Impedance Controlled LGA Interposer Assembly with Ground Shielding
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Solution Overview
Problem
Conventional interposer plates with short, closely spaced contacts experience increased signal impedance and cross-talk at high-frequency signal frequencies, degrading signal strength and reliability in high-speed circuit applications.
Innovation Solution
Incorporating through signal contacts with central impedance coupling sections surrounded by overmolded plastic, which reduces impedance between adjacent signal contacts, and using ground contacts to minimize cross-talk between pairs of signal contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional interposer plates with short, closely spaced contacts are used, then a large number of differential pair signal connections can be established, but signal impedance increases and signal strength degrades at high frequencies
Solution Approach 1:
The contact structure is segmented into multiple functional portions: a first contact portion extending from the first surface, a second contact portion extending from the second surface, and a central coupling section connecting them. This segmentation allows each portion to be optimized for its specific function, with the coupling section specifically designed to reduce impedance at high frequencies while the contact portions maintain reliable electrical connections.
Solution Approach 2:
Different sections of the contact have different geometries and properties tailored to their local functions. The central coupling section has a larger cross-sectional area compared to the contact portions, creating a localized impedance reduction zone. This local quality change allows the contact to maintain low impedance at the critical coupling region while preserving connection integrity at the substrate interfaces.
2Quantity of substance
If contacts are spaced very close together to establish large number of connections, then connection density increases, but cross-talk between adjacent pairs of signal contacts increases
Solution Approach 1:
Ground contacts serve as intermediary elements positioned between adjacent signal contact pairs. These ground contacts act as shields that electrically isolate the signal pairs from each other, reducing electromagnetic coupling and cross-talk. The ground contacts mediate the electromagnetic field distribution, preventing harmful interference between closely spaced signal connections.
3Speed
If high-frequency signals with fast rise times are transmitted through conventional interposer plates, then circuit speed increases, but signal impedance increases and signal quality degrades
Solution Approach 1:
The contact geometry parameters are changed, specifically increasing the cross-sectional area of the central coupling section. This parameter change directly affects the electrical characteristics of the contact, reducing its impedance. The modified geometry allows high-frequency signals with fast rise times to pass through with minimal impedance mismatch and signal degradation, maintaining signal quality at high circuit speeds.
Data Source
AI summary
An interposer plate assembly having an insulating plate and metal contacts in the plate with contact points above and below the plate and a central portion in the plate. Two cantilever arms extend from the central portion to each contact point. The central portion may be formed to have a large area to form an impedance shield for reducing impedance between adjacent signal contacts. Plastic bodies may be overmolded on separate contacts or on contact pairs and may have sliding fits in passages of the interposer plate. Contacts may be arranged as differential pairs with ground contacts located between the differential pairs.