Spring-Biased Floating Clamp for QFN Chuck Alignment
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Solution Overview
Problem
The challenge in testing punch QFN packages lies in controlling the chuck height due to dimensional variations, which can lead to damage from overdriving or insufficient chuck height, and the tapered side walls of punch QFN packages cause issues with mold heel cracking, bending, and delamination when using non-anvil chucks.
Innovation Solution
A chuck apparatus with a nozzle and a clamp featuring a recess and a spring-biased engagement surface that self-aligns with the device under test, accommodating dimensional variations and preventing contact with conductive lands, while a clamp spring ensures proper compression and maintains device flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-height chuck is used to engage punch QFN packages, then the chuck structure is simple, but dimensional variations cause damage from overdriving or insufficient chuck height
Solution Approach 1:
The chuck tip is made dynamically adjustable in height through a threaded rod mechanism that allows rotation and vertical movement. The motor-driven system enables the chuck tip height to be dynamically modified based on the specific package thickness, transforming a static fixed-height structure into a dynamic adjustable one that adapts to dimensional variations in punch QFN packages
Solution Approach 2:
The system changes the physical parameter of chuck tip height by rotating the threaded rod, which converts rotational motion into linear vertical displacement. This parameter change allows precise adjustment of the chuck tip position to match different package thicknesses, preventing both overdriving and insufficient engagement
2Device complexity
If non-anvil chucks are used, then the chuck design is simpler, but tapered side walls cause mold heel cracking, bending and delamination
Solution Approach 1:
The chuck tip is designed with a localized anvil structure at its lower end that provides a broad, flat engagement surface. This local quality change concentrates the support function at the critical contact point with the package, distributing the force evenly across the package bottom to prevent mold heel cracking and delamination caused by point loads from non-anvil chucks
3Adaptability or versatility
If chuck height is increased to accommodate thicker devices, then all devices can be engaged, but the chuck becomes too tall for other setups
Solution Approach 1:
The chuck tip height is made dynamically adjustable through a motor-driven threaded rod mechanism that enables vertical movement within a controlled range. This dynamic capability allows the chuck tip height to be optimized for each specific device being tested, accommodating thicker devices when needed while maintaining a compact profile for other setups by reducing the height for standard-thickness devices
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 solution effectively aligns and tests punch QFN packages without damaging them, accommodating thickness variations within tolerance ranges and ensuring low contact resistance, thus preventing mold heel cracking and delamination.
Implementation Method 1
a clamp spring biased in use toward the first end of the nozzle
Data Source
AI summary
A chuck apparatus includes a nozzle with a first end configured to engage a device under test (DUT), and a clamp extending around a portion of the nozzle proximate the first end. The clamp includes a recess to receive the DUT, and an engagement surface in the recess to engage the DUT. The chuck apparatus also includes a spring that biases a surface of the clamp toward the first end of the nozzle. A method includes translating a chuck to engage a nozzle with a DUT, further translating the chuck to engage and self-align an engagement surface of a spring mounted clamp with the DUT, further translating the chuck to seat the DUT in the spring mounted clamp, translating the chuck with the DUT to a contactor and translating the chuck with the DUT to engage conductive features of the DUT with conductive probes of the contactor.