Flexible PCB DIMM Transmission Lines for Signal Integrity
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Solution Overview
Problem
As computing system clock and signal frequencies increase, signal integrity issues arise at the interface between a dual in-line memory module (DIMM) and a system motherboard due to the lack of transmission lines with controlled characteristic impedance in the existing circuitry, leading to signal integrity problems as signal wavelengths become comparable to the dimensions of the circuit structures.
Innovation Solution
Incorporating well-controlled transmission lines in the connection circuitry between the DIMM and motherboard using flexible printed circuit boards (PCBs) with inner and outer conductors and dielectric layers to maintain signal integrity, and integrating the flexible PCBs with the DIMM PCB to form a single product with mechanical stability features such as base PCBs and connector designs that facilitate easy installation and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional circuitry without controlled impedance transmission lines is used in DIMM connection, then device complexity is reduced and ease of manufacture is improved, but signal integrity deteriorates at high frequencies
Solution Approach 1:
The patent changes the electrical parameters of the connection circuitry by implementing controlled impedance transmission lines with specific characteristic impedance values (e.g., 50 ohms). This involves adjusting physical dimensions such as trace width, spacing, and dielectric thickness to achieve the desired impedance characteristics, thereby maintaining signal integrity at high frequencies while managing the complexity through standardized design practices
Solution Approach 2:
The patent employs composite construction in the PCB assembly, combining rigid PCB materials with flexible cable assemblies. The rigid PCB provides structural support and controlled impedance traces, while the flexible cable portion allows for mechanical flexibility during insertion and removal. This composite approach maintains signal integrity through controlled impedance while managing mechanical stresses
2Stability of the object's composition
If rigid PCB structure is used for DIMM, then mechanical stability is improved, but stress-induced failures increase during insertion and removal
Solution Approach 1:
The patent divides the PCB into separate functional segments: a rigid PCB portion that provides mechanical stability and supports the memory chips, and a flexible cable portion that accommodates mechanical stress during insertion and removal. The segmentation allows each part to perform its optimal function without compromising the other
Solution Approach 2:
The patent introduces dynamic flexibility to the previously rigid structure by incorporating a flexible cable assembly that can bend and flex during connector engagement. This dynamic element absorbs mechanical stresses that would otherwise be transmitted to the rigid PCB and solder joints, reducing the risk of stress-induced failures
3Ease of operation
If flexible cable is used for connection, then ease of operation is improved, but signal integrity deteriorates due to lack of controlled impedance
Solution Approach 1:
The patent applies controlled impedance design principles to the flexible cable portion by carefully selecting conductor dimensions, spacing, and dielectric properties to achieve and maintain the required characteristic impedance (e.g., 50 ohms) throughout the flexible section. This ensures signal integrity is preserved even in the flexible, movable portion of the connection
Solution Approach 2:
The flexible cable assembly uses composite construction with carefully selected dielectric materials and conductor configurations that provide both mechanical flexibility and controlled electrical characteristics. The composite structure allows the cable to flex while maintaining consistent impedance for signal transmission
4Reliability
If transmission lines with controlled characteristic impedance are implemented, then signal integrity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent establishes specific parameter ranges for transmission line dimensions (trace width, spacing, dielectric thickness) that achieve the desired characteristic impedance. By defining these parameters within acceptable tolerances and using standardized fabrication processes, the patent balances signal integrity requirements with manufacturability
Solution Approach 2:
The patent incorporates impedance control considerations into the early design and fabrication stages, using pre-designed transmission line templates and standardized PCB fabrication processes that inherently provide controlled impedance. This preliminary planning reduces the need for post-manufacturing adjustments and simplifies the manufacturing process
Data Source
AI summary
An apparatus is described. The apparatus includes a memory module. The memory module includes a first printed circuit board having a first transmission line. The first printed circuit board has memory chips disposed thereon. The memory module includes a second printed board having a second transmission line that is coupled to the first transmission line to form a signal path through the first and second printed circuit boards. The second printed circuit board has greater flexibility than the first printed circuit board. The memory module includes a connector to align an I/O that is coupled to the second transmission line with a corresponding I/O that is associated with a motherboard that is to send and/or receive a signal to and/or from the signal path.