Folded Spring-Loaded Probe for High-Bandwidth WLT

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Solution Overview

Problem

Traditional wafer probe technologies are not suitable for the higher electrical performance required for Wafer-Level Test (WLT) due to shrinking pitch sizes and the need for high bandwidth, low inductance, and high current carrying capacity.

Innovation Solution

A test probe design with a first, second, and third portion, connected by hinges, allowing for compressibility from an uncompressed to a compressed state, utilizing sinuous flat springs and loops for enhanced electrical connectivity and current flow, and housed within a metal tube for reduced inductance and improved conductance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional wafer probe technologies are used, then manufacturing simplicity is maintained, but electrical performance (bandwidth, inductance, current carrying capacity) is insufficient for high-performance WLT applications

Engineering Contradiction:

Improveelectrical performanceVSAvoidprobe structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The probe is divided into three distinct portions (first, second, and third portions) with the second portion stacked between the first and third portions. This segmentation allows each portion to be optimized for specific functions: the outer portions provide compliance and contact force through compression springs, while the central portion provides low-inductance electrical connection, thereby improving overall electrical performance without requiring a completely new probe design

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second portion is nested within the structure formed by the first and third portions, with all three portions stacked in a compact arrangement. This nesting approach reduces the overall probe height and complexity while maintaining the specialized functions of each portion, resolving the contradiction between improved electrical performance and device complexity

Inventive Principle:

Principle #7Nested doll (Nesting)

2Volume of moving object

If pitch between contact points is reduced to accommodate smaller WLCSPs, then package size is reduced, but electrical performance requirements (bandwidth, inductance) increase

Engineering Contradiction:

Improvepackage sizeVSAvoidelectrical performance

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

Different portions of the probe are given different local qualities: the first and third portions contain compression springs for compliance, while the second portion is designed with low-inductance characteristics for high-frequency signal integrity. This local differentiation allows the probe to meet high electrical performance requirements in a compact form factor suitable for smaller pitch WLCSPs

Inventive Principle:

Principle #3Local quality

3Reliability

If compression springs are added to improve compliance and contact force, then mechanical performance is improved, but probe length and inductance increase

Engineering Contradiction:

Improvemechanical performanceVSAvoidprobe length

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

Instead of extending the probe length horizontally to accommodate compression springs, the design stacks the portions vertically in a compact arrangement. The first, second, and third portions are stacked between the upper and lower substrates, utilizing the vertical dimension to house the compliance mechanism without increasing the horizontal probe length, thereby maintaining low inductance while improving mechanical performance

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The test probe achieves improved electrical reliability, high bandwidth, and high current carrying capacity, enabling effective at-speed testing of RF devices and DC parametric tests with reduced RF signal discontinuities and improved mechanical performance.

Implementation Method 1

The test probe includes a first portion, a second portion, and a third portion, with hinges between the first and second portions and the second and third portions. The first portion folded at the first hinge over the second portion, the third portion folded at the second hinge over the second portion

Methodology Applied

Scientific EffectSpring: Spring

Implementation Method 2

at least one of the first portion, the second portion, or the third portion includes a spring

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

housed within a metal tube for reduced inductance and improved conductance

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS11268981B2Spring-loaded probe having folded portions and probe assembly

Publication Date: 2022.03.08 XCERRA CORP

AI summary

A test probe for use with a testing apparatus. The test probe includes a first portion, a second portion, and a third portion, with hinges between the first and second portions and the second and third portions. The first portion folded at the first hinge over the second portion, the third portion folded at the second hinge over the second portion, where the second portion is stacked between the first portion and the third portion. The test probe is compressible from a first uncompressed state to a second compressed state.