposer to use the most complex fine-pitch configuration.
Solution Approach 2:
Different regions of the interposer are assigned different local qualities in terms of pitch. The first region is designed with a first pitch for high-density I/O connections, while the second region uses a second pitch for standard-density connections. This local differentiation enables the system to achieve high I/O density where needed while maintaining manufacturing simplicity in other areas.
2Quantity of substance
If fine pitch I/O contacts are used on chip module, then I/O density increases, but manufacturing precision requirements increase
Solution Approach 1:
The I/O contact array is segmented into different pitch regions. Fine-pitch contacts are implemented only in the first region where high density is required, while the second region uses coarser pitch that is easier to manufacture. This reduces the overall manufacturing precision requirements compared to implementing fine pitch across the entire array.
Solution Approach 2:
The interposer provides different local qualities of pitch to match the requirements of different I/O contact regions. The first region receives fine-pitch interposer contacts to match fine-pitch I/O contacts, while the second region receives coarse-pitch contacts. This local matching reduces the overall manufacturing precision burden while still achieving high I/O density where needed.
3Quantity of substance
If I/O contact pitch on PCB is decreased, then I/O density increases, but manufacturing and economic feasibility decreases
Solution Approach 1:
The interposer acts as an intermediary between the chip module and the PCB. It provides fine-pitch contacts on its first region to match the fine-pitch I/O contacts on the chip module, while providing coarse-pitch contacts on its second region that can be easily manufactured on standard PCBs. This intermediary structure allows the system to achieve high I/O density without requiring the PCB itself to be manufactured with fine pitch, thus maintaining ease of PCB fabrication.
Data Source
AI summary
An electronic apparatus includes first and second level package structures and an LGA (land grid array) interposer. The first level package structure includes a package substrate, one or more integrated circuit chips mounted on a first surface of the package substrate, and a first pattern of I/O contacts with pitch P1 formed on a second surface of the package substrate opposite the first surface. The second level package structure includes a second pattern of I/O contacts with pitch P2, wherein P2 is not equal to P1. The LGA interposer is disposed between the first and second level package structures and provides space transform electrical interconnections between the first second patterns of I/O contacts, and further includes a dummy contact formed on at least a first or second surface of the LGA interposer and aligned to an LGA contact on an opposing surface of the LGA interposer.